title: The effect of the inspired oxygen fraction on arterial blood oxygenation in spontaneously breathing, isoflurane anaesthetized horses: a retrospective study.
abstract: OBJECTIVE
  To investigate the influence of two inspired oxygen fractions (FiO(2)) on the arterial oxygenation in horses anaesthetized with isoflurane.
  
  
  METHODS
  Retrospective, case-control clinical study.
  
  
  METHODS
  Two hundred equine patients undergoing non-abdominal surgery (ASA class 1-2), using a standardized anaesthetic protocol and selected from anaesthetic records of a period of three years, based on pre-defined inclusion criteria.
  
  
  METHODS
  In group O (n = 100), medical oxygen acted as carrier gas, while in group M (n = 100), a medical mixture of oxygen and air (FiO(2) 0.60) was used. Demographic data, FiO(2), arterial oxygen tension (PaO(2)) and routinely monitored physiologic data were recorded. The alveolar-arterial oxygen tension difference [P(A-a)O(2)] and PaO(2)/FiO(2) ratio were calculated. The area under the curve, standardized to the anaesthetic duration, was calculated and statistically compared between groups using t-tests or Mann-Whitney tests as appropriate. Categorical data were compared using Chi-square tests.
  
  
  RESULTS
  No significant differences in age, body weight, sex, breed, surgical procedure, position, anaesthetic duration or arterial carbon dioxide tension were found. Mean FiO(2) was 0.78 in group O and 0.60 in group M. Compared to group O, significantly lower values for PaO(2) and for P(A-a)O(2) were found in group M. In contrast, the PaO(2)/FiO(2) ratio and the percentage of horses with a PaO(2) <100 mmHg (13.33 kPa) were comparable in both groups.
  
  
  CONCLUSIONS
  Although a reduction of the inspired oxygen fraction resulted in a lower PaO(2), the P(A-a)O(2) was also lower and the number of horses with PaO(2) values <100 mmHg was comparable.
  
  
  CONCLUSIONS
  In healthy isoflurane anaesthetized horses, the use of a mixture of oxygen and air as carrier gas seems acceptable, but further, prospective studies are needed to confirm whether it results in a lower degree of ventilation/perfusion mismatching.
authors.affiliation: Department of Surgery and Anaesthesia of Domestic Animals, Faculty of Veterinary Medicine, University of Gent, Merelbeke, Belgium.
authors.forename: Stijn
authors.initials: S
authors.lastname: Schauvliege
authors.forename: Ioannis
authors.initials: I
authors.lastname: Savvas
authors.forename: Frank
authors.initials: F
authors.lastname: Gasthuys
mesh_terms: D000769:Anesthesia, Inhalation / Q000662:veterinary; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary*; D016022:Case-Control Studies; D006736:Horses / Q000502:physiology*; D007530:Isoflurane / Q000494:pharmacology*; D010100:Oxygen / Q000097:blood* / Q000494:pharmacology*; D010313:Partial Pressure; D011659:Pulmonary Gas Exchange / Q000187:drug effects; D012119:Respiration / Q000187:drug effects; D012189:Retrospective Studies
chemical_list: D018685:Anesthetics, Inhalation; D007530:Isoflurane; D010100:Oxygen
keywords: arterial oxygen tension; horse; inspired oxygen fraction