US20110232641A1 - System and method for ventilating lungs - Google Patents

Abstract

A system for ventilating lungs of a subject is disclosed herein. The system includes a control unit configured to control operation of the system. The system also includes a machine ventilator circuit configured to assist the breathing functions of the subject, the machine ventilator circuit includes an inspiration delivery unit, and an expiration circuit. The system also includes a manual ventilation circuit comprising a manual bag guiding a gas from the manual bag wherein a gas flow is guided out from the manual bag to assist an inspiration phase, a gas flow is received to fill the manual bag during an expiration phase, and wherein the gas flow received to fill the manual bag during the expiration phase at least partially comprises the gas flow guided to assist the inspiration phase

Description

BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The field of the invention relates generally to a system and method for ventilating lungs of a subject that enables the selection of one of a machine ventilation for assisting breathing functions and a manual ventilation with a manual bag which can be compressed for an inspiration.
• 2. Description of the Prior Art
• Presently, anesthesia machines are optimized for delivering anesthesia to a patient using volatile anesthetic agent liquids. In such systems, the anesthetic agent is vaporized and mixed into the breathing gas stream in a controlled manner to provide a gas mixture for anesthetizing the patient for a surgical operation. The most common volatile anesthetic agents are halogenated hydrocarbon chains, such as halothane, enflurane, isoflurane, sevoflurane, and desflurane. Additionally, nitrous oxide (N₂O) can be counted in this group of volatile anesthetic agents, although the high vapor pressure of nitrous oxide causes nitrous oxide to vaporize spontaneously in the high pressure gas cylinder, where it can be directly mixed with oxygen. The anesthetizing potency of nitrous oxide is seldom enough to anesthetize a patient and therefore is typically mixed with another volatile agent.
• Since volatile anesthetic agents are expensive and environmentally damaging to the atmospheric ozone layer, anesthesia machines have been developed to minimize the use of these gases. To keep patient's anesthetized, a defined brain partial pressure for the anesthetic agent is required. This partial pressure is maintained by keeping the anesthetic agent partial pressure in the lungs adequate. During a steady state, the lung and body partial pressures are equal, and no net exchange of the anesthetic agent occurs between the blood and the lungs. However, to provide oxygen and eliminate carbon dioxide, continuous lung ventilation is required.
• Anesthesia machines designed to deliver volatile anesthetic agents are designed to provide oxygen to the patient and eliminate carbon dioxide, while preserving the anesthetic gases. These goals are typically met using a re-breathing circuit, where an exhaled gas is reintroduced into the inhalation limb leading to the patient. In such a re-breathing circuit, carbon dioxide is absorbed from the expired gases by a carbon dioxide absorber. Before inhalation by the patient, the inhalation gas is supplied with additional oxygen and vaporized in aesthetic agents based upon the patient demand. In this arrangement, the additional gas flow added to the re-breathing circuit can be less than 0.5 L/min although the patient ventilation may be 5-10 L/min. The positive pressure inspiration is typically carried out using a ventilator, which is typically gas driven. In these ventilators, the patient breathing gas is pressurized by controlling a ventilator drive gas flow through a separate system maintaining the breathing gas separate from the ventilator drive gas. Such gas separation system may have form of a long reciprocating gas column or a physical flexible barrier construction.
• Intravenously administered drugs provide an alternative to the volatile anesthetic agents. When an intravenous anesthesia is utilized, the primary functionality of the anesthesia re-breathing circuit is no longer needed, since the vaporized anesthetic agent is no longer circulating with the breathing gases. When intravenously administered anesthetic drugs are utilized, the anesthesia machine may use an open breathing circuit where a mixture of fresh oxygen and nitrogen is provided at the rate required by the patient and the expired gases can be removed from the circulation. In such an open system, carbon dioxide absorption is no longer needed since the re-circulation has been eliminated. Further, the isolation between the patient gases and the drive gases are no longer needed when the ventilation gases are provided directly to the patient. Thus, an anesthesia ventilator optimized for the intravenous anesthesia does not need the gas separation system and the carbon dioxide absorber. Further, a vaporizer for the volatile anesthetic agents is also no longer needed. These simplifications provide advantages in equipment size, eliminate much of the cleaning requirements by reducing the number of contaminated components, and streamlines the anesthesia machine manufacturing process.
