to the editor: Approximately 50 percent of males in the United States undergo neonatal circumcision. The most common complication of circumcision is poor cosmesis, but local anesthetic toxicity does rarely occur. Systemic toxicity from local anesthetics manifests as depression of the central nervous system, seizures, and dysrhythmias. We report a case of central nervous system toxicity associated with bupivacaine (Marcaine) dorsal penile block used to facilitate a circumcision.
A 21-day-old male weighing 2,715 g (6.0 lb) presented to the pediatrician's office for elective circumcision. He had a history of intrauterine growth restriction caused by twin gestation and was born at 37 weeks and two days' gestation. A dorsal penile block was performed using bupivacaine. He received two 1-mL doses of 0.5% bupivacaine, spaced apart by two to three minutes. The estimated total dose was 3.7 mg per kg. Within minutes of the injections, he became lethargic. On arrival to the emergency department, the infant was noted to have disconjugate gaze, intermittent exotropia, and altered consciousness with hypotonia. A serum bupivacaine concentration, obtained 2.5 hours after injection, was 0.76 mcg per mL, which is consistent with previous reports of bupivacaine toxicity 1 and higher than bupivacaine concentrations reported in older boys after circumcision.2 He was admitted to the pediatric intensive care unit and observed overnight. Five hours after the bupivacaine exposure, he was responsive to painful stimuli, but was excessively somnolent and not latching on to breast-feed. He did not experience seizures, dysrhythmias, or cardiovascular instability, nor did he require specific antidotes, including intravenous lipid emulsion therapy. At 22 hours, he was awake and back to baseline.
Several factors may have contributed to the observed toxicity in this case: the small size of the neonate; the concentration and volume of anesthetic used; and the choice of bupivacaine for regional anesthesia.
Physicians who perform dorsal penile blocks for circumcision may decrease the risk of toxicity by using smaller doses of local anesthetic for low-weight neonates. This may be facilitated by using lower concentrations of bupivacaine, for example the 0.25% or 0.125% solutions that have been recommended for other neonatal regional anesthesia procedures,3 or by limiting 0.5% bupivacaine to 0.25 mL per kg2 or 1.5 to 2 mg per kg.4 In addition, lidocaine (Xylocaine) may offer a wider margin of safety than bupivacaine and may be the preferred agent in these cases. Dosing of 0.4 to 0.8 mL of 1% lidocaine for dorsal penile block is discussed in the American Academy of Pediatrics Policy Statement on Circumcision.5
Because of immature hepatic enzymes and decreased levels of α1-acid glycoprotein, bupivacaine has a longer half-life and a higher percentage of biologically-active drug in the neonate compared with adults.6 This case exemplifies the principle that relatively small volumes of bupivacaine may result in local anesthetic toxicity.