RELATION OF TRANS-CUTANEOUS TO ARTERIAL PO2 IN HYPOXEMIA, NORMOXEMIA AND HYPEROXEMIA - INVESTIGATIONS IN ADULTS WITH NORMAL CIRCULATION AND IN PATIENTS WITH CIRCULATORY INSUFFICIENCY
The transcutaneous O2 tension was monitored continuously by a heated cutaneous polarographic electrode in 7 adult intensive care patients, 12 patients without circulatory insufficiency and 5 healthy volunteers. Arterial PO2 [partial pressure of O2] values were varied from hypoxemia to normoxemia and hyperoxemia by variation of the inspired O2 concentration. In normal volunteers and in patients without circulatory failure, transcutaneous PO2 indicated on an average about 81-92% of the arterial PO2 [PaO2] in normoxemia and hyperoxemia with a correlation coefficient of 0.97. In hypoxemia there was an over-proportional decrease of the transcutaneous PO2 to a mean value of 44% of the arterial PO2. In 1 case the transcutaneous PO2 reproducibly dropped to zero at PaO2 values of 41-38 mm Hg (5.5-5.1 kPa [kilopaschals]). In intensive care patients the transcutaneous PO2 values were considerably lower than the PaO2 values. There was no constant transcutaneous to arterial PO2 ratio in most of the intensive care patients at different PO2 levels. In adults without disturbance of peripheral perfusion PaO2 can be predicted with satisfactory accuracy from transcutaneous PO2 values in normoxemia and in hyperoxemia. In hypoxemia and in circulatory insufficiency, the transcutaneous PO2 is only an indicator of the trend of the arterial PO2. It does not allow a quantitative estimate of PaO2 changes.