Before insufﬂation, the operator should try to detect whether the insufﬂation needle was malpositioned in the omentum, mesentery, blood vessels, or hollow organs such as the stomach or bowel. The most direct approach is to use a specially designed insufﬂation needle that has an integrated cannula through which a small diameter (2 mm) laparoscope can be passed to visualize the point of entry. Otherwise, indirect methods are necessary. Using a syringe attached to the insufﬂation needle, blood or gastrointestinal contents may be aspirated. To facilitate this examination, a small amount of saline may be injected into the syringe. If the needle is appropriately positioned, negative intra-abdominal pressure is created by lifting the abdominal wall. This negative pressure may be demonstrated by aspiration of a drop of saline placed over the open, proximal end of the needle or, preferably, by using the digital pressure gauge on the insufﬂator.
4.
Additional signs of proper placement may be sought after starting insufﬂation. The intra-abdominal pressure reading should be low, reﬂecting only systemic resistance to the ﬂow of CO2. Consequently, there should be little deviation from a baseline measurement, generally less than 10 mm Hg. The pressure varies with respiration and is slightly higher in obese patients. The earliest reassuring sign is the loss of liver “dullness” over the lateral aspect of the right costal margin. This sign may be absent if there are dense adhesions in the area, usually the result of previous surgery. Symmetric distention is unlikely to occur when the needle is positioned extraperitoneally. Proper positioning can be shown by lightly compressing the xiphoid process, which increases the pressure measured by the insufﬂator.
5.
The amount of gas transmitted into the peritoneal cavity should depend on the measured intraperitoneal pressure, not the volume of gas inﬂated. Intraperitoneal volume capacity varies significantly between individuals. Many surgeons prefer to insufﬂate to 25 to 30 mm Hg for positioning the cannulas, and a body of evidence exists supporting this approach (86). This level usually provides extra volume and enough counter pressure against the peritoneum, facilitating introduction of the cannula and potentially reducing the chance of bowel or posterior abdominal wall and vessel trauma. After placement of the cannulas, the pressure should be dropped to 10 to 15 mm Hg, which reduces the risk of subcutaneous insufﬂation leading to crepitus and essentially eliminates hypercarbia or decreased venous return of blood to the heart (84,86,87).
Laparoscopic cannulas (or ports) allow the insertion of laparoscopic instruments into the peritoneal cavity while maintaining the pressure created by the distending gas (Figs. 23.7 and 23.8). Cannulas are hollow tubes with a valve or sealing mechanism at or near the proximal end. The cannula may be fitted with a Luer-type port that allows attachment to tubing connected with the CO2 insufﬂator. Larger-diameter cannulas (8 to 15 mm) may be fitted with adapters or specialized valves that allow the insertion of smaller-diameter instruments without loss of intraperitoneal pressure.
The obturator is a longer instrument of slightly smaller diameter that is passed through the cannula, exposing its tip. Most obturators are called trocars because their tip is designed to penetrate the abdominal wall after the creation of an appropriately sized skin incision. Many disposable trocar-cannula systems are designed with a safety mechanism—usually a pressure-sensitive spring that either retracts the trocar or deploys a protective sheath around its tip after passage through the abdominal wall. None of these protective devices makes insertion safer, and they all increase the cost of the equipment.