Anesthesia for general abdominal, urologic surgery

Anesthetic considerations for laparoscopic surgery

General anesthesia is typically used for most laparoscopic surgery. Although the use of spinal anesthesia for laparoscopic pyloromyotomy has been reported ( ; ; ), clinical experience with awake regional anesthesia during laparoscopic surgery is otherwise limited. In addition to the usual considerations for general anesthesia in a young infant, the induction of pneumoperitoneum, subsequent insufflation of CO ₂ , and requirements for extremes of patient positioning produce unique intraoperative challenges for the anesthesiologist. These challenges require close coordination and an open and ongoing line of communication with the surgeon.

Pneumoperitoneum is typically produced by insufflation of carbon dioxide through a Veress needle placed blindly or via a small incision. The potential for surgical misadventure and puncture or laceration of intraabdominal vessels exists during this stage. Open incision compared with blind placement of the Veress needle is felt to decrease the risk for vessel perforation, particularly in small infants and children with prior abdominal surgery. The induction of pneumoperitoneum produces significant physiologic disturbances secondary to a marked increase of intraabdominal pressure (IAP) and ongoing systemic absorption of carbon dioxide. On occasion, severe reflex bradycardia may be associated with the increase in IAP, particularly in infants. Sudden asystole in infants requiring cardiopulmonary resuscitation (CPR) has been reported, typically in association with gas embolus ( ). After induction of pneumoperitoneum, the Veress needle is replaced by a cannula and a video laparoscope is introduced. Additional ports can subsequently be placed as dictated by the surgical procedure, using direct observation via the first endoscope.

Cardiovascular consequences of elevated intraabdominal pressure

As IAP increases with CO ₂ insufflation, significant changes in cardiovascular physiology occur ( Box 33.3 ). Increasing IAP produces changes in preload, systemic vascular resistance, and cardiac output. When the minimal IAP needed by the surgeon for adequate exposure is used, these changes are generally tolerated quite well. However, increasing levels of IAP result in progressive physiologic perturbations that may have profound effects, particularly for some subsets of patients, most notably patients with preexisting respiratory compromise or congenital heart disease. Fortunately, because of the increased compliance of the abdominal wall, adequate laparoscopic operating conditions can often be obtained at lower levels of IAP than in adults.

Cardiovascular response to elevated IAP generally consists of a decrease in preload, increased systemic vascular resistance, and a potential decrease in stroke volume and cardiac output. In most cases, blood pressure is maintained or increased. Infants and young children generally manifest these changes at lower levels of IAP than adults. In adults, an IAP <15 mm Hg may actually be associated with an increase in preload because of increased venous return from the compression of splanchnic vessels. However, in children IAP levels as low as 12 mm Hg have been associated with both decreased cardiac index and left ventricular hypokinesis. Infants are generally more affected by lower levels of IAP than are older children, but as mentioned previously, may require less for adequate operating conditions ( ; ). An IAP <15 mm Hg appears to be tolerated in otherwise healthy children who weigh more than 5 kg, whereas neonates should be limited to an IAP of ≤12 mm Hg.

Respiratory effects of pneumoperitoneum and carbon dioxide insufflation

Elevated IAP limits diaphragmatic excursion with subsequent decreases in functional residual capacity (FRC) (see Box 33.3 ). This may lead to intrapulmonary shunting and decreased oxygen saturation. Higher peak inspiratory pressures are required to maintain a constant tidal volume. The additional burden of ongoing CO ₂ absorption will likely require adjustments in minute ventilation to maintain a reasonable level of end-tidal CO ₂ (ETCO ₂ ). Further changes in cardiovascular status are produced by the systemic absorption of carbon dioxide and subsequent sympathetic stimulation, which may result in further increases in systemic vascular resistance, heart rate, and blood pressure.

Cardiorespiratory changes related to patient positioning

In open surgical procedures, manual distraction of tissues or mechanical displacement with surgical retractors is used to improve visualization and obtain adequate surgical exposure. However, during laparoscopic surgery, gravity is commonly used to facilitate exposure and access for instrumentation. Consequently, a variety of occasionally extreme patient positions are often required by the surgical team with attendant physiologic consequences. Steep Trendelenburg positioning and subsequent cephalad shift of the diaphragm can further decrease pulmonary compliance and FRC and increase the chance of endobronchial intubation (see Box 33.3 ). The possibility of endobronchial intubation and/or bronchospasm induced by the endotracheal tube (ETT) affecting the carina may be initially overlooked and erroneously attributed to the expected changes in pulmonary compliance associated with the Trendelenburg position. The reverse Trendelenburg position is also commonly used. This position may improve respiratory function as the diaphragm settles into a more caudad position. However, diminished preload may produce a decrease in blood pressure. In practice, when the surgeon asks for extremes of positioning, it is reasonable to proceed in incremental stages and allow the surgeon the opportunity to assess the patient at less severe degrees of positioning before proceeding further. The patient must be securely restrained on the bed and meticulous attention paid to proper midtracheal position of the ETT. The ETT should be securely taped to the patient and visible at all times.

