Microsurgery In Liver Research

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The use of an operating microscope in rat and mouse liver surgery makes it possible to obtain new experimental models and improve the already existing macrosurgical models. From the pioneer works of Sun Lee in the early 1960s through today, microsurgery has gained acceptance as an integral component of liver research. Portosystemic anastomosis, partial portal vein ligation, cholestasis, hepatectomies and liver transplantation stand out among the most frequently used liver microsurgical techniques in the rat and mouse. In essence, the experimental model resulting from these microsurgical techniques are the most used today in liver research.

Experiments on animals are the key to Surgical Clinical Research; its objective is to solve the unsolved problems in the clinical area. This chapter covers the ethical principles and investigator responsibilities. The principal environmental conditions, such as housing, husbandry and nutrition, are also described. Current studies indicate that rats and mice value opportunities to take cover, build nests, explore, gain social contact, and exercise some control over their social milieu; the inability to satisfy these needs is physically and psychologically detrimental, leading to impaired brain development and behavioral anomalies.

Microsurgery is characterized by the use of an operating microscope. It is associated with the use of fine microsurgical instruments. The microsurgical instruments correspond with the fundamental phases that make up a surgical operation, that is, incision, hemostasis, dissection and sutures. This chapter describes these surgical times, placing particular emphasis on microsurgical techniques. In microsurgery, the material used is equally important as how it is used with a correct technique.

Due to current attitudes to the use of animals in biomedical research any pain or distress caused to animals should be minimized. This can be achieved by the use of appropriate anesthetic and analgesic regimens. There are both sound ethical and scientific reasons for controlling pain in animals and can also make a substantial contribution to refinement of animal experiments. In this chapter recent trends in the administration of anesthetics and analgesics to laboratory rats and mice undergoing surgical procedures are assessed.

The extraction of multiple body fluids samples is frequently necessary when research studies involving laboratory rodents are developed. Thus, in the current chapter different techniques for collecting blood, bile and lymph samples are described. Methods for obtaining blood without anesthesia of the rat, as well as methods requiring anesthesia are explained. In addition, blood withdrawal by using long-term catheterization of blood vessels is described. Techniques of bile sample collection include catheterization of the common bile duct. Finally, techniques of lymph sample collection through catheterization of the thoracic lymph duct and mesenteric lymph duct are explained.

The types of laparotomy most frequently used in rodents are described. Usually, longitudinal or vertical abdominal incisions are preferred rather than transverse or horizontal ones.

In this chapter we describe the anatomy of the multilobed liver of the rat and mouse. Traditional gross anatomy divides the liver into four lobes: the middle, left lateral, right lateral and caudate, as well as the caudate process, which is found between the two aforementioned latter lobes. The study of the hepatic hilum with the operating microscopy makes it possible to observe that each of the four hepatic lobes and the caudate process have arterial and portal vascularization as well as individualized biliary drainage. By microdissection, the most frequent variations that these vascular and biliary structures present can be detected in the hepatic hilum. In addition, obtaining vascular casts allows for the study of the anatomical distribution of the hepatic venous system.

There is a widespread consensus that training in microvascular surgery has to start with non-living models. Harvested latex sheets and arteries are an example of excellent models for teaching basic microvascular techniques. Vascular microanastomoses could be performed by suture and non-suture methods. Microvascular suture techniques could be made interrupted or continuous. Alternatively, end-to-side microanastomoses could be performed by intussusception using only one or two stitches. Non-suture microvascular techniques include cuff-ligature, rings, clips, stents, adhesives and thermal or laser welding.

The most frequently used experimental models for portal microsurgery are those achieved through portal systemic shunts and partial portal vein ligation. Portacaval shunts are appropriate techniques for microsurgical training but also for researching chronic hepatic insufficiency and particularly hepatic encephalopathy. Portal hypertension by triple partial portal vein ligation, is associated with a low-grade inflammatory response at the splanchnic (enteropathy and liver steatosis) and systemic levels.

The serious repercussions of cholestasis on the liver and on the systemic level have led to the creation of many experimental models so as to better understand its pathogenesis, prophylaxis and treatment. Among the surgical techniques for developing extrahepatic cholestasis, the resection of the bile ducts that drain the lobes of the liver by means of a microsurgical technique stands out. In the long-term evolution, microsurgical extrahepatic cholestatic rats develop hepatic fibrosis with marked ductular proliferation and portal hypertension with collateral portosystemic circulation, hepatic encephalopathy and ascytes.

Hepatectomies in the rat can be improved using microsurgical techniques. The distribution variations of the vascular and biliar lobular branches of the liver are observed under magnification with an operating microscope and, therefore their dissection, ligation and section are more accurate. The vascularization and bile drainage of the caudate process, a liver sector located between the right lateral and caudate lobes can be identified using microsurgery. Removal of two-thirds (70%) of the liver represents the most valuable animal model of liver regeneration. The viability of the animal’s evolution after different types of subtotal hepatectomies depends on an effective identification of these vascular and biliary branches. Microsurgery also permits the use of various techniques for creating an anhepatic rat.

The different methods to achieve an effective liver preservation by simple cold storage are described in this chapter. Furthermore, the most used techniques of orthotopic and heterotopic liver transplantation as well as the postoperative complications, among which ischemiareperfusion injury and rejection stand out, are explained as well.