Soft Tissue Surgery

Chapter 21 Soft Tissue Surgery




There are substantial physiologic and anatomic differences between rabbits and species that are more familiar to veterinarians. Rabbit behavior—including reaction to stress and pain and poor acceptance of sutures, dressings, and coaptation devices—is unlike that of other pets. The surgeon should have a thorough knowledge of rabbit physiology and behavior prior to performing surgery in these patients.





Presurgical Treatment


The author provides food (grass hay) and water to rabbits up until the time of surgery, although some authors have suggested that a large volume of food in the rabbit’s stomach can cause variations in anesthetic doses.12 Begin antibiotic therapy in rabbits with systemic or localized bacterial infections, such as those with upper respiratory tract infections caused by Pasteurella species (“snuffles”) or with dental abscesses or infected wounds. Prophylactic antibiotics may be given if there is a significant chance of bacterial contamination during surgery. Quinolones, azithromycin, chloramphenicol, trimethoprim-sulfa combinations, and sulfa drugs generally do not negatively affect the normal cecal-colic microflora of rabbits. Use caution with beta-lactams, other macrolides, and other antibiotics that target gram-positive or anaerobic bacteria.


Parenteral fluids are not necessary in routine procedures. When supportive fluid therapy or vascular access is needed, a 20- to 26-gauge indwelling catheter is placed in the cephalic or lateral saphenous vein. Peripheral catheters work well during surgery and in the immediate recovery period. However, some rabbits do not tolerate a catheter when awake and must have the catheter and intravenous line covered with split-loom tubing or heavily bandaged to protect them. Alternatively, an intraosseous catheter may be placed within the greater trochanter. Moving the intravenous line away from the face results in better tolerance in some rabbits.


Rabbits are considered steroid-sensitive species,4 and steroids are administered only if indicated by the underlying disease process; they usually are not given for routine or elective surgery. Give atropine when indicated (0.1-0.2 mg/kg SC, IM; see Chapter 31) or glycopyrrolate (0.01-0.02 mg/kg SC) to control bradycardia, salivation, or respiratory secretions. These problems are rare when isoflurane anesthesia is used. Some rabbits produce atropine esterase; in such cases the dose of atropine may have to be repeated if signs recur.


The combination of thin skin and dense, fine fur makes it easy to cut a rabbit when clipping hair or shaving. Keep the skin spread flat in front of the blade and clip with the flat surface of the blade held parallel and close to the skin to minimize nicks and cuts. A fine No. 40 blade and an unhurried approach can help to prevent the fine hair from accumulating between the clipper blades, causing them to jam or cut poorly.



Postsurgical Monitoring



Blood Loss


The blood volume of the rabbit is reported to be approximately 57 mL/kg body weight.16,18 Most mammalian species experience a drop in arterial pressure and cardiac output with moderate blood loss. Loss of 15% to 20% of the total blood volume causes massive cholinergic release, with tachycardia and intense arterial constriction; thus blood is redistributed away from the gut and skin. In a 4-kg rabbit, this amounts to 34 to 45 mL of blood. An acute blood loss of 20% to 30% of total blood volume, or 45 to 68 mL in a 4-kg rabbit, is critical.




Surgical Techniques



Adhesion Formation


Problems resulting from adhesions are regularly found in rabbits; these are most often reflected in postoperative problems involving the cecum, colon and bladder and result from adhesions to the uterine stump, broad ligament, or ovarian pedicle. Adhesions associated with gastrotomy, enterotomy, and a variety of other types of gastrointestinal surgery may also occur. Symptoms include recurrent cystitis, cystic calculi, and microurinary calculi.14


Prevention of adhesions has been the subject of much study, often involving rabbits as animal models of human disease.6,7 A large number of substances have been used to combat adhesion formation, but the majority of these have proven to either be too toxic for use, to possess a high a complication rate, to be too difficult in application, or simply not to work. Promising substances include hyaluronic acid solutions10 and sodium carboxymethyl cellulose.5 Chondroitin sulfate20 has also been reported to be effective. These agents act by mechanical separation of surfaces as well as adding a protective “finish” to the viscera. Both mechanisms being a feature of their inert nature.


Thrombolytics, such as streptokinase,13 have been reported to be effective in adhesion prevention, but they present difficulties with local and systemic administration and the risk of hypersensitivity. There have been several studies using recombinant tissue plasminogen activator (rt-PA) in rabbits.3,19 In a rabbit adhesion model, rt-PA was found to reduce the primary and recurrent adhesion rates by 80%.3 Use of rt-PA was shown to be safe in the presence of colonic anastomoses and did not alter abdominal wound strength or increase postoperative hemorrhage.


