Pulsed Doppler ascending aortic, carotid, brachial, and femoral artery blood flows during caudal anesthesia in infants.

Hemodynamic effects of caudal bupivacaine anesthesia were studied in eight infants 6.5 +/- 0.5 months old (mean +/- SD), weighing 7.4 +/- 4.4 kg anesthetized with halothane 0.2% end-tidal and 60% nitrous oxide. Heart rate and systolic, diastolic, and mean arterial pressure remained unchanged. Cardiac index and stroke index assessed by pulsed Doppler and total vascular resistances were not altered by the caudal block. However, after caudal anesthesia, the authors observed a significant decrease (P less than 0.05) in brachial blood flow assessed by pulsed Doppler (from 49.0 +/- 28.3 to 31.7 +/- 24.6 ml-1.min) and a significant increase (P less than 0.05) in brachial vascular resistance (from 2.9 +/- 1.7 to 5.5 +/- 1.0 mmHg.min.ml-1). Blood flow and vascular resistance in both the femoral and carotid arteries did not change. This study suggests that, in supine position, caudal anesthesia in infants induces a blood pooling in the denervated lower extremities and a reflex vasoconstriction in innervated areas which maintains cardiac output. We conclude that volume loading is not necessary in normovolemic infants after caudal anesthesia with cutaneous analgesia below T5.