The transcutaneous oxygen sensor (PtcO2), which has been used to predict PaO2 in neonates, recently has been shown to follow changes in oxygen delivery, rather than PaO2 during shock and hypoxia in dogs. Six preterminal patients were continuously monitored with PtcO2 and monitored hemodynamically at frequent intervals during cardiac decompensation, arrest, and cardiopulmonary resuscitation (CPR). The weighted mean correlation coefficients between PtcO2 and O2 delivery as well as between PtcO2 and cardiac output were 0.94 and 0.96, respectively. Five patients died of severe ARDS and 1 patient died intraoperatively of hemorrhagic shock. Four patients were monitored 1-7 days before shock occurred. The correlation between PtcO2 and PaO2 was 0.91 during periods of normal cardiac output in the preterminal period. During cardiac decompensation, the cardiac output, PtcO2, and mixed venous oxygen tension (PcO2) of 25 torr was reached, the PtcO2 fell below the PvO2. This also corresponded to a decrease in VO2. The mean VO2 was 142 +/- 24 ml/min x M2 for PtcO2 values > torr, and 75 +/- 15 ml/min x M2 for PtcO2 < 25 torr (p < 0.01). A PtcO2 of > 40 torr corresponded to normal cardiac index, O2 delivery, VO2, PvO2, and arterial pH (pHa) while a PtcO2, of < 25 torr corresponded to large reductions of these variables. A PtcO2 of < 25 torr preceded cardiac arrest by 43 +/- 28 min.