Chapter 21 General Principles and Techniques The liver is the largest gland in the body. It is the primary site for detoxification of many substances and plays a central role in the metabolism of protein, fat, and carbohydrates. Unfortunately, clinical signs of hepatic disease may not be apparent until the disease is advanced and irreversible. Hepatic failure may affect many other organ systems including the central nervous system (CNS), kidneys, intestines, and heart. A clinical scoring system based on the presence or absence of ascites, hypoglobulinemia, hepatic encephalopathy, hypoalbuminemia, hyperbilirubinemia, and clinical signs was associated with survival in Labrador Retrievers undergoing hepatic biopsy for chronic hepatitis (Shih et al, 2007). Higher clinical scores were negatively associated with survival in that study. Ascites in Labrador Retrievers presenting for chronic hepatitis was also associated with a shorter survival time (Raffan et al, 2009). The liver produces most of the plasma proteins (i.e., albumin, α- and β-globulins, fibrinogen, and prothrombin). Hypoalbuminemia is common in patients with advanced hepatic disease. Fluid therapy may further dilute serum albumin, making plasma or colloid infusions needed in severely affected patients. Albumin levels below 2 g/dl may be associated with delayed wound healing. Potassium abnormalities are common in patients with hepatic disease. Coagulopathies may occur because of diminished synthesis of clotting factors or consumption. Preoperative evaluation of clotting function, especially mucosal bleeding time, is warranted; fresh whole blood transfusions may reduce intraoperative hemorrhage in selected patients. Some patients with hepatic disease are anemic because of nutritional deficiencies, coagulation abnormalities, and/or gastrointestinal hemorrhage. Animals with hematocrits below 20% and anemic animals that are clinically hypoxic or weak should be given preoperative blood transfusions (see Table 4-5 and Box 4-1 on pp. 34 and 30, respectively). Many patients with hepatic disease are anorexic, and some require preoperative nutritional supplementation (see Chapter 10). Hypoglycemia sometimes occurs with severe hepatic insufficiency: blood glucose levels may need to be monitored. Patients with massive ascites may be dyspneic owing to pressure on the diaphragm that restricts lung expansion; removing some abdominal fluid before induction of anesthesia is important to prevent further hypoventilation and hypoxemia. If ascites prevents the patient from lying in dorsal recumbency, ventilation during surgery will be extremely difficult. Because high ventilator pressures reduce hepatic blood flow, it is important to reduce this pressure by removing some fluid; if time allows, it may be best to do this gradually over a couple of days. Patients with severe hepatic encephalopathy should be treated symptomatically (e.g., controlled protein diet, antibiotics, cleansing enemas, fluids, lactulose; see p. 601) to diminish or eliminate clinical signs before surgery. Anesthetic Considerations for Animals With Hepatic Disease* *Patients with hepatic disease may have hypoalbuminemia with decreased binding as well as decreased clearance of many drugs. It is recommended to start with low doses and titrate slowly to effect. †Monitor for hyperthermia in cats. Because preservation of hepatic oxygenation has been shown to be extremely important in patients with liver dysfunction, hepatic blood flow must be maintained. Factors known to reduce hepatic blood flow, such as hypotension, excessive sympathetic stimulation (e.g., inadequate pain control), and high airway pressures, should be avoided by removal of ascites preoperatively. To increase oxygenation, preoxygenate before induction, keep inspired oxygen high during surgery, and do not rush extubation. Patients often need supplemental oxygen in the postoperative period. Hypotension needs to be treated promptly with vasopressors and/or inotropes (see Box 19-6 on p. 379). In patients with chronic liver disease and decreased liver mass, the circulatory system may be in a hyperdynamic state. Cardiac output is increased and is dependent on preload and systemic/pulmonary vasodilation. If chronic ascites has been present, some underlying renal dysfunction and impaired free water clearance may occur. Coupled with hypoalbuminemia, colloids are often warranted instead of large boluses of crystalloids. Fluid maintenance needs to be individualized based on underlying causes, severity of hepatic and renal dysfunction, degree of anemia and hypoalbuminemia, blood loss in surgery, and evaporative losses due to incision size. As a general rule, replace evaporative losses with crystalloids and blood loss with colloids to assist in maintaining adequate blood pressure. See recommendations on p. 602 for anesthetic management of animals with portosystemic shunts. Aerobic and anaerobic bacteria normally reside in the liver but may proliferate with hepatic ischemia or