Acute myocardial infarction complicated by respiratory failure. The effects of mechanical ventilation

The cardiopulmonary effects of ventilatory support were studied in 12 patients with an acute myocardial infarction complicated by respiratory failure. At constant end-expiratory pressure, controlled mechanical ventilation, intermittent mandatory ventilation with 50 percent mechanical support, and spontaneous breathing all resulted in acceptable blood gas values. Intermittent mandatory ventilation offered hemodynamic advantages over controlled mechanical ventilation, as evidenced by a higher cardiac index and a lower arteriovenous oxygen content difference. Electrocardiographic evidence of myocardial ischemia was observed in one patient during controlled mechanical ventilation, in one during partial ventilatory support, and in five patients during spontaneous breathing. Myocardial ischemia should be one of the major determinants of mechanical ventilation when a patient with ischemic heart disease is subjected to ventilator treatment. The total withdrawal of ventilatory support carries a risk of marked ischemia and is not recommended until the patient can be extubated.