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Eighty-one client-owned horses weighing between 114 and 925 kg. Fifty-seven underwent emergency abdominal surgery and 24 were anaesthetized for elective procedures.
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 PaO2 fell 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 Āµg kg1) was delivered via the endotracheal tube. Twenty minutes later, a second arterial blood sample was analysed.
There were no significant differences in mean arterial blood pressure, heart rate, arterial pH, base excess and bicarbonate before and after treatment. Arterial O2 tension increased significantly from a mean Ā± SD of 8.3 Ā± 1.7 kPa (62.4 Ā± 13.1 mm Hg) before administration to 15.9 Ā± 9.8 kPa (119.4 Ā± 57.7 mm Hg) after treatment. There was a small but significant decrease in PaCO2 from 7.4 Ā± 1.5 kPa (55.2 Ā± 11.2 mm Hg) to 7.0 Ā± 1.3 kPa (52.9 Ā± 9.8 mm Hg) between sample times. No changes in heart rhythm were observed. A high percentage (approximately 70%) of animals sweated following treatment.
Salbutamol administered at a dose of 2 Āµg kg1 via the endotracheal tube of anaesthetized horses with PaO2 values less than 9.3 kPa (70 mm Hg) resulted in an almost two-fold increase in PaO2 values 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 PaO2 may 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 PaO2 values cannot be conclusively determined.
Administration of a salbutamol aerosol is a simple but effective technique that can be used to improve PaO2 values in hypoxaemic horses during inhalant anaesthesia with no apparent detrimental side effects.
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