• Independently of the anesthesia practice, anesthesia ventilation involves ability for the clinician to manually ventilate the patient. This functionality is typically utilized during an anesthesia induction, weaning the patient from the anesthesia and ventilator, in assistance of spontaneous breathing and for the lung recruitment.
• A desired property of manual ventilation system is given haptic feedback of the patient breath volume. Such feedback is achieved when the patient exhalation volume is collected to the manual bag, which is done in the following state of the a solutions.
• The currently most used arrangement in ventilating manually is to have a breathing system equipped with an APL (Airway Pressure Limiting) valve. When using an airway pressure limiting valve the operating principle is that the valve is set to an predetermined setting and when the manual ventilation bag is squeezed the gas volume is initially delivered to the patient, but when the APL pressure limit is reached the valve starts to bleed gas out from the breathing system. The valve will form a resistance and as the bag is further squeezed some of the volume will go to the patient and some will bleed through the valve. The volume going to the patient, if any, is not possible to determine haptically by how much the bag is squeezed. Neither the patient flow resistance can be identified since that is parallel to the APL valve bleeding resistance. If the patient is not ventilated by squeezing the bag, fresh gas or ventilator bias flow will increase the pressure to the APL limit leading to a sustained pressure and possible barotrauma or volutrauma. It is not possible to deliver a PEEP (Positive End Expiratory Pressure) to the patient with the APL valve.
• Further development of mechanical manual ventilation valves has been done. An example of such valve is the “Berner valve”. This valve controls the breathing circuit and patient pressure at on low level during expiration and closes the valve during inspiration. The switchover between the phases is triggered with gas impulses caused by squeezing and releasing of the manual bag. To ventilate using this valve, both the bag compression and release actions need to be rigorous enough to generate the required impulse. Yielding from this, the Berner valve involves a safety problem related to every manual breath: Would the sensing of expiration fail, the valve remains closed resulting to unlimited breathing circuit and patient pressure increase. This problem related to the difficult use of the method, which has limited its clinical use.
• The explained solutions represent a separate pressure control during the manual ventilation and mechanical ventilation most often controlled electronically using another pressure control valve. Also a solution using the same pressure control valve in both ventilation modalities is known. Because of the electrical breathing circuit and patient pressure control, the control algorithm can follow either the “APL” or “Berner” principle. Ability to set a maximum pressure limit solves the disadvantage of the “Berner” method. Also the minimum pressure during expiration (PEEP) can be controlled according to clinical demand.
• For identification of the breathing phase, a predetermined control rule can be used. The controller of this system compares the measured breathing circuit pressure and/or breathing circuit flow pattern with the predetermined control rule, and based on this comparison, determines whether the manual breath cycle is inspiration or expiration: Compression of the manual bag increases the breathing circuit pressure and causes gas flow in the breathing circuit towards the patient. Respectively, release of the manual bag causes breathing circuit pressure decrease and breathing circuit flow from the patient towards the manual bag.
• Problem of the described system is that at the time the manual bag compression is started, the breathing circuit pressure control valve is open, and the compression necessarily does not yield to the breathing circuit pressure and/or flow pattern expected from the predetermined control rule. Therefore, even here the initial compression must be strong enough to cause the expected changes despite of the adjacent open pressure control valve.
SUMMARY OF THE INVENTION
• in an embodiment, a system for ventilating lungs of a subject includes a control unit configured to control operation of the system. The system for ventilating lungs of a subject also includes a machine ventilator circuit configured to assist breathing functions of the subject, the machine ventilator circuit includes an inspiration delivery unit and an expiration circuit. The system for ventilating lungs of a subject also includes a manual ventilation circuit, said manual ventilation circuit comprising a manual bag, wherein a gas flow is guided out from the manual bag to assist an inspiration phase, a gas flow is received to fill the manual bag during an expiration phase, and wherein the gas flow received to fill the manual bag during the expiration phase at least partially comprises the gas flow guided to assist the inspiration phase.
