title: Risk factors for colic in horses after general anaesthesia for MRI or nonabdominal surgery: absence of evidence of effect from perianaesthetic morphine.
abstract: BACKGROUND
  Post anaesthetic colic is a recognised risk of general anaesthesia (GA), but causes are poorly understood.
  
  
  OBJECTIVE
  To identify risk factors for development of colic following GA for magnetic resonance imaging (MRI) or nonabdominal surgery and to test whether the use of perianaesthetic morphine was associated with an increased risk of post anaesthetic colic.
  
  
  METHODS
  A total of 553 anaesthetic and clinical records of 500 horses anaesthetised at the Animal Health Trust were analysed, 342 (62%) involved MRI and 211 (38%) nonabdominal, predominantly orthopaedic surgery. Multivariable logistic regression analysis was used to examine the association between post anaesthetic colic and explanatory variables, including use of perianaesthetic morphine.
  
  
  RESULTS
  Twenty horses (3.6%) developed colic within 7 days of GA. A significantly larger (P = 0.001) proportion of the surgical cases developed post anaesthetic colic (7.1%) compared with MRI cases (1.5%). Having controlled for the effect of MRI/surgeon, there was evidence for a significantly increased risk of colic associated with maintenance of anaesthesia with isoflurane and administration of benzyl penicillin and/or ceftiofur. A reduction in risk of colic was associated with premedication with romifidine, longer duration of anaesthesia and sedation within 2 days of GA. Perianaesthetic morphine administration was not associated with increased risk.
  
  
  CONCLUSIONS
  This study identified apparently novel risk factors for colic in horses following GA. Use of morphine was not found, after controlling for other MRI and surgery related risk factors, to be associated with an increased risk. The low prevalence of colic after GA and resulting low study power mean that further larger, multicentre collaborative studies are warranted to corroborate findings in this study.
  
  
  CONCLUSIONS
  Better knowledge of risk factors should lead to achievable measures to reduce frequency of occurrence.
authors.affiliation: Animal Health Trust, Newmarket, Suffolk, UK.
authors.forename: M S
authors.initials: MS
authors.lastname: Andersen
authors.forename: L
authors.initials: L
authors.lastname: Clark
authors.forename: S J
authors.initials: SJ
authors.lastname: Dyson
authors.forename: J R
authors.initials: JR
authors.lastname: Newton
mesh_terms: D000768:Anesthesia, General / Q000009:adverse effects / Q000662:veterinary*; D000818:Animals; D003085:Colic / Q000139:chemically induced / Q000453:epidemiology / Q000209:etiology / Q000662:veterinary*; D005260:Female; D006734:Horse Diseases / Q000139:chemically induced / Q000453:epidemiology / Q000209:etiology*; D006736:Horses; D016015:Logistic Models; D008279:Magnetic Resonance Imaging / Q000662:veterinary; D008297:Male; D009020:Morphine / Q000009:adverse effects* / Q000627:therapeutic use; D009294:Narcotics / Q000009:adverse effects* / Q000627:therapeutic use; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors
chemical_list: D009294:Narcotics; D009020:Morphine