[The effect of pre-oxygenation on hemodynamics and oxygen consumption]

Pre-oxygenation is routinely used prior to anesthesia and intubation. In awake, premedicated patients scheduled for major aortic surgery we assessed the effects of breathing oxygen for 10 min via a loosely fitting face mask on hemodynamics and oxygen consumption (VO2). RESULTS. O2-breathing increased arterial PO2 to 51 +/- 13 kPa and decreased VO2 from 109 +/- 18 to 92 +/- 24 ml.min-1.m-2 (P less than 0.001 for both variables). This reduction of VO2 resulted from both a fall in cardiac index from 3.22 +/- 0.67 to 3.04 +/- 0.75 1.min-1/m-2 (P less than 0.05) and a decrease in arterio-venous oxygen content difference from 3.45 +/- 0.60 to 3.03 +/- 0.57 ml/dl (P less than 0.001). Systemic peripheral vascular resistance increased slightly from 1453 +/- 359 to 1538 +/- 383 dyne.s.cm-5.m-2 (P less than 0.05). CONCLUSIONS. These results indicate that an increase in F1O2 in patients without severe limitations of oxygen uptake by the lungs or oxygen transport to the tissues does not improve tissue oxygenation. We speculate that increased peripheral shunting acts to protect tissue PO2 during high arterial PO2 levels.