US20070062533A1 - Apparatus and method for identifying FRC and PEEP characteristics - Google Patents

Abstract

A ventilator for ventilating a patient also assists a clinician in determining a suitable PEEP for the patient. For this purpose, a graph or tabular display of a series of different value PEEPs and corresponding functional residual capacities of the patient may be provided. Or, the relationship between lung compliance and a series of different values of PEEP may be provided. Or, the amount of the lung volume recruited/de-recruited at various levels of PEEP may be determined for use in selecting a desired PEEP. To this end, the functional residual capacity of the lungs is determined for a first PEEP level. The PEEP is then altered to a second level and a spirometry dynostatic curve of lung volume and pressure data is obtained. The lung volume on the dynostatic curve at a lung pressure corresponding to the first PEEP value is obtained. The difference between the functional residual capacity of the lungs at the first PEEP level and that determined from the dynostatic curve represents the lung volume recruited/de-recruited when changing between said first and second PEEPs.

Description

CROSS REFERENCE TO RELATED APPLICATION
• The present application claims the priority of U.S. Provisional Application No. 60/719,329, filed Sep. 21, 2005, and comprises a continuation-in-part of U.S. patent application Ser. No. 11/358,573, filed Feb. 21, 2006, which application also claims priority of U.S. Provisional Application No. 60/719,329.
BACKGROUND AND SUMMARY
• The present invention relates to an apparatus and method for determining and displaying functional residual capacity data and other pulmonary parameters, such as positive end expiratory pressure (PEEP) data, for patients breathing with the aid of a mechanical ventilator, such as a critical care ventilator. The invention also determines and displays relationships between these and other parameters.
• Functional residual capacity (FRC) is the gas volume remaining in the lungs after unforced expiration or exhalation. Several methods are currently used to measure functional residual capacity. In the body plethysmography technique, the patient is placed in a gas tight body box. The patient's airway is sealingly connected to a breathing conduit connected to the exterior of the body box. By measuring lung pressures and pressures in the box, at various respiratory states and breathing gas valve flow control conditions, the functional residual capacity of the patient can be determined.
• Another technique for measuring functional residual capacity is the helium dilution technique. This is a closed circuit method in which the patient inhales from a source of helium of known concentration and volume. When the concentration of helium in the source and in the lungs has reached equilibrium, the resulting helium concentration can be used to determine the functional residual capacity of the patient's lungs.
• A further technique for determining functional residual capacity is the inert gas wash-out technique. This technique is based on a determination of the amount of gas exhaled from the patient's lungs and corresponding changes in gas concentrations in the exhaled gas. The gas used for the measurement is inert in the sense that it is not consumed by metabolic activity during respiration. While a number of gases may be used for such a measurement of functional residual capacity, it is convenient to use nitrogen for this purpose.
• In a straightforward example in which the patient is initially breathing air, the lung volume forming the functional residual capacity of the lung will contain nitrogen in the same percentage as air, i.e. approximately 80%, the remaining 20% of air being oxygen. In a wash-out measurement, the subject commences breathing gases in which oxygen is at a different concentration than 20%. For example, the patient commences breathing pure oxygen. With each breath, nitrogen in the lungs is replaced by oxygen, or, stated conversely, the nitrogen is “washed out” of the lungs by the oxygen. While the breathing of pure oxygen could continue until all nitrogen is washed out of the lungs, in most cases, the breathing of oxygen continues until the nitrogen concentration in the exhaled breathing gases falls below a given concentration. By determining the volume of inert gas washed out of the lungs, and knowing the initial concentration of the inert gas in the lungs, the functional residual capacity of the lungs may be determined from these quantities.
• Methods for determining functional residual capacity in this manner are well known and are described in such literature as The Biomedical Engineering Handbook, CRC Press, 1995, ISBN 0-8493-8346-3, pp. 1236-1239, Critical Care Medicine, Vol. 18, No. 1, 1990, pp. 8491, and the Yearbook of Intensive Care and Emergency Medicine, Springler, 1998, ISBN 3-540-63798-2, pp. 353-360. By analogy to the above described wash out measurement technique, it is also possible to use a wash in of inert gas for measurement of functional residual capacity. Such a method and apparatus is described in European Patent Publication EP 791,327.
• The foregoing methods are used with spontaneously breathing patients and are typically carried out in a respiratory mechanics laboratory. But in many cases, patients that could benefit from a determination of functional residual capacity are so seriously ill as to not be breathing spontaneously but by means of a mechanical ventilator, such as a critical care ventilator. This circumstance has heretofore proven to be a significant impediment in obtaining functional residual capacity information from such patients. Additionally, the patient's illness may also make it impossible or inadvisable to move the patient to a laboratory or into and out of a body box for the determination of functional residual capacity.
• It would therefore be highly advantageous to have an apparatus and method by which the functional residual capacity of mechanically ventilated patients could be determined. It would be further advantageous to associate the apparatus for carrying out the determination of functional residual capacity with the ventilator to reduce the amount of equipment surrounding the patient and to facilitate set up and operation of the equipment by an attending clinician. Such apparatus would also enable the determination of functional residual capacity to be carried out at the bedside of the patient, thus avoiding the need to move the patient.
• A single determination of functional residual capacity provides important information regarding the pulmonary state of the patient. However, it is often highly desirable from a diagnostic or therapeutic standpoint to have available trends or changes in the functional residual capacity of a patient over time.
• It would also be helpful to be able to relate functional residual capacity to other pulmonary conditions existing in the lungs or established by the ventilator and to changes in these conditions. For example, it is known that the pressure established by the ventilator in the lungs at the end of expiration, the positive end expiratory pressure or PEEP, affects the functional residual capacity of the lungs.
• Typically, an increase in PEEP increases functional residual capacity. There are two components to the increased functional residual capacity as PEEP is increased. One component is due to stretching of the lung by the increased pressure. A second component, particularly in diseased lungs, occurs from the effect of PEEP during breathing by the patient. As a patient expires, the pressure in the lungs drops until it approaches airway pressure. As the pressure within the lungs drops, the alveoli or air sacs in the lungs deflate. If alveolar sacs collapse completely, more pressure is required upon inspiration to overcome the alveolar resistance and re-inflate the alveolar sacs. If this resistance cannot be overcome, the volume of such sacs are not included in the functional residual capacity of the patient's lungs.
• By applying PEEP, in the patient's airway, the additional pressure in the patient's lungs keeps more of these alveolar sacs from completely collapsing upon expiration and, as such, allows them to participate in ventilation. This increases the functional residual capacity of the patient's lungs and the increase is often described as “recruited volume.” Volume reductions are termed “de-recruitments.”
• However, setting the PEEP too high can cause excessive lung distension. There may also be compression of the pulmonary bed of the lung, loading the right side of the heart and reducing the blood volume available for gas exchange. Either of these circumstances present the possibility of adverse consequences to the patient.
• It would, therefore, be desirable to provide an apparatus and method by which a clinician could quickly, easily, and definitely determine an optimal PEEP for a given patient at a given point in the therapeutic regimen for the patient. An optimal PEEP is one that keeps the lung open but avoids overpressurization of the lung. It is often termed the “open lung PEEP.”
• Still further, action such as performing a suction routine, administering a nebulized medication, or changing the ventilation parameters of the ventilator can also influence functional residual capacity and it would be helpful to be able to easily determine the effect of such actions on functional residual capacity.
• An apparatus and method that would possess the foregoing characteristics and that would easily and cogently make such information available would be highly beneficial in conveniently obtaining a full understanding of the pulmonary condition of the patient and how the patient is reacting to the mechanical ventilation and to any associated therapeutic measures. The clinician could then carry out appropriate action beneficial to the patient in a timely and informed manner.
BRIEF DESCRIPTION OF THE PRESENT INVENTION
• An embodiment of the present invention comprises an apparatus and method that achieves the highly advantageous features noted above. Thus, with the present invention the functional residual capacity of a mechanically ventilated patient may be determined at the bedside of the patient without the need to move the patient to a laboratory. By associating the apparatus with the ventilator, only a single device need be employed to both ventilate the patient and determine functional residual capacity.
• The determined functional residual capacity may be advantageously displayed in conjunction with earlier determinations and in conjunction with other pulmonary conditions, such as PEEP. Changes, or trends, in functional residual capacity over time may thus be discerned, along with changes in the other pulmonary conditions.
• The foregoing provides an attending clinician with significant information for assessing the state of, and trends in, the functional residual capacity of the patient, as well as the relationship between the patient's residual capacity and the other factors, so that the clinician can fully discern the functional residual capacity condition of the patient.
• With respect to assisting the clinician in adequately determining an optimal PEEP for the patient, as noted above, the apparatus and method of the present invention determines and displays related PEEP and functional residual capacity values. This enables the clinician to note, for example, the point at which increases in PEEP produce little, if any, further increases in functional residual capacity.
