Effects of tracheal extubation on coronary blood flow, myocardial metabolism and systemic haemodynamic responses.

Global coronary blood flow and metabolism were measured in seven patients on the first postoperative day following coronary revascularization to test the hypothesis that tracheal extubation produces adverse haemodynamic responses akin to those observed during tracheal intubation. Regional coronary flow and metabolic measurements were made in five of the seven patients. Extubation from a continuous positive airway pressure (CPAP) of 5 cm H2O was associated with a statistically significant rise in cardiac index from 3.44 +/- 0.23 L.min-1.m-2 to 3.73 +/- 0.15 L.min-1.m-2 related to an increase in stroke index, without significant changes in heart rate, mean arterial and pulmonary capillary wedge pressure. Consequently the changes in myocardial oxygen consumption (8.52 +/- 0.55 to 8.85 +/- 0.93 ml.min-1) and coronary blood flow (172 +/- 18 to 179 +/- 17 ml.min-1) were less prominent than those reported during intubation, where substantial rises in myocardial oxygen consumption and coronary flow occurred. Two patients experienced cardiac lactate production but there were no changes in systemic or coronary haemodynamics, nor were there clinical or electrocardiographic signs of ischaemia. We conclude that extubation does not appear to be associated with adverse systemic or coronary haemodynamic responses in patients following coronary bypass grafting. However, the revascularized myocardium may remain vulnerable to anaerobic metabolism in the immediate postoperative period.