US20180103905A1 - Fluid titration system - Google Patents

Abstract

A fluid titration system has an optical sensor, a physiological monitor, a titration controller and an infusion device. The optical sensor transmits multiple wavelengths of light into a tissue site of a person and detects the optical radiation after attenuation by pulsatile blood flowing within the tissue site. The physiological monitor receives a resulting sensor signal and derives a plethysmograph that corresponds to the pulsatile blood flow. The monitor also calculates a plethysmograph variability measure that is responsive to changes in perfusion at the tissue site. A titration controller generates a fluid control output according to the variability measure. The infusion device administers a liquid solution via an intravenous (IV) connection to the person according to the fluid control output so as to regulate at least one of a fluid flow start, rate and stop.

Description

REFERENCE TO RELATED APPLICATION
• The present application claims priority benefit under 35 U.S.C. § 120 to, and is a continuation of U.S. patent application Ser. No. 13/287,060, filed on Nov. 1, 2011, entitled “Fluid Titration System,” which is a continuation of U.S. patent application Ser. No. 12/208,998, filed on Sep. 11, 2008, entitled “Fluid Titration System,” now U.S. Pat. No. 8,048,040, which claims priority benefit under 35 U.S.C. § 119(e) from U.S. Provisional Application No. 60/993,584, filed Sep. 13, 2007, entitled “Fluid Titration System;” the disclosures of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
• FIG. 1 illustrates aphysiological monitoring system100 having aphysiological monitor120, anoninvasive sensor130 attached to atissue site1, and asensor cable140 interconnecting themonitor120 and thesensor130. Physiological monitoring systems for measuring constituents of circulating blood have gained rapid acceptance in a wide variety of medical applications, including surgical wards, intensive care and neonatal units, general wards, home care, physical training, and virtually all types of monitoring scenarios. Thenoninvasive sensor130 has light emitting diodes (LEDs) and a detector. The LEDs transmit optical radiation into thetissue site1, and the detector responds to the intensity of the optical radiation after absorption by pulsatile blood flow within the tissue site. Based upon this response, thephysiological monitor120 determines measurements for physiological parameters. Thephysiological monitoring system100 may incorporate pulse oximetry, which is a widely accepted noninvasive procedure for measuring physiological parameters, such as oxygen saturation and pulse rate among others. Thephysiological monitoring system100 may also incorporate advanced features, such as a multiple wavelength sensor and advanced processes for determining other physiological parameters, such as carboxyhemoglobin, methemoglobin and total hemoglobin, as a few examples. Thephysiological monitor120 displays the physiological parameters and typically provides visual and audible alarm mechanisms that alert a caregiver when these parameters are outside of predetermined limits.
• Pulse oximeters capable of reading through motion induced noise are disclosed in at least U.S. Pat. Nos. 6,770,028, 6,658,276, 6,650,917, 6,157,850, 6,002,952, 5,769,785, and 5,758,644; low noise pulse oximetry sensors are disclosed in at least U.S. Pat. Nos. 6,088,607 and 5,782,757; all of which are assigned to Masimo Corporation, Irvine, Calif. (“Masimo”) and are incorporated by reference herein.
• Physiological monitors and corresponding multiple wavelength optical sensors are described in at least U.S. patent application Ser. No. 11/367,013, filed Mar. 1, 2006 and entitled Multiple Wavelength Sensor Emitters and U.S. patent application Ser. No. 11/366,208 [Ser. No. 11,367,033], filed Mar. 1, 2006 and entitled Noninvasive Multi-Parameter Patient Monitor, both assigned to Masimo Laboratories, Irvine, Calif. (Masimo Labs) and both incorporated by reference herein.
• Further, physiological monitoring systems that include low noise optical sensors and pulse oximetry monitors, such as any of LNOP® adhesive or reusable sensors, SofTouch™ sensors, Hi-Fi Trauma™ or BIue™ sensors; and any of Radical®, SatShare™, Rad-9™, Rad-S™, Rad-5v™ or PPO+™ Masimo SET® pulse oximeters, are all available from Masimo. Physiological monitoring systems including multiple wavelength sensors and corresponding noninvasive blood parameter monitors, such as Rainbow™ adhesive and reusable sensors and RAD-57™ and Radical7™ monitors for measuring SpO₂, pulse rate, perfusion index, signal quality, HbCO and HbMet among other parameters are also available from Masimo.