• The apparatus and method of the present invention also determines and displays a showing of the amount of lung volume recruited or de-recruited as the PEEP is changed. This allows the clinician to distinguish between changes in functional residual capacity due to lung stretching or contracting and those arising from recruitment or de-recruitment.
• Further features of the apparatus and method of the present invention will be apparent from the following detailed description, taken in conjunction with the associated drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a general diagram of a mechanical ventilator and associated apparatus for ventilating a patient.
• FIG. 2 shows an endotracheal tube with a tracheal pressure sensor suitable for use in the present invention.
• FIG. 3 shows a ventilator display unit presenting an initial display screen for use in the present invention.
• FIG. 4 is a chart showing the relationship among a plurality of screens employed in the present invention.
• FIG. 5 shows a display screen for displaying functional residual capacity data and related data.
• FIG. 6 shows a display for use in scaling the display shown inFIG. 5.
• FIG. 7 is a flow chart showing the steps for carrying out a measurement of functional residual capacity.
• FIG. 8 shows a display displaying a log of events and actions that may impact the determination of functional residual capacity.
• FIG. 9 shows a display showing the effect of changes in PEEP on functional residual capacity.
• FIG. 9A shows a display showing changes in PEEP and functional residual capacity before and after a recruitment maneuver.
• FIG. 9B shows a display showing the relationship of changes in PEEP to corresponding changes in functional residual capacity.
• FIG. 10 shows a display showing spirometry data.
• FIG. 11 shows a display for making setup adjustments for the screen shown inFIG. 10.
• FIGS. 12aand12bshow a display showing relationships among functional residual capacity, PEEP, and recruited lung volume.
• FIG. 13 is a flow chart showing the steps for carrying out a method for obtaining the relationships shown inFIGS. 12aand12b.
• FIG. 14 is a graph showing the manner in which recruited/de-recruited volume is determined by the present invention.
DETAILED DESCRIPTIONThe Mechanical Ventilator and Airway Gas Module
• FIG. 1 showsmechanical ventilator10 for providing breathing gases topatient12.Ventilator10 receives air inconduit14 from an appropriate source, not shown, such as a cylinder of pressurized air or a hospital air supply manifold.Ventilator10 also receives pressurized oxygen inconduit16 also from an appropriate source, not shown, such as a cylinder or manifold. The flow of air inventilator10 is measured byflow sensor18 and controlled byvalve20. The flow of oxygen is measured byflow sensor22 and controlled byvalve24. The operation ofvalves20 and24 is established by a control device such ascentral processing unit26 in the ventilator.
• The air and oxygen are mixed inconduit28 ofventilator10 and provided toinspiratory limb30 ofbreathing circuit32.Inspiratory limb30 is connected to one arm of Y-connector34. Another arm of Y-connector34 is connected topatient limb36. During inspiration,patient limb36 provides breathing gases tolungs38 ofpatient12.Patient limb36 receives breathing gases from the lungs of the patient during expiration.Patient limb36 may include components such as a humidifier for the breathing gases, a heater for the breathing gases, a nebulizer, or a water trap (not shown). The breathing gases expired bypatient12 are provided throughpatient limb36 and Y-connector34 toexpiratory limb46 ofbreathing circuit32. The expired breathing gases inexpiratory limb46 are provided throughvalve54 andflow sensor56 for discharge fromventilator10.Valve54 may be used to establish the PEEP forpatient12.
• Patient limb36 includes gas flow andpressure sensor57 which may be of the type shown in U.S. Pat. No. 5,088,332. A pair of pressure ports andlines58,60 are placed on either side of a flow restriction in the sensor and the pressure difference developed across the flow restriction is used byflow measurement unit62 ingas module64 to measure gas flow inpatient limb36. One of the pressure lines is connected to pressuremeasurement unit66 to measure the pressure inpatient limb36.Sensor57 also provides for agas sampling line68 which is connected togas analyzer70.Gas analyzer70 may measure the amount of oxygen and carbon dioxide in the breathing gases. Knowing the amounts of oxygen and carbon dioxide in the breathing gases enables the amount of nitrogen to be determined as the total amount less the amounts of carbon dioxide and oxygen. Respiratory andmetabolic gas module64 may comprise that made and sold by GE Healthcare as a Datex-Ohmeda MCOVX gas module. The output ofgas module64 is provided indata bus72 tocentral processing unit74 inventilator display unit76.Central processing unit26 inventilator10 is also connected tocentral processing unit74 viadata bus78.
The Endotracheal Tube
• To obtain an accurate indication of the pressure inlungs38 of thepatient12,endotracheal tube90 shown inFIG. 2 may be used.Endotracheal tube90 hasend92 for connection topatient limb36. In use,endotracheal tube90 extends through the mouth and into the trachea ofpatient12 to provide an airway passage tolungs38.
• Endotracheal tube90 includespressure sensor catheter94 that extends fromend96 to provide a pressure sampling point that is close tolungs38 ofpatient12 when the endotracheal tube is inserted in the patient and can thus obtain a highly accurate indication of the pressure in the lungs. An intermediate portion ofcatheter94 may lie withinendotracheal tube90. The proximal portion exits the endotracheal tube and is connected via A-A to a pressure transducer and to an auxiliary input toventilator display unit76. The pressure obtained fromcatheter94 is termed Paux. WhileFIGS. 1 and 2 show a connection toventilator display unit76 for this purpose, the connection may, alternatively, be togas module64.
• An endotracheal tube of the type shown inFIG. 2 is described in U.S. Pat. No. 6,315,739.
Ventilator Display Unit
• Display unit76 ofventilator10 receives information from the ventilator andgas module64 and is used by the clinician to control the pneumatic control components ofventilator10 that deliver breathing gases topatient12 viadata bus78. Additionally,central processing unit74 indisplay unit76 carries out the determination of functional residual capacity, recruited/de-recruited volumes, and other quantities employed in the present invention. It will be appreciated that other CPU configurations, such as a single CPU for the ventilator and its display unit may be used, if desired.
• Ventilator display unit76 includesuser interface100 anddisplay102.Display102 is shown in greater detail inFIG. 3.Display102 is divided into a number ofdisplay portions102a-gfor displaying inputted, sensed, and computed information. Display portions62athough102frelate primarily to the operation ofventilator10 and the ventilation ofpatient12 and are discussed briefly below.Display screen portion102gdisplays information and relationships in accordance with the present invention, as described in detail below.
• Display portion102aprovides for the display of operating information ofventilator10. The portion shows the type of ventilation being performed byventilator10, in the exemplary case ofFIG. 3, synchronized, intermittent, mandatory ventilation, or SIMV-volume controlled ventilation.Portion102aalso provides a display of operating information inputted intoventilator10 including the percentage of oxygen for the breathing gases, tidal volume (TV), breathing rate, inspiration time (T_insp), amount of positive end expiratory pressure (PEEP) and the pressure limit (P_limit) set for the volume controlled ventilation. To input these operating parameters intoventilator10, an appropriate one of buttons104athrough104fis actuated.Control knob106 is rotated to enter a desired value for the selected option and pressed to confirm the new parameter value. Further ventilator functions may be controlled by pressing a button that controls a specialized function such asventilator setup button72 that establishes other ventilation modes forpatient12,spirometry button74 for showing and controlling the display of spirometry information, 100% 0₂button76,nebulizer button78, andprocedures button80 that controls specialized procedures forventilator10.
• Display portion102bofdisplay102 shows airway pressure data as measured fromsensor57.Portion102cshows textual information relating to the flow of breathing gases to the patient obtained fromsensor57, andportion102dshows pressure data fromcatheter94 in theendotracheal tube90 during ventilation ofpatient12.
• Portion102eofdisplay102 shows the information inregions102b,102c, and102din graphic form and includes an indication of certain other operating information, such as the mode of ventilation SIMV-VC, and whether certain features of the present invention are operational or not.
• Display portion102fofdisplay102 shows additional data as selected by the clinician. In the example ofFIG. 3 end tidal CO₂(E_tCO₂), lung compliance, expiratory alveolar minute volume (MVe (alv)), respiratory rate, total positive end expiratory pressure, and inspiratory alveolar minute volume (MVi (alv)) are being shown.
• Display portion102a-fremain generally unchanged as the present invention is practiced although, as noted above, the clinician may select the information to be shown in certain portions, such asportion102f.
Display Screen of Present Invention
• Display screen102gis the part ofdisplay102 employed in the present invention. As shown inFIG. 4 and inFIGS. 5, 6,8 and9-12, the content of this screen will change, depending on the inventive feature being utilized, the different content inscreen102gbeing identified as102g1,102g2,102g3, etc. in the appropriate figures of the drawing.
• In general, eachscreen102gwill include a menu orcontrol portion108, agraphic portion110 andtabular portion112. For this purpose,graphic portion110 contains a pair of orthogonal axes by which data can be graphically presented. The clinician may navigate and control the screen usingcontrol knob106.Control knob106 is rotated to scroll through the menu options displayed inmenu portion108, depressed to select a menu option, rotated again to establish a numerical value for the selected option when appropriate, and depressed again to enter the value intoventilator display unit76 or to confirm selection of the menu option.
• FIG. 3 shows an initial content forscreen102grelating to spirometry. As hereinafter noted, spirometry illustrates the relationship between inspired gas volumes and the pressure in the lungs as the patient breathes. The graphic form of the data is normally in a loop, a portion of which is formed during inspiration and the other portion of which is formed during expiration in the manner shown inFIG. 10. Thetabular portion112 provides fields in which various obtained and computed ventilation and lung properties may be displayed.
• Menu portion108 allows the clinician to select a number of options with respect to the display and use of the information shown in graphic andtabular portions110 and112.Menu portion108 also allows the clinician to select a further screen at116 for adjusting the scaling for the abscissa and ordinate ofgraph110 and the setup for spirometry measurements at118.
• Frommenu portion108, the clinician may also select screens that allow the functional residual capacity (FRC) features of the present invention and the spirometry features of the present invention to be carried out by selectingitems120 and122, respectively. The spirometry features of the present invention are identified by applicant as SpiroDynamics or the abbreviation SpiroD.
