Skin-surface CO2 measurement in sick preterm and term infants

To evaluate the clinical usefulness of a heated CO2 electrode at 43 degrees C for measurement of skin surface PCO2, we made 157 simultaneous determinations of PSCO2 and arterial PCO2. Arterial samples were drawn from an umbilical artery catheter, and the PaCO2 was measured within two minutes and was corrected for body temperature. We obtained two to 43 paired samples per infant from 22 infants (gestational age = 27 to 40 weeks) during the first 12 days of life. Over a four-hour period there was no significant drift of the electrode calibration and no significant change in PSCO2-PaCO2 (delta). Over the range PaCO2 26 to 72 torr, PaCO2 was linearly related to PSCO2 (PaCO2 = 0.37 PSCO2, + 17.46) r = 0.79). To pursue the factors which determine delta, we performed step-wise multiple regression analysis and found that the only significant independent variables were PSCO2 and postnatal age (delta = 0.79 CO2 [torr] - 1.2 age [days] - 23.9 [r = 0.93]). Insignificant independent variables were blood pressure, gestational age, hematocrit, weight at time of study, and drug therapy.