Cardiopulmonary bypass, inhaled nitric oxide

A 72-year-old woman, who underwent emergency resection of a giant left atrial myxoma, had pulmonary hypertension (pulmonary artery pressure 40 mmHg) and a low cardiac output (2.21/minute). Inhaled nitric oxide, 40 ppm, before cardiopulmonary bjrpass resulted in pulmonary vasodilatation and a fall in pulmonary artery pressure from 39 to 31 mmHg. This was accompanied by a fall in cardiac output from 2.4 to 1.5 1/minute and a fall in mixed venous oxygen saturation. After bypass, inhaled nitric oxide improved pulmonary and systemic hemodynamics and resulted in a rise in cardiac output from 3.0 to 3.5 l/minute. 

Wessel, D. L., Adatia, I., Giglia, T. M., Thompson, J. E., and Kulik, T. J. (1993). Use of inhaled nitric oxide and acetylcholine in the evaluation of pulmonary hypertension and endothelial function after cardiopulmonary bypass. Circulation 88, 2128-2138. 

Immediately following cardiopulmonary bypass an elevation in pulmonary vascular resistance is poorly tolerated. The pulmonary vasculature of such children is prone to intense vasoconstriction in response to stress that may result in pulmonary hypertensive crises. This may necessitate therapeutic maneuvers, including continued paralysis and anesthesia, to blunt the stress response " and hyperventilation and alkalosis to promote pulmonary vasodilation. The realization that inhaled nitric oxide could act as a selective pulmonary vasodilator " holds great promise for this patient population, and a number of studies have attested to its efficacy both in the preoperative evaluation during cardiac catheterization and postoperatively in the intensive care unit " . 

In our initial studies we used inhaled nitric oxide as a probe to test the effect of cardiopulmonary bypass on pulmonary endothelial function. Cardiopulmonary bypass may result in damage to the pulmonary endothelium, and the degree of pulmonary hypertension is correlated with the extent of such damage. Acetylcholine-induced vasodilation is attenuated in a number of vascular diseases that impair endothelial function,and preconstricted pulmonary artery rings from explanted lungs of patients with... 

We challenged 12 patients with congenital heart disease and pulmonary hypertension preoperatively in the cardiac catheterization laboratory and nine postoperative patients (after cardiopulmonary bypass) with a 2-min infusion of 10 M acetylcholine into the pulmonary artery. The nine postoperative patients received a 15-min trial of inhaled nitric oxide following the infusion of acetylcholine. The results are shown in Figs. 4 and 5. The decrease in pulmonary artery pressure and resistance in the preoperative patients in response to acetylcholine was markedly attenuated postoperatively. The percentage reductions in pulmonary artery pressure preoperatively were 27% 4% and 9% 2% P < 0.003) postoperatively. Similarly, pulmonary vascular resistance decreased by 46% 5% compared to 11% 4% P < 0.002). However, the response to inhaled nitric oxide in the postoperative patients was marked vasodilation contrasted with the blunted effect of acetylcholine. Mean pulmonary artery pressure (34.4 2.6 versus... 

Alternatively, the increased pulmonary vascular resistance may be due to an increase in a circulating vasoconstrictor such as endothelin or thromboxane, both of which have been reported to be elevated in children with congenital heart disease following cardiopulmonary bypass. It is noteworthy that the excretion of thromboxane has been found to be elevated during a pulmonary hypertensive crisis ° and that in animal studies inhaled nitric oxide is effective in reversing the pulmonary vasoconstriction induced by thromboxane mimetics. ... 

We have reported the effect of inhaled nitric oxide in 10 patients (median age, 3.3 years range, 0.4-11.1 years) with symptomatic congenital mitral stenosis.These studies were performed during interventional cardiac catheterization or after surgery requiring the use of cardiopulmonary bypass. Six patients had additional left ventricular outflow tract obstruction (median, 25 mm Hg range, 15-50 mm Hg). Effective relief of the mitral gradient was present after intervention. 

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