Spontaneous ventilation test vs intermittent mandatory ventilation. An approach to weaning after coronary bypass surgery.

T he timing of tracheal extubation after open heart surgery may accelerate recovery without increasing mortality. However, the manner of weaning from controlled mechanical ventilation (CMV) varies widely in different centers. Since 1972 an alternative means of ventilatory “support” advocated is that of intermittent mandatory ventilation ( IMV), in which an inadequate minute volume produced by the patient is supplemented by mechanical means, with intermittent hyperinflation of the lungs occurring at regular preset intervals. Downs et al’ proposed IMV as a superior method of weaning patients from mechanical ventilation. They emphasized that this technique allows the patient not only to breathe spontaneously through a oneway valve, but also offers a preset, but diminishing number of mechanical ventilations per minute. However, only a few studies of the postoperative use of IMV following cardiopulmonary bypass have been reported.”2 We performed a prospective randomized study to compare two groups of patients who underwent either a spontaneous ventilation test (SVT) or IMV. After a weaning trial, all patients were extubated and cardiopulmonary measurements were repeated two hours later. The purpose was to determine whether the postoperative SVT or IMV affected cardiopulmonary stability, hemodynamic performance, patient stress, or rate of recovery in good-risk, stable coronary artery bypass patients. resulted in significant increases in V02, VCO2, PaCO2, and cardiac index, with simultaneous decreases in SVo and PaO, values in both groups. There were no significant differences in the responses between SVT and IMV during the weaning trial.