Heart rate changes with test dose and total dose during caudal epidural block in children as a test to predict correct needle placement

This study was conducted to confirm whether bupivacaine-epinephrine test dose and total dose of bupivacaine induce a decrease in heart rate when injected through a correctly placed caudal needle. Fifty paediatric patients (£12years) undergoing infra-umbilical surgery were recruited in the study. After inhalational induction of anaesthesia and placement of caudal epidural needle the baseline heart rate was recorded. Caudal epidural test dose (0.1mLkg^-1 of 0.25% bupivacaine with 0.5μgkg^-1 epinephrine) followed by total dose (1 mLkg^-1 of 0.25% bupivacaine) were administered. The change in heart rate, with respect to baseline heart rate, one minute following the injection of test dose and during the injection of total dose was recorded. Caudal block was successful in 45 (90%)children. Successful block was associated with significant decrease in heart rate following test dose injection (mean difference[MD], 95% confidence interval [CI]), 5 beats per minute (bpm) [4bpm to 6bpm] (P=0.000) and during total dose injection (mean [95% CI], 9bpm [8bpm to 10bpm]) (P=0.000). In the failed block group, heart rate remained similar to the baseline values during administration of test dose and total dose (MD [95% CI], 0.4bpm [-2bpm to 3bpm] and 0.4bpm [-4 to 5bpm] respectively) (P>0.05). The decrease in the heart rate following the injection of the bupivacaine-epinephrine test dose and the total dose of local anaesthetic, is a reliable test to predict the success of paediatric caudal block.