Carbon dioxide is the most widely used peritoneal distention medium, largely because the rapid absorption of CO2 in blood reduces the significance of gas emboli. If large amounts of CO2 gain access to the central venous circulation, if peripheral vasoconstriction occurs, or if the splanchnic blood ﬂow is decreased by excessively high intraperitoneal pressure, severe cardiorespiratory compromise may result.
The signs of CO2 embolus include sudden and otherwise unexplained hypotension, cardiac arrhythmia, cyanosis, and heart murmurs. The end-tidal CO2 level may increase, and findings consistent with pulmonary edema may manifest (103). Accelerating pulmonary hypertension may occur, resulting in right-sided heart failure.
Because gas embolism may result from direct intravascular injection through an insufﬂation needle, the proper placement of the insufﬂation needle must be ensured. Although the initial intraperitoneal pressure may be set at 20 to 30 mm Hg for port placement, it should be maintained at 8 to 12 mm for the rest of the case (104). The risk of CO2 embolus is reduced by careful hemostasis because open venous channels are the portal of entry for gas into the systemic circulation. The anesthesiologist should continuously monitor the patient’s color, blood pressure, heart sounds, heartbeat, and end-tidal CO2 to allow early recognition of the signs of CO2 embolus.
If CO2 embolus is suspected or diagnosed, the surgeon must evacuate the CO2 from the peritoneal cavity and place the patient in the left lateral decubitus position, with the head below the level of the right atrium. A large-bore central venous line should be inserted immediately to allow aspiration of gas from the heart. Because the findings are nonspecific, the patient should be evaluated for other causes of cardiovascular collapse.
Cardiac arrhythmias occur relatively frequently during laparoscopic surgery and are related to a number of factors, the most significant of which are hypercarbia and acidemia.
Early reports of laparoscopy-associated arrhythmia were associated with spontaneous respiration; therefore, most anesthesiologists adopted the practice of mechanical ventilation during laparoscopic surgery. The incidence of hypercarbia is reduced by operating with intraperitoneal pressures at levels less than 12 mm Hg (105).
The risk of cardiac arrhythmia may be reduced by using NO2 as a distending medium (see the preceding discussion in “Peritoneal Access”). Although NO2 is associated with a decreased incidence of arrhythmia, it is insoluble in blood and, therefore, its use may increase the risk of gas embolus. External lifting systems avoid the complication of hypercarbia and can provide protection against cardiac arrhythmia (106).
Hypotension can occur because of decreased venous return secondary to very high intraperitoneal pressure, and this condition may be potentiated by volume depletion. Vagal discharge may occur in response to increased intraperitoneal pressure, which can cause hypotension secondary to cardiac arrhythmias (106). These side effects should be considered when performing surgery on patients with preexisting cardiovascular disease.
Gastric regurgitation and aspiration can occur during laparoscopic surgery, especially in patients with obesity, gastroparesis, hiatal hernia, or gastric outlet obstruction. In these patients, the airway must be maintained with a cuffed endotracheal tube, and the stomach must be decompressed (e.g., with a nasogastric tube). The lowest necessary intraperitoneal pressure should be used to minimize the risk of aspiration. Patients should be moved out of the Trendelenburg position before being extubated. Routine preoperative administration of metoclopramide, H2-blocking agents, and nonparticulate antacids reduces the risk of aspiration.