PEEP reverses nitroglycerin-induced hypoxemia following coronary artery bypass surgery

Intravenous nitroglycerin is increasingly used during and after cardiac surgery to control blood pressure and improve subendocardial and peripheral circulation. A dramatic decrease in arterial oxygenation has, however, been reported in a number of poorly controlled clinical trials. In the present investigation 16 patients were studied 2-4 h after coronary artery bypass procedures. All were treated with a continuous infusion of nitroglycerin (1 microgram X kg-1 X min-1). Utilizing an on-off-on drug design, it was clearly established that nitroglycerin depresses arterial oxygenation by increasing the pulmonary venous admixture. Three possible underlying mechanisms are discussed, but at the present time no firm conclusion can be drawn as to the nature of the changes. Eight patients were ventilated with 1 kPa (10 cmH2O) positive end-expiratory pressure (PEEP) during the nitroglycerin infusion. PEEP-ventilation reversed nitroglycerin-induced changes in arterial oxygenation and pulmonary shunting without adversely affecting hemodynamic stability.