Evaluation of the effect of general anaesthesia on ultrasonographic images of the small intestine in horses.

ultrasonography is currently more and more used in equine acute abdominal disease as well as in the follow-up of surgical colic patients because of its sensibility for the detection of small intestinal distension. General anaesthesia is known to diminish gastrointestinal motility even if there are no clinical signs associated with it. The aim of this study was to evaluate the effect of general anaesthesia on transabdominal ultrasonographic images of the small intestine in horses undergoing routine non abdominal surgeries. The ultrasonographic exams were performed in 19 horses before and after the general anaesthesia (immediately after the recovery and then 2h, 12h and 24h after it). Each ultrasonographic exam focused on the duodenum, the jejunum and the presence of peritoneal fluid. For the jejunum, 5 locations were used: on the ventral midline just caudally to the sternum, on the left and right cranial ventral parts of the abdomen, on the left and right inguinal regions. Other parameters such as the gut sounds and the postoperative fecal output were also recorded. Anova and Chi-square tests were used for
the statistical analysis. No horse showed colic signs. No significant difference was found between
the pre and post anaesthetic period considering the maximal diameter of the duodenum, the
maximal diameter of the jejunum on the 5 locations and the peritoneal fluid. The contractions of
the duodenum were increased at the recovery compared to before the anaesthesia (p= 0,0299). The small intestine was most visible at the recovery (57,5%) and then at 2 hours after it (38,3%). It seemed that the ventral midline just caudally to the sternum and the right and left inguinal regions were the best locations to observe the jejunum (with a mean of respectively 44,6%, 39,8% and 38,5% of visualization of the jejunum).The gut sounds were very significantly decreased at the recovery (p < 0,0001) and at 2h after it (p = 0,0006). The postoperative fecal output was not decreased. In conclusion, even if general anaesthesia seems to reduce temporarily the intestinal activity (decreased gut sounds in the early post anaesthetic period), it does not cause significant distension of the small intestine (almost the small intestinal diameters were in the normal range). If an increased diameter of small intestine is observed by ultrasonography after surgery it should therefore be attributed to a pathological process and not to the anaesthesia.