Smart oxygenation system employing automatic control using SpO2-to-FiO2 ratio

Abstract

A system for assessing lung function in a patient is enclosed. The oxygen delivery system in the system (e.g., a ventilator or portable standalone system) preferably includes an oximeter sensor for receiving SpO2 from a patient. The assessing lung function in a patient includes an FiO2 adjust algorithm operable in logic circuitry in the ventilator that can control an oxygen fraction FiO2 provided to the patient in a closed loop fashion. In a preferred example, the algorithm controls FiO2 using the SpO2, but also displays a ratio of SpO2-to FiO2 (S/.sub.CLCF) as a function of time. One or more S/.sub.CLCF ratio threshold may be used to allow the clinician and/or the algorithm to understand a degree of lung injury, and to allow the algorithm to adjust FiO2 appropriately. Preferably, the algorithm keeps SpO2 to a range of 88-95%.

Claims

1. A system for providing oxygenation to a patient, comprising: an oxygen delivery system configured to continually provide a fraction of inspired oxygen (FiO2) to the patient; an oximeter configured to continually measure a percentage oxygen saturation of blood hemoglobin (SpO2) of the patient and report the measured SpO2 to the oxygen delivery system; logic circuitry configured to continually calculate a ratio of the measured SpO2 to the provided FiO2 (S/.sub.CLCF ratio); an algorithm operable in the logic circuitry and configured to continually adjust the FiO2 provided to the patient given the currently-measured SpO2 and the currently-measured S/.sub.CLCF ratio to try and maintain SpO2 within a desired range; and a display monitor, wherein the logic circuitry is configured to cause the display monitor to display the S/.sub.CLCF ratio as a function of time.

2. The system of claim 1, wherein the logic circuitry is further configured to cause the display monitor to display one or both of measured SpO2 and a calculated rate of change of the S/.sub.CLCF ratio as a function of time.

3. The system of claim 2, wherein the display monitor is integrated within a body of the oxygen delivery system.

4. The system of claim 1, wherein the desired SpO2 range comprises 88% to 95%.

5. The system of claim 1, wherein the logic circuitry is configured to issue an alert when the S/.sub.CLCF ratio falls below a predetermined threshold.

6. The system of claim 5, wherein the predetermined threshold comprises 250.

7. The system of claim 1, further comprising a tube, wherein the FiO2 is provided to the patient by the tube.

8. The system of claim 1, further comprising a mask, wherein the FiO2 is provided to the patient by the mask.

9. The system of claim 1, further comprising a chamber, wherein the FiO2 is provided to the patient by the chamber.

10. The system of claim 1, wherein the oxygen delivery system is mechanical.

11. The system of claim 1, wherein the oxygen delivery system is configured to be portable and standalone.

12. The system of claim 1, wherein the oxygen delivery system comprises a ventilator.

13. The system of claim 1, wherein the oxygen delivery system is configured to home oxygen therapy use.

14. The system of claim 1, wherein the algorithm is further configured to continually adjust a pressure at which the FiO2 is provided to the patient.

15. The system of claim 1, further comprising an antenna, wherein the logic circuitry is configured to cause the antenna to transmit to an external device any one or more of SpO2, the S/.sub.CLCF ratio, and a calculated rate of change of the S/.sub.CLCF ratio, as a function of time.

16. The system of claim 1, wherein FiO2 is provided at an oxygen flow rate.

17. A method for assessing lung function in a patient, comprising: providing a fraction of inspired oxygen (FiO2) to the patient from an oxygen delivery system; determining a percentage of oxygen saturation of blood hemoglobin (SpO2) of the patient and reporting the measured SpO2 at the oxygen delivery system; calculating a ratio of SpO2 to FiO2 (S/.sub.CLCF ratio); and automatically adjusting at the oxygen delivery system the FiO2 provided to the patient using the measured SpO2 and the calculated S/.sub.CLCF ratio to maintain SpO2 within a desired range; and graphing the S/.sub.CLCF ratio, and one or both of measured SpO2 and the calculated rate of change of the S/.sub.CLCF ratio, as a function of time.

18. The method of claim 17, further comprising graphing the measured SpO2 and the calculated rate of change of the S/.sub.CLCF ratio as a function of time.

19. The method of claim 17, wherein the desired range is from 88% to 95%.

20. The method of claim 17, further comprising issuing an alert from the oxygen delivery system when the S/.sub.CLCF ratio falls below a predetermined threshold.

