Do iatrogenic serosal tears result in small bowel perforation in a rabbit model
Tsai, Ming - Chih
Introduction A common decision faced by surgeons during laparotomy is how to manage iatrogenic small bowel serosal tears. Surgical dogma dictates that serosal tears should be repaired; as not doing so may result in the bowel becoming ischemic and likely perforation. This would result in significant morbidity and potentially mortality and re -‐ laparotomy with either repair of the perforation or bypass management options. However, we do not know if serosal tears result in a localised area of bowel ischaemia as no study has been performed to test this assumption. Methods I designed two experiments wherein I determined whether or not serosal tears result in localized bowel ischemia in a rabbit model using adult -‐ size white rabbits. The first experiment demonstrated the intra -‐ luminal pressure required for perforation to occur at the site of a small bowel serosal tear. In the second experiment I investigated whether delayed serosal tears occur in-‐vivo. The WITS Animal Ethics Committee approved both experiments. The rabbit model consisted of adult -‐ sized white rabbits were subjected to a mid – line laparotomy under ketamine -‐ xylazine anaesthesia with the assistance of the Central Animal Service veterinary nurses and staff. Serosal tears of various lengths and circumferences were created while wearing 2.5x surgical loupes. Rabbits were euthanized at the end of the procedure. The bowel was harvested for histology to check for viability of the mucosa. iv Experiment 1. Twelve rabbits were used in this experiment. In order not to compromise the vascular supply of the bowel, the bowel was clamped approximately 3cm away on either side of the serosal tear. Two 18 gauge jelcos were inserted into the isolated bowel lumen. One jelco was used to incrementally infuse the normal saline solution. The other jelco was connected to a manometer or a pressure transducer and used to measure intraluminal pressure generated by the normal saline. Experiment 2. A mid – line laparotomy was performed as above on another ten rabbits, of which a 4 cm x 100 % circumferential serosal tear was created on a segment of small bowel. Their abdomens were closed with PDS suture and the rabbits were observed after the operation for signs of bowel perforation and then terminated at either 72 hours or 120 hours to harvest the bowel for histological examination. Results The mean intraluminal pressure for bowel perforation was: 26.4 cm H₂O for sham rabbits, 23.0 cm H₂O for 1cm serosal tears in length and 23.3 cm for 4cm in length. There is no statistically difference between the mean intraluminal pressures of 1cm and 4 cm. For serosal tears involving the circumference with 1 cm in length, the intraluminal pressure of perforation was: 27.7 cm H₂O for 25 % circumference, 30.6 cm H₂O for 50 % circumference, 23.8 cm H₂O for 75 % circumference, 25.4 cm for 100 % circumference. At normal physiological intraluminal pressure of 6 – 8 cm H₂O during peristalsis, no perforation of the serosal tear present in this experiment. Findings of the second experiment also demonstrated no obvious bowel perforation at 72 hours and 120 hours after the operation. Histological examination of the small bowel serosal tear site also showed that the mucosa and the submucosal layers, at the tear sites, were intact and viable without signs of ischemia. Conclusion In the acute setting, small bowel serosal tears up to 4 cm in length or, up to 100% of the bowel circumference did not perforate at physiological pressures of 6 -‐ 8 cm H₂0, which are encountered during normal peristalsis. Furthermore, serosa of the small bowel does not appear to affect the tensile strength of the bowel wall nor does it contribute significantly to mucosal and submucosal blood supply. No small bowel perforation occurred within 72 -‐ 120 hours after creating serosal tears.