• FIG. 4 shows the architecture of thescreens102gused in the present invention. As noted above, the spirometry screen shown inFIG. 3 asscreen102g1 is the initial screen appearing asscreen102g. As noted above, associated with this screen are screens for spirometry scaling and spirometry setup.
• By means ofmenu items120 and122, the clinician can select either a screen relating to functional residual capacity, namely screen102g2 shownFIG. 5 or a screen relating toSpiroDynamics comprising screen102g3 ofFIG. 10. The screen format ofFIG. 5 is termed “FRC INview.” The view ofFIG. 10 is termed “spiroD”.
• The FRC INview showing of102g2 includes screen shown inFIG. 6 that allows for scaling of the quantities shown graphically inFIG. 5.
• A further selection on the FRC INview screen allows the clinician to select the FRC log screen shown inFIG. 8 asscreen102g4.
• Selections on either of theFRC INview screen102g2 or theSpiroDynamic screen102g3 allows selection of a PEEP INview screen shown inFIG. 9 as102g5. As hereinafter described, this screen allows the clinician to see the relationship between functional residual capacity and PEEP to assist in selecting an appropriate PEEP forpatient12.
• Finally, an on/off selection option inPEEP INview screen102g5 allows the clinician to displaylung INview screen102g6 shown inFIG. 12. The information contained in this screen relates functional residual capacity, PEEP, and recruited/de-recruited lung volumes to further assist the clinician in setting the appropriate level of PEEP.
FRC Determination and Display
• The flow chart ofFIG. 7 shows a method for determining and displaying functional residual capacity information forpatient12. The clinician uses a screen in the format of102g2 ofFIG. 5. It is assumed that the clinician has previously established an oxygen percentage for the breathing gases to be provided byventilator10 using button104a,control knob106 andscreen region102a, atstep200. In the example shown inFIG. 3, the oxygen percentage is 50%.Ventilator10 can be operated with the set percentage of oxygen to provide breathing gases topatient12 atstep202.
• As noted above, in order to determine the functional residual capacity ofpatient12 by a gas wash-out/wash-in technique, it is necessary to alter the composition of the breathing gases supplied topatient12. To this end, the clinician sets a different level for the oxygen content of the breathing gases. This is performed by selecting theFRC 0₂field206 inmenu portion68 ofscreen102g1 and appropriately establishing theFRC 0₂value. The amount of change may be an increase or decrease from the previously set level established atstep200; however it must be an amount sufficient to perform the functional residual capacity analysis. A change of at least 10% is preferable in order to obtain an accurate indication of the functional residual capacity. To ensure that appropriate oxygen concentrations are supplied topatient12 it is usually desired to increase the oxygen level and, unless the current oxygen level is very high (greater than 90%), a default setting of a 10% increase over the current setting may be provided. The level of oxygen set by the clinician “tracks” changes made in the oxygen content of the breathing gases at the ventilator, as for example by actuating button104a. Thus, for example, if the ventilator oxygen is originally 50% as shown inFIG. 3, and theFRC 02 shown inFIG. 5 is 60%, if the ventilator oxygen setting is later changed to 70%, theFRC 02 amount will automatically move to 80%. Lowering the ventilator oxygen setting, however, will not result in lowering theFRC 02 amount, thereby avoiding the possibility of low oxygen breathing gases for the patient. The alteration of the oxygen content of the breathing gases is carried out instep208 ofFIG. 7. For exemplary purposes, below, an alteration in the form of an increase to 75% O₂is shown inFIG. 5.
• Next, the clinician must select the frequency, or interval, at which the functional residual capacity measurements will be carried out. This is performed atstep210. A single functional residual capacity determination by the present method may be selected by theappropriate field212 inmenu68. Alternatively, a series of FRC determinations or cycles may be selected, with a series interval, set infield214, between each determination. The interval may be between one and twelve hours in increments of one hour. The time when the next functional residual capacity determination begins is shown infield215.
• Alternatively, functional residual capacity measurements can be set to occur automatically in conjunction with certain procedures controlled byventilator10, such as immediately prior and/or after a period of nebulized drug therapy, recruitment maneuvers, a suction procedure, or a change in ventilator setting. Functional residual capacity measurement may be initiated, terminated, delayed, interrupted, or prevented in accordance with the occurrence of events, such as those noted above, that may affect the accuracy of the functional residual capacity measurement. For example, a functional residual capacity measurement may be terminated for a high oxygen procedure forpatient12 and then resumed or started after a “lock out” period.
• The initial or base line amount of nitrogen in the expired breathing gases is determined atstep216. As noted above this may be determined by subtracting the amounts of oxygen and carbon dioxide, as determined bygas analyzer70, from the total amount of the breathing gases, as determined usingflow sensor62.
• While the present invention is described using nitrogen as the inert gas, it will be appreciated that other inert gas may also be used. For example, the breathing gases forpatient12 may include the inert gas helium and amounts of helium expired by the patient could be used in a functional residual capacity measure in the manner described herein.
• To commence the determination of functional residual capacity, breathing gases having the increased amount of oxygen shown in data field105 are provided topatient12 instep218. The increased percentage of oxygen in the breathing gases will wash a portion of the nitrogen or other inert gas out oflungs38 ofpatient12 with each breath of the patient. The amount of breathing gases inspired and expired bypatient12 with each breath, i.e. the tidal volume, is a lung volume that is in addition to the residual volume of the lungs found after expiration. The tidal volume is also smaller than the residual volume. For a healthy adult a typical tidal volume is 400-700 ml whereas the residual volume or functional residual capacity is about 2000 ml. Therefore, only a portion of the nitrogen in thelungs38 ofpatient12 is replaced by the increased amount of oxygen with each breath.
• The amount of nitrogen washed out of the lungs in each breath is determined by subtracting the amount of oxygen and carbon dioxide from the amount of breathing gases expired bypatient12 during each breath obtained usingflow sensor68. Seestep220. Knowing the amount of expired breathing gases, the initial amount of expired nitrogen and the amount expired in each expiration bypatient12, a functional residual capacity quantity can be determined for each successive breath insteps222a,222b. . .222n. Any inert gas wash out/wash in functional residual capacity measurement technique may be used, a suitable technique for determining functional residual capacity for use in the present invention being described in U.S. Pat. No. 6,139,506.
• The functional residual capacity quantity as determined after each successive breath, will tend to increase as nitrogen continues to be washed out of the lungs of the patient by the increased oxygen in the breathing gases. This results from the fact that the breathing gases that are inspired bypatient12, i.e., the tidal volume, are not fully equilibrated inside the entire functional residual capacity volume before being exhaled by the patient. In particular, functional residual capacity volume that lies behind intrinsic lung resistance does not mix as quickly with inspired gases compared to functional residual capacity volume that is pneumatically connected to the trachea through a lower resistance path. As such, the magnitude of breath-to-breath increases in functional residual capacity that are noted are an indication of the amount of intrinsic resistance within the lung gas transfer pathways. Thought of another way, additional functional residual capacity volume that is registered many breaths into the functional residual capacity measurement procedure is lung volume that is not participating well in the gas transfer process.
• As the determination of functional residual capacity proceeds, the determined values for functional residual capacity for the breaths are displayed ingraphic portion110 ofscreen102g2 as a capacity or volume curve224 insteps226a,226b. . .226cat the end of the determination for each breath. This confirms to the clinician that the determination of functional residual capacity is working properly. Also, as curve224 forms from left to right, the shape of the curve is an indication to the clinician of the intrinsic resistance and quality of ventilation of lung functional residual capacity, as discussed above. In the example shown, the clinician can appreciate thatpatient12 has a homogeneously ventilated lung volume, as indicated by the qualitative flatness of the functional residual capacity curve, with a lung capacity of about 2500 ml.
• The scaling ofgraph110 ofFIG. 5 may be automatically altered to provide a scale appropriate to the functional residual capacity data being shown.
• It will be appreciated that, if desired, the data relating breath number to the corresponding functional residual capacity value can also be displayed in tabular form inportion112 ofdisplay portion102g. This could comprise a column containing the breath numbers and a column containing the corresponding functional residual capacity values.
• Mechanical ventilator10 continues to supply breathing gases having increased oxygen concentration for x number of breaths, for example, 20 breaths. A final value for functional residual capacity is determined at the end of the x breaths atstep228 and volume or capacity curve224 extends to this breath to show the final determination of functional residual capacity at the end of 20 breaths. The functional residual capacity measurement may conclude earlier if sufficient stability of breath-to-breath functional residual capacity is found in curve224.
• Thereafter, atstep230 the concentration of oxygen in the breathing gases is altered to the original level of, for example 50%, set atstep208 andventilator10 is operated atstep232 to repeat steps216-228 to make a second determination of functional residual capacity with this alteration of the oxygen concentration in the breathing gases. It will be appreciated that this determination uses a wash-in of nitrogen, rather than a wash-out. This second determination is graphed and displayed ingraphic portion110 asgraph234, in the same manner as graph224, described above. The values for the two final functional residual capacity determinations are shown indata field237 oftabular portion112 ofscreen102g2 instep236. In the example shown, these values are 2500 and 2550 ml.
