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.