Response of tissue oxygenation to systemic hyperoxia after cardiac surgery

The opening of the peripheral circulation was studied in eight patients in the immediate postoperative phase after coronary artery bypass grafting. The patients were coupled to a respirator, and the FIO2 was maintained at 0.3 except for two 30-min periods of ventilation with 100% oxygen. Oxygen exposures occurred 1 and 8 h after ICU admission. Transcutaneous PO2 (PtcO2), subcutaneous PO2 (PscO2), laser-Doppler skin red cell flux (RCF), and peripheral skin temperature (Tft) were recorded continuously in the upper extremity. The opening of peripheral circulation was reflected as an increase of cardiac index and a decline of mean arterial pressure and systemic vascular resistance. Concurrently, the Tft, PscO2, and RCF rose clearly, whereas the PtcO2 remained unchanged. During both periods of oxygen ventilation, the PaO2 similarly rose and was closely followed by an increase in PtcO2. The PscO2 showed no response to the first period of systemic hyperoxia, but increased promptly during the second exposure to oxygen. To summarize, peripheral tissue oxygenation in postoperative cardiac patients cannot be efficiently elevated by systemic hyperoxia until the peripheral vascular bed is opened.