The various aspects of different laparoscopic access techniques can be grouped under the acronym MIS: M, method (blind vs. open); I, access instrument (push vs. pull trocar); and S, access site (umbilical, retrocostal, or other). Regardless of the method, instrument, and site used for abdominal access, the surgeon must carefully consider the tissue layers to be traversed, the instrument design, and the penetration force.¹² Most surgeons hold a conventional trocar and cannula assembly with the dominant hand and apply significant linear force generated by the shoulder and trunk muscles toward the body part being accessed. This linear propulsion dictates that the instrument design involves a pointed or sharp end to decrease the entry force necessary to transect the different tissue layers during port placement.¹³ Additionally, when the peritoneal layer has been transfixed, a sudden loss of resistance is registered. A more sudden and uncontrolled loss of resistance induces a greater extent of trocar overshoot and hence a greater likelihood of inadvertent injury.

The trocar type, trocar or Veress needle (VN) handling technique, and local anatomic characteristics of the patient can contribute to displacement of the peritoneum during abdominal entry. This effect, known as peritoneal tenting or the curtain effect, can have deleterious consequences if the trocar or VN is inadvertently advanced to a deep subperitoneal location without reaching the intraabdominal cavity.

The first access, whether blind or open, should be performed in an area with low tissue resistance to limit the linear force necessary for entry into the abdominal cavity. Thus, in both human and small animal laparoscopic techniques, the first entry is generally performed along the linea alba in the periumbilical region. Use of this location also guarantees that abdominal wall vessels will not be encountered during penetration. Although the placement of ports for various instruments is considered to be essential, no consensus on trocar–cannula assembly placement, even for the same procedures, has been reached. The explanations of port location among various studies are often vague and leave substantial room for error, especially in the hands of novice surgeons. This was illustrated in one study in which the performance of two different trocar placement techniques described in the veterinary literature was tested among 64 students in their final year of veterinary medical school. Correct placement was achieved by only 40.8% of the students. In contrast, after introducing a mapping system (a coordinate system of the abdominal wall), correct placement was achieved by 95% of the students. These findings support the need for development of an accurate system with which to adequately locate the ports.¹⁴

A trocar is a pen-shaped instrument with a sharp triangular point at one end. This pointed end is typically located within a hollow tube, known as a cannula, and is used to create an opening into the body through which the cannula may be introduced. This process provides a surgical access port. Such devices have been in use for thousands of years. A gas-tight valve is usually located at the top of the trocar to allow for insertion and removal of instruments during a procedure without permitting escape of the insufflated CO₂. The appearance of the pointed pyramidal tip can differ; the outer diameter typically ranges from approximately 2 to 15 mm but may even reach several centimeters for placement of specialized instruments such as staplers or tissue morcellators. The trocar may also have either a blunt or cutting tip (bladed trocar). Bladed trocars reduce the amount of force needed to pass the instrument through the abdominal wall. For increased safety, some designs include a spring-loaded plastic shield that automatically covers the blade as it enters the abdominal cavity. The use of these spring-loaded safety shields is generally recommended in veterinary medicine because the distance between the abdominal wall and the spleen, aorta, or other large vessels is relatively small in veterinary patients. Conical tips can be either metal or plastic and require the creation of a small initial incision using a scalpel. They pass through the tissues of the abdominal wall by stretching rather than cutting the tissues. This leads to improved sleeve retention. However, both blunt and conical tips require a higher linear force to enter the abdomen.

Trocar–cannula assemblies may be for single-patient-use, reusable, or a hybrid. Reusable trocars and cannulae, or those with reusable components, may be the most economical choice for veterinary clinical practice. However, many veterinary practitioners who perform minimally invasive procedures currently reprocess and sterilize laparoscopic instruments, including trocars and cannulae, for reuse.¹⁵