Heat-induced changes in PO2 and PCO2 of blood.

In vitro differences in blood PO2 and PCO2 at 37 degrees C and 42-44 degrees C were measured in 100 samples from 10 patients, aged 54-79 years. PO2 was measured amperometrically with Clark electrodes, PCO2 was measured with Severinghaus electrodes. PO2 increased with heating and the relative PO2 increment declined with increasing PO2. At 10 kPa the relative increment was approximately 7% per degrees C; at 40 kPa it was less than 2% per degrees C. No correlation between the temperature coefficient and temperature, haemoglobin concentration or pH could be demonstrated. The observed changes were in agreement with the Severinghaus correction formula r = 0.99 (P less than 0.0001). PCO2 increased by 4.6% per degrees C (s.d. = 0.8%) with heating. The PCO2 temperature coefficient did not vary significantly with the PCO2, pH or temperature (P greater than 0.3). No significant difference was seen between the measured values and values calculated according to Severinghaus and Nunn et al. (4.4% per degrees C) or Siggaard-Andersen (4.8% per degrees C), r = 0.95 (P less than 0.0001). It is concluded that the recommended temperature correction formulas for PO2 and PCO2 changes in the blood can be applied even in the temperature level 37-44 degrees C, and thus for analysis of PO2 and PCO2 on the heated skin surface.