• FIG. 2 illustrates thestandard plethysmograph waveform200, which can be derived from a pulse oximetry system, as described above. Theplethysmograph waveform200 illustrates light absorption at the tissue site, shown along the y-axis10, versus time, shown along thex-axis20. The total absorption includes components ofstatic absorption210 andvariable absorption220.Static absorption210 is due to tissue, venous blood and a base volume of arterial blood.Variable absorption220 is due to the pulse-added volume of arterial blood. That is, theplethysmograph waveform200 is a visualization of the tissue site arterial blood volume change over time, and is a function of heart stroke volume, pressure gradient, arterial elasticity and peripheral resistance. Theideal waveform pulse230 displays a broad peripheral flow curve, with a short,steep inflow phase232 followed by a 3 to 4 timeslonger outflow phase234. Theinflow phase232 is the result of tissue distention by the rapid blood volume inflow during ventricular systole. During theoutflow phase234, blood flow continues into the vascular bed during diastole. Theplethysmograph baseline240 indicates the minimum basal tissue perfusion.
SUMMARY OF THE INVENTION
• FIG. 3 illustrates ahypovolemic plethysmograph waveform300, i.e. a plethysmograph displaying characteristics of a person having an abnormal decrease in blood volume. Hypovolemia is often caused from blood loss during surgery or due to an injury. Under hypovolemic conditions, a respiration-induced cyclical variation occurs in aplethysmograph baseline340. In particular, thebaseline340 varies with a period corresponding to therespiration rate350. This cyclical variation is particularly evident in patients undergoing positive ventilation. The amount of cyclical variation correlates to a person's blood volume, i.e. the less blood volume the greater the cyclical variation in the plethysmograph waveform. Accordingly, a measure of plethysmograph variation may be indicative of hypovolemic conditions.
• FIG. 4 illustrates aplethysmograph400 plotted on anamplitude axis30 versus atime axis40. As described above, the amplitude may be responsive to light absorption of pulsatile blood flow with a person's tissue. Theplethysmograph400 has multiple pulses460 each with apeak462 and avalley464 and extending over atime period466. A perfusion index (PI) value can be defined for each pulse460:
• 
  PI=AC/DC  (1)
• where “AC”454 designates apeak amplitude462 minus avalley amplitude464 for a particular pulse and where “DC”456 designates apeak amplitude462 for a particular pulse. In an embodiment, an IR channel plethysmograph from a detector response to an IR wavelength LED is utilized to calculate PI. A plethysmograph variability index (PVI) is then calculated that is responsive to variations in perfusion index, as described below.
• In an embodiment, PVI calculations utilize only PI values resulting from acceptable plethysmograph pulses. For example, a red channel plethysmograph responsive to a red wavelength LED is used to verify acceptable pulses in the IR channel. Physiological plethysmograph identification is disclosed in U.S. Pat. No. 7,044,918 titled Plethysmograph Pulse Recognition Processor, which is incorporated by reference herein. PVI values are calculated from a sorted and trimmed buffer representing a sliding time window of PI values. The sort orders the PI values from the minimum PI at one end of the buffer to the maximum PI at the other end of the buffer. A predetermined number of both maximum and minimum PIs are deleted from each end of the buffer and PVI is calculated as:
• 
  PVI=[(PI_MAX−PI_MIN)/PI_MAX]×100  (2)
• That is, PVI is the PI variation, expressed as a percentage of the difference between the maximum and minimum PIs remaining in the buffer. In an embodiment, a median PVI is calculated from PVIs stored in a second buffer. PVI is described in U.S. Provisional Patent App. No. 60/873,663 filed Dec. 9, 2006 titled Plethysmograph Variability Index, incorporated by reference herein. A PVI enabled physiological monitor advantageously provides a noninvasive numerical measure of hypovolemic conditions so as to titrate patient fluids.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is an illustration of a physiological monitoring system;
• FIG. 2 is an absorption versus time graph of a standard pulse oximeter plethysmograph;
• FIG. 3 is an absorption versus time graph of a plethysmograph exhibiting a respiration-induced, baseline cyclical variation;
• FIG. 4 is a plethysmograph illustrating measurement of a plethysmograph variability index (PVI);
• FIG. 5 is a general block diagram of an intravenous fluid titration system;
• FIG. 6 is a general block diagram of a physiological monitoring system configured for a fluid titration application; and
• FIGS. 7-8 are illustrations of intravenous fluid titration system embodiments.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
