Arterial hypoxemia following the administration of sublingual nitroglycerin

The effect of nitroglycerin on arterial blood gases and cardiovascular hemodynamics were studied in patients with coronary artery disease. In 13 premedicated patients blood gases and cardiovascular hemodynamics were studied before and 10 minutes after sublingual nitroglycerin (0.6 mg). In eight unpremedicated patients only blood gases were determined before and 10 minutes after sublingual nitroglycerin 0.6 mg. All studies were performed before induction of anesthesia with the patients in the supine position breathing room air. In both groups, arterial PO2 decreased significantly (p less than 0.001); pH and pCO2 did not change. In the 13 patients on which hemodynamic studies were performed, the mean arterial pressure (p less than 0.001), cardiac index (p less than 0.001), central venous pressure (p less than 0.001), pulmonary artery (p less than 0.001) and pulmonary artery wedge pressure (p less than 0.001) decreased. Calculated values for systemic and pulmonary vascular resistance were not significantly altered (p greater than 0.4). This study gives conclusive evidence that nitroglycerin reduces arterial PO2 in most patients with coronary artery disease breathing room air in the supine position. The possible mechanisms and clinical implications are discussed.