title: Continuous positive airway pressure (CPAP) decreases pulmonary shunt in anaesthetized horses.
abstract: OBJECTIVE
  To evaluate the effects of continuous positive airway pressure (CPAP) on intrapulmonary shunt, cardiac output and oxygen delivery in horses subjected to a 6 hour period of general anaesthesia.
  
  
  METHODS
  Randomized, experimental, crossover study.
  
  
  METHODS
  Ten healthy adult horses.
  
  
  METHODS
  Following medetomidine, diazepam and ketamine administration, orotracheal intubation was performed and horses positioned in dorsal recumbency. Anaesthesia was maintained with isoflurane carried in an oxygen and air mix (FiO20.5) combined with a medetomidine infusion. Horses were anaesthetized twice and either CPAP (8 cmH2O) or physiologic airway pressure (NO CPAP) was applied to the lungs for 6 hours; the order of treatments was randomly assigned. Following induction of anaesthesia, cardiovascular and respiratory variables (including arterial blood gas analysis) were recorded every 30 minutes, cardiac output was measured every 60 minutes using the lithium dilution technique and oxygen delivery calculated. If PaCO2exceeded 100 mmHg (13.3 kPa), controlled ventilation was initiated and horses excluded from further data collection. Groups were compared using a general linear model.
  
  
  RESULTS
  Data from eight horses were analysed. PaO2was 15-56 mmHg (2.00-7.45 kPa) higher (p < 0.001) and shunt fraction 6-14% lower (p < 0.001) in the CPAP group. No differences were seen for cardiac output and oxygen delivery. The lack of difference in oxygen delivery was attributed to lower haemoglobin levels in the CPAP group than in the NO CPAP group.
  
  
  CONCLUSIONS
  CPAP of 8 cmH2O can be used in dorsally recumbent horses to decrease pulmonary shunt fraction without causing a decrease in cardiac output during longterm anaesthesia.
authors.affiliation: Division of Anaesthesiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland. mmosing@vetclinics.uzh.ch.
authors.forename: Martina
authors.initials: M
authors.lastname: Mosing
authors.affiliation: Langford Veterinary Services, University of Bristol, Bristol, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: MacFarlane
authors.affiliation: School of Veterinary Clinical Science, University of Liverpool, Neston, UK.
authors.forename: David
authors.initials: D
authors.lastname: Bardell
authors.affiliation: Division of Anaesthesiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
authors.forename: Laura
authors.initials: L
authors.lastname: Lüthi
authors.affiliation: School of Veterinary Clinical Science, University of Liverpool, Neston, UK.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Cripps
authors.affiliation: Division of Anaesthesiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
authors.forename: Regula
authors.initials: R
authors.lastname: Bettschart-Wolfensberger
mesh_terms: D000771:Anesthesia, Intravenous / Q000662:veterinary*; D000818:Animals; D002302:Cardiac Output / Q000187:drug effects; D002319:Cardiovascular System / Q000187:drug effects; D045422:Continuous Positive Airway Pressure / Q000662:veterinary*; D018592:Cross-Over Studies; D006736:Horses; D008168:Lung / Q000187:drug effects; D010100:Oxygen; D010313:Partial Pressure; D011446:Prospective Studies; D012119:Respiration / Q000187:drug effects
chemical_list: D010100:Oxygen
keywords: cardiac output; equine; oxygen delivery; oxygenation; spontaneous ventilation