Experimental surgical techniques

Training

Gastrointestinal tract

Liver

Training techniques

Three surgical procedures in dogs are described as useful for training by Markowitz{3761}: thyroidectomy, adrenalectomy and nephrectomy. Thyroidectomy differs in species according to the anatomy and relationship of the parathyroids to the thyroid and thymus; in the dog the two paired parathyroids are inextricable from the paired thyroids, whereas in the pig the thyroid is a single centrally-located gland and the parathyroids are embedded in the cranial aspect of the thymus. Right adrenalectomy in the dog is tricky as the gland must be carefully separated from the vena cava.

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Surgery of the GIT

The classic 1964 text by J. Markowitz has excellent line drawings of surgical procedures used in dogs, with comments upon the comparative aspects of human surgery.{3761}

Suture patterns

When performing intestinal surgery, two suture techniques with assorted variations are of crucial importance: the method of Lembert, who showed in 1826 that inversion of the serosal edges was necessary for good healing; and Connell, who used the same principles but changed the orientation from vertical to horizontal. A Cushing suture pattern is the same as a Connell but the suture does not penetrate the lumen; it is used for the second layer if needed.

GI anastomosis 

Anastomosis of two segments of intestine is best accomplished by using scrupulously clean technique and placing suture lines carefully. Doyen clamps are used to provide atraumatic clamping of the opened ends, and the site is carefully packed off. Carmalts are used to crush the anastomosis site, which is then transected. Stay sutures are placed so that the mesenteric edges are not quite exactly matched up. When sutured, Dr. Mayo claimed that this "insures that the triangular bare space at the root of the mesentery is covered." The cut ends are then sutured together beginning with a line of Connell suture pattern, beginning in the middle of the wall farthest from the surgeon and continuing in both directions. After turning the corners, thumb forceps may be necessary to help invert the mucosal edges to form a tight seal. A second layer of Cushing sutures may be placed, but is generally not considered necessary and may increase the "diaphragm" that forms inside the anastomosed ends.{3761}

Other atraumatic techniques have been promoted, mostly to avoid any exposure of the abdomen to GI fluids. The "Murphy button" and Furniss clamp represent a variety of mechanical devices. Another technique utilizes completely closed techniques of suturing, in which the edges are clamped or basted and then sutured. The Parker-Kerr basting method is possibly the easiest of these techniques.

Experimental fistulas

A Pavlov fundic pouch at left.

Gastric fistulas have been used to study physiology, particularly relating to ulcer development and digestive hormones. There was much interest in the so-called "three types of digestion": nervous, mechanical and chemical. Simple fistulas were described by Pavlov using a spool-shaped device held in place by double purse-string sutures. Mann and Bollman developed a similar technique in the intestine, and Witzel described a tunneled enterostomy or gastrostomy utilizing a rubber tube that is tunneled within a fold in the gastric wall and the abdominal wall to prevent leakage.

Various pouches were developed to study fluid production in different anatomical sites. Pavlov developed the Pavlov fistula (shown here and above) by creating a pedicle flap of the stomach based on the right gastroepiploic artery along the greater curvature. This fundus pouch could be used to form a stoma for collection of stomach fluid. It maintains vagus innervation. Goldberg and Mann improved on the technique by tunneling part of the fistula through the body wall, so that fluid remained in the fistula until tapped. Priestley and Mann described a pouch of pylorus, and showed that gastric acid secretion is initiated from the pylorus, which is alkaline and produces gastrin.

The simplest method of jejunostomy is the Thiry fistula, which creates a blind test-tube-shaped pouch with a single stoma, leaving the two ends of jejunum from which the pouch was created anastomosed together. The Thiry-Vella fistula is similar but involves a loop of jejunum and two stomata.

Pavlov’s enteral fistula uses a thimble-shaped cannula to exit the abdomen, and can be placed anywhere. Important features to consider include (1) placing 2 purse-string sutures to ensure that no mucosa is exposed, (2) looping omentum over the exit site, and (3) pre-placing four tacking sutures through the intestine and through the abdominal wall to ensure formation of a tight seal.

Mann-Bollman ileal fistula

One of the most significant postoperative complications of fistulas is their tendency to leak abdominal contents onto the skin. Mann and Bollman conceived of a fistula in which peristaltic waves are used to prevent this from happening. It is based on the Maydl jejunostomy, utilizing the jejunum as the conduit and reanastomosing the intestine where the segment was harvested. With the Mann-Bollman fistula an entire segment of jejunum is released and turned to orient peristalsis away from the ostomy site. A simple catheter can be used to collect intestinal contents. They used this procedure to measure pH at various levels of the GI tract.

