Effect of inspired oxygen on the cardiovascular effects of protamine after cardiopulmonary bypass

We have performed a randomized prospective study of the effects of inspired oxygen fraction (FIO2) on the haemodynamic changes after protamine infusion. Thirty-four patients undergoing first time coronary artery bypass surgery were allocated randomly to receive either an FIO2 of 1.0 (group O) or 0.35 (group A) after cardiopulmonary bypass. Before and after infusion of protamine, haemodynamic measurements were obtained, including mean arterial pressure (MAP), mean pulmonary artery pressure, central venous pressure, pulmonary capillary wedge pressure (PCWP), cardiac index (CI), pulmonary vascular resistance index (PVRI) and systemic vascular resistance index (SVRI). In group O, there were increases in mean MAP (8%), PVRI (48%) and SVRI (18%), and decreases in mean CI (10%) and PCWP (15%). Group A showed changes of 0%, -8%, -6%, +3% and +32%, respectively. We found a significant difference between groups in changes in PVRI (P < 0.0001), SVRI (P < 0.01), CI (P < 0.05) and PCWP (P < 0.001). During infusion of protamine, 31% of patients in group O and 6% of patients in group A had a decrease in systolic arterial pressure to less than 80 mm Hg (ns, chi-square test). These observations suggest that FIO2 alters the haemodynamic effects of protamine.