• For future use, the final determination of functional residual capacity made instep232 is compared to that determined instep228. This is carried out atstep238. It is then determined, instep240, whether the difference between the two determinations of functional residual capacity is less or greater than some amount, such as 25%. If the difference is less than 25%, the two values are averaged and will be subsequently displayed in text form indata field245 instep244 when determination becomes part of the chronological record following a later functional residual capacity determination.
• If the difference between the two values for the functional residual capacity is greater than some amount, such as than 25%, both the final value determined atstep228 and the final value determined instep232 will be displayed bystep246 indata field245 ofFIG. 5 and in thegraph110. This display of the functional residual capacity determination informs the clinician that the accuracy of the functional residual capacity determination is questionable.
• The final value(s) for the functional residual capacity are preferably displayed intabular portion112 ofscreen102g2 along with additional associated data such as the time and date at which functional residual capacity was determined, or the values of PEEPe and PEEPi existing when the functional residual capacity determination was made. PEEPe is the end expiratory pressure established byventilator10. PEEPi, also known as auto PEEP, is the intrinsic end expiratory pressure and is a measurement in pressure of the volume of gas trapped in the lungs at the end of expiration to the PEEPe level.
• While the determination of functional residual capacity has been described as being carried out for a given number of breaths, such as 20, it can be terminated sooner if it is apparent that the functional residual capacity measurement has become stable on a breath-to-breath basis. This can be conveniently determined by measuring the O₂content of the expired breathing gases at the end of the patient's expirations, that is, the end tidal oxygen level. When the amount of oxygen in the expired breathing gases attains and remains at the altered level, it is an indication that the wash out/wash in the inert gas is complete and that the functional residual capacity determination can be terminated.
• Thereafter, if a series of functional residual capacity determinations has been selected atstep210,steps218 through246 are repeated after the time interval indicated indata field214 with the start of the functional residual capacity determination occurring at the time displayed in data field248. The predetermined time interval may be overridden or the functional residual capacity determination terminated by appropriate commands from the clinician entered intomenu68.
• The volume curves, such as224,234, and functional residual capacity data, such as that infield237, generated in the course of successive functional residual capacity determinations are saved byventilator display unit76 and, as such, can be compared to data from previous or subsequent functional residual capacity determinations. This comparison requires that a previous determination of functional residual capacity be selected as a reference curve using the time at which it was obtained as identified indata field250. When a reference curve is selected, an indication is made indata field250 and that functional residual capacity curve is displayed as thereference curve252.Curve252 shows a lung that is not well ventilated. Further indication of the reference curve and reference curve values may be made by a color indication for this data, different from that of the other functional residual capacity data ingraph110 and table112. The result is a visual indicator that can easily be referred to by the clinician to quickly assess improvement or deterioration in the functional residual capacity condition ofpatient12 over time. In the example shown inFIG. 5, there has been an increase in the functional residual capacity ofpatient12 for each eight hour interval.
• Also, it is common practice to alter, usually increase, the PEEP to improve ventilation oflungs38 ofpatient12 by opening areas of the lung that are not being properly ventilated. Tabulating the actual measured values for PEEPe and PEEPi, along with the corresponding functional residual capacity determination, as shown inFIG. 5, allows the clinician to see the effect, if any of applied PEEPe therapy on the volume of the functional residual capacity of the patient's lungs, as well as on the intrinsic PEEP. As also shown inFIG. 5, a history of a certain number of functional residual capacity determinations and PEEP pressures are shown indisplay region70 to present trends and the history of these quantities. In the example shown there, an increase in PEEPe has resulted in an increase in functional residual capacity ofpatient12.
FRC Events Log
• Certain clinical or other events can affect the value for functional residual capacity determined from the method steps shown inFIG. 7. Such events may include performing a suction routine onpatient12 to remove accumulated secretions, administering a nebulized medication, changing the ventilation mode, or changing one or more ventilation parameters, such as tidal volume (TV), breath rate, PEEP, or other parameter.
• By selecting theFRC Log field252 inmenu68 ofscreen102g2 shown inFIG. 5, screen102g4 ofFIG. 8 will be shown to provide a log of the events that may effect functional residual capacity indata field254 along with the time(s) and date(s) the event took place. The log also includes the time, date and value of any periodic functional residual capacity determinations made in the manner described above. The clinician may scroll through the events of the log usingcontrol knob106 to review the functional residual capacity event history in relation to the measured values of functional residual capacity to determine if specific actions had a positive or negative effect on the determined functional residual capacity for the patient.
PEEP Determination and Display
• An aspect of the present invention allows the clinician to ascertain the relationship between the functional residual capacity ofpatient12, and PEEP applied to the patient, thereby to assist the clinician in establishing a PEEP level deemed optimal forpatient12. An optimal PEEP level, in the present context, is one beyond which diminishing functional residual capacity increases in association with PEEP increases is noted. ThePEEP INview screen102g5 ofFIG. 9 may be used for this purpose. Forscreen102g5, a series of periodic functional residual capacity determinations is made, preferably in the manner shown inFIG. 7, with each determination being at a different incremented level of PEEP. For this purpose, inmenu108, the clinician sets an altered concentration of oxygen to be used in the functional residual capacity determination indata field400. The clinician also enters an initial PEEP value atdata field402 and an end PEEP value atdata field404. The initial PEEP value may be low and the end value high, as shown inFIG. 9, or the initial value high and the end value low. The clinician also sets the number of functional residual capacity measurements to be made between the initial and end PEEP values indata field406. In the example shown inFIG. 9, five such measurements are to be made. In an alternative embodiment, the incremental PEEP associated with each measurement, for example an incremental change of 3 cmH₂O for each measurement, may be set. While use of the method of determining functional residual capacity ofFIG. 7 is described below, it will be appreciated, that for the purpose of determining a suitable PEEP, any method of determining functional residual capacity may be employed.
• The series of measurements of functional residual capacity starting at the initial value of PEEP and incrementally moving to the end value of PEEP is then performed as in a manner of steps216-228 or steps216-246 shown inFIG. 7. These functional residual capacity determinations are graphically displayed ingraph110 ofFIG. 9 as points/curve408.Graph110 ofscreen102g5 has functional residual capacity on the ordinate and PEEP on the abscissa. The corresponding numeric functional residual capacity data is displayed in table112 that contains the functional residual capacity values and the PEEP values at which that functional residual capacity value was obtained.
• Curve408 and table112 provide guidance to the clinician in selecting a PEEP level for ventilatingpatient12. For example, from the graph and table ofFIG. 9 it can be seen that increasing the PEEP from 2 to 6 cmH₂O increases functional residual capacity by 500 ml whereas increasing PEEP beyond 6 cmH₂O provides a relatively small increase in functional residual capacity. This suggests to the clinician that 6 cmH₂O would be an appropriate PEEP for the patient.
• Curve408 can be saved in a memory inventilator10 ordisplay unit76. If ventilator settings are not changed or are not changed in any significant way, curves408 obtained at different times in the course of the patient's treatment can be usefully presented ingraphic portion110 ofscreen102gto enable the clinician to note changes in the PEEP curve over time by comparing the data of two ormore curves408 over time.
• Also, while the foregoing has described obtaining and presenting a graph and table of functional residual capacity and PEEP, other aspects of the ventilation ofpatient12 byventilator10 may affect the functional residual capacity. For example, the respiration rate, or the related quantities of expiration time and inspiratory:expiratory (I:E) ratio, can affect functional residual capacity primarily through the mechanism of intrinsic PEEP. Determining and displaying the relationship of one or more of these quantities to functional residual capacity may be useful to a clinician. To this end, the functional residual capacity of thelungs38 ofpatient12 can be determined at differing respiration rates and the data displayed in graphic or tabular form to show the relationship between functional residual capacity and respiration rate. Ingraphic portion110, the abscissa would show the respiration rate while the abscissa continues to show functional residual capacity. A tabular presentation comprises a column of respiration rates and a column of corresponding functional residual capacity determinations.
• FIG. 9B shows an example of a further manner of obtaining and displaying functional residual capacity and PEEP data. InFIG. 9B, the abscissa presents PEEP and the ordinate presents the change in functional residual capacity volume for a given change in PEEP, or ΔFRC/ΔPEEP.
• The relationship between changes in lung volume and changes in lung pressure is termed the “compliance” of the lung. As a general expression of lung characteristics, it describes the elasticity or “stiffness” of the lungs. Lungs of high compliance are elastic and a large change in volume occurs for a small change in pressure. The reverse is true for a stiff lung. Some lung conditions decrease lung compliance. Others, such as emphysema, increase lung compliance.
• In the present context, the presentation of changes in functional residual capacity volume, ΔFRC, to changes in PEEP, ΔPEEP, inFIG. 9B as compliance properties of the lung serves to emphasize clinically important data presented in graphic and textual form inFIG. 9 and to aid the clinician in selecting an appropriate PEEP for the patient. For this purpose, the ordinate ofgraph110 inFIG. 9B is labeled as compliance. The data inFIG. 9 presented in the manner ofFIG. 9B shows that the incremental 2 cmH₂O pressure increase in PEEP from 2 to 4 cmH₂O PEEP produced a functional residual capacity volume increase of 200 ml, giving a compliance of 100 ml/cmH₂O, as graphically shown inFIG. 9B at the left hand point in the graph. In the same manner, the incremental 2 cmH₂O PEEP increase from 4 to 6 cmH₂O PEEP produced a functional residual capacity volume increase of 300 ml, giving a compliance of 150 ml/cmH₂O at the second point, proceeding to the right in the graph ofFIG. 9B. Corresponding determinations are made for the incremental PEEP increases from 6 to 8 and from 8 to 10 cmH₂O and shown by the remaining points inFIG. 9B. The data may also be presented in tabular form in table112 ofFIG. 9B.