• FIG. 5 illustrates afluid titration system500 having asensor510 attached to aperson2, aphysiological monitor520, afluid titration controller530 and an intravenous (IV)infusion device540. Advantageously, thefluid titration system500 utilizes a perfusion variability parameter, such as PVI described above, to regulate the administration of fluids to a person so as to control or prevent low blood volume or a hypovolemia. A noninvasive,optical sensor510 allows a measure of tissue blood perfusion by detecting the absorption of sensor transmitted light by pulsatile blood flow within a tissue site, such as a finger, foot or ear to name a few. Asensor signal512 responsive to that absorption is received and processed by thephysiological monitor520, which derives a plethysmograph variability index (PVI) or other measure of plethysmograph variability or, similarly, blood perfusion variability. Afluid titration controller530 is responsive toPVI522 and in particular to relatively large values of PVI indicating relatively large variations in perfusion index, a potential indicator of hypovolemia. Thefluid titration controller530, in turn, provides acontrol output532 to an intravenous (IV)infusion device540 so as to regulate circulating fluids and alleviate a hypovolemic condition in theperson2. TheIV infusion device540 administers a liquid solution, such as blood products or nutrient fluids injected directly into a vein (usually in the arm) at a prescribed rate over a period of time. In a closed-loop embodiment, thefluid titration controller530 is responsive toPVI522 or similar measure so as to start, control the rate of, or stop the infusion of fluids into theperson2. In an open-loop embodiment, thefluid titration controller530 presents a display orother indicator534 to acare provider3 who manually inputs an adjustment or other setting541 into theinfusion device540 so as to start, control the rate of, or stop the infusion of fluids into theperson2.
• As shown inFIG. 5, thefluid titration controller530 may be implemented in thephysiological monitor520, implemented in theIV infusion device540, distributed between thephysiological monitor520 and theIV infusion device540, or implemented as a standalone processing device. In an embodiment, thefluid titration controller530 is a firmware process executed within thephysiological monitor520, as described with respect toFIG. 6, below. Physically, thephysiological monitor520 and theIV infusion device540 may be separate units, as described with respect toFIG. 7, below, or combined into a single unit, as described with respect toFIG. 8, below.
• FIG. 6 illustrates aphysiological monitoring system600 capable of generating one or more blood parameter measurements such as oxygen saturation, perfusion index, carboxyhemoglobin and methemoglobin, to name a few. Themonitoring system600 has asensor510 and aphysiological monitor520. Thesensor510 attaches to atissue site1 and includes a plurality ofemitters610 capable of irradiating thetissue site1 with various wavelengths of light, such as the red and infrared (IR) wavelengths utilized in pulse oximetry or multiple wavelengths different than or in addition to pulse oximetry wavelengths such as for measuring abnormal hemoglobin constituents. Thesensor510 also includes one ormore detectors612 capable of detecting the emitted light after attenuation by thetissue site1.
• As shown inFIG. 6, thephysiological monitor520 communicates with thesensor510 to receive one or more intensity signals614 responsive to one or more physiological parameters, then calculates and displays the parameter values. Thephysiological monitor520 hasdrivers620 that convert digital control signals into analog drive signals capable of driving theemitters610. A front-end630 converts composite analog intensity signal(s)614 from the detector(s)612 intodigital data632 input to a digital signal processor (DSP)640. The inputdigital data632 is referred to herein as a plethysmograph waveform or a “plethysmograph” for short. In an embodiment, the inputdigital data632 is a multiplexed data stream including a red channel plethysmograph and an IR channel plethysmograph generated from alternate activation of red andIR wavelength emitters610. TheDSP640 may comprise a wide variety of data and/or signal processors capable of executing processes in one or more of hardware, software and firmware for determining physiological parameters from theinput data632. In an embodiment, theDSP640 generatesPVI measurements642 responsive to an IR channel plethysmograph portion of thedigital data632.
• Also shown inFIG. 6, a fluid titration process, such as firmware executing on the DSP, inputs thePVI measurements642 and generatescontrol values644 that are communicated directly or indirectly to an IV infusion device540 (FIG. 5) so as to start, stop, continue or modify the infusion of fluids into a person2 (FIG. 5). In an embodiment, thefluid titration process670 is closed-loop andcontrol values644 are communicated to an IV infusion device540 (FIG. 5) without human intervention. In an embodiment, thefluid titration process670 is open-loop andcontrol values644 are communicated to a care provider3 (FIG. 5) via adisplay662,audible indicator664 or other human interface device so that the care provider can manually adjust or provide settings for the IV infusion device540 (FIG. 5) so as to regulate fluid infusion into the person2 (FIG. 5).
