CALIBRATION OF A HEATED TRANS-CUTANEOUS CARBON-DIOXIDE ELECTRODE TO REFLECT ARTERIAL CARBON-DIOXIDE

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Abstract
The CO2 measured by a heated skin surface electrode is greater than arterial CO2. The magnitude of this difference was determined retrospectively, the calibration of the heated transcutaneous CO2 electrode was adjusted to reflect this difference; and the validity of the calibration procedure was tested prospectively. The retrospective study consisted of 252 simultaneous arterial and transcutaneous measurements on 38 infants and children (age range, 1 day-6 yr). A linear regression analysis showed PtcCO2 [transcutaneous CO2 tension] = 1.61 .cntdot. PaCO2 [CO2 arterial partial pressure] -0.01 mm Hg, r = 0.90 (P < 0.0001). Because the intercept was virtually zero, the calibration procedure was changed by dividing the transcutaneous electrode reading by 1.61. The prospective study consisted of 269 more simultaneous arterial and transcutaneous measurements from 57 consecutive infants and children (age range, 1 day-18 yr) using this calibration procedure. Regression analysis showed PtcCO2 = 1.02 .cntdot. PaCO2-2.3 mm Hg, r = 0.96 (P < 0.0001). The transcutaneous CO2 electrode, using this technique, reliably predicted the arterial CO2.

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