The hemodynamic effects of phenoxybenzamine in neonates, infants, and children.

Study Objectives: To evaluate the hemodynamic effects of the long-acting, alpha-adrenergic blocker, phenoxybenzamine, in children of different age groups.

Design: Retrospective chart review.

Setting: Tertiary-care, congenital cardiac surgery center.

Measurements: The data of 75 pediatric patients who received phenoxybenzamine while undergoing surgical repair of congenital heart defects on cardiopulmonary bypass (CPB) were studied. Patients were selected in three age groups: younger than one month (n = 25), one to 12 months (n = 25), and one to 5 years (n = 25). All patients received a full dose of phenoxybenzamine 1 mg/kg. Demographics, CPB duration, mean arterial pressure on CPB, mean flow on CPB (normalized to body surface area), and central-to-peripheral temperature gradients were recorded. Systemic vascular resistance index (SVRI) was calculated.

Main Results: Cardiopulmonary bypass duration was significantly longer in the age group of younger than 1 mo than in the older groups. Mean CPB flow/body surface area was similar in all children (3.45 +/- 0.9, 3.74 +/- 0.69, and 3.48 +/- 0.59 L/min/m2, respectively; P < 0.28). However, mean SVRI was significantly lower in children younger than 1 mo (997.3 +/- 233, 1196.9 +/- 394, and 1168.83 +/- 227 dynes/cm2m5; P < 0.04). Temperature gradient was significantly narrower in patients younger than one month than those who were one to 12 months and one to 5 years at the end of cooling (0.90 degrees C +/- 0.1 degrees C, 1.04 degrees C +/- 3.61 degrees C, 1.4 degrees C +/- 3.07 degrees C; P < 0.001) at end-rewarming and termination of CPB (4.58 degrees C +/- 2.36 degrees C, 6.23 degrees C +/- 4.17 degrees C, 7.32 degrees C +/- 3.46 degrees C; P < 0.02). Multivariate analysis showed that patient age was a significant variable affecting response to phenoxybenzamine, after adjusting for duration of CPB (P = 0.31), mean hematocrit on CPB (P = 0.86), and core cooling temperature (P = 0.34).

Conclusion: The effect of phenoxybenzamine on SVRI, cooling, and rewarming on CPB varies with age as shown by more profound vasodilatation and narrower temperature gradients.