“aspiration test,” “hiss sound test,” “waggle test,” and “hanging drop test.” Unfortunately, most of these tests have been shown to be unreliable [5]. In fact, waggling the Veress needle from side to side was considered contraindicated in clinical guidelines for MD surgeons because of the risk of organ laceration [6]. Two studies have looked at the diagnostic accuracy of tissue impedance measurement interpretation for correct Veress needle placement in cats and dogs [7, 8]. In dogs, the impedance measurement had a 89.7% sensitivity, 100% specificity, and 90% accuracy [7]. In cats, tissue impedance measurement resulted in 94.7% sensitivity, 20% specificity, and 79.2% accuracy [8]. The differences between cats and dogs were thought to be due to the overdeveloped retroperitoneal fat pad in cats as well as their small size. A recent study also looked at not only different Veress needle types but also different positions for safe placement into the abdomen to decrease penetration to abdominal organs [9]. The results of this study recommended placement of the Veress needle at the 9th intercostal space over para‐, supra‐ and subumbilical positions [9].
Figure 4.16 Veress needle.
Source: © 2014 Photo courtesy of KARL STORZ SE & CO, KG.
Figure 4.17 Close up photograph of the specialized tip to a Veress needle.
Source: © 2014 Photo courtesy of KARL STORZ SE & CO, KG.
After an adequate volume of gas has been insufflated, the Veress needle is removed. In the blind technique for initial trocar insertion, a bladed trocar or trocar with a sharp obturator is inserted through an adequately sized incision. Trocar assemblies with sharp obturators are most commonly used in veterinary medicine; laparoscopic surgeons in human medicine tend to use bladed trocars. Bladed trocars are equipped with a spring‐loaded safety shield that retracts when passed through the abdominal wall. This is often accompanied by an audible click as the blade retracts. Advancement of the trocar assembly is stopped at this point, and the bladed trocar or sharp obturator is removed from its outer cannula. The laparoscope can then be inserted to confirm the successful placement of the cannula in the peritoneal cavity and to rule out intraabdominal injury from either Veress needle or trocar insertion. If the cannula is appropriately located, the insufflation tubing is connected to the gas port of the cannula, and insufflation to the predetermined pressure occurs. The remaining cannulas are then placed under direct visualization.
Direct Insertion Technique
In the direct insertion technique, the primary cannula–trocar assembly is placed without preinsufflation. This technique is not regularly performed in veterinary medicine but can be performed with either a bladed trocar and a blind technique or an optical trocar under some measure of direct visualization. Theoretical advantages include decreased time to establish abdominal laparoscopic access, but potential disadvantages may include a higher rate of trocar‐related intraabdominal injuries. Several published series evaluating the direct trocar placement technique have demonstrated that very low rates of injury are possible [10]. For inexperienced surgeons, the direct access technique is likely associated with unnecessary increased risk compared with alternative techniques [4, 11].
Optical trocar assemblies can also be placed with a direct technique. A gradual twisting motion is used, and distinct layers of the abdominal wall can be seen during entry.
Hasson Technique
In an effort to decrease the incidence of injuries associated with the blind penetration of the abdominal cavity during laparoscopy, Hasson [12] proposed a mini‐laparotomy technique. He developed a reusable device similar to a standard laparoscopic port with a corkshaped sleeve on the outside. The sleeve could be slid up or down on the cannula shaft depending on the thickness of the patient's abdominal wall [11]. Sutures in the fascia were used to anchor the outer sleeve and to create an airtight seal. Hasson‐type cannulas that are fixed to the abdominal wall between a balloon and a dense foam cuff are also now commercially available.
In the open technique, the peritoneal cavity is entered under direct visualization. Theoretical advantages to the open technique may include a decreased likelihood of injury to adherent bowel or major vascular injuries during initial trocar insertion. Potential disadvantages may include increased operative time (especially in obese patients) and an increased risk of late port‐related complications such as hematoma, wound infection, or hernia [13]. Leakage of gas around the cannula is occasionally a problem. If resulting in a loss of pneumoperitoneum, sutures may be placed around the cannulas to act as a purse string.
Alternatively, a balloon‐tipped fixation trocar or a dilating “Olive” can be added to the trocar can be placed to seal the leak [1, 14].
Types of Trocar Assemblies
Multiple types of cannula–trocar assemblies are available in human and veterinary medicine. They can be divided into reusable or single use, rigid or flexible, and by the various fixation methods they used. Various designs of each type are available. Although the initial cost of a reusable trocar assembly is high, the per‐use cost is significantly less than that of disposable types. However, reusable trocars can be difficult to sterilize because of the number of small parts that comprise the valve and gas inlet assemblies. Additionally, over time, the tips can become blunt and the valves leaky and stiff. Some manufacturers now offer a combination type using a reusable sleeve and piercing stylus in conjunction with a single‐use valve assembly.
Disposable Trocar Assemblies
Disposable cannulas are very common in human medicine, but their cost limits their use in veterinary medicine. There are multiple different types of disposable trocars, including bladeless trocars with safety shields (Figure 4.18), inflatable flanges to help with retention, and optical trocars (Figure 4.19). Optical trocars have a transparent plastic sleeve, into which the laparoscope may be fitted before insertion of the trocar, enabling the surgeon to monitor the passage of the instrument through the layers of the abdominal wall. The internal surface of the sleeve must be nonreflective to avoid light from the laparoscope interfering with the surgeon's view.
Nondisposable Trocar Assemblies
Reusable trocar assemblies are the most common type used in veterinary medicine. These include smooth and threaded, a.k.a. Ternamian, stainless steel trocars (Figures 4.20 and 4.21). These have the advantages of being easy to clean and sterilize with a long shelf life. The plastic valves that attach to these trocars are also autoclavable, but they eventually wear or crack over time. The threaded cannulas can be used without an obturator as the distal end is shaped to penetrate the body wall and screw into place, avoiding the need for retention sutures. These may be difficult to place through very thick tissue planes without appropriate insufflation pressures or without an appropriately sized skin incision.
