Gas exchange alterations associated with weaning from mechanical ventilation following coronary artery bypass grafting.

This study was done to clarify the effects of positive-pressure mechanical ventilation on gas exchange in the lungs of conscious patients. Nine hemodynamically stable patients were studied following coronary artery bypass grafting at the time they were weaned from mechanical ventilation. The adequacy of gas exchange was assessed by traditional measurements as well as the multiple inert gas technique used to measure the ventilation-perfusion (VA/Q) distribution. During mechanical ventilation, gas exchange was characterized by a variable degree of VA/Q inequality as well as a substantial shunt ranging from 11.9 to 27.7 percent. Following removal from mechanical ventilation, there was a decrease in the mean VA/Q subsequent to a decrease in the minute ventilation. However, there was no significant change in the level of shunt or in the amount of VA/Q inequality.