Cardiovascular effects of breathing 95 percent oxygen in children with congenital heart disease.

The hemodynamic effects of breathing 95% oxygen were evaluated in 26 children with congenital heart disease. Aortic, pulmonary arterial, right atrial, and pulmonary arterial wedge pressure, aortic and pulmonary artery oxygen saturation, and blood gas, cardiac index, and heart rate were measured in room air and after each patient had breathed 95% oxygen for 10 (n = 26) and 20 (n = 5) minutes. Measurements were repeated with the patient again breathing room air for 10 (n = 11) and 20 (n = 6) minutes. After 10 minutes of 95% oxygen, arterial partial pressure of oxygen increased from 85 +/- 13 to 420 +/- 89 torr (p less than 0.001). Aortic mean pressure increased from 80 +/- 10 to 83 +/- 10 mm Hg (p less than 0.01), and systemic vascular resistance increased from 20 +/- 7 to 26 +/- 8 U (p less than 0.001). The cardiac index decreased by 21% from 3.96 +/- 0.94 to 3.12 +/- 0.74 liters/min/m2 (p less than 0.001) and the stroke index decreased by 11% (p less than 0.001). A 23% decrease in oxygen consumption (p less than 0.001) was observed, and oxygen transport decreased from 763 +/- 179 to 600 +/- 161 ml O2/min/m2 (p less than 0.001). Cardiac index, stroke index, and systemic vascular resistance did not return to normal until 20 minutes after cessation of oxygen breathing. To determine whether reflex bradycardia is responsible for these oxygen-induced hemodynamic changes, heart rate was kept constant by atrial pacing in a second group of 5 patients. In these children, significant decreases in cardiac index, stroke index, and oxygen consumption, and increases in systemic vascular resistance also occurred with 95% oxygen. Thus, in children with acyanotic congenital heart disease, hyperoxia increases aortic pressure and systemic vascular resistance and decreases cardiac index, stroke index, oxygen consumption, and oxygen transport.