• In another embodiment, a method for ventilating lungs of a subject with a system comprising a control unit configured to control operation of the system, a machine ventilator circuit configured to assist breathing functions of the subject and a manual ventilation circuit comprising a manual hag and a sensor is provided. The method for ventilating lungs of a subject in the manual ventilation includes increasing pressure to guide a gas flow to assist an inspiration phase by using the control unit to compress the manual bag. The method for ventilating lungs of a subject in the manual ventilation also includes guiding, with the control unit, a gas flow that at least partially comprises the gas flow guided to assist the inspiration phase to fill the manual bag during an expiration phase. The method for ventilating lungs of a subject in the manual ventilation further includes detecting a flow direction inside the manual ventilation circuit with the sensor, producing a signal, with the sensor, based on the detected flow direction, and guiding, with the control unit, a discharge of extra gas volume based on the detected flow direction, wherein the extra gas volume is discharged during the expiration phase in order to reach a pressure level of an expiratory pressure, and wherein the extra gas volume is discharged during the inspiration phase in order to limit the pressure level to an inspiratory pressure.
• Various other features, objects, and advantages of the embodiments of the invention will be made apparent to those skilled in art from the accompanying drawings and detailed description thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 illustrates an operational diagram of a system for providing an inspiration gas to a subject;
• FIG. 2 is an operational diagram of a system for providing an inspiration gas to a subject according to another embodiment; and
• FIG. 3 presents the breathing circuit pressure and subject flow responses when using a manual ventilation.
DETAILED DESCRIPTION OF THE INVENTION
• Specific embodiments are explained in the following detailed description making a reference to accompanying drawings. These detailed embodiments can naturally be modified and should not limit the scope of the invention as set forth in the claims.
• The embodiments are directed to a system and a method for a use in an intensified breathing, and for a use whenever anesthesia is being delivered to a subject.
• Thesystem10 for providing an inspiration gas to the subject12 utilizing a re-breathing system is shown inFIG. 1. Thesystem10 comprises amachine ventilator circuit14 for assisting breathing functions of the subject, abreathing circuit16 for connecting lungs of the subject and themachine ventilator circuit14 to exchange the gas in the lungs, amanual ventilation circuit18 for enabling the manual ventilation of the subject and acontrol unit21 for controlling an operation of thesystem10. Themanual ventilation circuit18 and themachine ventilator circuit14 can be alternatively selected an operator. The manual ventilation circuit can be in a gas flow connection with at least a part of the machine ventilator circuit for making a pneumatic contact with the lungs of the subject when the manual ventilation method is chosen. Thesystem10 shown inFIG. 1 may also comprise auser interface25 for entering any information needed while ventilating the subject and agas mixer27 for supplying a fresh gas for the subject breathing.
• Themachine ventilator circuit14 generally comprises aninspiration delivery unit20 for delivering the gas such as drive gas needed to enable an inspiration of the subject, anexpiration circuit22 for controlling a discharge of the expiration gas and areciprocating unit23 such as a well-known bellows and bottle combination, where the bellows are arranged within the bottle, or a long gas flow channel as shown inFIG. 1 for compressing the gas under a control of the drive gas pressure towards lungs of the subject to facilitate the inspiration. Both theinspiration delivery unit20 and theexpiration circuit22 are controlled by thecontrol unit21.
• As illustrated inFIG. 1, theinspiration delivery unit20 comprises acompressed gas interface24 connected to a compressed gas supply (not shown). The compressed gas can be either oxygen or air. Also a mechanism selecting the other if one gets de-pressurized can be applied (not shown). Theinspiration delivery unit20 comprises also afilter29 for filtering impurities, apressure regulator30 for regulating a pressure of gases flowing from the gas interface, aflow sensor32 for measuring an inspiration delivery flow from the gas interface and aflow control valve34 for opening or closing the inspiration delivery flow. Theflow sensor32 andflow control valve34 are each coupled to thecontrol unit21 to control the inspiration delivery to the subject12. Further theinspiration delivery unit20 may comprise apressure sensor36 for measuring the gas pressure flowing along theconduit26 and aninspiration branch28 towards the reciprocatingunit23.
• Theexpiration circuit22 comprises anexpiration valve37 for discharging the expiration gas and aflow sensor38, which is optional, for measuring the flow discharged through theexpiration valve37. The expiration circuit is in flow connection along anexpiration branch39 with thereciprocating unit23 and themanual ventilation circuit18.