hypoxia. Therefore, prophylactic antibiotics are warranted in patients with severe hepatic disease that are undergoing hepatic surgery besides simple biopsy. The pharmacokinetics of antibiotics may be altered in these patients by depressed hepatic metabolism, alterations in hepatic arterial or portal blood flow, hypoalbuminemia, or reductions in biliary excretion. Antibiotics are specifically indicated in the treatment of hepatic encephalopathy (see p. 601), bacterial cholangitis/cholangiohepatitis, and hepatic abscess. Broad-spectrum antibiotics effective against anaerobes (e.g., penicillin derivatives, metronidazole, clindamycin) are appropriate and relatively safe in patients with hepatocellular compromise (Box 21-1). Potentially hepatotoxic antibiotics (e.g., chlortetracycline, erythromycin) should be avoided if possible. The diaphragmatic surface (parietal surface) of the liver is convex and lies mainly in touch with the diaphragm. The visceral surface faces caudoventrally and to the left and contacts the stomach, duodenum, pancreas, and right kidney. Six hepatic lobes are present (Fig. 21-1). The borders of the liver are normally sharp but appear more rounded in young animals and in those with infiltrated, congested, or scarred livers. The liver has two afferent blood supplies: a low-pressure portal system and a high-pressure arterial system. The portal vein drains the stomach, intestines, pancreas, and spleen and supplies four-fifths of the blood that enters the liver. The remainder of the afferent blood supply is derived from the proper hepatic arteries. These arteries are branches of the common hepatic artery and may number between two and five. Efferent drainage of the liver occurs through the hepatic veins. In the fetal pup, the ductus venosus shunts blood from the umbilical vein to the hepatic venous system. The ductus venosus becomes fibrotic after birth and is known as the ligamentum venosum. Bile, formed in the liver, is discharged into bile canaliculi lying between the hepatocytes. These canaliculi unite to form interlobular ducts that ultimately merge to form lobar or bile ducts (see p. 619). The portal vein, bile ducts, hepatic artery, lymphatics, and nerves are contained in the lacelike and nonsupporting portion of the lesser omentum known as the hepatoduodenal ligament. Hepatic biopsies are commonly indicated in patients known to have or suspected of having hepatic disease. Several breeds have been associated with hepatopathies, including Bedlington Terrier, Doberman Pinscher, Cocker Spaniel, West Highland White Terrier, Dalmatian, Skye Terrier, and, recently, Labrador Retriever (Shih et al, 2007; Poldervaart et al, 2009). Chronic hepatitis of Labrador Retrievers occurs in middle-aged to older dogs; it causes no or vague clinical signs and is likely associated with copper accumulation (Hoffmann et al, 2009). Anorexia, hypoglobulinemia, and prolonged partial thromboplastin time (PTT) were associated with shorter survival; however, the median survival was 1 year, with some affected dogs surviving as long as 8 years. Biopsies may be obtained percutaneously, with laparoscopy (see p. 590), or at surgery. Partial hepatectomies are less commonly performed but may be indicated for focal neoplasms or trauma. The standard approach for hepatic surgery is a cranial ventral midline abdominal incision. The caudal aspect of the sternum can be split if additional exposure is needed. Fine needle aspiration is most likely to be diagnostic in patients with diffuse hepatic neoplasia (e.g., lymphosarcoma, diffuse hepatic histoplasmosis, feline idiopathic hepatic lipidosis). However, inability to diagnose these conditions on a fine needle aspirate does not preclude disease, and even if one of these conditions is found, other, undiagnosed diseases could be present. This latter possibility is particularly important in cats, because almost all sick, anorexic cats will have some fat vacuoles in the hepatocytes. However, before clinical illness due to hepatic lipidosis can be diagnosed, one must determine that fat in the hepatocytes is sufficient to cause hepatic dysfunction. Furthermore, diagnosing hepatic lipidosis does not guarantee that there is not another hepatic disease present that was not found by the fine needle technique. Cytologic evaluation of ultrasound-guided fine needle aspirates is most likely to agree with histopathologic findings when the animal has vacuolar hepatopathy; however, this condition is commonly misdiagnosed by cytology. In one study, overall agreement between cytology and histopathology in dogs and cats was 30.3% and 51.2%, respectively (Wang et al, 2004). In another study, in which morphologic diagnoses were made with the use of an 18 gauge Tru-Cut–type needle, concurrence with wedge biopsy specimens was approximately 50% in both dogs and cats (Cole et al, 2002). The substantial limitations of diagnosing hepatic disease in dogs and cats by percutaneous techniques should be recognized by clinicians. With the animal in dorsal recumbency, clip