Effects of hypoxia and shock on transcutaneous PO2 values in dogs.

Abstract

Transcutaneous Po2 (PtcO2) was measured with transcutaneous oxygen electrode sensors and correlated with Pao2, Pvo2, cardiac output, and O2 delivery during changes in FIO2 and standardized hypovolemic shock in anesthetized dogs. Simultaneously, cardiorespiratory variables were measured: intravascular pressures, arterial and mixed venous gases, and cardiac output. Before the shock experiments, these physiologic variables were measured while the FIO2 was varied from 0.21–1.0. Then the FIO2 was held constant while the animal was subjected to hemorrhagic shock and resuscitation. PtcO2 followed PaO2 values (r = 0.96) during variations in the FIO2 when the cardiac output was in the normal range. The 95% response time was less than 15 sec. In the active hemorrhage stage, PtcO2, Pvo2, and cardiac output simultaneously decreased. As the cardiac output dropped, the PtcO2 fell from values near that of the PaO2 and approached the falling PvO2. At the point of 20 torr, the PtcO2 fell below the PvO2. During these shock experiments, when the PtcO2 was greater than 20 torr, the PvO2 was less than PtcO2, but when the PtcO2 was less than 20 torr, the PvO2 was greater than the PtcO2. This PtcO2-PvO2 crossing point corresponded to a cardiac output of 25–30% of the control and a decrease in total body oxygen consumption of 30%. With fluid resuscitation, the PtcO2 responded more quickly at first than the increase in cardiac output. Throughout the shock period, the PaO2 did not vary significantly from the preshock control value. The oxygen delivery was the variable that the PtcO2 followed most closely during the entire hypoxia and hemorrhagic shock experiments, rw = 0.82. It was concluded that the PtcO2 is an accurate, noninvasive, continuous method for monitoring peripheral oxygen delivery and a valuable tool for the study of disturbed circulation in various shock states. In the latter conditions, it does not follow PaO2, but rather, oxygen delivery.