Method and apparatus for monitoring respiratory gases during anesthesia

• US 20030176804A1
• Filed: 06/24/2002
• Published: 09/18/2003
• Est. Priority Date: 01/22/2002
• Status: Active Grant

• Current Assignee: University of Florida Research Foundation, Incorporated (State University System of Florida)
• Original Assignee: University of Florida Research Foundation, Incorporated (State University System of Florida)
• Inventors: Melker, Richard J.
• Granted Patent: US 6,981,947 B2
• Time in Patent Office: Days
• US Class Current: 600/532
• CPC Class Codes: A61B 5/08 Detecting, measuring or recording devices for evaluating the respiratory organs A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/082 Evaluation by breath analysis, e.g. determination of the chemical composition of exhaled breath A61B5/083, A61B5/091 take precedence
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: A61B 5/4821 Determining level or depth of anaesthesia A61B5/1106 takes precedence
• CPC Class Codes: A61B 5/7267 involving training the classification device
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/01 specially adapted for anaesthetising A61M16/104, A61M16/18 take precedence
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• CPC Class Codes: A61M 2016/1035 the anaesthetic agent concentration
• CPC Class Codes: A61M 2230/437 the anaesthetic agent concentration
• CPC Class Codes: A61M 5/142 Pressure infusion, e.g. using pumps
• CPC Class Codes: A61M 5/1723 using feedback of body parameters, e.g. blood-sugar, pressure measurement of body parameters A61B5/00

Abstract

A method and system is provided for monitoring delivery of anesthesia (inhalational and intravenous) and detecting the depth of anesthesia wherein at least one anesthetic agent is absorbed in patient'"'"'s bloodstream during the administration of anesthesia, which includes sampling inspired and expired gas; analyzing the gas for concentration of at least one substance indicative of the anesthetic agent using sensor technology such as free (unmetabolized) anesthetic agent or its metabolites; determining the effect of the agent based on that concentration; and determining depth of anesthesia based thereon.

Claims

1. A method of monitoring a patient during administration of anesthesia wherein said patient is connected to a breathing circuit, comprising:

exposing at least one sensor to inspired and expired gases;

detecting one or more target substances with said sensor.

2. The method of claim 1 wherein said target substance is an anesthetic agent.

3. The method of claim 1 wherein said target substance is a physiologic gas.

4. The method of claim 1 wherein said target substance is a gas supplied to a breathing circuit.

5. The method of claim 1 wherein at least one anesthetic agent is administered through said breathing circuit.

6. The method of claim 1 wherein at least on anesthetic agent is delivered intravenously.

7. The method of claim 5, wherein at least one additional anesthetic agent is delivered intravenously.

8. The method of claim 1 further comprising:

determining depth of anesthesia based on the concentration of at least one target substance detected in said expired gases.

9. The method of claim 1 wherein separate sensors are exposed to inspired and expired gases.

10. The method of claim 1 wherein one or more target substances are detected after a predetermined period of time.

11. The method of claim 1 further comprising the step of using at least one flow sensor to detect flow of gases.

12. The method of claim 8 further comprising controlling an infusion pump for delivering an agent intravenously based on the depth of anesthesia determined.

13. The method of claim 1 wherein the detecting step comprises detecting both presence and concentration of the target substance.

14. The method of claim 1 wherein the steps are repeated periodically to monitor trending over time.

15. The method of claim 2 wherein the agent is for amnesia.

16. The method of claim 2 wherein the agent is for analgesia.

17. The method of claim 2 wherein the agent is for muscle relaxation.

18. The method of claim 2 wherein the agent is for sedation.

19. The method of claim 2 wherein a combination of agents is administered.

20. The method of claim 8 wherein the concentration is measured to determine anesthetic blood concentration.

21. The method of claim 8 wherein the concentration is measured to determine analgesic blood concentration.

22. The method of claim 8 wherein the concentration is measured for a level indicative of recovery.

23. The method of claim 1 wherein the detecting is continuous.

24. The method of claim 1 wherein the detecting is periodic.

25. The method of claim 1 wherein said sensor is selected from the group consisting of semiconductor gas sensor technology;

conductive polymer gas sensor technology;

aptamer sensor technology;

amplifying fluorescent polymer (AFP) sensor technology;

or surface acoustic wave gas sensor technology.

26. The method of claim 25 wherein the sensor technology produces a unique electronic fingerprint to characterize the concentration of said at least one substance.

27. The method of claim 1 further comprising the step of recording data from said sensor.

28. The method of claim 1 further comprising the step of transmitting data from said sensor.

29. The method of claim 1 further comprising comparing the substance detected with a predetermnined signature profile.

30. The method of claim 1 further comprising capturing a sample of expired gases prior to exposing said sensor to expired gases.

31. The method of claim 1 further comprising

dehumidifying expired gases prior to exposing said sensor to expired gases.