• Themanual ventilation circuit18 comprises amanual bag40 for providing a gas flow such as drive gas flow to increase a pressure needed for the subject inspiration and for receiving the gas flow for the expiration when the subject is expiring, abag valve42 for connecting and disconnecting the drive gas flow between themanual bag40 and theexpiration branch39 or thebreathing circuit16, asensor44 such as a flow sensor for detecting a flow direction inside themanual ventilation circuit18 and apressure sensor46 for measuring a pressure of themanual ventilation circuit18. The drive gas flow to and from themanual bag40 is arranged through abag branch48 and which flow can be detected by thesensor44 based on which a signal can be produced and which signal can be received bycontrol unit21 for determining the flow direction and based on which thecontrol unit21 is able to guide a discharge of extra gas volume. Themanual bag40 can be filled due to the expiration gas flow. It can be filled with the drive gas used when guiding the inspiration. Typically during the expiration themanual bag40 is filled at least partly with the gas used when guiding the gas from the manual bag to assist the inspiration preceding the present expiration making possible a direct pneumatic contact between the expiration gas flow coming from the lungs of the subject and the manual bag. Also during expiration the manual bag (40) may be filled partly with the gas used when guiding the gas from the manual bag to assist the inspiration and to be filled partly with one of the fresh gas supplied by thegas mixer27 and the gas flow delivered by theinspiration delivery unit20.
• Thegas mixer27 is arranged to supply the fresh gas through afresh gas outlet50 to thebreathing circuit16 for the subject breathing. Typically the fresh gas comprises of oxygen and air or nitrous oxide. Oxygen is delivered through anoxygen delivery line51 comprising of afilter52, apressure regulator54, anoxygen flow sensor56 and an oxygenflow control valve58. The air is delivered through anair delivery line61 comprising offilter62, apressure regulator64, anair flow sensor66, and airflow control valve68. For a delivery of nitrous oxide respective components may be provided (not shown). After metering the individual gas flows, they are merged together for fresh gas mixture delivered to avaporizer70 which completes the fresh gas mixture with a volatile anesthesia agent vapor before delivery to thebreathing circuit16 at thefresh gas outlet50 and to the subject breathing.
• Thebreathing circuit16, which is operably connected to themachine ventilator circuit14 at abreathing circuit connection71 and to thefresh gas outlet50, comprises aninspiration limb72 for an inspired gas, anexpiration limb74 for an exhaled gas, a carbon dioxide (CO2) remover76 such as CO2 absorber to remove or absorb carbon dioxide from the exhaled gas coming from the subject12, a first one-way valve78 for an inspired gas to allow an inspiration through theinspiration limb72, a second one-way valve80 for an expired gas to allow an expiration through theexpiration limb74, a branchingunit82 such as a Y-piece having at least three limbs, one of them being for the inspired gas, a second one being for the expired gas and a third one being for both the inspired and expired gases and being connectable to by means of thepatient limb84 to the lungs of the subject12. Also the breathing circuit may comprise apressure sensor85 for measuring a pressure of thebreathing circuit16.
• In mechanical ventilation themanual bag valve42 is maintained closed. During the inspiration phase of the machine ventilation theexpiration circuit22 of themachine ventilator circuit14 closes theexpiration valve37 under the control of thecontrol unit21. This guides the inspiration gas flow from theinspiration delivery unit20 through theinspiration branch28 of agas branching connector86 and through theconnection88 of thereciprocating unit23 pushing the breathing gas out from thebreathing circuit connection71 to thebreathing circuit16. The inspirationgas delivery unit20 controlled by thecontrol unit21 delivers the gas flow either to reach the given gas volume or a pressure at subject lungs. For this control theflow sensor32 for measuring the inspiration flow and thepressure sensor85 of thebreathing circuit16 are used. Also the volume delivered from thefresh gas mixer27 is taken into consideration in the delivery of the gas volume.
• The first one-way valve78 for the inspired gas and the second one-way valve80 for the expired gas of thebreathing circuit16 guide the gas flow direction in the circuit. The inspiration flow is guided through thecarbon dioxide remover76 to remove or absorb from the expiration gas carbon dioxide and further the carbon dioxide free gas is guided through the first one-way valve78 for an inspired gas to theinspiration limb72 where it is mixed with the fresh gas flow and therefrom through the branchingunit82 to thepatient limb84 and finally to the lungs of the subject12.
• At the end of the inspiration phase thebreathing circuit16 and the subject lungs are pressurized. For the expiration under the control of thecontrol unit21 the inspiration deliveryflow control valve34 is closed stopping the inspiration delivery and theexpiration valve37 is opened to allow the gas release from theexpiration branch39 of the drivegas branching connector86 and further through theconnection88 from thereciprocating unit23. This allows the pressure release and breathing gas flow from breathingcircuit16 and the lungs of the subject12 to thereciprocating unit23. The breathing gas flows from the subject12 through thepatient limb84, the branchingunit82, theexpiration limb74, the second one-way valve80 for the expired gas and thebreathing circuit connection71 to thereciprocating unit23. The pressure release is controlled for a desired expiration pressure such as a positive end expiration pressure (PEEP) target, which may be set using theuser interface25. For this control theventilator control21 uses the breathing circuit pressure measured by thepressure sensor85 and theexpiration valve37. The expiration gas flow may be measured using theflow sensor38 located in this embodiment at theexpiration branch39 or at the outlet theexpiration valve37 as shown inFIG. 1.