• The peak in the graph ofFIG. 9B suggests to the clinician that a PEEP of 6 cmH₂O would be advantageous for the patient.
Recruitment /De-recruitment of Lung Volume
• Whilescreen102g5 ofFIG. 9 provides valuable insight and information to the clinician, it may also be helpful for the clinician to have a better idea of how much of an increase in functional residual capacity is due to distension of the lung by increased PEEP and how much is due to making previously closed alveolar sacs available, i.e., opening of the lung by “recruitment” of lung volume.
• One way such information may be obtained using thePEEP INview screen102g5 ofFIG. 9 is as follows. Functional residual capacity is determined for a series of PEEPs, in the manner described above to produce a curve, such ascurve408. Thereafter a recruitment maneuver is carried out onpatient12 to open the alveolar sacs of the lungs of the patient. This would ordinarily be the provision of a high level of PEEP that, while it may only be tolerated by a patient for a short period of time, serves to open the alveolar sacs of the patient lungs. This is ordinarily carried out by the clinician by operatingventilator10 independently ofscreen102g5. For this maneuver, it is preferable to use a recruitment PEEP greater than the highest PEEP set inmenu108 ofscreen102g5 to ensure the alveolar sacs open.
• After the recruitment maneuver has been completed, the functional residual capacity is again determined for the same series of PEEPs used prior to performing the recruitment maneuver to produce anothercurve408a. The two curves can be displayed ingraphic portion110 ofscreen102g5 in the manner shown inFIG. 9A. If the recruitment maneuver resulted in the recruitment of lung volume, i.e. in the opening of previously closed alveolar sacs,curve408awill show a higher functional residual capacity thancurve408, as shown inFIG. 9A.Curves408 and408awill tend to come together at the PEEP level at which de-recruitment of lung volume begins to occur. This suggests to the clinician that a PEEP level greater than one at which de-recruitment begins to occur would be appropriate for the patient.
• Another way such information can be obtained using the spirometry aspects of the present invention, as shown in theSpiroD screen102g3 ofFIG. 10 and, particularly, thelung INview screen102g6 ofFIG. 12.
• In general, spirometry is used to determine the mechanics of a patient's lungs by examining relationships between breathing gas flows, volumes, and pressures during a breath of a patient. A commonly used relationship is that between inspired/expired breathing gas flows and volumes that, when graphed, produces a loop spirogram. The size and shape of the loop is used to diagnose the condition of the lung.
• A relationship also exists between inspired/expired gas volumes and pressure in the lungs. In the past, a problem with the use of this relationship has been that pressure has been measured at a point removed from the lungs so that the measured pressure may not be an accurate reflection of actual pressure in the lungs thus lessening the diagnostic value of the pressure-volume loop. Through the use ofcatheter94 extending fromendotracheal tube90 shown inFIG. 2, a far more accurate indication of lung pressure is obtained. For a healthy lung, a graph of the relationship between volume and pressure is roughly an elongated, narrow loop of positive uniform slope. That is, constant increments of inspired volume increase lung pressure by constant increments. The loop is formed because there remains some amount of lung resistance below the pressure sensing point at the end ofcatheter94. In a diseased lung, the loop may be wider and may also reflect a non-linear lung volume pressure relationship. For such a lung, the volume-pressure relationship over the course of an inspiration/expiration may be in a form such as that shown inFIG. 10 by420, and a curve illustrating the volume-pressure relationship resulting from a mathematical computation using loop data is plotted, as shown inFIG. 10 byreference numeral422. Thecurve422 shown inFIG. 10 in often termed a “dynostatic curve” and is used for diagnostic purposes. A typical dynostatic curve is shown inFIG. 10 to contain a middle portion of somewhat linear positive slope and a pair of inflection points separating end portions of differing slopes. The dynostatic curve and its generation is described in Practical Assessment of Respiratory Mechanics by Ola Stenqvist, British Journal of Anesthesia 91(1), pp. 92-105 (2003) and “The Dynostatic Algorithm in Adult and Paediatric Respiratory Monitoring“by Soren Sondergaard, Thesis, University Hospital, Gothenburg University, Sweden (2002).
• Ingraph110 ofFIG. 10, the abscissa of the graph is lung pressure measured at the end ofcatheter94 connected to the auxiliary input A ofventilator display unit76 and is termed “Paux”. The ordinate is scaled in volume of breathing gases inspired/expired bypatient12. It will be appreciated that this volume comprises the tidal volume for the patient. The tidal volume moves into and out of the lungs in a manner that can be described as being “above” the functional residual capacity. That is, for normal breathing, a patient starts a breath with the volume of the lungs at the functional residual capacity which may, for example be 2000 ml. During inhalation, the volume of the lungs increases by the tidal volume of, for example 500-700 ml, and during exhalation, the volume of the lungs decreases by approximately that amount. The same situation occurs when a patient is being provided with breathing gases from a mechanical ventilator, such asventilator10. It must thus be appreciated that the ordinate of thegraph110 inFIG. 10 is scaled in the relative volume of inspiration/expiration for which the origin of the graph is zero, not in absolute volume that would also take into consideration functional residual capacity and for which the origin of a graph would be the amount of the functional residual capacity. The scaling ofgraph110 ofFIG. 10 may be automatically altered to provide a scale appropriate to the spirometry data being shown.
• With PEEP applied topatient12 byventilator10, there will be a movement of the graph away from the origin of the axes along the abscissa. The graph will move right by the amount of the PEEP, i.e. the lung pressure at the end of expiration bypatient12.
• Themenu portion108 ofSpiroD screen102g3 shown inFIG. 10 allows the user to open up a set up menu, shown inFIG. 11 that allows the clinician to turn a purge flow throughcatheter94 on or off or to zero the Paux sensor connected tocatheter94 when the purge flow is on andendotracheal tube90 has been inserted inpatient12. The SpiroD set-up menu also allows the clinician to set the scaling for the graphical portions of the display. A “Paux Alarm” screen, reached from the SpiroD setup screen ofFIG. 11, allows the clinician to set appropriate alarms for patient lung pressure, as sensed bycatheter94.
• Various other selections onmenu108 ofscreen102g3 ofFIG. 10 allow the clinician to save the current data and to view this information as a first or second reference for use and display with subsequently obtained data. Up to a given number of loops, for example, six loops and curves, may be saved for analytical purposes. The “erase reference” option allows the user to determine which information to save and which to delete.
• The “SpiroD loops” and “SpiroD curves” menu items may be turned on or off. Selecting “on” for both the curve and loop will display both the loop and the curve at once in the manner shown inFIG. 10. For easier comparison among loops and curves obtained at various times, either the loop or curve showing may be turned “off.” The “cursor” option allows the clinician to scroll along the horizontal axis and display the actual pressure and volume measurements associated with the loops or curves that are displayed.
• For the graphical showing ofgraph110 of thescreen102g3 inFIG. 10, volumes and pressures are obtained fromsensor57 andcatheter94 and the spirometry data, computed and displayed for every third breath if the respiratory rate is less than some desired number, for example,15 breaths per minute. If the respiratory rate is greater than that number, every fifth breath used. Theloop420 for a complete inspiratory/expiratory breathing cycle is displayed in the graph ofscreen102g3 ofFIG. 10. Thedynostatic curve422 is then calculated for display ingraph110.
• Various compliance values for the patient's lungs are shown in the table112 ofscreen102g3 ofFIG. 10. Compliance can be seen as the amount by which the volume of the lung increases for an incremental increase in lung pressure. The data necessary to determine compliance can be obtained fromsensor57 andgas module64. Compliance is represented by the slope ofdynostatic curve422. It is an indication of the stiffness or elasticity of the lung. In a stiff lung, an incremental increase in pressure results in a smaller increase in volume over a lung that is more elastic and the slope ofcurve422 is more horizontal. In an elastic lung, the reverse is true. To aid the clinician in analyzing the lungs ofpatient10, the compliance is computed at the beginning, middle, and end of the respiratory cycle of the patient. As shown in the example inFIG. 10, the middle portion ofdynostatic curve422 indicates a portion of greater compliance than the end portions. This is reflected in the greater slope of the middle portion over those of the end portions. The table of the screen sets out numerical values. Ordinarily, the highly compliant, middle portion ofcurve422 shown inFIG. 10 is that in which the lung is most effectively ventilated.
• The table112 ofdisplay102g3 ofFIG. 10 also shows the peak pressure achieved in the lungs during the breath, the PEEP pressure, and the airway resistance, Raw. The airway resistance is the pressure drop experienced by breathing gas flow of the lungs and is expressed in units of pressure per unit of flow. Airway resistance can also be determined with data fromsensor57 andgas module64 in a manner described in the Stenqvist reference noted above.
• The present invention provides a unique way of viewing the relationship among functional residual capacity, PEEP, and recruited:de-recruited lung volume that is deemed helpful in enabling a clinician to determine a suitable value for PEEP. To carry this out, thePEEP INview screen102g5 shown inFIG. 9 is reached. Among the menu items present inPEEP INview screen102g5 is “Lung INview on/off” infield424. When “Lung INview” is turned “on” ascreen102g6 in the format ofFIGS. 12aand12bis present inventilator display unit76. As shown inFIG. 4, thePEEP INview screen102g6 ofFIG. 9 can be reached either via theFRC INview display102g2 described above and shown inFIG. 5 at field426 or the SpiroD display102g3 shown inFIG. 10 atfield428. When the former route is chosen to reach the PEEP INview screen ofFIG. 9, the spirometry data described above will still be obtained and calculated inventilator display unit76 but the screen ofFIG. 10 will not be displayed in the display unit.
