Hemodynamic effects of ketamine, hypoxia and hyperoxia in children with surgically treated congenital heart disease residing greater than or equal to 1,200 meters above sea level. Little data are available on the hemodynamic effects of premedications and anesthetic agents on infants and children. Ketamine is the most frequently used anesthetic agent for cardiac catheterization procedures in pediatric patients with congenital heart disease. Previous reports both suggest and deny ketamine's pulmonary vasoreactive effects. Since the advent of sophisticated noninvasive equipment, one of the few indications for cardiac catheterization is to obtain accurate pressure data. If ketamine alters pulmonary vascular resistance, it would negate the primary reason for the procedure. Because the patient population studied herein resides greater than or equal to 1,200 meters above sea level, concerns about pharmacologic effects on pulmonary vascular resistance are enhanced. Simultaneous pulmonary artery and aortic pressures, thermodilution cardiac outputs, and blood gases were measured in room air (16% oxygen) and with ketamine infusion in 14 patients at cardiac catheterization. Reaction to hypoxia identified 3 groups: normal, intermediate and hyperresponders. The normal responders had normal resistance ratios (0.11) in room air and had little resistance ratio response to hypoxia (+0.02), hyperoxia (-0.03) or ketamine (+0.01). The intermediate responders had a slightly higher but normal resistance ratio (0.20) in room air, and a moderate reaction to hypoxia (+0.13), hyperoxia (-0.08) and ketamine (+0.11). The hyperresponders had an elevated resistance ratio (0.42) in room air and a striking reaction to hypoxia (+0.65), hyperoxia (-0.17) and ketamine (+0.49). Hypoxia and ketamine have a greater effect on resistance ratio than hypoxia alone in patients with reactive pulmonary vascular beds. Ketamine should not be used in children undergoing procedures to establish operability based on pulmonary vascular resistance or pulmonary vascular reactivity. 