• For the manual ventilation thebag valve42 is opened. Preferably, thebag valve42 may be electrically or pneumatically actuated. However, that may also have a direct access actuator button or lever for immediate manual access as an alternative. Themanual bag valve42 provides a gas flow path from theexpiration branch39 of themachine ventilator circuit14 through thesensor44 for detecting the flow direction inside themanual ventilation circuit18 and thebag branch48 to themanual bag40.
• Thissensor44 is utilized to identify the bag operations including the flow to themanual bag40 and out from the manual bag and to trigger the inspiration and expiration phases of the breath cycle when on the manual ventilation mode. Thus thesensor44 produces for the control unit21 a signal to determine the flow direction to guide theexpiration circuit22. As a response to the inspiration triggering, theexpiration valve37 of theexpiration circuit22 is closed to guide the bag compression-induced drive gas flow towards the lungs of the subject.
• The operation of thesystem10 during the manual ventilation will now be described. Thepressure sensor85 is used to monitor the pressure within thebreathing circuit16. The fresh gas is supplied to thebreathing circuit16 at a required flow rate and theexpiration valve37 is operated by means of thecontrol unit21 to maintain the given desired expiration pressure in the circuit. The required fresh gas flow rate may be given by the user by means of theuser interface25 or is determined automatically from the required subject gas concentrations. Also the inspiration flow can be used to achieve and maintain the pressure. Because themanual bag40 is now connected to thebreathing circuit16, themanual bag40 is also loaded to this same pressure. When the manual inspiration is required, themanual bag40 is squeezed, causing the pressure within the bag to rise over the desired expiration pressure. The bag squeeze induces the gas flow out from themanual bag40. This flow direction is detected and determined and the flow is measured with thesensor44. During the manual ventilation this flow corresponds with the inspiration delivery flow of the mechanical ventilation. Thecontrol unit21 identifies the flow out from themanual bag40 during the manual inspiration mode meaning that an inspiration phase is active and triggers the ventilation control to the inspiration state. At this state theexpiration valve37 is closed guiding the drive gas from themanual bag40 towards the reciprocatingunit23, which forces the breathing gas from thebreathing circuit connection71 to thebreathing circuit16 and further through theinspiration limb72 to the lungs of the subject12. During the inspiration theexpiration valve37 is maintained closed. However, for safety purposes the lungs must be protected for excessive pressure. Therefore theexpiration circuit22 may be programmed to open theexpiration valve37 in case the measured patient pressure increases beyond the given maximum pressure limit and thus limit the inspiratory pressure.
• The inspiration turns to the expiration phase when themanual bag40 is released. Thecontrol unit21 identifies that the expiration phase is active as the reduced manual bag pressure below the breathing circuit pressure initiates the gas flow from theexpiration branch39 towards themanual bag40 when thesensor44 is able to determine the flow direction inside themanual ventilation circuit18. This triggers the expiration control of the manual breath cycle. This flow can be measured with thissensor44. As a safety against the sustained pressure, the expiration phase may also be initiated if the inspiration duration exceeds the preset inspiration maximum time or the breathing circuit pressure measured with thepressure sensor85 exceeds the preset maximum pressure safety limit. Both preset values may be entered using theuser interface25.
• During the expiration phase, the breathing gas flows out from the lungs of the subject12 through thepatient limb84, the branchingunit82, theexpiration limb74, second one-way valve80 for the expired gas and thebreathing circuit connection71 of the reciprocating unit to thereciprocating unit23. This forces the drive gas out from theconnection88 of the reciprocating unit to thegas branching connector86 and further to theexpiration branch39. Because at the beginning of the expiration, when the expiration phase is active, the bag pressure is low, theexpiration valve37 guided by thecontrol unit21 remains in closed position and the gas flow continues towards themanual bag40 filling the bag. This gas from the subject lungs to themanual bag40 at the early expiration phase gives the haptic feedback of the subject exhaled volume. The fresh gas flow and inspiration flow continues the manual bag filling until the bag pressure achieves the desired expiration pressure such as the target PEEP. For this purpose themanual bag40 is equipped with thepressure sensor46. Alternatively, the pressure measured with thepressure sensor36 may be used for the purpose. When the bag pressure reaches the desired expiration pressure, thecontrol unit21 guides during the expiration mode theexpiration valve37 to an open position to allow the extra gas flow out in order to maintain the desired predetermined pressure measured with thepressure sensor85 until the next inspiration is detected.