• Also shown inFIG. 6, theinstrument manager650 may comprise one or more microcontrollers controlling system management, such as monitoring the activity of theDSP640 and communicating with I/O devices660. In an embodiment, I/O devices660 include one or more of adisplay662, anaudible indicator664, auser input666 and a device interface688. Adisplay662 includes for example a readout, colored light or graphic generated by one or more of an LED, LCD, plasma screen or CRT, to name a few. Anaudible indicator664 includes, for example, one or more of a speaker or other audio transducer. Theuser input device666 may include, for example, one or more of a keypad, touch screen, pointing device, voice recognition device, or the like, or a network, computer or similar device that provides an external input capability.
• Further shown inFIG. 6, thedisplay662, theaudible indicator664 or both in combination are capable of conveying information so that a caregiver3 (FIG. 5) can manually adjust or otherwise provide inputs for a medical instrument, such as an IV infusion device540 (FIG. 5), according todigital data632 derived from anoptical sensor510 and processed by theDSP640, theinstrument manager650 or both. For example, besides displaying indicia representative of calculated physiological parameters such as one or more of a pulse rate (PR), signal quality and values of blood constituents in body tissue, thedisplay662 is capable of guiding manual adjustment of an IV infusion device, such as by indicating a +, −, “on” and “off” to prompt a manual increase, decrease, stop or start of fluid flow.
• In an embodiment, theinstrument manager650 provides acontrol signal659 responsive to controlvalues644 calculated by thefluid titration firmware670. Thecontrol signal659 communicates with adevice interface668 so as to generate a corresponding IVinfusion device control532. For example, the instrument manager360 converts PVI measurements344 to acontrol signal644 and transmits the control signal via thecontrol port659 to adevice interface668.
• In an embodiment, aninput port658 responds to auser input device666, such as a keypad, network, computer or similar device that provides an external interface. Using this interface, a caregiver3 (FIG. 5) can initialize theinstrument manager650 with patient information, infusion device type and fluid type to name a few. During operation, the instrument manager converts the control values644 to anappropriate control signal659 according to the initialization information.
• Thefluid titration process670 may be DSP firmware that executes a closed-loop algorithm for controlling anIV infusion device540 based upon PVI or other measured plethysmograph or perfusion variability parameter. In an embodiment, thefluid titration process670 triggers acontrol output644 so as to disable fluid flow from theIV infusion device540 if PVI falls below a predetermined threshold or otherwise reflects that hypovolemia may no longer be indicated for a patient2 (FIG. 5). In an embodiment, thefluid titration process670 triggers acontrol output644 so as to enable fluid flow from theIV infusion device540 if PVI increases above a predetermined threshold or otherwise reflects that hypovolemia may no longer be indicated for a patient2 (FIG. 5). In an embodiment, thefluid titration process670 modifies acontrol output644 so as to adjust the rate of fluid flow or total administered amount of fluid flow from theIV infusion device540 according to changes in PVI that reflect that hypovolemia may be decreasing or increasing in severity.
• FIG. 7 illustrates a fluidtitration system embodiment700 having anoptical sensor710 attached to aperson2; aphysiological monitor720; asensor cable730 interconnecting thesensor710 and monitor720; anIV infusion device740; acontrol cable750 interconnecting themonitor720 andinfusion device740; and anIV tube760 also attached to theperson2. Theoptical sensor710 provides a sensor signal via asensor cable730 to thephysiological monitor720. Thephysiological monitor720 generates blood parameter measurements and processes those parameters to generate monitor and control outputs, as described with respect toFIGS. 5-6, above. In particular, thephysiological monitor720 generates control signals via acontrol cable750 to theIV infusion device740, which provides fluids to theperson2 via theIV tube760.
• FIG. 8 illustrates another fluidtitration system embodiment800 having anoptical sensor810 and anIV tube840 attached to aperson2 at one end and an integratedphysiological monitor820 at another end. The integratedphysiological monitor820 incorporates the functions of a physiological monitor520 (FIG. 6) and an IV infusion device within a single unit or within physically connected units.
• A fluid titration system has been disclosed in detail in connection with various embodiments. These embodiments are disclosed by way of examples only and are not to limit the scope of the claims that follow. One of ordinary skill in art will appreciate many variations and modifications.