21. The method of claim 20, wherein the predetermined threshold comprises 250.

22. The method of claim 20, further comprising intubating the patient in response to the alert.

23. The method of claim 17, wherein the FiO2 is provided to the patient by a tube.

24. The method of claim 17, wherein the FiO2 is provided to the patient by a mask.

25. The method of claim 17, wherein the FiO2 is provided to the patient by a chamber.

26. The method of claim 17, wherein the oxygen delivery system is configured to be portable and is carried to the patient.

27. The method of claim 17, wherein the method is used in a home of the patient.

28. The method of claim 17, further comprising continually adjusting a pressure at which the FiO2 is provided to the patient.

29. The method of claim 17, further comprising wirelessly transmitting to an external device any one or more of SpO2, the S/.sub.CLCF ratio, and a calculated rate of change of the S/.sub.CLCF ratio, as a function of time.

30. The method of claim 17, wherein the FiO2 provided to the patient is increased if the S/.sub.CLCF ratio falls below a predetermined threshold value.

31. The method of claim 30, wherein the predetermined threshold value is 300, 200, 250, or 100.

32. The method of claim 30, wherein the predetermined threshold value is 250.

33. The method of claim 17, wherein adjusting the FiO2 provided to the patient comprises increasing or initiating PEEP, increasing or initiating positive or negative pressure, or increasing tidal volume.

34. The method of claim 17, wherein the patient has acute respiratory distress syndrome.

35. The method of claim 17, wherein the patient has suffered a traumatic injury.

36. The method of claim 17, wherein the patient has chronic obstructive pulmonary disease (COPD).

37. The method of claim 17, wherein the patient has congestive heart failure (CHF).

38. The method of claim 17, wherein the method is performed on the patient after being anesthetized.

39. The method of claim 17, wherein the method is performed after the patient has been extubated.

40. The method of claim 17, wherein the patient is a neonate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a SpO2/PaO2 oxygen dissociation curve, in accordance with the prior art.

(2) FIG. 2 shows a prior art ventilation system, including an oximeter sensor to report SpO2 to the ventilator, in accordance with the prior art.

(3) FIG. 3 shows a display of an improved ventilation system, displaying an SpO2/FiO2 (S/F) ratio, SpO2, and a rate of change of S/F, in accordance an example of the invention.

(4) FIG. 4 shows the improved ventilation system, which in conjunction with an FiO2 adjust algorithm can control FiO2 provided to the patient in accordance to achieve an appropriate SpO2 range, such as 88-95%, in accordance with an example of the invention.

DETAILED DESCRIPTION

(5) Existing ventilation systems adjust FiO2 in a closed loop fashion with the goal of maintaining SpO2 within a set range. Closed Loop Control has also been used in conjunction with the S/F ratio described earlier. See, e.g., M. Kinsky, Smart Oxygen Monitors to Diagnose and Treat Cardiopulmonary Injuries, U.S. Army Award Number W81XWH-12-1-0598 (Annual Report, October 2014) (2014 Report). The 2014 Report discloses use of closed loop ventilation systems similar to those shown in FIG. 2 to diagnose and treat lung injury, and identifies SpO2:CLC-FiO2i.e., using the S/.sub.CLCF ratio to control FiO2 in a closed loop fashionas a new vital sign. The 2014 report further identifies thresholds for S/.sub.CLCF that indicate adequate pulmonary function and pulmonary distress, and suggest that a display e.g., the display monitor 22 of FIG. 2 should display the variables over time for SpO2, CLC-FIO2, and its ratio [S/.sub.CLCF].

(6) Thus, the 2014 Report and subsequent reports show the promise of using the S/F ratio as a variable to control FiO2 in a closed loop. See also M. Kinsky, Smart Oxygen Monitors to Diagnose and Treat Cardiopulmonary Injuries, U.S. Army Award Number W81XWH-12-1-0598 (Annual Report, Oct. 29, 2015) (2015 Report).

(7) However, in the inventors' opinion, mere use of the S/.sub.CLCF ratio to control FiO2 administered to the patient may not always result in ideal oxygenation therapy. In part this is because an S/F ratio by itself is agnostic as to the value of SpO2, as well as its rate of change.

