Plasma concentrations of ropivacaine following a single-shot caudal block of 1, 2 or 3 mg/kg in children

Background: For documenting the properties of ropivacaine used for regional anaesthesia in children, the relationship between dose and resulting syste mic exposure is essential. The aim of this pharmacokinetic part of a random ised, multicentre, double-blind study was to determine the free and total p lasma levels of ropivacaine in children aged between 4 and 12 years followi ng a single-shot caudal dose of 1, 2 or 3 mg/kg of ropivacaine for postoper ative pain management. Method: Following induction of a standardised general anaesthetic (halothan e; nitrous oxide: oxygen 60:40), a caudal block using 1 ml/kg ropivacaine i n concentrations of 1, 2 or 3 mg/ml was performed in 43 ASA I children (bod y weight 12-25 kg) scheduled for elective inguinal surgery. Blood samples w ere collected prior to and 15, 30, 45, 60 and 240 min after placement of th e caudal block for determination of total and free ropivacaine plasma conce ntrations. Results: The peak plasma concentration of total ropivacaine, reached within 15-241 min after the block, increased in pro- portion to dose, with mean v alues at 0.27, 0.64 and 0.90 mg/l following 1, 2 and 3 mg/kg respectively. The peak plasma level of free ropivacaine also increased in a dose-proporti onal manner, with mean levels at 0.014, 0.030 and 0.042 mg/l. The highest i ndividual peak plasma level of free ropivacaine was 0.070 mg/l, well below the threshold levels of CNS toxicity described in adults. No clinical signs of systemic toxicity were observed. Conclusion: Following single-shot caudal doses of 1-3 mg/kg in children up to 25 kg and aged between 4 and 12 years, plasma levels of free ropivacaine increase in proportion to dose and all were shown to be within safe limits .