Pediatric caudal block with mepivacaine, bupivacaine or a mixture of both drugs: requirement for postoperative analgesia and plasma concentration of local anesthetics.

STUDY OBJECTIVES

To assess the effects of pediatric caudal block using mepivacaine, bupivacaine, or a mixture of both drugs on postoperative analgesia, and to examine plasma concentrations of the local anesthetics after caudal injection.

DESIGN

Prospective, randomized, double-blind study.

SETTING

Operating room and pediatric surgical ward.

PATIENTS

60 ASA physical status I children weighing 10 to 20 kg (26 females, 34 males), and scheduled for inguinal herniorrhaphy.

INTERVENTIONS

Patients randomly received caudal block with 1 mL/kg of mepivacaine 1% (Group M, n = 20), 1 mL/kg of bupivacaine 0.25% (Group B, n = 20), or a mixture of 0.5 mL/kg of mepivacaine 1% and 0.5 mL/kg of bupivacaine 0.25% (Group MB, n = 20) after induction of anesthesia with sevoflurane in 50% oxygen (O2). Anesthesia was maintained with 66% nitrous oxide in O2 supplemented with sevoflurane at an end-tidal concentration of less than 1%.

MEASUREMENTS AND MAIN RESULTS

Postoperative pain scores using a pediatric pain scale and plasma concentration of each local anesthetic were measured. In Group M, four patients required postoperative analgesics within the first 24 hours. However, no patients required postoperative analgesics in Groups B and MB. In Group M, the plasma concentration of mepivacaine of two patients exceeded 5 microg/kg of the level of toxicity. However, these patients did not show any toxic symptoms. Because a mixture of two local anesthetics halves the concentration of each local anesthetic, the plasma concentrations of mepivacaine and bupivacaine in Group MB were significantly lower than those of Groups M and B.

CONCLUSIONS

Pediatric caudal block with a mixture of mepivacaine and bupivacaine is effective for intraoperative and postoperative analgesia.