• The subject expiration may, however, not give enough volume to fill themanual bag40 to the desired expiration pressure. This is because during the manual ventilation thebreathing circuit16 is often leaking. Therefore the fresh gas flow and inspiration flow are adjusted to provide a complementary volume to resume the desired expiration pressure after the inspiration. The fresh gas flow rate may be adjusted for the purpose automatically by means of thecontrol unit21 or the clinician may prefer to select the constant flow rate large enough to reach the target. After reaching the target thecontrol unit21 guides to maintain the pressure at the target using theexpiration valve37.
• During the manual ventilation the subject may also take spontaneous breaths. Typically this happens during the expiration phase of the breath cycle. If the subject demand exceeds the delivered fresh gas flow rate, the breathing circuit pressure measured by thepressure sensor85 drops below the desired expiration pressure and thecontrol unit21 guides to close theexpiration valve37. Further the subject demand promotes the gas flow from themanual bag40 towards the subject12, which change in the flow direction is detected with thesensor44 inside themanual ventilation circuit18 and thecontrol unit21 identifies as an inspiration. A forthcoming spontaneous expiration, or bag filling from the fresh gas flow and inspiration flow during the subject's spontaneous inspiration hold period is then respectively detected by thesensor44 as the flow towards themanual hag40 and thecontrol unit21 identifies again the expiration phase.
• FIG. 2. shows thesystem10 of another embodiment having an open breathing system. Such system neither has separate fresh gas supply nor dedicated drive gas but the drive gas is the mixture of oxygen and air provided directly through itsinspiration branch28, theconnection88, and thepatient limb84 to lungs of the subject12. In this setting theinspiration delivery unit20 of themachine ventilator circuit14 comprises twoseparate conduits26 for the gas such as the drive gas. One of those conduits may be for oxygen and another one may be for the air. Bothconduits26 comprises the compressedgas interfaces24 for inspiration delivery connected to compressed gas supplies (not shown), thefilter29, thepressure regulators30, theflow sensors32 for measuring the inspiration delivery flow and theflow control valves34. These components have been introduced hereinbefore when explaining theFIG. 1 embodiment. After metering the individual gas flows to produce the required gas mixture having the desired O₂concentration and desired total flow rate the gas flows are merged to a gas mixture, which may still be measured for cross referencing the sensor operational condition withtotal flow sensor90. Also it is desired to measure the pressure of the merged gas mixture by means of thepressure sensor36.
• InFIG. 2 theexpiration circuit22 of the open breathing system just as theFIG. 1 embodiment also comprises theexpiration valve37 and optionally theflow sensor38 connected either downstream or upstream to theexpiration valve37. Further in this embodiment theexpiration circuit22 may comprise apressure sensor92 for measuring the pressure prevailing in theexpiration branch39. Thebag branch48 of themanual ventilation circuit18 connects through thebag valve42 to theexpiration branch39. Themanual ventilation circuit18 is equipped with thesensor44 for detecting the flow direction inside themanual ventilation circuit18. Optionally themanual ventilation circuit18 is also equipped with thepressure sensor46 just as the embodiment inFIG. 1.
• In operation of the manual ventilation with the open breathing circuit as shown inFIG. 2 theinspiration delivery unit20 provides a gas flow towards theinspiration branch28 and theconnection88 and thepatient limb84 to pressurize the lungs of the subject12 and themanual bag40 to the desired expiration pressure such as a given PEEP pressure. Once that is achieved, theexpiration circuit22 regulates theexpiration valve37 to maintain the desired expiration pressure.
• When themanual bag40 is squeezed the gas flow direction out from themanual bag40 is detected with thesensor44. Theexpiration valve37 is closed as a response to this and the gas flow deflating from the compressedmanual bag40 flows through theexpiration branch39, theconnection88, andpatient limb84 to the lungs of the subject12. The inspiration flow delivered through theflow control valves34 may complete the lung filling or alternatively the gas flow from theinspiration delivery unit20 may be stopped for the inspiration to give the full haptic feel of the lung filling.
