Method of monitoring the dry cleaning progress of a transcutaneous sensor

Abstract

The proposed invention provides a method of monitoring the dry cleaning progress of a transcutaneous sensor having an electrode for measuring pCO.sub.2 and an electrode for measuring pO.sub.2, both electrodes opening into a measuring surface of the sensor. The method comprises receiving an AC signal from the pCO.sub.2 electrode, initiating a cleaning of the sensor, and monitoring the cleaning progress by analyzing AC signals subsequently received from the pCO.sub.2 electrode.

Claims

1. A method of monitoring a dry cleaning progress of a transcutaneous sensor comprising an electrode for measuring pCO.sub.2 and an electrode for measuring pO.sub.2, both electrodes opening into a measuring surface of the sensor, the method comprising: initiating a cleaning of the sensor, receiving an signal from the pCO.sub.2 electrode in response to the initiating the cleaning of the sensor, monitoring the dry cleaning progress by analyzing AC signals subsequently received from the pCO.sub.2 electrode, and informing a user of a status of the dry cleaning progress.

2. The method according to claim 1, wherein initiating the cleaning of the sensor comprises a user manually starting the cleaning.

3. The method according to claim 1, wherein initiating the cleaning of the sensor comprises determining that an AC signal created at the pCO.sub.2 electrode is a cleaning signal.

4. The method according to claim 1, wherein the AC signals received from initiating the cleaning provide a signal function f(t).

5. The method according to claim 4, wherein the cleaning progress is determined by analysis of derivatives of the signal function f(t).

6. The method according to claim 5, wherein the analysis comprises analysis of first and/or second derivatives of the signal function f(t).

7. The method according to claim 1, wherein the dry cleaning progress is determined in cleaning intervals, each interval being generated when a predetermined criterion has been met.

8. The method according to claim 7, wherein the sensor is determined to be sufficiently cleaned when a predetermined number of intervals have been performed.

9. The method according to claim 1, wherein the information to the user is provided by a monitor connected to the sensor.

10. The method according to claim 9, wherein the monitor is kept in a cleaning mode as long as the sensor shall be cleaned.

11. A monitor for monitoring signals measured by a transcutaneous sensor comprising an electrode for measuring pCO.sub.2 and an electrode for measuring pO2, both electrodes opening into a measuring surface of the sensor, the monitor being adapted to monitor a cleaning progress of said transcutaneous sensor by: receiving an input initiating a cleaning of the sensor, receiving an AC signal from the pCO.sub.2 electrode in response to the receiving the input initiating the cleaning of the sensor, monitoring the cleaning progress by analyzing AC signals subsequently received from the pCO.sub.2 electrode, and informing a user of a status of the cleaning progress.

12. The monitor according to claim 11, wherein the monitor is adapted for receiving input from a user and initiating the cleaning of the sensor comprises a user manually starting the cleaning by providing input to the monitor.

13. The monitor according to claim 12, herein the monitor is kept in a cleaning mode as long as the sensor is being cleaned.

14. The monitor according to claim 12, wherein the user is informed of the cleaning progress based on a number of cleaning intervals, each interval being generated when a predetermined criterion has been met.

15. The monitor according to claim 11, wherein the monitor is kept in a cleaning mode as long as the sensor is being cleaned.

16. The monitor according to claim 15, wherein the user is informed of the cleaning progress based on a number of cleaning intervals, each interval being generated when a predetermined criterion has been met.

17. The monitor according to claim 11, wherein the user is informed of the cleaning progress based on a number of cleaning intervals, each interval being generated when a predetermined criterion has been met.

Description

(1) The invention will now be further described with reference to the figures.

(2) FIG. 1 shows a TC sensor 1 for the method as described herein.

(3) FIG. 2 shows the AC signal measured by the pCO.sub.2 electrode as a function of time when cleaning the sensor surface of the TC sensor 1 of FIG. 1.

