Fluid titration system

[0001] The present application 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,” which is incorporated herein by reference.

[0002] FIG. 1 illustrates a physiological monitoring system 100 having a physiological monitor 120, a noninvasive sensor 130 attached to a tissue site 1, and a sensor cable 140 interconnecting the monitor 120 and the sensor 130. 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. The noninvasive sensor 130 has light emitting diodes (LEDs) and a detector. The LEDs transmit optical radiation into the tissue site 1, 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, the physiological monitor 120 determines measurements for physiological parameters. The physiological monitoring system 100 may incorporate pulse oximetry, which is a widely accepted noninvasive procedure for measuring physiological parameters, such as oxygen saturation and pulse rate among others. The physiological monitoring system 100 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. The physiological monitor 120 displays the physiological parameters and typically provides visual and audible alarm mechanisms that alert a caregiver when these parameters are outside of predetermined limits.

[0003] 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.

[0004] 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, 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.

[0005] 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 Blue™ sensors; and any of Radical®, SatShare™, Rad-9™, Rad-5™, 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 Radical-7™ monitors for measuring SpO₂, pulse rate, perfusion index, signal quality, HbCO and HbMet among other parameters are also available from Masimo.

[0006] FIG. 2 illustrates the standard plethysmograph waveform 200, which can be derived from a pulse oximetry system, as described above. The plethysmograph waveform 200 illustrates light absorption at the tissue site, shown along the y-axis 10, versus time, shown along the x-axis 20. The total absorption includes components of static absorption 210 and variable absorption 220. Static absorption 210 is due to tissue, venous blood and a base volume of arterial blood. Variable absorption 220 is due to the pulse-added volume of arterial blood. That is, the plethysmograph waveform 200 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. The ideal waveform pulse 230 displays a broad peripheral flow curve, with a short, steep inflow phase 232 followed by a 3 to 4 times longer outflow phase 234. The inflow phase 232 is the result of tissue distention by the rapid blood volume inflow during ventricular systole. During the outflow phase 234, blood flow continues into the vascular bed during diastole. The plethysmograph baseline 240 indicates the minimum basal tissue perfusion.

[0007] FIG. 3 illustrates a hypovolemic plethysmograph waveform 300, 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 a plethysmograph baseline 340. In particular, the baseline 340 varies with a period corresponding to the respiration rate 350. 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.

[0008] FIG. 4 illustrates a plethysmograph 400 plotted on an amplitude axis 30 versus a time axis 40. As described above, the amplitude may be responsive to light absorption of pulsatile blood flow with a person's tissue. The plethysmograph 400 has multiple pulses 460 each with a peak 462 and a valley 464 and extending over a time period 466. A perfusion index (PI) value can be defined for each pulse 460:
PI=AC/DC  (1)
where “AC” 454 designates a peak amplitude 462 minus a valley amplitude 464 for a particular pulse and where “DC” 456 designates a peak amplitude 462 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.

[0009] 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.

[0017] FIG. 5 illustrates a fluid titration system 500 having a sensor 510 attached to a person 2, a physiological monitor 520, a fluid titration controller 530 and an intravenous (IV) infusion device 540. Advantageously, the fluid titration system 500 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 sensor 510 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. A sensor signal 512 responsive to that absorption is received and processed by the physiological monitor 520, which derives a plethysmograph variability index (PVI) or other measure of plethysmograph variability or, similarly, blood perfusion variability. A fluid titration controller 530 is responsive to PVI 522 and in particular to relatively large values of PVI indicating relatively large variations in perfusion index, a potential indicator of hypovolemia. The fluid titration controller 530, in turn, provides a control output 532 to an intravenous (IV) infusion device 540 so as to regulate circulating fluids and alleviate a hypovolemic condition in the person 2. The IV infusion device 540 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, the fluid titration controller 530 is responsive to PVI 522 or similar measure so as to start, control the rate of, or stop the infusion of fluids into the person 2. In an open-loop embodiment, the fluid titration controller 530 presents a display or other indicator 534 to a care provider 3 who manually inputs an adjustment or other setting 541 into the infusion device 540 so as to start, control the rate of, or stop the infusion of fluids into the person 2.

[0018] As shown in FIG. 5, the fluid titration controller 530 may be implemented in the physiological monitor 520, implemented in the IV infusion device 540, distributed between the physiological monitor 520 and the IV infusion device 540, or implemented as a standalone processing device. In an embodiment, the fluid titration controller 530 is a firmware process executed within the physiological monitor 520, as described with respect to FIG. 6, below. Physically, the physiological monitor 520 and the IV infusion device 540 may be separate units, as described with respect to FIG. 7, below, or combined into a single unit, as described with respect to FIG. 8, below.

[0019] In an embodiment, the fluid titration process 670 triggers a control output 644 so as to enable fluid flow from the IV infusion device 540 if PVI increases above a predetermined threshold or otherwise reflects that hypovolemia may no longer be indicated for a patient 2 (FIG. 5). In an embodiment, the fluid titration process 670 modifies a control output 644 so as to adjust the rate of fluid flow or total administered amount of fluid flow from the IV infusion device 540 according to changes in PVI that reflect that hypovolemia may be decreasing or increasing in severity.

[0020] FIG. 7 illustrates a fluid titration system embodiment 700 having an optical sensor 710 attached to a person 2; a physiological monitor 720; a sensor cable 730 interconnecting the sensor 710 and monitor 720; an IV infusion device 740; a control cable 750 interconnecting the monitor 720 and infusion device 740; and an IV tube 760 also attached to the person 2. The optical sensor 710 provides a sensor signal via a sensor cable 730 to the physiological monitor 720. The physiological monitor 720 generates blood parameter measurements and processes those parameters to generate monitor and control outputs, as described with respect to FIGS. 5-6, above. In particular, the physiological monitor 720 generates control signals via a control cable 750 to the IV infusion device 740, which provides fluids to the person 2 via the IV tube 760.

[0021] FIG. 8 illustrates another fluid titration system embodiment 800 having an optical sensor 810 and an IV tube 840 attached to a person 2 at one end and an integrated physiological monitor 820 at another end. The integrated physiological monitor 820 incorporates the functions of a physiological monitor 520 (FIG. 6) and an IV infusion device within a single unit or within physically connected units.

[0022] 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.