• The manual bag release is detected by thesensor44, when the gas flow direction is changed towards themanual bag40. During the expiration, after the manual bag pressure reaches the desired expiration pressure level measured with thepressure sensor46 of themanual ventilation circuit18 or thepressure sensor92 of theexpiration circuit22, theexpiration valve37 is regulated by means of thecontrol unit21 for the desired expiration pressure at theexpiration branch39 measured with thepressure sensor36 of theinspiration branch28 or thepressure sensor92 in flow connection with theexpiration branch39. Filling themanual bag40 from the subject expiration gives clinician the haptic feedback of subject expiration volume.
• Thesensor44 shown inFIGS. 1 and 2 for detecting the flow direction inside themanual ventilation circuit18 can be of any known type used for detecting the flow direction or sensing flow rate. These include hot wire anemometer, ultrasonic flow sensor or a flow restriction type flow sensor where the differences in pressure generated by the flow rate through the flow restriction is measured. This pressure can be measured with a differential type pressure sensor connected over the flow restriction, or alternatively, thecontrol unit21 can calculate the pressure difference using the pressures measured with thesensor44 of themanual ventilation circuit18, in case thesensor44 is a pressure sensor comparing the pressure of themanual ventilation circuit18 and outside pressure prevailing outside thesystem10, and some other pressure sensor which may be part of thesystem10 and themachine ventilation circuit14 outside themanual ventilation circuit18, which is typically thepressure sensor36 in flow connection with theinspiration branch28 and measuring the drive gas pressure or thepressure sensor92 in flow connection with theexpiration branch39 and measuring the expiration gas pressure of themachine ventilator circuit14. To determine the flow direction thepressure sensor36 or thepressure sensor92 as well as thesensor44 provide a signal to thecontrol unit21. Examples of usable flow restrictions are an orifice or variable orifice. Even thebag valve42 can be utilized as a flow restriction.
• In connection to the open breathing system as shown inFIG. 2, the manual inspiration is pushing the gas from theexpiration branch39 to the subject. The expiration gas from the subject as well flows through theexpiration branch39. This expiration gas contains carbon dioxide and the oxygen concentration is low. Therefore, advantageous to the manual ventilation of the embodiment is that theexpiration branch39 is filled with the gas from theinspiration delivery unit20 before the new inspiration. This requires a controlled gas flow from theinspiration delivery unit20 during the expiration directly through theconnection88 toexpiration branch39 and when the desired expiration pressure is achieved, further through theexpiration valve37 out from theexpiration branch39 or themachine ventilator circuit14. This by-flow should be at least equal to minute ventilation volume, which is typically for adult subjects 5-6 L/min but can be 10 L/min or even higher if needed. This requires also that theexpiration branch39 accommodates the volume of one inspiration, which is for adult subjects typically 500 mL and less than 1000 mL. With typical 22 mm diameter expiration branch this corresponds to 3 m expiration tube length.
• FIG. 3 describes graphically the pressure and flow time characteristics of the manual ventilation of the embodiment. An ordinate of agraph201 denotes the manual ventilation pressure on thebreathing circuit211 and an abscissa defining a time. Anarrow208 determines the given maximum breathing circuit pressure and anarrow209 the desired expiration pressure. Adot line212 represents a pressure thecontrol unit21 is working with. Agraph202 ordinate is the respective flow, inspiration onupward direction203 and expiration downdirection204. Thethick line214 represents the subject flow and athin line215 represents the gas flow out from the breathing system.FIG. 3 presents also the manual ventilation phases with symbolic variation of the manual bag size comprising aninspiration205,expiration206 andearly expiration207.
• At aninspiration phase213 the manual bag squeeze is gentle and the breathing circuit pressure is not increasing up to the given maximum pressure. At this breath all the gas flow reaches the patient. Following anexpiration flow218 inflates themanual bag40 giving the feedback of the successful breath. During the expiration thecontrol unit21 guides to deliver further gas to the breathing circuit to reach the desired expiration pressure and regulates theexpiration valve37 to maintain that throughout the expiration.
• At aninspiration phase216 the bag pressing is more aggressive and thedot line212 of the maximum pressure limit is achieved atpoint217. At this point the further manual bag depression causes increasing gas flow out from the breathing system instead of the subject in order to limit further inspiratory pressure increase.
• The advantage of the embodiments is that triggering between the inspiration and expiration phases of the breath cycle using the flow inside themanual ventilation circuit18 is sensitive and independent of the strength by which themanual bag40 is compressed. The embodiments also provide a protection for sustained lung pressure and barotrauma during the manual ventilation and provide a user adjustable desired expiration pressure. It also provides haptic feedback on both true inspired and expired gas volumes to the user.
• The written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims (23)