the hair from the area surrounding the xiphoid process and prepare it for aseptic surgery. Make a small incision in the skin on the left side between the costal arch and the xiphoid process. Insert the biopsy needle through the skin incision in a craniodorsal direction, angling it slightly toward the left of midline. Advance the needle until ultrasound guidance shows the needle to be positioned at the surface of the liver. Advance the biopsy needle into the hepatic tissue, and obtain the biopsy sample (see Fig. 21-2). Alternatively, use a harmonic scalpel to harvest liver samples. Collect a 2 × 1 cm sample of liver using a harmonic scalpel with a working blade length of 15 mm and set to a power level of 3 (Barnes et al, 2006). Hemorrhage routinely occurs when the sample is torn off the liver, but one must be aware that the laparoscope will magnify any hemorrhage that occurs. Typically, less than 1 to 5 ml of blood is lost with a biopsy. Less hemorrhage was noted when the liver was sampled with the harmonic scalpel; however, significantly more coagulation necrosis, cavitational fragmentation, and fibrosis were associated with the harmonic scalpel (Barnes et al, 2006; Vasanjee et al, 2006). Although less than 25% or up to 1.3 mm of the sample was necrotic, appropriately sized samples should be obtained to offset the tissue damage. Sampling from central regions of the liver with the harmonic scalpel seemed to rely on natural coagulation rather than vessel sealing (Vasanjee et al, 2006). Needle biopsies least often result in adequate samples for histopathologic evaluation. A centrally located sample of liver parenchyma may be taken with a Baker biopsy punch. The recommended size for collection of at least six to eight portal triads is 6 mm in diameter. Press the punch against the area to be sampled and advance it using a clockwise and counterclockwise twisting motion (Vasanjee et al, 2006). Use Metzenbaum scissors to separate the deep margin of the sample from the parenchymal attachment. If needed, insert hemostatic gelatin sponge material into the defect to aid in hemostasis. A biopsy of the hepatic margin may be obtained by the “guillotine” method. Place a loop of suture around the protruding margin of a liver lobe. Pull the ligature tight and allow it to crush through the hepatic parenchyma before tying it (Fig. 21-3, A). As the suture tears through the soft hepatic tissue, vessels and biliary ducts are ligated. Hold the liver gently between the fingers, and with a sharp blade, cut the hepatic tissue approximately 5 mm distal to the ligature (allowing the stump of crushed tissue to remain with the ligature). To avoid crushing the biopsy sample and causing artifacts, do not handle it with tissue forceps. Place a portion of the sample in formalin for histologic examination; reserve the remainder for culture and cytologic study. Check the biopsy site for hemorrhage. If hemorrhage continues, place a pledget of absorbable gelatin foam over the site. As an alternative, if a focal (nonmarginal) area of the liver is to be biopsied, use a punch biopsy or a Tru-Cut biopsy (see Fig. 21-2), or place several overlapping guillotine sutures around the margin of the lesion and excise it (Fig. 21-3, B). Use caution with a punch biopsy to avoid penetrating more than half the thickness of the liver with each biopsy. Apply pressure to the site until bleeding stops. If hemorrhage continues, place a pledget of absorbable gelatin sponge over the site. Determine the line of separation between normal hepatic parenchyma and that to be removed, and sharply incise the liver capsule along the selected site (Fig. 21-4, A). Bluntly fracture the liver with the fingers (Fig. 21-4, B) or the blunt end of a Bard-Parker scalpel handle, and expose the parenchymal vessels. Ligate large vessels (hemoclips may be used), and electrocoagulate small bleeders encountered during the dissection (Fig. 21-4, C). As an alternative, place a stapling device (Autosuture TA 90, 55, or 30; Ethicon, Somerville, N.J.) across the base of the lobe and deploy the staples. Excise the hepatic parenchyma distal to the ligatures or staples. Before closing the abdomen, make sure the raw surface of the liver is dry and free of hemorrhage. In small dogs and cats, several overlapping guillotine sutures (as described previously) may be placed along the entire line of demarcation (Fig. 21-5). Be sure that the entire width of the hepatic parenchyma is included in the sutures. After tightening the sutures securely, use a sharp blade to cut the hepatic tissue distal to the ligature, allowing a stump of crushed tissue to remain with the ligature. Partial lobectomy in medium-sized dogs (24.3 kg) has been described using a single pre-tied loop ligature of 0 glycolide-lactide copolymer, a vessel-sealing device (see p. 83), and a harmonic scalpel (Risselada et al, 2010). Intraoperative hemorrhage occurred with pre-tied loops and the harmonic scalpel, resulting in additional ligation or clip application. None of the