Impact of general anaesthesia on intestinal motility in horses undergoing non-abdominal surgery

Background
Morbidity and mortality related to general anaesthesia is higher in horses than in most other domestic animal species (Johnston et al. 2002). A multi-centre study showed that colic is the most common post-anaesthetic complication in horses (Senior et al. 2007). However, the reason for this has not been investigated. Many drugs used in equine anaesthesia may have an impact on intestinal motility, which may explain the high incidence of colic after non-abdominal surgery.

Objectives
The aim of the study was (1) to evaluate the impact of general anaesthesia on the motility of the gastrointestinal tract in horses undergoing non abdominal surgery and (2) to assess the feasibility of ultrasound as a simple tool for the evaluation of gastrointestinal motility.

Methods
Twenty-five horses hospitalized for elective procedures were studied before and after general anaesthesia consisting of acepromazine and xylazine premedication, and midazolam and ketamine induction followed by gaseous or total intravenous anaesthesia. Post-operative time points for ultrasonography and auscultation were immediately after the recovery, 2 to 4 h, 12 to 18 h and 24 h after it. Ultrasound imaging based on a previously established protocol (Busoni et al. 2011) was used to assess the size of the stomach, the diameter and the contractility of the duodenum, the diameter and the visibility of the jejunum and the presence or absence of peritoneal fluid. Abdominal auscultation in the post-operative period was also recorded. Statistical analysis was carried by ANOVA and Chi-Square tests.

Results
None of the horses showed signs of colic in the post-operative period. There was a significant decrease of gut sounds in the immediate postoperative period compared to pre-anaesthetic evaluation. Ultrasound analysis in the post-operative period revealed a smaller stomach, less duodenal contractions, more visualisation of the small intestine which had a greater diameter than pre-operatively. These values returned to normal towards the end of the 24h period.

Conclusions
The study showed that abdominal ultrasonography is a useful tool for the real-time evaluation of gastric and small intestinal dimensions and motility in the postoperative period. Smaller stomach, larger small intestinal diameter, and less small intestinal contractions suggest a reduced small intestinal motility after non-abdominal surgery in horses. Further studies should evaluate the sensitivity of the method, investigate the impact of different anaesthetic protocols and include a population of horses suffering from post-anaesthetic colic.

References
Johnston, G.M., Eastment, J.K., Wood, J.L.N., Taylor, P.M. (2002) The confidential enquiry into perioperative equine fatalities (CEPEF): mortality results of phases 1 and 2. Vet. Anaesth. Analg. 29, 159-170.

Senior, J.M., Pinchbeck G.L., Allister R., Dugdale A.H.A.,Clark L., Clutton R.E., Coumbe K., Dyson S., Clegg P.D. (2007) Reported morbidities following 861 anaesthetics given at four equine hospitals. Vet Rec., 160, 407-408.

Busoni, V., De Busscher, V., Lopez, D., Verwhilgen, D., Cassart, D. (2011) Evaluation of a protocol for fast localised abdominal sonography of horses (FLASH) admitted for colic. Vet Journal, 188, 77-82.