(8) FIG. 3 shows an example of an S/.sub.CLCF ratio as may be displayed by an oxygen delivery system 12 over time on its monitor display 22. As shown, the S/.sub.CLCF ratio is classified into different regions indicating different levels of ARDS severity, with S/.sub.CLCF>300 indicating no apparent ARDS, or generally speaking normal lung function (30a); 200-300 indicating mild ARDS (30b); 100-200 indicating moderate ARDS (30c); and S/.sub.CLCF<100 indicating severe ARDS (30d). Thus, different S/.sub.CLCF thresholds of 300, 200, and 100 are identified, and are adapted from the Berlin criteria. See N. Ferguson et al., The Berlin Definition of ARDS: An Expanded Rationale, Justification, and Supplementary Material, Intensive Care Medicine, 38:1573-82 (2012). An S/.sub.CLCF ratio of 250 (in the middle of the mild ARDS range), can generally be considered as a threshold (T) requiring a change of FiO2 in a closed loop system, although other thresholds (at S/.sub.CLCF=100, 200, 30, etc.) could also be used. One or more alerts (either graphical alerts on the display monitor 22, or audible alerts) may be issued by the oxygen delivery system 112 when one or more S/F thresholds are crossed.

(9) FIG. 4 shows a system 100 useable to provide the display shown in FIG. 3, and which includes an improved FiO2 adjustment algorithm 120 capable of adjusting FiO2 in a close loop fashion depending on SpO2 with the goal of keeping SpO2 within a given range (e.g., 88-95%), which as noted above can provide a sufficient but minimal amount of oxygen, and therefore keep FiO2 to a minimum during closed loop control. See http://www.ardsnet.org/files/ventilator_protocol_2008-07.pdf (downloaded 2016).

(10) The algorithm 120 also calculates the S/.sub.CLCF ratio, and tracks it versus one or more S/.sub.CLCF thresholds, such as S/.sub.CLCF=T=250, and the S/.sub.CLCF ratio is preferably graphed on display monitor 22 as a function of time. The S/.sub.CLCF ratio can be calculated using SpO2 as reported by the oximeter sensor, and using the current value of FiO2 being provided by the closed loop control oxygen delivery system 112. S/.sub.CLCF thresholds can be stored in memory 132 in the ventilator 112. When S/.sub.CLCF falls below a threshold (e.g., T=250) as shown in FIG. 3, an alarm can issue for instance. In the example shown, it is seen that when SpO2 falls below its desired range (e.g., <88%), the S/F ratio is also low. As the algorithm increases FiO2 (e.g., from 0.21 to 0.5) to try and increase SpO2, both SpO2 and the S/.sub.CLCF ratio begin to rise to acceptable levels.

(11) The FiO2 adjustment algorithm 120 in an alternative example also adjusts FiO2 in accordance with the S/.sub.CLCF ratio as well as the current value of SpO2. See http://www.ardsnet.org/files/ventilator_protocol_2008-07.pdf (downloaded 2016). Because FiO2 adjustment algorithm 120 considers both the S/.sub.CLCF ratio and SpO2 when adjusting FiO2, the algorithm may need to balance competing interests, and generally with the conservative goal as always ensuring that the patient has sufficient oxygen. For example, if the S/.sub.CLCF ratio is sufficient (e.g., 300), but SpO2 is low (e.g., 87%), algorithm 120 will preferably increase FiO2. Likewise, if the S/.sub.CLCF ratio is low (e.g., 280), but SpO2 is sufficient (e.g., 90%), algorithm 120 may again preferably increase FiO2. Again, conservative automatic control of FiO2 is desired.

(12) FiO2 adjustment algorithm 120 may also along with the S/.sub.CLCF ratio takes into account the rate by which the S/.sub.CLCF ratio may be changing ((S/.sub.CLCF)/t), which parameter may be computed and stored in memory 132. Rate of change of S/.sub.CLCF can be different from patient to patient, and can be significant as to how aggressively the algorithm 120 should adjust FiO2. For example, as shown in FIG. 3, the patient begins to experience significant impairment in lung function at around 23 hours (when S/.sub.CLCF decreases below 300). In this example, the rate of change of S/.sub.CLCF is relatively sharp, suggesting that FiO2 might perhaps be increased by a significant amount (e.g., to FiO2=0.7). Were S/.sub.CLCF decreasing more slowly, FiO2 might be changed to a lesser amount (e.g., to FiO2=0.35).