three methods leaked upon postmortem perfusion until supraphysiologic pressures in the hepatic artery or portal vein were reached, suggesting that further investigation into these techniques may be warranted (Risselada et al, 2010). Analgesics (e.g., hydromorphone, butorphanol, buprenorphine) should be provided to patients after surgery (see Table 12-3 on p. 141). For severe pain, a fentanyl-lidocaine-ketamine combination given as a constant rate infusion (CRI) may be indicated (see Box 12-2 on p. 138). Dogs with acute hepatitis may progress to chronic hepatitis and cirrhosis; repeat liver sampling should be considered to assess response to therapy (Poldervaart et al, 2009). The most common and serious complication of hepatic surgery is hemorrhage. This may result from ligatures slipping off friable hepatic tissue. Care should be taken to ensure that a stump of tissue remains distal to the ligature when encircling sutures are used for biopsy or partial hepatectomy. With hepatic trauma, anaerobic bacteria may proliferate in hypoxic portions of the liver and cause sepsis; therefore, broad-spectrum antibiotics should be used in patients with severe hepatic trauma and in those undergoing hepatic surgery. Complications after major hepatic resection include portal hypertension, ascites, fever, hemorrhage, hypophosphatemia, or persistent bile drainage. Dogs with ascites undergoing hepatic biopsy have a significantly shorter mean survival time than those without ascites (0.4 m and 24 m from the time of biopsy, respectively) (Raffan et al, 2009). Icterus, hypoalbuminemia, a left shift on the leukogram, and enlarged portal lymph nodes were also associated with shorter survival in dogs with primary hepatitis (Poldervaart et al, 2009). Barnes, RF, Greenfield, CL, Schaeffer, DJ, et al. Comparison of biopsy samples obtained using standard endoscopic instruments and the harmonic scalpel during laparoscopic and laparoscopic-assisted surgery in normal dogs. Vet Surg. 2006;35:243. Cole, TL, Center, SA, Flood, SN, et al. Diagnostic comparison of needle and wedge biopsy specimens of the liver in dogs and cats. J Am Vet Med Assoc. 2002;220:1483. Covey, JL, Degner, DA, Jackson, AH, et al. Hilar liver resection in dogs. Vet Surg. 2009;38:104. Hoffmann, G, Jones, PG, Biourge, V, et al. Dietary management of hepatic copper accumulation in Labrador retrievers. J Vet Intern Med. 2009;23:957. Poldervaart, JH, Favier, RP, Penning, LC, et al. Primary hepatitis in dogs: a retrospective review (2002-2006). J Vet Intern Med. 2009;23:72. Proot, SJM, Rothuizen, J. High complication rate of an automatic Tru-Cut biopsy gun device for liver biopsy in cats. J Vet Intern Med. 2006;20:1327. Raffan, E, McCallum, A, Scase, TH, et al. Ascites is a negative prognostic indicator in chronic hepatitis in dogs. J Vet Intern Med. 2009;23:63. Risselada, M, Polyak, MM, Phil, M, et al. Postmortem evaluation of surgery site leakage by use of in situ isolated pulsatile perfusion after partial liver lobectomy in dogs. Am J Vet Res. 2010;71:262. Shih, JL, Keating, JH, Freeman, LM, et al. Chronic hepatitis in Labrador retrievers: clinical presentation and prognostic factors. J Vet Intern Med. 2007;21:33. Vasanjee, SC, Bubenik, LJ, Hosgood, G, et al. Evaluation of hemorrhage, sample size, and collateral damage for five hepatic biopsy methods in dogs. Vet Surg. 2006;35:86. Wang, KY, Panciera, DL, Al-Rukibat, RK, Radi, ZA. Accuracy of ultrasound-guided fine-needle aspiration of liver and cytologic findings in dogs and cats: 97 cases (1990-2000). J Am Vet Med Assoc. 2004;224:75. Specific Diseases FIG 21-7 Multiple shunts near the left kidney in a dog with hepatic disease and portal hypertension. Arteriovenous (A-V) fistulae account for about 2% of single shunts and may be congenital or acquired. Acquired A-V fistulae occur secondary to trauma, tumors, surgical procedures, or degenerative processes that cause arteries to rupture into adjacent veins. The fistulae typically are macroscopic communications that form between branches of the hepatic artery and portal vein; however, microscopic hepatic A-V fistulae have also been suspected. As congenital lesions, they are believed to develop as a result of failure of the common embryologic capillary plexus to differentiate into an artery or a vein. Affected animals usually develop portal hypertension and multiple collateral shunting vessels, resulting in acute onset of low-protein transudative ascites between the ages of 2 and 18 months (Figs. 21-8 and 21-9). In contrast, dogs with congenital PSS rarely have ascites.
Surgery of the Liver
Preoperative Concerns
Anesthetic Considerations
TABLE 21-1
Antibiotics
Surgical Anatomy
Surgical Techniques
Percutaneous Liver Biopsy
Percutaneous blind biopsy
Laparoscopic Liver Biopsy
Surgical Liver Biopsy
Partial Lobectomy
Postoperative Care and Assessment
Complications
References
Portosystemic Vascular Anomalies
General Considerations and Clinically Relevant Pathophysiology
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