title: Aerosolized salbutamol (albuterol) improves PaO2in hypoxaemic anaesthetized horses - a prospective clinical trial in 81 horses.
abstract: OBJECTIVE
  To compare the arterial pH and blood gas values, heart rate and mean arterial blood pressure, in hypoxaemic anaesthetized horses, before and after treatment, with a salbutamol (albuterol) aerosol.
  
  
  METHODS
  Eighty-one client-owned horses weighing between 114 and 925 kg. Fifty-seven underwent emergency abdominal surgery and 24 were anaesthetized for elective procedures.
  
  
  METHODS
  Pre-anaesthetic medication included xylazine, detomidine, butorphanol and morphine, alone or in various combinations. Induction of anaesthesia was achieved with guaifenesin and ketamine, diazepam and ketamine, or guaifenesin and thiopental. The trachea of all animals was intubated and anaesthesia maintained with either halothane (33 horses) or isoflurane (48 horses) in oxygen. Heart rate and rhythm were monitored continuously. Arterial blood pressure was monitored directly, and arterial blood collected for pH and blood gas analyses. When arterial PaO2fell below 9.3 kPa (70 mm Hg) and failed to respond to corrective measures including positive pressure ventilation and treatment of hypotension (mean arterial blood pressures <70 mm Hg), a salbutamol aerosol (2 μg kg-1) was delivered via the endotracheal tube. Twenty minutes later, a second arterial blood sample was analysed.
  
  
  RESULTS
  There were no significant differences in mean arterial blood pressure, heart rate, arterial pH, base excess and bicarbonate before and after treatment. Arterial O2tension increased significantly from a mean ± SD of 8.3 ± 1.7 kPa (62.4 ± 13.1 mm Hg) before administration to 15.9 ± 9.8 kPa (119.4 ± 57.7 mm Hg) after treatment. There was a small but significant decrease in PaCO2from 7.4 ± 1.5 kPa (55.2 ± 11.2 mm Hg) to 7.0 ± 1.3 kPa (52.9 ± 9.8 mm Hg) between sample times. No changes in heart rhythm were observed. A high percentage (approximately 70%) of animals sweated following treatment.
  
  
  CONCLUSIONS
  Salbutamol administered at a dose of 2 μg kg-1via the endotracheal tube of anaesthetized horses with PaO2values less than 9.3 kPa (70 mm Hg) resulted in an almost two-fold increase in PaO2values within 20 minutes of treatment. No changes in heart rate or mean arterial blood pressure were associated with the use of salbutamol in this study. The improvement in PaO2may be a result of bronchodilatation and improved ventilation, increased perfusion secondary to an increase in cardiac output, or a combination of these two factors. Cardiac output and ventilation-perfusion distribution were not measured in this study; therefore, the reason for the increase in PaO2values cannot be conclusively determined.
  
  
  CONCLUSIONS
  Administration of a salbutamol aerosol is a simple but effective technique that can be used to improve PaO2values in hypoxaemic horses during inhalant anaesthesia with no apparent detrimental side effects.
authors.affiliation: Department of Large Animal Clinical Sciences, University of Florida, Gainesville, Florida, USA. Electronic address: robertsons@mail.vetmed.ufl.edu.
authors.forename: Sheilah A
authors.initials: SA
authors.lastname: Robertson
authors.affiliation: VASC Corporation, Veterinary Referral Center of Colorado, Englewood, CO, USA.
authors.forename: James E
authors.initials: JE
authors.lastname: Bailey
keywords: albuterol; anaesthesia; horse; hypoxaemia; salbutamol