Measurement of transcutaneous PO2, PCO2 and skin blood flow at different probe temperatures using mass spectrometry.

Transcutaneously measured partial pressures of oxygen and carbon dioxide (PtcO2, PtcCO2) approximate the corresponding arterial values at a probe temperature of 44 degrees C. The temperature-dependent increase of PtcO2 and PtcCO2 is caused by an increased skin perfusion, a decrease in the mean diffusion path, a change of skin metabolism, a decrease of tissue solubility of oxygen and carbon dioxide and a right shift of the oxygen and carbon dioxide binding curves of blood. Seven healthy volunteer test subjects participated in the study. A transcutaneous probe connected to a mass spectrometer was placed on the earlobe of the test subject. Four measurements of the transcutaneous PO2, PCO2 and skin blood flow (from the washout kinetics of argon) were determined on each test subject. The first measurement was made with a transcutaneous probe temperature of 37 degrees C. The probe temperature was then increased to 44 degrees C before the next determination. Finally, two determinations were made at 37 degrees C, separated by a time interval of 1 h. The PtcO2 and skin blood flow increased when the probe temperature increased from 37 degrees C to 44 degrees C. However, when the probe temperature was decreased again from 44 degrees C to 37 degrees C, the estimated skin blood flow returned to the initial value while the PtcO2 remained unchanged. It required a further 1 h before the PtcO2 returned to the initial value at 37 degrees C. The most likely explanation of the experimental results is that heating of the skin to 44 degrees C causes a reversible decrease in the skin metabolism.