[Method of evading the overshoot phenomenon of transcutaneous P(CO2) measurement at the ear lobe].

BACKGROUND

Kagawa et al. confirmed the overshoot of transcutaneous P(CO2) (Ptc(CO2)) during the early stage of measurement with Ptc(CO2) monitor (TOSCA, Linde Medical Sensors AG, Basel, Switzerland). We examined the method to evade this phenomenon.

METHODS

Eight adult patients under general anesthesia were examined. Two probes were mounted each on the left and right ear lobes after constant end expiratory P(CO2) had been obtained for ten to fifteen minutes. One P(CO2) probe was set at 42 degrees C. Another one was set at 45 degrees C for the first 15 minutes and then decreased to 42 degrees C.

RESULTS

With the probe heated at 42 degrees C, overshoot was observed in 5 out of 8 cases, the peak of which is 44 +/- 5.5 mmHg at 8.2 +/- 1.1 minutes and then these values went down to 39 +/- 4.0 mmHg at 19 +/- 1.3 minutes and stayed stable. Probes heated at 45 degrees C and placed on the opposite side did not show this phenomenon and were stabilized at 5 +/- 0.9 minutes.

CONCLUSIONS

With this apparatus, we found that it is effective to avoid overshoot to heat the probe at 45 degrees C and to change at 42 degrees C after 15 minutes.