Use of Ultrasound to Evaluate Outcome Following Colic Surgery for Equine Large Colon Volvulus
Large colon volvulus (LCV) is one of the most fatal forms of colic. In horses with LCV, diagnosis can be made pre-operatively using ultrasound to identify edema in the wall of the ventral colon; however, the post-operative response of the equine large colon wall after surgically corrected LCV has not been investigated. This study was designed to test the hypothesis that a longer time to colon wall involution following surgical correction of large colon volvulus would correlate with an increased rate of post-operative morbidity and mortality. Transcutaneous abdominal ultrasound was used to determine colon wall involution. Outcome was evaluated by comparing time to colon wall involution between 1) survivors and non-survivors and 2) horses that developed multiple organ dysfunction syndrome (MODS) during the post-operative period to those that recovered without evidence of MODS. Multiple organ dysfunction was identified in any horse having evidence of compromise in 2 or more organ systems.
Horses that were admitted to the North Carolina State University Veterinary Teaching Hospital between September 1, 2006 and September 5, 2007, had surgical correction of LCV and were recovered from anesthesia were included in this study. Ultrasonographic examination of the ventral large colon was performed at the time of anesthetic recovery and then every 6 to 8 hours until the colon wall returned to normal thickness (<5mm). Images were obtained approximately 2 cm caudal to the xiphoid using a Megas ES ultrasound machine and an 8-5 MHz curvilinear probe. Physical examination was recorded every 6 hours for the first 72 hours, and then every 8 hours for the duration of hospitalization. Complete blood count and serum biochemistry were collected every 48 to 72 hours. Owner permission was obtained for participation in the study and post-operative management was at the discretion of the attending clinician. A 1-way ANOVA was used to compare colon wall involution time between the designated groups of horses.
Fifteen horses met the initial inclusion criteria. Two horses were excluded due to euthanasia prior to colon wall involution. Of the 13 remaining horses, 5 developed MODS during hospitalization and 8 did not. Three of the 5 horses diagnosed with MODS were either euthanized or died postoperatively, while 2 survived to discharge. The 8 horses that did not develop MODS all survived to discharge. Horses that recovered without evidence of MODS had a significantly shorter time to colon wall involution (< 5mm) compared to horses diagnosed with MODS (Mean ±SEM: 19.2 hours ± 2.8 vs. 40.8 hours ± 6.7 respectively, P=0.006). There was no significant difference in mean time to colon wall involution between survivors and non-survivors.
A shorter time to colon wall involution was positively correlated with decreased postoperative morbidity in horses presented for surgical correction of large colon volvulus without resection.