title: Metabolic acidosis in healthy mules under general anaesthesia with halothane.
abstract: OBJECTIVE
  To report the severe metabolic acidosis identified in a group of 11 healthy mules anaesthetized with halothane for castration.
  
  
  METHODS
  Data generated from a prospective study.
  
  
  METHODS
  Eleven mules aged 2.5-8 years, weighing 230-315 kg and 11 horses aged 1.5-3.5 years, weighing 315-480 kg.
  
  
  METHODS
  Animals were anaesthetized for castration as part of an electroencephalographic study. Preanaesthetic medication was acepromazine (0.03 mg kg(-1) ) administered through a preplaced jugular venous catheter. Anaesthesia was induced 30-90 minutes later with intravenous thiopental (10 mg kg(-1) ). After orotracheal intubation, anaesthesia was maintained with halothane vaporised in oxygen. The animals' lungs were ventilated to maintain the end-tidal CO(2) concentration between 3.9 and 4.5 kPa (29-34 mmHg). Anaesthetic monitoring included invasive blood pressure measurement via the auricular artery (mules) and submandibular branch of the facial artery (horses). Arterial blood gas samples were drawn from these catheters at three time points during surgery and pH, PaCO(2) , base excess (ecf) and were measured. Values were compared between groups using a Mann-Whitney test. p was taken as <0.05. Results are reported as median (range).
  
  
  RESULTS
  PaCO(2) did not differ between groups but pH was significantly lower in mules [7.178 (7.00-7.29)] compared to horses [7.367 (7.24-7.43)] (p=0.0002). values were significantly lower in the mules [16.6 (13.0-22.3) mM] compared to horses [23.7 (20.9-23.7) mM] (p=0.0001), whilst base excess (ecf) was significantly more negative in the mules [-11.4 (-1.27 to -16) mM] compared to horses [-1.3 (-5.8 to +2.4) mM] (p=0.0004).
  
  
  CONCLUSIONS
  This study demonstrated severe metabolic acidosis in healthy mules, which may have prompted intervention with drug therapies in a clinical arena. It is probable that the acidosis existed prior to anaesthesia and caused by diet, but other possible causes are considered.
authors.affiliation: School of Veterinary Sciences, University of Bristol, Langford, Bristol, UK. nicki.grint@bris.ac.uk
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Grint
authors.forename: Silvia E R de Sa
authors.initials: SE
authors.lastname: Lorena
authors.forename: Craig B
authors.initials: CB
authors.lastname: Johnson
authors.forename: Stelio P L
authors.initials: SP
authors.lastname: Luna
authors.forename: Helen R
authors.initials: HR
authors.lastname: Whay
authors.forename: Joanna C
authors.initials: JC
authors.lastname: Murrell
mesh_terms: D000136:Acid-Base Equilibrium / Q000187:drug effects; D000138:Acidosis / Q000139:chemically induced / Q000662:veterinary*; D000768:Anesthesia, General / Q000009:adverse effects / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000009:adverse effects*; D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D001794:Blood Pressure / Q000187:drug effects; D001831:Body Temperature / Q000187:drug effects; D018397:Equidae / Q000378:metabolism; D006221:Halothane / Q000009:adverse effects*; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D016343:Monitoring, Intraoperative / Q000662:veterinary; D009919:Orchiectomy / Q000662:veterinary
chemical_list: D018685:Anesthetics, Inhalation; D006221:Halothane