Implanted cannulas can also be used to collect ileal contents for digestion studies, although there are complications. Cannulas have been placed successfully in pigs, dogs, rabbits, ruminants, horses, and chickens. In cats, there are more bacteria in the ileum than in the more proximal small intestine, and possibly more than in other species. Placement of Delron cannulas was unsuccessful in cats, due to systemic illness, local abscesses, and one case of surgical failure.{3980}

Sometimes, intestinal cannulas are combined with portal vein access to study the effects of drug absorption and first-pass elimination. Silastic catheters rather than rigid cannulas can be inserted into the intestine and connected to buried access ports if they will be used for administration of compounds rather than collection of intestinal contents. One such method employs catheters implanted into the duodenum (10cm distal to the pylorus in the Beagle), ileum (2/3 the distance from the pylorus to the ileocecal valve), and colon (10cm distal to the ileocecal valve); and a portal vein catheter inserted into the vein near its origin from the splenic vein. Intestinal catheters were most successful if they were tunneled using a Witzel technique. A commercial catheter with a circular fiber disk, which was supposed to aid in forming a tight seal around the insertion site, usually eroded into the intestine due to peristaltic movement; a catheter with beads worked better. Access ports were located near the vertebral column. Dogs were maintained for up to 11 months. The portal vein catheters were flushed weekly with saline and filled with heparin (1000U/ml, 1 ml). Contents were collected monthly for culture and antibiotic susceptibility testing. Intestinal catheters were flushed with 10ml 50% dextrose to prevent them from becoming occluded with intestinal contents; this was not always successful and a major complication was occlusion of the catheters. The access ports were another source of complications; sometimes they were inadvertently punctured or ruptured during access, allowing leakage of either the test compound or intestinal contents, resulting in the need for removal.{4089}

Markowitz described experimental production of chronic peptic ulcer as a "beautiful piece of craftsmanship." The duodenum was separated from the pylorus at its oral end, and the stomach rejoined to the jejunum, creating a blind-ended duodenal pouch whose contents joined that of the stomach at the duodenal-jejunal junction. He concluded that the obvious cause of peptic ulcers is the failure to neutralize gastric acid, the "chemical factor" being the prominent villain. However, the "mechanical factor", that being the anatomic site subjected to the ejection of stomach contents, was also important.{3761}

Several methods of exteriorizing bowel loops were described in Markowitz, their use being the study of the action of purgatives or the emotional effects upon intestinal motility. Biebl’s method was to simply exteriorize a segment of intestine, and enfold it in a double-pedicle skin flap. Using this technique, the following results were described:

Markowitz speculated on the effects of intestinal obstruction. The two leading hypotheses were that death results from either dehydration and alkalosis from the vomiting with high obstruction, or from toxemia due to bacterial overgrowth. Dragstedt realized that the cause of death differs depending on the site of obstruction. With high obstruction, death results from the failure of the duodenum to absorb gastric and pancreatic contents; saline can prolong life in these cases. Alternatively, with high obstruction, the large volume of secretion by the duodenum (30cc/day) accelerates distension and subsequent toxemia. Blood chemistries include high urea, low chloride and alkalosis. The jejunum has little absorptive capacity and only slight fluid secretion (1cc/3 days). If the obstruction is low, i.e. in the distal ileum, distension of the intestine enables bacterial toxemia to occur; if the obstruction is resected the animal can be saved. Blood chemistries are not affected as much. Penicillin can have dramatic effects upon survival, because the distension from bacterial gas production does not occur.{3761}

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Surgery of the Liver

In all vertebrates blood passes from the GIT through the liver before entering the heart. Von Eck, a Russian military surgeon, developed a technique in 1877 for side-to-side anastomosis of the vena cava to the portal vein, so that blood is shunted from the portal vein into the vena cava. Over the succeeding 8 weeks the liver undergoes atrophy. The surgical technique, which has been modified since, is still known as an Eck fistula.{3761}

Bile duct cannulation can be accomplished using a number of methods, but the use of a synthetic tube (Rous and McMaster) is easiest to perform. The common bile duct of the dog is ligated close to the duodenum, and a piece of tubing tied into the duct. A long length is left in the abdomen to prevent torsion or tension. It is exteriorized through the right side just below the costal margin along the mammary line. Bennett Cohen improved on the technique by using two lengths of Tygon tubing, one in the duodenum and the other in the bile duct. When not collecting bile the two tubes could be reconnected, thus enabling normal bile flow.{3761}

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©1999, Janet Becker Rodgers, DVM, MS

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Comments? Send an email to rodgers@uky.edu