title: Factors influencing MAC reduction after cardiopulmonary bypass in dogs.
abstract: BACKGROUND
  Anaesthetic requirements may be reduced following surgery employing cardiopulmonary bypass (CPB). This study, in dogs, determined the role of a) volatile agents (enflurane [E] vs isoflurane [I]), b) oxygenator (bubble [B] vs membrane [M]), and c) presence [FL] vs absence [NoFL] of an in-line arterial filter in the bypass circuit in altering anaesthetic requirements following CPB.
  
  
  METHODS
  Male mongrel dogs were anaesthetized with either enflurane (n = 24) or isoflurane (n = 24). They were randomly assigned to one of eight groups (n = 6 per group); Group 1 (E/B/FL), Group 2 (E/M/FL), Group 3 (E/M/NoFL), Group 4 (E/B/NoFL), Group 5 (I/M/FL), Group 6 (I/B/FL), Group 7 (I/M/NoFL) or Group 8 (I/B/NoFL). MAC was determined using the tail-clamp method at hourly intervals, twice before and three times after a one hour normothermic perfusion using aortoatrial cannulation and CPB.
  
  
  RESULTS
  Prior to CPB, MAC was reproducible (enflurane: MAC1 2.17 +/- 0.29 vs MAC2 2.14 +/- 0.28%; isoflurane: MAC1 1.42 +/- 0.31 vs MAC2 1.41 +/- 0.33%) and differed among groups only for the volatile agent employed. Following CPB, MAC was reduced in all groups (P < 0.05 vs pre-CPB measurements) except Group 1 (E/B/FL). The degree of MAC reduction in other groups ranged from 39-64% and was not different based on type of agent employed, use of a membrane or bubble oxygenator, or presence or absence of an in-line arterial filter.
  
  
  CONCLUSIONS
  In dogs, MAC reduction following CPB was variable, not related to type of volatile agent employed, use of a membrane or bubble oxygenator, or presence or absence of an in-line arterial filter. The explanation for reductions in anaesthetic requirements following CPB in this model remains speculative.
authors.affiliation: Department of Anaesthesia, Dalhousie University, Halifax, Nova Scotia, Canada.
authors.forename: M W
authors.initials: MW
authors.lastname: Neumeister
authors.forename: G
authors.initials: G
authors.lastname: Li
authors.forename: G
authors.initials: G
authors.lastname: Williams
authors.forename: G
authors.initials: G
authors.lastname: Doak
authors.forename: J A
authors.initials: JA
authors.lastname: Sullivan
authors.forename: R I
authors.initials: RI
authors.lastname: Hall
mesh_terms: D000777:Anesthetics / Q000493:pharmacokinetics*; D018685:Anesthetics, Inhalation / Q000493:pharmacokinetics; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002315:Cardiopulmonary Bypass; D004285:Dogs; D004737:Enflurane / Q000493:pharmacokinetics; D007530:Isoflurane / Q000493:pharmacokinetics; D008297:Male; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D011650:Pulmonary Alveoli / Q000378:metabolism*; D013997:Time Factors
chemical_list: D000777:Anesthetics; D018685:Anesthetics, Inhalation; D004737:Enflurane; D007530:Isoflurane