32. The method of claim 1 further comprising

detecting exhalation of the patient'"'"'s breath with a sensor.

33. The method of claim 1 wherein said target substance is a free anesthetic agent indicative of the anesthetic agent.

34. The method of claim 1 wherein said target substance is a metabolite of an anesthetic agent indicative of the anesthetic agent.

35. The method of claim 1 wherein said target substance is a free anesthetic agent and a metabolite of an anesthetic agent indicative of the anesthetic agent.

36. The method of claim 13 further comprising

assigning a numerical value to the concentration as analyzed upon reaching a level of anesthetic effect in said patient and, thereafter, assigning higher or lower values to the concentration based on its relative changes.

37. The method of claim 36 further comprising monitoring the concentration by monitoring changes in said value and adjusting administration of anesthesia to maintain a desired anesthetic effect.

38. A method of monitoring a patient during administration of anesthesia wherein said patient is connected to a breathing circuit, comprising:

exposing a first sensor to inspired gases, wherein at least one inspired gas is an anesthetic agent;

exposing a second sensor to expired gases;

detecting one or more target substances with said first and second sensors; and

determining concentration of said target substances.

39. An anesthetic agent delivery and monitoring system for delivering balanced anesthesia to a patient through a breathing circuit and an IV comprising:

an anesthetic gas supply having a controller for controlling the amount of volatile anesthetic agent provided by the supply to the breathing circuit;

an intravenous anesthetic agent supply having a controller for controlling the amount of IV anesthetic agent administered to the patient intravenously;

an inspired gas analyzer for analyzing the concentration of anesthetic gas in the breathing circuit;

an expired gas analyzer for analyzing the patient'"'"'s breath for concentration of at least one substance indicative of anesthetic agent concentrations in the patient'"'"'s bloodstream that provides at least one signal to indicate the anesthetic agent concentration delivered to the patient; and

a system controller connected to each of the anesthetic supplies which receives the signal and controls the amount of anesthetic agents administered based on the signal.

40. The system of claim 39 wherein the inspired gas analyzer and expired gas analyzer comprise a sensor for analyzing the gas for concentration of at least one substance indicative of the anesthetic agent concentration and a processor for calculating the effect of the agent based on the concentration and determining depth of anesthesia.

41. The system of claim 40 wherein the sensor is selected from semiconductor gas sensor technology, conductive polymer gas sensor technology, or surface acoustic wave gas sensor technology.

42. An apparatus for administering balanced anesthesia to a patient comprising:

at least one supply of at least one intravenous anesthetic agent;

intravenous delivery means for controllably intravenously delivering said at least one intravenous anesthetic agent to the patent;

at least one supply of at least one inhalational anesthetic agent;

a breathing circuit for delivery of said inhalational anesthetic agent;

an inspired gas analyzer for analyzing gas in said breathing circuit for said inhalational agent;

an expired gas analyzer for analyzing the patient'"'"'s breath for concentration of at least one substance indicative of anesthetic agents in the patient'"'"'s bloodstream that provides a signal to indicate anesthetic agent concentration delivered to the patient;

a system controller connected to the intravenous delivery means which receives the signal and controls the amount of anesthetic agent based on the signal; and

a system controller connected to the breathing circuit which receives the signal and controls the amount of anesthetic agent based on the signal.

43. A device for detecting target substances in a breathing circuit comprising:

at least one surface-acoustic wave sensor capable of detecting the presence of said target substance in inspired and expired gas, wherein said sensor responds to the target substance by a shift in the resonant frequency;

an oscillator circuit having said sensor as an active feedback element;

a frequency counter in communication with said oscillator circuit to measure oscillation frequency which corresponds to resonant frequency of the sensor; and

a processor for comparing the oscillation frequency with a previously measured oscillation frequency of the target substance and determining presence and concentration of the target substance therefrom.

44. A device for detecting target substances in a breathing circuit comprising:

a sensor having an array of polymers capable of detecting the presence of said target substance in inspired and expired gas, wherein said sensor responds to the target substance by changing the resistance in each polymer resulting in a pattern change in the sensor array;

a processor for receiving the change in resistance, comparing the change in resistance with a previously measured change in resistance, and identifying the presence of the target substance from the pattern change and the concentration of the substance from the amplitude.

45. The device of claim 44 wherein the processor comprises a neural network for comparing the change in resistance with a previously measured change in resistance to find a best match.

46. A method of determining the rate of washout of a target substance in a patient comprising:

obtaining a sample of expired breath at a first interval;

analyzing said sample with sensor technology to determine the concentration of said substance;

obtaining at least one additional sample of expired breath at a later interval;

analyzing said additional sample with sensor technology to determine the concentration of said substance; and

comparing the concentration of the first sample with the concentration of additional samples to determine rate of washout of said target substance.

47. The method of claim 46 wherein the target substance is an anesthetic agent.