Morphine administration in horses anaesthetized for upper respiratory tract surgery
Article first published online: 19 DEC 2005
Veterinary Anaesthesia and Analgesia
Volume 33, Issue 3, pages 179–188, May 2006
How to Cite
Love, E. J., Geoffrey Lane, J. and Murison, P. J. (2006), Morphine administration in horses anaesthetized for upper respiratory tract surgery. Veterinary Anaesthesia and Analgesia, 33: 179–188. doi: 10.1111/j.1467-2995.2005.00247.x
- Issue published online: 19 DEC 2005
- Article first published online: 19 DEC 2005
- Received 20 October 2004; accepted 28 February 2005.
- blood gases;
Objective To determine the effect of morphine administration on commonly monitored cardio-respiratory variables and recovery quality in horses undergoing anaesthesia and surgery.
Study design Prospective, randomized clinical study.
Animals Thirty-eight thoroughbred horses, 32 geldings and six mares, 3–13 years old, weighing 411–600 kg.
Materials and methods A standard anaesthetic technique was used. Twenty minutes after induction of anaesthesia horses received 0.1 mg kg−1 (0.1 m) or 0.2 mg kg−1 (0.2 m) morphine by intravenous injection. A control group did not receive morphine. Heart rate, respiratory rate (fr), mean arterial pressure (MAP) and blood gases were measured before morphine administration and every 10 minutes thereafter. Horses were positioned for 35 minutes in right lateral recumbency for tension palatoplasty by cautery and were then moved into dorsal recumbency for additional intraluminal surgery comprising one or more of aryepiglottic fold resection, sub-epiglottal mucosal resection, ventriculectomy and cordectomy. A subjective recovery score from 0 (worst) to 5 (best) was assigned by a single observer who was unaware of treatment group. Two-way repeated measures anova, one-way anova, Kruskal–Wallis test, Mann–Whitney test, Pearson and Spearman correlation coefficients, and chi-squared tests were used to analyse the data where appropriate.
Results Arterial partial pressure of oxygen (PaO2) decreased significantly over time and was significantly lower in horses that received morphine. One horse in the control group and two horses in each of the morphine groups had a PaO2 <13 kPa. No other significant cardiopulmonary effects were detected. Recovery scores [median (range)] were higher in morphine recipients: 4 (2–5) in 0.1 m, 4 (3–5) in 0.2 m compared with 3 (2–4) in the control group.
Conclusions and clinical relevance The lower PaO2 in morphine recipients did not appear to be of clinical significance in healthy horses because the number of horses with a low PaO2 was similar between groups. The quality of recovery was significantly better in morphine recipients. These results indicate that morphine may be considered for use in clinical cases although further work is required to assess the analgesic properties of the drug in this species.