Detection of pain/awakening integral value

• US 20100056943A1
• Filed: 11/08/2007
• Published: 03/04/2010
• Est. Priority Date: 11/10/2006
• Status: Active Grant

• Current Assignee: Med Storm Innovation AS
• Original Assignee: Med Storm Innovation AS
• Inventors: Storm, Hanne
• Granted Patent: US 8,239,016 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0531 Measuring skin impedance
• CPC Class Codes: A61B 5/4035 Evaluating the autonomic nervous system
• CPC Class Codes: A61B 5/4821 Determining level or depth of anaesthesia A61B5/1106 takes precedence

Abstract

The invention relates to a method and an apparatus for monitoring the autonomous nervous system of a sedated patient. A skin conductance signal is measured at an area of the patient'"'"'s skin during a measurement interval. A first measure and a second measure, both reflecting the state of the autonomous nervous system of the patient, is calculated by means of certain integral functions. The largest one of the first and second measures is then selected as the output signal (Y) that reflects the state of the autonomous nervous system of the sedated patient.

Claims

1. Method for monitoring the state of the autonomous nervous system of a sedated patient, the method comprising the steps of:

providing a skin conductance signal measured at an area of the patient'"'"'s skin during a measurement interval,

identifying local minimum points in the skin conductance signal through the measurement interval,

selecting intervals between said identified, subsequent minimum points as integrating intervals,

for each integrating interval,

calculating a linear ramp function defined by the skin conductance signal at the starting point and the ending point of the integrating interval,

in subsets of the integrating interval wherein the skin conductance signal exceeds the linear ramp function, calculating the integral of the difference between the skin conductance signal and the linear ramp function, and

calculating the sum of said integrals through the measurement interval as a first measure that reflects the state of the autonomous nervous system of said sedated patient.

2. Method according to claim 1, the method further comprising the steps of

selecting a subset of the measurement interval, starting at the first minimum point in the measurement interval,

selecting the skin conductance value at the first minimum point in the measurement interval as a constant value,

in subsets of the measurement interval subset wherein the skin conductance signal exceeds the constant value, calculating the integral of the difference between the skin conductance signal and the constant value, and

calculating the sum of said integrals through the measurement interval as a second measure that reflects the state of the autonomous nervous system of said sedated patient.

3. Method according to claim 2, wherein the endpoint of said subset of the measurement interval is selected at the last minimum point of the skin conductance value through the measurement interval.

4. Method according to claim 2, wherein the endpoint of said subset of the measurement interval is selected at the last point in the measurement interval.

5. Method according to claim one of the claims 2-4, further comprising the step of

providing the largest of the first and second measures as an output signal (Y) that reflects the state of the autonomous nervous system of the sedated patient.

6. Method according to claim 5,

further comprising the step of displaying said output signal (Y) on a display.

7. Method according to one of the claims 1-6,

wherein said measurement interval is in the range 5 to 30 seconds, or more preferably in the range 10 to 25 seconds, or more preferably about 15 seconds.

8. Method according to one of the claims 5-7,

further comprising the step of

setting a pain indication signal if the output signal (Y) is within a predetermined range (<

Y1, Y2>

) of output signal values.

9. Method according to claim 8,

wherein Y1 is in the range <

0.05 μ

Ss, 0.20 μ

Ss> and

more preferably about 0.1 μ

Ss, and

wherein Y2 is in the range <

0.5 μ

Ss, 3.0 μ

Ss> and

more preferably about 2.0 μ

Ss.

10. Method according to one of the claims 5-9,

further comprising the step of

setting an awakening indication signal if the output signal (Y) is larger than a predetermined output signal value (Y3).

11. Method according to claim 10,

wherein Y3 is in the range <

0.5 μ

Ss, 3.0 μ

Ss> and

more preferably about 2.0 μ

Ss.

12. Method according to one of the claims 1-11,

further comprising the preceding step of exerting a pain inducing stimulus such as a standardised noxious stimulus to the patient.

13. Apparatus for monitoring the state of the autonomous nervous system of a sedated patient, comprising

measurement equipment for providing a skin conductance signal measured at an area of the patient'"'"'s skin, and

a control unit, configured for performing a method according to one of the claims 1-12.