CHAPTER 85 Use of Laparoscopy in Abdominal Disease
Laparoscopy is a minimally invasive technique used in equine practice to perform elective procedures in horses such as removal of cryptorchid testes in stallions and normal or pathologic ovaries in mares. Less common but established elective procedures include nephrosplenic space ablation in horses with recurrent left dorsal colonic displacement, inguinal herniorrhaphy, colopexy, and nephrectomy. Furthermore, laparoscopic exploration of the equine abdomen has been undertaken to obtain biopsy specimens of liver, kidney, spleen, intra-abdominal masses, and small intestine.
EQUIPMENT, INSTRUMENTATION, AND TECHNIQUE
Laparoscopy involves introduction of a rigid endoscope into the abdominal cavity in one of many locations, depending on the procedure. Endoscopes most commonly used in the horse are 58 cm long, 10-mm–diameter, rigid telescopes (30-degree Hopkins telescope). The telescope is attached to a video camera and light source. The video camera is a standard endoscopic camera that is commonly used for arthroscopy. This, combined with a powerful light source (a 300W xenon light source is commonly used), enables the examiner to view the abdominal viscera on a monitor on an endoscopic tower located near the horse.
The endoscope is inserted through the abdominal wall via an outer cannula through which a sharp or blunt ended trocar is advanced. The trocar enables penetration of the abdominal wall and is removed. The cannula remains in place and during the procedure serves as the point of transit of the endoscope. This combination of trocar and cannula is referred to as the portal. Trocar points are very sharp, and newer systems have a built-in spring-loaded shield that acts as a safety mechanism aimed at minimizing accidental bowel injury during insertion. In horses under general anesthesia, endoscopic portals are commonly placed at the level of the umbilicus or slightly cranial, depending on the intent of the procedure. A common location for portal placement in the standing horse is the paralumbar fossa or the last intercostal space. Cannulas can be disposable or nondisposable and are of variable length. They are usually equipped with a side stopcock to permit attachment of tubing for insufflation of gas to induce pneumoperitoneum.
Insufflation of carbon dioxide (CO2) is vital during laparoscopy to induce abdominal distension and to create the operative space between the viscera and abdominal wall. Carbon dioxide is commonly used in equine laparoscopy and is preferred over oxygen, room air, and nitrous oxide because it is noncombustible, soluble in blood, and eliminated via the lungs during expiration. Insufflators record the flow rates and total volume of CO2 delivered while maintaining a constant intra-abdominal pressure of 10 to 15 mm Hg. Although well tolerated in the horse, pneumoperitoneum is not without consequences. Cardiovascular variations associated with CO2 insufflation include impairment in venous return and cardiac output and increases in heart rate, peripheral vascular resistance, and systemic arterial pressure.
Once the endoscopic portal has been established, additional instrument portals are strategically placed, depending on the procedure goals. Various specialized equipment is available, including grasping devices, scissors, tissue manipulators, and ligating and dividing endostapling instruments, to allow the surgeon to safely manipulate and transect tissues while ensuring hemostasis. Tissues can be divided via laparoscopic cautery and long-handled scissors equipped with an electrode hookup placed near the handle piece. More recently, development of vessel-sealing technologies enables arteries up to 7 mm in diameter to be safely obliterated by condensing the collagen and elastin within the tissue. Advantages of these new technologies are reduced thermal spread and injury of neighboring tissues and no sticking or charring following transection.
Another important factor to be considered pertains to variations in patient body position that may be necessary when the horse is under general anesthesia. Body position changes are required during laparoscopy to improve exposure by shifting the abdominal viscera away from the surgical field. In the horse, the head-down position (i.e., operating table tilted approximately 30 degrees) is used for surgery of the reproductive tract (cryptorchidectomy and ovariectomy). Reverse tilt (head up) is also used during procedures involving the diaphragm, liver, and stomach. Horses in a tilted head-down position may undergo substantial cardiopulmonary compensation, including marked increases in peripheral arterial blood pressure, intracranial pressures, and pulmonary arterial pressure. Coupled with pneumoperitoneum, body position changes may impact the anesthetic management of horses undergoing pelvic procedures, and specific knowledge of the procedure and preoperative planning are needed to prevent complications.
ADVANTAGES AND DISADVANTAGES OF LAPAROSCOPY
Laparoscopic procedures allow access to areas of the abdomen that are otherwise inaccessible. The close proximity of the operative site and camera magnification allow precision and accuracy, which are important for ensuring appropriate hemostasis.
Laparoscopic procedures are frequently performed with the horse standing and sedated, thus avoiding the inherent risks associated with general anesthesia and recovery. Furthermore, because laparoscopic procedures are completed through small incisions, shorter periods of hospitalization and rehabilitation are typically needed. Horses that have undergone flank laparoscopy appear to be more comfortable than those undergoing celiotomy through the paralumbar fossa. Small laparoscopic incisions heal quickly and do not require extensive care, so postoperative care and costs are reduced. In contrast, the specialized equipment and facilities needed to perform these procedures safely actually may render the procedure more costly than traditional surgery. Other limitations include an inability to view all portions of the abdomen. This may mean that a horse could need both standing laparoscopy and celiotomy under general anesthesia to complete the desired procedure. Other complicating factors of laparoscopy are associated mainly with the inherent high degree of difficulty of this technique and therefore can be avoided through attending specialized training programs and gaining experience. Accidental trauma to large body wall vessels or bowel during trocar placement and insufflation of gas out of the abdominal cavity (retroperitoneal insufflation) are some of these avoidable problems.