Transcutaneous PO2 monitoring during sodium nitroprusside infusion

To determine the effect of vasodilator-induced hypotension on the relationship between transcutaneous PO2 (PtcO2) and PaO2, six mongrel dogs and 20 patients were monitored before and during infusion of sodium nitroprusside (SNP), with PtcO2 sensors heated to 45 degrees C. First, SNP infusion was used to lower the mean arterial pressure (MAP) of anesthetized dogs, in steps of approximately 25%, to 49 +/- 3 (SD) mm Hg. There were no significant changes in cardiac output, oxygen consumption, PtcO2, PaO2, or PtcO2 index (PtcO2/PaO2). Twenty patients were monitored during general anesthesia. Fifteen patients were being treated for acute hypertension with SNP, and in five patients hypotension was induced with SNP to minimize blood loss. There was a significant decrease in MAP, PaO2, and PtcO2, and a significant increase in alveolar-arterial PO2 difference during SNP infusion. PtcO2 index did not change significantly from its preinfusion value in either group.