DETAILED DESCRIPTION

(4) FIG. 1 shows a TC sensor 1 as known in the art. The TC sensor 1 has a temperature sensor 2 in the shape of a thermistor and a buffer amplifier 3 for pCO.sub.2 electrode voltage amplification and pO.sub.2 electrode current to voltage conversion. The TC sensor 1 further comprises a pO.sub.2 measuring electrode 4 in the shape of a Pt cathode, an Ag/AgCl reference electrode 5, a pCO.sub.2 electrode 6 comprising a pH glass electrode and a heating element 7 for heating the TC sensor 1 to make the skin permeable for CO.sub.2 and especially for O.sub.2 The pO.sub.2 electrode 4, the reference electrode 5 and the pCO.sub.2 electrode 6 all open into a measuring surface 8 of the TC sensor 1. A membrane system 9 covers the measuring surface 8, an electrolyte solution (not shown) being embedded between the membrane system 9 and the measuring surface 8 to secure transfer of the O.sub.2 and CO.sub.2 diffused through the membrane system 9 to the measuring surface 8. The TC sensor 1 is to be mounted on a patients' skin by means of an adhesive 11 ring, a contact fluid 10 being placed between the skin and the measuring surface 8. The TC sensor 1 is via a cable 12 connected to a monitor (not shown) controlling the functioning of and processing data from the sensor. The TC sensor 1 has an outer diameter of around 15 mm.

(5) When in use dendrites will over time grow on the Pt cathode 4 at the place where it opens into the measuring surface 8, thus increasing the surface of the Pt cathode 4. As mentioned above, this will result in an increase in the sensitivity of the pO.sub.2 sensor 4. In order to remove the dendrites the user will have to remove the dendrites from the Pt cathode 4 by cleaning (scrubbing) the measuring surface 8. When cleaning the Pt cathode 4, the user will scrub the entire measuring surface 8 including the surface of the pH glass electrode 6, thus creating a detectable AC signal at the pH glass electrode 6.

(6) FIG. 2 shows an example of the recording of the AC signal of the amplified pCO.sub.2 signal recorded with a scope as a function f(t) of time during dry cleaning the sensor surface of the TC sensor 1 of FIG. 1.

(7) Prior to the time t.sub.1, the TC sensor 1 is in a state where it is held in open air. At t.sub.1 a user starts a cleaning process. At first the user presses a cleaning button on the monitor screen initiating a cleaning in the system and setting the monitor in cleaning mode. The user then starts scrubbing the measuring surface 8 of the TC sensor 1 with a dry cloth. As can be seen from FIG. 2, the dry cleaning (scrubbing) of the measuring surface results in AC signals received at the pCO.sub.2 electrode that are significantly different than the signals received at the pCO.sub.2 electrode at the first state (prior to t.sub.1). The AC signals are collected from t.sub.1 and onwards and processed in the monitor. In this particular system, monitoring of the dry cleaning progress of the TC sensor 1 comprises an analysis of the signal function f(t) using first and second derivatives of the signal function f(t).

(8) Thus, during the monitoring of the signals from the pCO.sub.2 electrode, the following averaged values are calculated at 1 Hz:
g(t)=abs[d/dt f(t)](1)
G(t)=d/dt abs[f(t)](2)
h(t)=abs[d/dt g(t)](3)
H(t)=d/dt abs[g(t)](4)
wherein g(t) is the first derivative, G(t) is the first absolute derivative, h(t) is the 2.sup.nd derivative, and H(t) is the 2.sup.nd absolute derivative.

(9) If one of the following criteria (5) and (6) is met, an Interval is generated as a cleaning interval:
h(t)>0.26 mV AND {g(t)>2.61 mV OR G(t)>2.61 mV OR H(t)>0.65 mV}(5)
h(t)>0.13 mV AND {g(t)>2.61 mV AND G(t)>2.61 mV AND H(t)>0.65 mV}(6)

(10) Each cleaning interval corresponds to the cleaning progress of 10% and thus, the cleaning will be complete after 10 intervals. The cleaning progress is at all times during the cleaning shown at the monitor screen by displaying a window where the user is informed of how far (how many % complete) the cleaning is. During the cleaning, the monitor will remain in cleaning mode.

(11) When the system has reached the 100% cleaning (10 intervals), the dendrites have been removed from the cathode 4. The monitor will then leave cleaning mode and the TC sensor 1 is now ready to receive a new membrane system 9 prior to being used for further measurements of pCO.sub.2 and pO.sub.2.