• To proceed with the Lung INview display, in thePEEP INview screen102g5 shown inFIG. 9, the menu item “Lung INview on/off”424 is toggled “on” and the ventilator display unit will show screen102g6 in the format ofFIGS. 12aand12b.
• For an embodiment of the invention using a wash in/wash out determination of functional residual capacity, infield430 ofmenu108 ofdisplay102g6 ofFIG. 12a/b, the clinician sets the altered oxygen level to be used in the functional residual capacity measurement employed to produce the Lung INview data. To begin the process of providing data fordisplay102g6, the clinician establishes initial and end PEEPs values atfields432 and434, as well as the number of measurements to be taken within the range of PEEP so established atfield436, in the same general manner as described above in connection with thePEEP INview display102g5 ofFIG. 9. Alternatively, and if desired,field436 can show the incremental/decremental PEEP step, for example a step of 3 cmH₂O. In the example shown inFIG. 12, the initial PEEP is 25 cmH₂O, the end PEEP is 5 cmH₂O, and five measurements will be taken within that range of PEEP, namely measurements at 25, 20, 15, 10, and 5 cmH₂O of PEEP. It is deemed preferable to initiate the process of determining the optimal PEEP by using the highest value of the selected range and thereafter decrementing the applied PEEP to the lower end level. However, as noted in connection with the description ofscreen102g5 ofFIG. 9, the invention can also be practiced with incrementing PEEP from a low value to a high value, depending on the preference of the clinician.
• Thegraph110 ofscreen102g6 ofFIG. 12 has the abscissa scaled in PEEP and the ordinate scaled in functional residual capacity. The table112 ofscreen102g6 provides columns for the set PEEP, functional residual capacity and airway resistance (Raw). The table also includes a column for “difference” that, as hereinafter described, contains a numerical indication of the lung volume that is recruited/de-recruited in the lungs as the PEEP is incremented/decremented.
• As shown inFIG. 13, atstep500, a recruitment maneuver is preferably run onpatient12 to open the lungs of the patient. As noted above, such recruitment maneuver would typically be the provision of a high level of PEEP opens the alveolar sacs of the patient lungs. It is preferable to use a recruitment PEEP greater than the highest PEEP set inmenu108 ofscreen102g6 to ensure the alveolar sacs open. Instep502, the functional residual capacity and PEEP parameters are established inmenu108 ofdisplay102g6, shown inFIG. 12, as previously described. Step502 may occur beforestep500 reversing the order shown inFIG. 13. Thereafter, instep504, the patient is ventilated byventilator10 with the PEEP at the initial level found in the menu. In the present exemplary instance,patient12 is initially ventilated with a PEEP of 25 cmH₂O instep504.
• Instep506, the functional residual capacity ofpatient12 is determined by the wash in/wash out technique using the altered oxygen concentration level as described above in connection withFIGS. 5 and 7 or using some other appropriate technique for measuring functional residual capacity. The determined value is graphically displayed ingraph110 at the corresponding value of PEEP aspoint508. The values are also entered in tabular form in table112 ofscreen102g6 ofFIG. 12.
• Next, the PEEP pressure is altered to the next decremental level, in the present instance from 25 cmH₂O to 20 cmH₂O, and the patient is ventilated at the new PEEP level instep510. Instep512, the functional residual capacity is again determined and displayed with respect to PEEP in the same manner as instep506 atpoint514.Curve516 is formed ingraph110 frompoints508 and514.
• A dynostatic curve is also obtained for the ventilation of the patient's lungs at the PEEP of 20 cmH₂O.FIG. 14 shows the spirometry data obtained atstep518 for the PEEP of 20 cmH₂O. For ease of explanation, the spirometry loop is shown simply as anellipse520 anddynostatic curve522 shown as a straight line, it being understood that the spirometry loops and curves will actually resemble those shown inFIG. 10. However, the ordinate of the graph ofFIG. 14 is scaled in absolute volume, not the relative volume ofFIG. 10, so as to show functional residual capacity, as noted insteps506 and512.
• The origin fordynostatic curve522 will be the PEEP value of 20 cmH₂O and the associated functional residual capacity value so that the origin corresponds to point514 ofFIG. 12 andFIG. 14.FIG. 14 can be seen as an enlargement ofFIG. 12 showing the data used to generate the data ofFIG. 12 and also showing dynostatic loops and curves.FIG. 14 shows a significant amount of data relating to the condition of the lungs ofpatient12. Thegraph110 ofscreen102g6 ofFIG. 12 shows the salient features of that data, thereby to assist and facilitate the selection of an optimal PEEP forpatient12 by the clinician.
• Steps510,512 and518 are then repeated for the next decremented PEEP of 15 cmH₂O. This produces anew point530 of functional residual capacity and PEEP incurve516 inFIGS. 12aand12band inFIG. 14. It also produces a new spirometry loop anddynostatic curve532.Steps510,512, and518 are again repeated for a PEEP of 10 cmH₂O to producepoint534 anddynostatic curve536 shown inFIG. 14.
• Steps524,526 and528 are used to determine the amount of recruited or de-recruited volume obtained in the lungs ofpatient12. At PEEPs of 15 and 10 cmH₂O, some de-recruitment of lung volume is noted and steps524,526 and528 ofFIG. 13 are explained in conjunction with these PEEPs. Instep524 and using thedynostatic curve536 for the reduced PEEP of 10 cmH₂O, the volume of the lungs at a pressure corresponding to that of the previous PEEP of 15 cmH₂O is determined. Graphically, this may be accomplished by establishingvertical line538 in ofFIG. 14 at the previous PEEP of 15 cmH₂O and noting the intersection ofline538 anddynostatic curve536 atpoint540.
• The amount of volume on the ordinate scale represented by theline segment538abetweenpoints530 and540 is also determined. In the present instance, this amounts to approximately 180 ml. Instep528, this value is placed in table112 ofscreen102g6 in association with the previous PEEP of 15 cmH₂O. Instep526,point540 is placed ingraph110 ofscreen102g5 as shown inFIGS. 12aand12b.
• FIG. 12bshows the completed Lung INview process, including the final measurement of functional residual capacity at a PEEP of 5 cmH₂O. This is carried out by repeatingsteps510,512, and518, for a PEEP of 5 cmH₂O to produceplot542 of functional residual capacity and PEEP anddynostatic curve544.Repeating steps524,526, and528 producespoint546 andline segment548arepresenting a volume of about 120 ml. The data is displayed in a manner corresponding to that described above ingraph110 and table112 ofscreen102g6. As the determination of the “difference” requires both functional residual capacity measurement taken at a previous PEEP and a dynostatic curve from subsequent PEEP and is referenced to the previous PEEP, no difference value will appear in the graph and table ofscreen102g6 ofFIG. 12bfor the 5 cmH₂O level of PEEP.
• Reverting now to the situation with respect to the PEEPs of 25 and 20 cmH₂O, as noted above, at these higher PEEPs, there is little de-recruitment of lung volume as the alveolar sacs are continuously open during the respiratory cycle. This is expressed inFIG. 14 by the fact thatdynostatic curve522 for a PEEP of 20 cmH₂O passes throughpoint508 formed using the functional residual capacity for a PEEP of 25 cmH₂O. Thus, no difference of the type represented bylines538aand548awill be seen when the PEEP is reduced from 25 cmH₂O to 20 cmH₂O . This fact is shown as 0 difference in table112 for a PEEP of 25 cmH₂O, since, as noted atstep528, the difference is tabulated to the previous PEEP.
• An analogous situation exists fordynostatic curve532 generated for the PEEP of 15 cmH₂O. That is,dynostatic curve532 passes throughpoint514 formed using the functional residual capacity for 20 cmH₂O. Again, there is a zero difference as tabulated in table112 for 20 cmH₂O. Ingraph110 ofFIGS. 12aand12b, where the difference approximates zero, the differences determined instep528 and the plot of the functional residual capacity at the previous PEEP are roughly the same and overlapping.
• However, as the PEEP is further decremented, de-recruitment of lung volume begins to occur. For example,point530 shows that for a PEEP of 15 cmH₂O, when the lung pressure is at that level, the lung volume is about 1800 ml. But when the PEEP is lowered to 10 cmH₂O, for a pressure in the lungs of 15 cmH₂O, the lung volume is only about 1620 ml, as evidenced by the plot ofpoint540. There has thus been a lung volume de-recruitment of approximately 180 ml when the PEEP was lowered from 15 cmH₂O to 10 cmH₂O, as evidenced by the length ofline segment538a.
• An analogous situation exists when the PEEP is lowered from 10 cmH₂O to 5 cmH₂O as shown byline segment548a. The de-recruitment of lung volume in that case is about 120 ml.
• It will be appreciated, that a clinician may readily discern an optimal PEEP forpatient12 from the graphic and tabular data provided inscreen102g6 ofFIG. 12b. Right after the recruitment maneuver ofstep500, and for the higher PEEPs of 25 and 20 cmH₂O, the alveolar sacs will remain generally open during breathing due to the higher pressures. While this is advantageous from the standpoint of lung volume, the high pressure may be injurious to the patient. There is little reduction, or de-recruitment of lung volume as expiration proceeds to the end expiratory pressure, as shown inFIG. 12.
• As PEEP is further reduced to 15 cmH₂O and then to 10 cmH₂O, a difference in volume will occur andcurve548 will separate belowcurve516 ingraph110. The clinician will be able to note that at a PEEP of 10 cmH₂O, a portion of the lung volume that had been open at a PEEP of 15 cmH₂O will remain closed as pressure is increased from the PEEP of 10 cmH₂O to 15 cmH₂O during the course of inspiration while moving up the dynostatic curve. This difference, 180 ml in the example shown inFIGS. 12aand12bandline segment538aofFIG. 14, represents the “de-recruitment” of lung volume as the PEEP was reduced from 15 cmH₂O to 10 cmH₂O. Conversely, a volume would be “recruited” if the PEEP was increased from 10 cmH₂O to 15 cmH₂O.
• Further lowering the PEEP to 5 cmH₂O results in an additional de-recruited loss of lung volume of 120 ml as shown byline segment548a. As can be seen from the graph, the lung begins to lose volume or “derecruits” at PEEP settings below 15 cmH₂O and this suggests that 15 cmH₂O is a PEEP that is best suited or optimal forpatient12. In selecting an optimal PEEP, the clinician may set the PEEP at 15 cmH₂O so as to obtain some recruitment of lung volume over a PEEP of 10 cmH₂O. This may be preceded by a recruitment maneuver, such as atstep500, if desired. Or, the clinician may leave the PEEP at 10 cmH₂O since some recruitment is obtained at that level of PEEP.
• As described above in connection with the determination of functional residual capacity, the determination of a suitable PEEP can be set to automatically occur in conjunction with certain procedures carried out byventilator10 or treatment procedures carried out onpatient12.
• While the foregoing describes an example in which PEEP is decreased as the amount of recruitment or de-recruitment is determined, it will be appreciated that the technique may also be carried out using incremented, increasing values of PEEP.
• Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.