(13) In short, in the disclosed system 100, the FiO2 adjustment algorithm 120 in the oxygen delivery system 112 preferably uses SpO2 as a closed loop variable to adjust FiO2, with the goal of keeping SpO2 with a desired range (88-95%), and may additionally use the S/.sub.CLCF ratio and the rate of change of the S/.sub.CLCF ratio (((S/.sub.CLCF)/t)) to control FiO2 provided to the patient as well. If both S/.sub.CLCF and (S/.sub.CLCF)/t are considered along with SpO2, FiO2 adjustment algorithm 120 can balance or weigh these parameters as appropriate to provide the desired closed loop control to achieve the desired SpO2 range.

(14) As well as increasing the amount of oxygen provided to the patient (FiO2) using SpO2, and optionally the S/.sub.CLCF ratio and the rate of change of that ratio, the FiO2 adjust algorithm 120 could automatically escalate intervention in other ways, such as by increasing or initiating PEEP, increasing or initiate positive or negative pressure, increasing tidal volume, or taking other actions that affect the manner in which the inspired oxygen is provided to the patient, assuming that the oxygen delivery system 112 in question allows such variables to be changed. Further, the FiO2 adjustment algorithm may also indicate to the clinician (e.g., on the display monitor or audibly), that other interventions are warranted, such intubation. Likewise, FiO2 adjustment algorithm may also deescalate the intervention by automatically reducing or stopping these inspiration parameters, and by indicating extubation.

(15) In a preferred example, the logic circuitry in which FiO2 adjustment algorithm 120 operates in the oxygen delivery system 112 provides data to the display monitor 22 so that it may be displayed to a clinician. In a preferred example, the S/.sub.CLCF ratio is graphed over time as is SpO2, as shown in FIG. 3. Various S/.sub.CLCF thresholds (e.g., 100, 200, 250, 300) may also be displayed, and may perhaps be highlighted with different colors to highlight the different regions of ARDS severity (30a-30d). Additionally, the rate of change of the S/.sub.CLCF ratio(S/.sub.CLCF)/tmay also be calculated and graphed as a function of time, although this is not shown in FIG. 3. Such graphed parameters on the display monitor 22 may be overlaid, or graphed as separate non-overlapping traces. The current values for each of these parameters may also be shown on the display monitor 22. Finally, the FiO2 being provided by the oxygen delivery system 112 may also be graphed as a function of time, and/or its current values shown, although again this isn't shown in FIG. 3. Display of one or more of these parameters will assist the clinician in understanding how the FiO2 adjustment algorithm 120 is operating, and how the patient's oxygenation therapy is progressing.

(16) These parameters may also be transmittable from the oxygen delivery system 112 to other external devices. In the regard, the oxygen delivery system 112 can include a port 134 for receiving a cable to transmit parameters through the cable to an external device such as a clinician's computer, personal computer, lap top computer, tablet, cell phone, etc., or other computer system operable at a hospital handling electronic medical records (EMRs) for example. Alternatively, the oxygen delivery system 112 can include an antenna 136 and associated transceiver circuitry to wirelessly transmit such parameters to such devices.

(17) It should be understood that while the disclosed ventilator system 100 has been described as measuring SpO2 continuously, calculating S/.sub.CLCF and the rate of change of S/.sub.CLCF continuously, and adjusting FiO2 continuously, this does not imply that the such measuring, calculating, and adjusting occur at all times without stopping. Instead, continuous in this context means on some sort of time scale which may be periodic or which can occur as necessary.

(18) The improved oxygen delivery system 112 and FiO2 adjust algorithm 120 is expected to be useful with patients having acute respiratory distress syndrome (ARDS); patients having chronic obstructive pulmonary disease (COPD); patients having congestive heart failure (CHF); neonate patients; patients that have suffered a traumatic injury, such as in a military field or as a result of a mass causality; patients being triaged (e.g., in an emergency room); patients that have recently been extubated (e.g., as a monitor for extubation failure); and patients that have been anesthetized (e.g., use in post-anesthesia care unit (PACU)).

(19) Although particular embodiments of the present invention have been shown and described, it should be understood that the above discussion is not intended to limit the present invention to these embodiments. It will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention. Thus, the present invention is intended to cover alternatives, modifications, and equivalents that may fall within the spirit and scope of the present invention as defined by the claims.