Claims (21)

1-19. (canceled)

20. A method of managing a blood volume of a patient, the method comprising:

noninvasively detecting, with a detector of an optical sensor, light attenuated by tissue of the patient at a measurement site;

outputting, with the optical sensor, a signal responsive to the light;

determining, with one or more hardware processors, a first measure of variability from at least a ratio of a pulsatile component to a nonpulsatile component of the signal, the pulsatile component and the nonpulsatile component being indicative of a blood volume in the tissue, the pulsatile component being responsive to variable absorption and the nonpulsatile component being responsive to static absorption;

determining, with the one or more hardware processors, that the first measure of variability indicates a need for the patient to receive a liquid solution; and

in response to determining that the first measure of variability indicates the need, outputting a first infusion indication for presentation to a caregiver, the first infusion indication indicating to administer the liquid solution to the patient.

21. The method ofclaim 20, further comprising:

determining, with the one or more hardware processors, a second measure of variability from at least the ratio of the pulsatile component to the nonpulsatile component of the signal at a first time, the first time being different from a second time at which the first measure of variability is determined;

determining, with the one or more hardware processors, that the second measure of variability does not indicate the need; and

in response to determining that the second measure of variability does not indicate the need, outputting a second infusion indication for presentation to the caregiver, the second infusion indication indicating not to administer the liquid solution to the patient.

22. The method ofclaim 21, further comprising visually presenting the first infusion indication and the second infusion indication to the caregiver on a display.

23. The method ofclaim 21, further comprising:

visually presenting the first infusion indication to the caregiver on a display as +, on, increase, or start; and

visually presenting the second infusion indication to the caregiver on the display as −, off, decrease, or stop.

24. The method ofclaim 21, further comprising audibly presenting the first infusion indication and the second infusion indication to the caregiver.

25. The method ofclaim 21, further comprising:

comparing the first measure of variability with a threshold to determine whether the first measure of variability indicates the need; and

comparing the second measure of variability with the threshold to determine whether the second measure of variability indicates the need.

26. The method ofclaim 20, further comprising visually presenting the first infusion indication to the caregiver on a display as +, on, increase, or start.

27. The method ofclaim 20, wherein the first measure of variability is responsive to a dehydration condition of the patient.

28. The method ofclaim 20, wherein the first measure of variability is responsive to a hemorrhaging condition of the patient.

29. The method ofclaim 20, wherein the liquid solution comprises blood products.

30. The method ofclaim 20, wherein the liquid solution comprises nutrient fluids.

31. The method ofclaim 20, further comprising administering the liquid solution to the patient subsequent to said outputting the first infusion indication for presentation to the caregiver.

32. The method ofclaim 31, wherein said administering the liquid solution to the patient is performed using an infusion device separate from a patient monitor comprising the one or more hardware processors.

33. The method ofclaim 20, further comprising comparing the first measure of variability with a threshold to determine whether the first measure of variability indicates the need.

34. The method ofclaim 20, wherein said determining the first measure of variability comprises processing a respiration-induced cyclical variation in the signal.

35. The method ofclaim 20, wherein said determining the first measure of variability comprises determining the first measure of variability from at least a change in the ratio of the pulsatile component to the nonpulsatile component.

36. The method ofclaim 20, wherein the first measure of variability comprises a measure of perfusion index variability of the signal.

37. The method ofclaim 20, further comprising irradiating, with one or more emitters of the optical sensor, the tissue with red and infrared wavelengths.

38. The method ofclaim 20, wherein the measurement site comprises a finger.

39. The method ofclaim 20, further comprising determining, with the one or more hardware processors, a parameter measurement from the signal, the parameter measurement comprising carboxyhemoglobin or methemoblobin.

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