Resolution of Intraluminal Obstructions through Ventral Midline Celiotomy
For intraluminal obstructions that are known preoperatively to be located in the right dorsal colon, transverse colon, and oral descending colon, the celiotomy incision should be positioned relatively more cranial on ventral midline, starting at least 5-10 cm cranial to the umbilicus (Hassel 2002). If the location of the obstruction is not known preoperatively (fecalith, foreign body, false negative radiographs for enteroliths), extending the incision more cranially may aid exteriorization of these intestinal segments.
The basic strategy for mobilizing right dorsal colon and oral to mid transverse colon obstructions is hydropulsion. This entails using intraluminal lavage through a pelvic flexure enterotomy to evacuate all ingesta oral to the obstruction (right dorsal colon, including ampulla coli, and oral transverse colon, as applicable). Once the colon is emptied of ingesta, water distension of the colon combined with gentle ballottement of the obstruction can free it from the mucosa and allow it to move orally into the ampulla coli where it then can be manipulated within the dorsal colon and exteriorized from the abdomen (Hanson and Schumacher 2021; Hassel 2002; Oreff et al 2020; Pierce 2009). This author has observed on some occasions that the transverse colon appears to spasm orally to obstructions in the transverse colon, and this spasming does not consistently relax with fluid distension. One strategy that may ease intestinal spasming is topical application of 2% lidocaine (Hassel and Yarbrough 1998). Conservative doses (~0.1 mg/kg IV) of butylscopolammonium bromide appears to be helpful in relaxing these intestinal spasms, allowing oral movement of the obstruction, and resolving the obstruction, although the author is mindful of the cardiovascular effects of this drug in the anesthetized horse (Loomes 2020). Typically, intraluminal obstructions within the right dorsal colon or transverse colon are too large to be removed via the pelvic flexure enterotomy, so a second enterotomy must be performed or if appropriate, a lithotripsy technique used such as described by Machado Amaral Rosa et al (2023).
For obstructions that are not resolved by hydropulsion, particularly obstructions in the mid to distal transverse colon and very oral descending colon or the very aboral descending colon, retropulsion or retrograde flushing may be a useful technique (Hanson and Schumacher 2021; Klohnen 2013; Pierce 2009; Pierce et al 2010; Oreffet al 2020; Schumacher and Mair 2002; Taylor et al 1979). Retropulsion was used in 13% of descending colon enterolith obstructions in one case series (Pierce et al 2010). Retropulsion is the use of water distension and hydropressure of the intestine aboral to the obstruction via a high enema. The success of this technique requires the emptying of ingesta from oral to the obstruction and relaxation of the oral segment to allow movement of the obstruction. Retropulsion should only be used for obstructions that cannot be accessed otherwise, because the intestine adjacent and oral to an obstruction is often compromised by some degree of mural damage and may be prone to rupture (Pierce et al 2010).
To facilitate elevation of oral segments of the descending colon to the level of the abdominal incision, the use of nondepolarizing neuromuscular blocking agents, such as atracurium, pancuronium, etc., by the anaesthetist may allow relaxation of the body wall so that the abdominal incision can be manually pushed downward to allow exteriorization of most oral descending colon (Hassel 2002). Another suggested technique is to temporarily remove the horse from positive pressure ventilation to decrease the abdominal movements with each breathe and facilitate exteriorization of the very oral descending colon (Klohnen 2013). It is important to emphasize that neuromuscular blocking agents and removal of positive pressure ventilation cannot be performed together because neuromuscular blocking agents also paralyze the respiratory muscles and positive pressure ventilation is an essential requirement during neuromuscular blockade. The applicability of either of these techniques will depend on the experience, comfort, and pharmaceutical repertoire of the anaesthesia staff.
Another technique to facilitate aboral movement of an intraluminal obstruction within the descending colon is partial thickness taeniotomy (Hassel 2002; Hassel and Yarbrough 1998; Klohnen 2013; Pierce 2009; Schumacher and Mair 2002). This technique can be used to advance an obstruction a few centimeters (4-15 cm) aborally to allow the enterotomy to be made in a more exteriorized segment of descending colon or in a segment of descending colon that has not been compromised by the pressure of the obstruction (Hassel and Yarbrough 1998). A partial thickness taeniotomy is performed by creating a seromuscular incision in the middle of the antimesenteric taenia approximately 8-15 cm aboral to the obstruction (Hassel 2002; Hassel and Yarbrough 1998). The partial thickness seromuscular incision is extended orally to the level of the obstruction using Metzenbaum scissors or a scalpel blade. This incision allows maximum stretching of the mucosa within the taeniotomy, effectively increasing the intraluminal diameter. Gentle pressure is applied to the obstruction to advance it aborally, being careful to monitor when the stretched mucosa begins to rupture or the desired location for the enterotomy is achieved (Hassel 2002; Hassel and Yarbrough 1998). At that time, manipulations should be stopped and the enterotomy is extended through the mucosa in a controlled manner to allow removal of the enterolith. Closure of the enterotomy is routine, as described earlier.