Impact of laparoscopy on unique patient physiology

Although most pediatric patients tolerate the physiologic trespass of laparoscopy with appropriate anesthetic care, some patients may be more vulnerable.

Patients with preexisting respiratory compromise

Although patients with significant respiratory compromise may benefit postoperatively from the laparoscopic approach, because of the issues detailed previously, the intraoperative course may be much more challenging than in patients with normal pulmonary physiology. In these patients, preoperative pulmonary function should be optimized and a preoperative discussion should be held as to whether laparoscopy will be tolerated. The preoperative discussion should also assess if an open approach is feasible if the laparoscopic approach is not tolerated once surgery commences.

Patients with congenital heart disease

As noted earlier, elevated IAP can have dramatic effects on cardiovascular indices such as preload, heart rate, and stroke volume. When combined with requirements for increased ventilator pressures in response to elevated IAP, cephalad shift of the diaphragm, and elevated levels of partial pressure of carbon dioxide (Pa co ₂ ), the potential for significant cardiovascular compromise in patients with preexisting congenital heart disease is apparent. Nonetheless, laparoscopy may be feasible in many of these patients, and successful laparoscopic surgery has been reported, even in patients with single-ventricle physiology ( ; ; ). A discussion with the patient’s cardiologist should be considered preoperatively, with specific attention paid to an estimation of how the patient may respond to changes in preload, afterload, hypercarbia, and hypoxemia. They may require an escalation in preoperative testing (repeat echocardiogram [ECHO], catheterization), monitoring (arterial catheter), and vasoactive support. As with many medically complex pediatric patients, surgical and anesthetic planning should be performed on a case-by-case basis.

Patients with elevated intracranial pressure

Increasing levels of carbon dioxide in addition to steep levels of Trendelenburg positioning represent obvious barriers to maintaining appropriate levels of intracranial pressure (ICP). In theory, concern exists that the increase in IAP may also interfere with proper shunt function in children with preexisting ventriculoperitoneal shunts. The surgeon may also encounter adhesions from the prior shunt surgery. Nonetheless, successful laparoscopic surgery in children with preexisting shunts has been reported in small case series ( ).

General principles of anesthetic management of pediatric laparoscopic surgery

The type of induction of anesthesia (mask vs. intravenous with or without neuromuscular blockade for intubation) should be guided by the patient’s physiology and comorbidities. Although the use of laryngeal mask airways (LMAs) has been described for laparoscopic surgery ( ), because of the previously discussed changes in respiratory physiology, endotracheal intubation with a cuffed ETT is most commonly used. Long periods of steep Trendelenburg positioning can on occasion produce inspissated secretions in the ETT. For this reason, it is advantageous to have appropriately sized suction catheters available for intermittent suctioning. The depth needed to ensure complete suctioning of the tube without producing damage to the tracheal mucosa or carina should be established before induction. The tip of the catheter should protrude very slightly from the end of the tube to ensure that suctioning does not tamponade secretions into the tip of the tube. A precordial stethoscope securely taped over the left chest is a useful aid to detect inadvertent endobronchial intubation during position changes. After induction of anesthesia, an oral gastric tube is placed to decompress the stomach, which may assist in optimizing ventilation and improve the surgeon’s ability to visualize the intraabdominal anatomy.

Neuromuscular blockade may be requested by the surgeon to facilitate exposure and may be useful in ventilator management of respiratory changes secondary to elevated IAP and steep Trendelenburg positioning. The use of nitrous oxide is controversial, in part because of the potential for bowel distention and emetogenic effects. In general, it is best to avoid using it. Because of the elevated incidence of nausea and vomiting after laparoscopic surgery, prophylactic use of antiemetic agents such as ondansetron and dexamethasone is typical. Intraoperative use of clonidine, ketorolac, and intravenous acetaminophen may reduce or eliminate the need for intraoperative narcotics. Laparoscopic repair is typically associated with less postoperative pain than open approaches, and typically neuraxial regional anesthesia is not indicated. In pediatric patients undergoing cholecystectomy, noted that port site injections were as effective as paravertebral blocks for postoperative pain. However, showed that ultrasound-guided transversus abdominis plane (TAP) block was superior to local infiltration in pediatric laparoscopic surgery. Postoperative discomfort can occasionally be severe. In addition to incisional pain, severe discomfort can be caused by residual gas in the abdomen, typically presenting as shoulder pain.