Other studies have evaluated the use of endoscopy to correct adhesions as compared with traditional laparotomy.23 These have shown that laparoscopic adhesiolysis is associated with a significantly reduced formation of new postoperative adhesions as compared with laparotomy.





Common Procedures



Ovariohysterectomy


The reproductive tract of the female rabbit is unusual compared with that of the dog or cat (Fig. 21-1). The uterus is bicornate. Each uterine cornua possesses a cervix (there is no uterine body). At maturity it is coiled in the caudal abdomen, cranial and just dorsal to the urinary bladder. Long uterine (tuba uterina) and infundibular tubes (infundibulum tubae) extend between the cornua and the ovary.21 The uterus is easily exteriorized but is more fragile than that of other species. In a healthy doe, the caudal portion of the broad uterine ligament (ligamentum latum uteri), the mesometrium, is a principal fat-storage site that makes identifying and ligating uterine vessels difficult. The urethra of the female rabbit empties into the proximal end of a deep vaginal vestibule. Expression of the bladder with the animal in dorsal recumbency often leads to retrofilling of the vaginal vault. This can be a source of contamination of the peritoneal cavity during uterine surgery. It is also important not to confuse the vaginal vault with the bladder.



With the rabbit anesthetized before surgery, empty the rabbit’s bladder by gentle palpation. Shave and prepare the abdominal area and restrain the rabbit on the surgery table in dorsal recumbency, draped for surgery. Make a 2- to 3-cm midline incision centered over the cranial pole of the bladder, about half the distance between the umbilicus and the cranial rim of the pubis. Lift the narrow linea alba from the abdominal contents as you make a stab incision into the abdomen; be very careful in entering the abdominal wall, because the thin-walled cecum and bladder are often pressed firmly against the ventral abdomen. In the reproductively mature rabbit, the uterus can typically be seen as it lies cranial and dorsal to the cranial pole of the bladder and may be lifted through the incision with forceps. A spay (snook) hook is not necessary and may cause damage to the cecum. Follow the uterus to the uterine/infundibular tubes. The uterine/infundibular tubes are coiled in a large loop. They are several times longer than those of a dog or cat; be careful not to leave any portion of them. Multiple vessels are associated with the ovary, but they are smaller than those of many mammals. Carefully identify each and double ligate them with transfixing sutures of chromic gut or synthetic absorbable suture. Hemorrhage is seldom a problem with these vessels. The uterine vessels stand as much as a centimeter off the uterus and may be of significant size in mature does. Double ligate these vessels with transfixing ligatures to the vaginal serosa. The mesometrium may then be stripped away from the cervix and vagina. Ligate the uterus just caudal to the cervices. Avoid contaminating the abdomen with urine or vaginal contents if a caudal ligature is used. Ligate each uterine horn if removed cranial to the cervix, or carefully ligate at the dorsal vagina if the uterus is removed caudal to the cervices. Closure of the abdomen is routine. Close the skin with surgical staples, an intradermal suture pattern, or tissue cement.



Orchidectomy (Castration)


Sexually active male rabbits (bucks) have obnoxious sexual mounting and urine-marking behaviors that generally lead their owners to want to have them neutered. Furthermore, bucks may become territorial and possessive about their environment and owners, leading to aggressive behavior.


The rabbit’s testes are similar to those of the cat but may move freely from the scrotum to the abdomen through an open inguinal canal. Soft tissue herniation and strangulation of bowel loops is prevented by a large mass of fat associated with the epididymis, which rests in the inguinal canal when the testicle is in the scrotum.


For castration, anesthetize and restrain the buck in dorsal recumbency. Carefully shave the hair from the scrotum and surrounding area and surgically prepare and drape the area to minimize contamination. Make a 1- to 1.5-cm incision with a No. 15 scalpel blade through the skin and vaginal tunic on the ventral surface of both sides of the scrotum (Fig. 21-2). Remove the testis from the tunic and carefully tear the ligament of the testicle from the tunic with a dry gauze sponge. Pull the testis caudally to expose a section of the vas deferens and the vascular structures of the spermatic cord, then tie them in an overhand knot with a small Mayo needle holder or mosquito forceps. Alternatively, ligate the duct and vasculature with 2-0 to 3-0 synthetic absorbable suture. Cut the duct and vessels distal to the knot or ligature and return the spermatic cord to the inguinal canal in such a way that it can be recovered if bleeding occurs. Return the tunic to the scrotum and repeat the process for the remaining testis.


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Sep 6, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Soft Tissue Surgery

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