Coronary haemodynamics and myocardial metabolism during weaning from mechanical ventilation in cardiac surgical patients.

The present clinical study was undertaken to assess the alterations in myocardial metabolism and coronary haemodynamics during weaning from mechanical ventilation in postoperative cardiac surgical patients. Global and regional myocardial blood flow and metabolism were assessed using a dual port coronary sinus-great cardiac vein thermodilution catheter in 17 patients who had undergone coronary revascularization and who were being weaned from mechanical ventilation. Anaerobic myocardial metabolism, as demonstrated by the production of myocardial lactate, manifested in 8 of 17 patients during at least one of the weaning phases. There were no differences in coronary blood flow between patients who produced myocardial lactate and those who maintained aerobic cardiac metabolism. However, lactate producers exhibited larger changes in systemic vascular resistance and mean arterial pressure than the non-lactate producers. This metabolic manifestation of myocardial ischaemia was not accompanied by electrocardiographic changes of ischaemia, nor presence of chest pain, and may represent another form of silent ischaemia. We conclude that despite coronary revascularization, the myocardium may remain vulnerable to ischaemic anaerobic metabolism in the immediate postoperative period.