Claims (59)

1-55. (canceled)

56. A ventilator for ventilating a patient and for determining a relationship between a ventilator parameter and the functional residual capacity of the patient, said ventilator comprising:

at least one gas flow control valve (20,24,54) in a flow path (32) for breathing gases of the patient and a controller (26 or74) for said at least one gas flow control valve establishing and altering a parameter of the ventilation supplied to the patient;

a gas analyzer (70) measuring a compositional characteristic of the breathing gases of the patient;

a sensor (62) measuring a quantitative characteristic of the breathing gases of the patient;

a central processing unit (26 or74) coupled to said gas analyzer and sensor and determining the functional residual capacity of the patient at a plurality of parameter values; and

a display (102) coupled to said central processing unit and displaying data relating functional residual capacity to corresponding parameter values.

57. The ventilator according toclaim 56 wherein said at least one gas flow control valve and controller establish and alter a parameter comprising the PEEP supplied to the patient, said central processing unit is further defined as determining the functional residual capacity of the patient at a plurality of PEEPs, and said display displays data relating functional residual capacity to corresponding PEEP levels.

58. The ventilator according toclaim 57 wherein said at least one gas flow control valve and controller increment or decrement the PEEP.

59. A ventilator according toclaim 56 wherein said central processing unit determines the functional residual capacity of the patient by an inert gas wash-in or wash-out technique.

60. The ventilator according toclaim 59 wherein the ventilator provides breathing gases containing oxygen and nitrogen to the patient and wherein said at least one gas flow control valve and said controller alter the amount of oxygen contained in the breathing gases supplied to the patient.

61. The ventilator according toclaim 57 wherein said display displays data relating PEEP to the corresponding functional residual capacity in graphic form.

62. The ventilator according toclaim 57 wherein said display displays data relating PEEP to the corresponding functional residual capacity in tabular form.

63. The ventilator according toclaim 62 wherein the tabular display includes an indication of PEEPe and PEEPi with the corresponding functional residual capacity.

64. The ventilator according toclaim 57 wherein said controller sets one or more of initial PEEP, end PEEP, number of measurements, or increment/decrement of PEEP alteration.

65. The ventilator according toclaim 56 further defined as including a memory for storing data relating functional residual capacity to corresponding parameter values.

66. The ventilator according toclaim 56 wherein said display displays data obtained at different times.

67. The ventilator according toclaim 56 wherein said at least one gas flow control valve and controller alter one of a respiration rate, expiration time, or inspiratory:expiratory ratio parameter; said central processing unit determines the functional residual capacity of the patient at a plurality of different values for the altered parameter, and said display displays data relating functional residual capacity to corresponding parameter values.

68. The ventilator according toclaim 57 wherein said at least one gas flow control value and said controller carry out a recruitment maneuver and said display displays data obtained prior and subsequent to the recruitment maneuver.

