Ropivacaine undergoes slower systemic absorption from the caudal epidural space in children than bupivacaine

We compared the systemic absorption of ropivacaine and bupivacaine after caudal epidural administration in children. Twenty ASA physical status I or II children aged 1-7 yr undergoing elective hypospadias repair were randomized after the induction of general anesthesia to receive a single caudal epidural injection of 2 mg/kg of either ropivacaine 0.2% (R) or bupivacaine 0.2% (B) in a double-blinded fashion. Peripheral venous blood samples (1 mL) were obtained before and 1, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, and 120 min after the caudal injection. The total R and B concentration was measured in plasma by using high-performance liquid chromatography. All blocks were successful, and there were no complications. The peak plasma concentration (mean +/- SD) (R = 0.67 +/- 0.16 and B = 0.73 +/- 0.23 mug/mL) and the area under the plasma concentration curve (R = 61.9 +/- 20.6 and B = 62.7 +/- 18.2 mug . mL(-1) . min(-1)) were comparable between the two study groups. The median (range) time to attain peak plasma concentration was significantly slower in children who received ropivacaine (R = 65 [10-120] min and B = 20 [15-50] min, P < 0.05). We conclude that ropivacaine undergoes slower systemic absorption from the caudal epidural space in children than does bupivacaine.