1-20. (canceled)

21. A system for ventilating lungs of a subject, the system comprising:

a control unit configured to control operation of the system;

a machine ventilator circuit configured to assist breathing functions of the subject, the machine ventilator circuit comprising an inspiration delivery unit and an expiration circuit; and

a manual ventilation circuit comprising:

a manual bag, wherein a gas flow is guided out from the manual bag to assist an inspiration phase, a gas flow is received to fill the manual bag during an expiration phase, and wherein the gas flow received to fill the manual bag during the expiration phase at least partially comprises the gas flow guided to assist the inspiration phase; and

a sensor, wherein the sensor is configured to detect a flow direction inside the manual ventilation circuit and to provide a signal to the control unit based on the detected flow direction.

22. The system according toclaim 21, wherein the machine ventilator circuit and the manual ventilation circuit can be alternatively selected.

23. The system according toclaim 21, wherein the expiration circuit comprises an expiration valve.

24. The system according toclaim 23, wherein the control unit is configured to identify whether the inspiration phase or the expiration phase is active and to guide the expiration valve based on the detected flow direction.

25. The system according toclaim 23, wherein the control unit guides the expiration valve to a closed position when the inspiration phase is active.

26. The system according toclaim 23, wherein the control unit guides the expiration valve to a closed position when the expiration phase is active, and wherein the control unit further guides the expiration valve to an open position when a predetermined pressure is reached in the manual bag.

27. The system according toclaim 21 further comprising:

a user interface for entering information while ventilating the subject.

28. The system according toclaim 21, wherein direct pneumatic contact is made between the manual bag and the gas flow received to fill the manual bag during the expiration phase.

29. The system according toclaim 21 further comprising:

a gas mixer configured to supply fresh gas to the subject and a breathing circuit connecting lungs of the subject and the machine ventilator circuit to exchange gas in the lungs.

30. The system according toclaim 29, wherein the gas flow received to fill the manual bag during the expiration phase further comprises at least one of the fresh gas supplied by the gas mixer and a gas flow delivered by the inspiration delivery unit, and wherein direct pneumatic contact is made between the manual bag and the gas flow received to fill the manual bag during the expiration phase.

31. The system according toclaim 21, wherein the sensor is a flow sensor.

32. The system according toclaim 21, wherein the sensor is a first pressure sensor, and the system further comprises a second pressure sensor disposed outside the manual ventilation circuit,

wherein the second pressure sensor detects a pressure outside the manual ventilation circuit and provides a signal to the control unit based on the pressure outside the manual ventilation circuit, and

wherein the control unit uses the signal from the first pressure sensor and the signal from the second pressure sensor to determine a pressure difference between the two detected pressures.

33. A method for ventilating lungs of a subject with a system comprising a control unit configured to control operation of the system, a machine ventilator circuit configured to assist breathing functions of the subject and a manual ventilation circuit comprising a manual bag and a sensor, the method comprising:

increasing pressure to guide a gas flow to assist an inspiration phase by using the control unit to compress the manual bag;

guiding, with the control unit, a gas flow that at least partially comprises the gas flow guided to assist the inspiration phase to fill the manual bag during an expiration phase;

detecting a flow direction inside the manual ventilation circuit with the sensor;

producing a signal, with the sensor, based on the detected flow direction; and

guiding, with the control unit, a discharge of extra gas volume based on the detected flow direction, wherein the extra gas volume is discharged during the expiration phase in order to reach a pressure level of an expiratory pressure, and wherein the extra gas volume is discharged during the inspiration phase in order to limit the pressure level to an inspiratory pressure.

34. The method according toclaim 33, wherein the signal based on the detected flow direction provides information about when the inspiration phase is active and when the expiration phase is active.

35. The method according toclaim 33 further comprising setting a predetermined pressure level for the expiratory pressure and setting a predetermined pressure level for limiting an inspiratory pressure.

36. The method according toclaim 33, wherein filling the manual bag during the expiration phase with a gas flow that at least partially comprises the gas flow guided to assist the inspiration phase creates direct pneumatic contact between the manual bag and the gas flow received to fill the manual bag during the expiration phase

37. The method according toclaim 33, further comprising supplying a gas flow of fresh gas to the subject.

38. The method according toclaim 37, wherein filling the manual bag during an expiration phase further comprises the gas flow of fresh gas.

39. The method according toclaim 33, wherein the machine ventilator circuit and the manual ventilation circuit can be alternatively selected.

40. The method according toclaim 39, wherein the manual ventilation circuit is in gas flow connection with at least a part of the machine ventilator circuit to create a pneumatic contact with the lungs of the subject when the manual ventilation circuit is selected, and the manual ventilation circuit being in gas flow connection with an expiration circuit to achieve a predetermined pressure level under the control of the control unit, the method further comprises:

increasing pressure by compressing the manual bag to guide a gas flow to assist an inspiration phase in the manual ventilation circuit and in a part of the machine ventilator circuit in flow communication with the manual ventilation circuit; and

releasing the manual bag for an expiration phase.

41. The method according toclaim 40 further comprising setting a predetermined pressure level for the expiratory pressure and setting a predetermined pressure level for limiting an inspiratory pressure.

42. The method according toclaim 40, wherein filling the manual bag during the expiration phase with a gas flow that at least partially comprises the gas flow guided to assist the inspiration phase creates direct pneumatic contact between the manual bag and the gas flow received to fill the manual bag during the expiration phase.

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