Instrument Design

Instruments for minimally invasive surgery (MIS) consist of the same basic parts as traditional instruments (Figure 4.1). Their shafts are long and thin to allow them to pass through an instrument portal into a body cavity. Some shafts are insulated to allow for monopolar or bipolar electrosurgical applications. If using an insulated shaft with electrosurgery, it is very important to regularly inspect the shafts for cracks or wear. Defects in the shaft insulation may lead to inadvertent electrical burns to other tissues. Shafts come in straight, articulating, and roticulating designs. Straight instruments are the basic instruments for MIS and are most commonly used for novice surgeons and in multiple-port surgery. Whereas articulating shafts bend in a single plane, roticulating shafts are able to rotate and bend in multiple planes, more accurately mimicking the motion of the human wrist. Articulating and roticulating instruments are used with multiple-port surgery but are also particularly advantageous for single-port surgery because they allow for easier visualization of tissues and avoid conflict with the telescope and with each other.

Most instruments have either ratcheted or nonratcheted ringed handles (Figure 4.2). Ratcheted handles lock via one of several ratchet mechanisms, depending on the manufacturer. Laparoscopic needle holders, however, have a straight handle design with either a hemostat-style or a disengageable ratchet locking mechanism to allow for easier manipulation of suture and needle within a body cavity. Ringed handles are held in the same tripod manner as traditional instruments, with the thumb and ring finger in the rings and the index finger stabilizing the shaft. A dial that is easily reached by the index finger allows for 360-degree rotation of the shaft around its longitudinal axis. Shaft rotation allows for optimal positioning of the instrument jaws when working within a confined space. Handles intended for use with insulated shafts for monopolar or bipolar electrocoagulation also have a high-frequency connector for application of an electrical current from an electrosurgical generator. Monopolar and bipolar handles and shafts are distinct from one another and cannot be interchanged.

Instrument jaws come in a variety of shapes and sizes according to their intended function as graspers, dissectors, scissors, retractors, biopsy forceps, or needle holders. The working end of an endoscopic instrument may have a single- or double-action mechanism (Fig­ure 4.3). With single-action instruments, one side of the jaw is hinged so that it opens and closes against a stationary opposing jaw. Double-action working ends are hinged in both jaws, allowing both sides to open and close and resulting in a wider and often stronger grasp.

Both disposable, single-use instruments and reusable instruments are available. For veterinary practice, reusable instruments are more economical. Early instrument designs may be more difficult to adequately clean and sterilize than more current designs, a fact that should be considered when purchasing laparoscopic equipment. Instruments are available as single-piece or as modular units, depending on the manufacturer, and can be made of high-grade plastic or stainless steel. There are benefits for each design type. Single-piece instruments avoid the possibility of mismatching components; however, as mentioned previously, older models may be difficult to decontaminate. Newer designs have portals that allow for cleaning of the shaft lumen. They also avoid nooks and crevices that are difficult to reach, making cleaning and decontamination easier. Modular units allow for the use of a variety of shafts and working ends with the same handles. Additionally, individual components are easier to thoroughly clean, can be sterilized separately or as a complete instrument, and can be replaced if they break rather than replacing the entire instrument.

Regular endoscopic instruments come in 5- and 10-mm diameters. For most small animal applications, 5-mm instruments are adequate. Common exceptions are the use of 10-mm Babcock or Duval forceps for grasping thicker tissues such as the stomach wall. Mini-laparoscopic instrumentation is now available for small dogs and cats weighing less than 10 kg. These come in 2-, 2.3-, and 3-mm-diameter sizes, depending on the manufacturer. The available shaft length depends on the instrument diameter and should be chosen based on patient size, with shorter shafts used for small patients and longer shafts for large or obese patients. Using a shaft that is either too long or too short for the patient can be awkward for the operator and can inhibit the ability to reach tissues inside the body cavity. Short and long shaft lengths vary by manufacturer but are similar. In general, 5- and 10-mm instruments range from 33 to 36 cm for the short length and from 43 to 45 cm for the long length. Mini-laparoscopy instruments range from 20 to 30 cm in length.

Forceps

Grasping forceps are used to grasp tissue for stabilization, relocation, or hemostasis. Noncrushing forceps most commonly used in small animal laparoscopy and thoracoscopy are Babcock and Duval forceps (Figure 4.4). The jaws of endoscopic Babcock forceps are identical to their open surgical counterparts. They are most commonly used to grasp and manipulate the pyloric antrum during laparoscopic-assisted gastropexy. Duval forceps are similar to Babcock forceps except that the jaws are slightly longer and offer a more aggressive grasp. For both Babcock and Duval forceps, a double-action mechanism allows for a wider grasp to include more tissue and better prevent slipping.

Many other types of grasping instruments are provided by the different manufacturers (Figure 4.5A). Basic designs include toothed graspers (varying number of teeth at the end of the instrument jaw), fenestrated graspers (a fenestrated slit is present down the length of the jaw), DeBakey graspers, Allis graspers, alligator graspers (pronounced transverse serrations for a stronger tissue grip), bowel graspers (longitudinal serrations, similar to a DeBakey), straight and curved atraumatic graspers (for grasping and removing hollow organs), and bullet-nosed graspers (blunt-nosed, atraumatic jaws for grasping delicate tissues). Although technically described as dissecting forceps, Kelly forceps can also be used to carefully grasp and move tissues such as the proper ligament during laparoscopic ovariectomy. Grasping forceps are usually placed on locking handles to facilitate a more secure grip of tissues during surgery.

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