title: Vecuronium pharmacokinetics and pharmacodynamics during hypothermic cardiopulmonary bypass in infants and children.
abstract: OBJECTIVE
  To determine the effect of moderate and deep hypothermic cardiopulmonary bypass (CPB) on the pharmacokinetic and pharmacodynamic behaviour of vecuronium in infants and children.
  
  
  METHODS
  We studied 12 patients undergoing surgery for congenital heart disease under narcotic-nitrous oxide anesthesia. Neuromuscular blockade was maintained constant (TI 4-10% by Datex electromyograph) by adjusting a vecuronium infusion. Plasma vecuronium concentrations (Cpss) were analysed by HPLC to describe a pseudosteady-state during each of the pre-CPB, CPB and post-CPB phases. Paired arterial blood samples were taken 20 min apart after at least 20 min of constant infusion.
  
  
  RESULTS
  Nine cases were analysed, mean age 20 mo, mean weight 9 kg. Three patients had deep and six moderate hypothermia. In the pre-CPB phase Cpss fell into two groups (mean +/- SD: 330 +/- 42 ng x ml(-1); 127 +/- 27 ng x ml(-1); P < 0.001); similarly the clearances showed a bimodal distribution (mean +/- SD: 5.08 +/- 0.94; 11.51 +/- 0.2 ml x min(-1) x kg(-1) P < 0.001), although in different patients. During CPB this bimodal distribution disappeared. Vecuronium infusion rate (VIR) decreased by 84% and 92% from pre-CPB to CPB phase in deep and moderate hypothermia groups respectively (P < 0.05), paralleled by decreases in Cpss of 36% (P > 0.05) and 52% (P < 0.05).
  
  
  CONCLUSIONS
  Changes in vecuronium requirements and plasma concentrations during CPB demonstrate that vecuronium pharmacokinetics and pharmacodynamics are both affected by hypothermic CPB in infants. The finding of bimodal distributions for plasma vecuronium and vecuronium clearance highlights the need for individual monitoring of neuromuscular blockade in this age group.
authors.affiliation: Department of Anaesthesia, McGill University, Montreal Children's Hospital, Quebec, Canada. mdwi@musica.mcgill.ca
authors.forename: D
authors.initials: D
authors.lastname: Withington
authors.forename: G
authors.initials: G
authors.lastname: Menard
authors.forename: J
authors.initials: J
authors.lastname: Harris
authors.forename: P
authors.initials: P
authors.lastname: Kulkarni
authors.forename: F
authors.initials: F
authors.lastname: Donati
authors.forename: F
authors.initials: F
authors.lastname: Varin
mesh_terms: D000758:Anesthesia; D002315:Cardiopulmonary Bypass; D002648:Child; D002675:Child, Preschool; D004576:Electromyography; D005260:Female; D006801:Humans; D007036:Hypothermia, Induced; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D016343:Monitoring, Intraoperative; D019148:Neuromuscular Blockade; D003473:Neuromuscular Nondepolarizing Agents / Q000008:administration & dosage / Q000493:pharmacokinetics; D014673:Vecuronium Bromide / Q000008:administration & dosage / Q000493:pharmacokinetics
chemical_list: D003473:Neuromuscular Nondepolarizing Agents; D014673:Vecuronium Bromide