69. A method determining a relationship between a ventilation parameter and the functional residual capacity of a ventilated patient, said method comprising the steps of:

(a) causing alteration in a parameter of the ventilation supplied to the patient;

(b) determining the functional residual capacity of the patient at a plurality of parameter values; and

(c) displaying data relating to functional residual capacity to corresponding parameter values.

70. The method according toclaim 69 wherein step (a) is further defined as causing an alteration in the PEEP supplied to the patient, step (b) is further defined as determining the functional residual capacity of the patient at a plurality of PEEPs, and step (c) is further defined as displaying data relating functional residual capacity to corresponding PEEP levels.

71. The method according toclaim 70 wherein step (a) is further defined as incrementing or decrementing the PEEP.

72. The method according toclaim 70 wherein step (b) is further defined as determining the functional residual capacity of the patient by an inert gas wash-in or wash-out technique.

73. The method according toclaim 72 wherein the ventilated patient is provided with breathing gases containing oxygen and nitrogen and wherein step (b) is further defined as altering the amount of oxygen contained in the breathing gases provided to the patient.

74. The method according toclaim 70 wherein step (c) is further defined as displaying data relating PEEP to the corresponding functional residual capacity in graphic form.

75. The method according to claim14 wherein step (c) is further defined as displaying data relating PEEP to the corresponding functional residual capacity in tabular form.

76. The method according toclaim 75 wherein step (c) is further defined as displaying an indication of PEEPe and PEEPi with the corresponding functional residual capacity.

77. The method according toclaim 70 including a step for setting one or more of initial PEEP, end PEEP, number of measurements, or increment/decrement of PEEP alteration.

78. The method according toclaim 69 further defined as storing data relating to functional residual capacity to corresponding parameter values.

79. The method according toclaim 78 further defined as displaying data obtained at different times.

80. The method according toclaim 69 wherein step (a) is further defined as causing an alteration in one of a respiration rate, expiration time, or inspiratory:expiratory ratio parameter; step (b) is further defined as determining the functional residual capacity of the patient at a plurality of different values for the altered parameter, and step (c) is further defined as displaying data relating functional residual capacity to corresponding parameter values.

81. The method according toclaim 69 further including step of carrying out a recruitment maneuver and step (c) is further defined as displaying data obtained prior and subsequent to the recruitment maneuver.

82. Apparatus for indicating recruitment/de-recruitment of lung volume in association with varying levels of PEEP for a ventilated patient, said apparatus comprising:

at least one gas flow control valve in a breathing gas flow path and a controller for said at least one valve for ventilating the patient from a ventilator, said at least one gas flow control valve and controller ventilating the patient with a first level of PEEP, altering the PEEP to a second level, different than said first level, and ventilating the patient with the second level of PEEP;

means for measuring the functional residual capacity of the patient at one of the first and second levels of PEEP;

means for determining a spirometry dynostatic curve for the breathing action of the patient at the other of said first and second levels of PEEP;

means for determining a lung volume difference for the functional residual capacity at the one level of PEEP and a point on the dynostatic curve for the other level of PEEP corresponding to the one level of PEEP; and

a display for displaying the lung volume difference as recruited/de-recruited volume in the lungs when changing between the first and second levels of PEEP.

83. The apparatus according toclaim 82 wherein said at least one gas flow control valve and controller alters the PEEP from a higher level to a lower level.

84. The apparatus according toclaim 82 wherein said means for determining a spirometry dynostatic curve is further defined as determining a spirometry dynostatic curve on an absolute scale using functional residual capacity.

85. The apparatus according toclaim 82 wherein said display displays the lung volume differences at various PEEPs in conjunction with functional residual capacities of the lungs.

86. The apparatus according toclaim 85 wherein said display graphically displays the lung volume differences and functional residual capacities.

87. The apparatus according toclaim 85 wherein said display displays the recruited/de-recruited volumes and functional residual capacities in tabular form.

88. The apparatus according toclaim 82 further including means for performing a recruitment maneuver on the patient.

89. A method for indicating recruitment/de-recruitment of lung volume in association with varying levels of PEEP for a ventilated patient, said method comprising the steps of:

(a) ventilating the patient with a first level of PEEP, altering the PEEP to a second level, different than said first level, and ventilating the patient with the second level of PEEP;

(b) measuring the functional residual capacity of the patient at one of the first and second levels of PEEP;

(c) determining a spirometry dynostatic curve for the breathing action of the patient at the other of said first and second levels of PEEP;

(d) determining a lung volume difference for the functional residual capacity at the one level of PEEP and a point on the dynostatic curve for the other level of PEEP corresponding to the one level of PEEP; and

(e) displaying the lung volume difference as recruited/de-recruited volume in the lungs when changing between the first and second levels of PEEP.

90. The method ofclaim 89 wherein step (a) alters the PEEP from a higher level to a lower level.

91. The method according toclaim 89 further including an initial step of performing a recruitment maneuver on the patient.

92. The method according toclaim 89 wherein step (c) is further defined as determining a spirometry dynostatic curve on an absolute scale using functional residual capacity.

93. The method according toclaim 89 further defined as displaying the lung volume differences at various PEEPs in conjunction with functional residual capacities of the lung.

94. The method according toclaim 93 further defined as graphically displaying the lung volume differences and functional residual capacities.

95. The method according toclaim 93 further defined as displaying the recruited/de-recruited volumes and functional residual capacities in tabular form.

96. The method according toclaim 89 further defined as repeating the steps of the method by ventilating the patient at the other of the first and second levels of PEEP, altering the PEEP to a third level, and carrying out the corresponding steps of the method.

97. A ventilator for ventilating a patient and for determining a relationship between a ventilator parameter and a functional residual capacity characteristic of the patient, said ventilator comprising:

at least one gas flow control valve in a flow path for breathing gases of the patient and a controller for said at least one gas flow control valve for establishing and altering a PEEP supplied to the patient;

a gas analyzer measuring a compositional characteristic of the breathing gases of the patient;

a sensor measuring a quantitative characteristics of the breathing gases of the patient;

a central processing unit coupled to said gas analyzer and sensor for determining the functional residual capacity of the patient at a plurality of PEEP values and for determining the relationship between increments in the alteration in PEEP and resulting differences in functional residual capacity; and

a display coupled to said central processing unit and displaying data presenting the relationship determined by said central processing unit to corresponding values of PEEP.

98. The ventilator according toclaim 97 wherein said at least one gas flow control valve and controller increment or decrement the PEEP.

99. A ventilator according toclaim 97 wherein said central processing unit determines the functional residual capacity of the patient by an inert gas wash-in or wash-out technique.

100. A ventilator according toclaim 99 wherein said ventilator provides breathing gases containing oxygen and nitrogen to the patient and wherein said at least one gas flow control valve and controller alter the amount of oxygen contained in the breathing gases supplied to the patient.

101. The ventilator according toclaim 97 wherein said display displays data presenting the relationship determined by said central processing unit to corresponding PEEP values in graphic form.

102. The ventilator according toclaim 97 wherein said display displays data presenting the relationship determined by said central processing unit to corresponding PEEP values in tabular form.

103. The ventilator according toclaim 102 wherein the tabular display includes an indication of PEEPe and PEEPi with corresponding PEEP values.

104. The ventilator according toclaim 97 wherein said controller sets one or more of initial PEEP, end PEEP, number of measurements, or increment/decrement of PEEP alteration.

105. The ventilator according toclaim 97 further defined as including a memory for storing data relating the relationship determined by means (c) to corresponding PEEP values.

106. A method determining a relationship between a ventilation parameter and a functional residual capacity characteristic of a ventilated patient, said method comprising the steps of:

(a) causing alteration in a PEEP supplied to the patient;

(b) determining the functional residual capacity of the patient at a plurality of PEEP values;

(c) determining the relationship between increments in the alteration in PEEP and resulting differences in functional residual capacity; and

(d) displaying data presenting the relationship determined in step (c) to10 corresponding values of PEEP.

107. The method according toclaim 106 wherein step (a) is further defined as incrementing or decrementing the PEEP.

108. The method according toclaim 106 wherein step (b) is further defined as determining the functional residual capacity of the patient by an inert gas wash-in or wash-out technique.

109. The method according toclaim 106 wherein step (d) is further defined as displaying data presenting the relationship determined in step (c) to corresponding PEEP values in graphic form.

110. The method according toclaim 106 wherein step (c) is further defined as displaying data presenting the relationship determined in step (c) to corresponding PEEP values in tabular form.

111. The method according toclaim 110 wherein step (d) is further defined as displaying an indication of PEEPe and PEEPi with the corresponding PEEP values.

112. The method according toclaim 106 including a step for setting one or more of initial PEEP, end PEEP, number of measurements, or increment/decrement of PEEP alteration.

113. The method according toclaim 106 further defined as storing data relating the relationship determined in step (c) to corresponding PEEP values.

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