Anesthesia for Abdominal Surgery - Anesthetic Considerations for Specific Abdominal Procedures
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Laparoscopic Surgery. Laparoscopic approaches are applied to an increasing number of surgical procedures, including appendectomy, cholecystectomy, hernia repair, fundoplication, nephrectomy, weight loss surgery, liver resection, and colon resection. Benefits of laparoscopic surgery include smaller incision, reduced postoperative pain, decreased postoperative ileus, early ambulation, shorter hospital stay, and earlier return to normal activities.
- Operative technique involves intraperitoneal insufflation of CO2 through a needle inserted into the abdomen via a small infraumbilical incision until intra-abdominal pressure reaches 12 to 15 mm Hg. Patient positioning is used to facilitate operative exposure: steep reverse Trendelenburg improves visualization of upper abdominal structures; Trendelenburg helps to visualize lower abdominal structures.
- Anesthetic considerations
- Hemodynamic changes associated with laparoscopy are influenced by the intra-abdominal pressure needed for the creation of pneumoperitoneum, volume of CO2 absorbed, the patient's intravascular volume status, positioning, and anesthetic agents used. Generally, intra-abdominal pressures of 12 to 15 mm Hg are well tolerated in healthy patients. Mean arterial pressure and systemic vascular resistance usually increase with the creation of pneumoperitoneum in healthy patients; cardiac output is unaffected. Patients with coexisting cardiac disease may develop decreased cardiac output and hypotension associated with pneumoperitoneum. Absorption of CO2 across the peritoneal surface can cause hypercarbia, resulting in sympathetic nervous system stimulation and increased blood pressure, heart rate, and cardiac output.
- The reduction in FRC associated with GA is compounded by the creation of pneumoperitoneum. FRC may be further compromised by the Trendelenburg position and patient body habitus. Frequent recruitment and high PEEP may be necessary to treat alveolar collapse.
- Because patients may be positioned in steep Trendelenburg or reverse Trendelenburg, changes in venous return must be anticipated and monitored. Also, frequent attention must be given to patients' arms to prevent brachial plexus injury.
- Temperature control. Heat loss may occur from intraperitoneal insufflation of cold gas.
- Embryonic channels between the peritoneal and pleural/pericardial cavities may open with increased intraperitoneal pressure, resulting in pneumomediastinum, pneumopericardium, and pneumothorax. Diffusion of gas cephalad from the mediastinum can lead to subcutaneous emphysema of the face and neck.
- Vascular injuries secondary to the introduction of the needle or trocar can produce sudden blood loss and necessitate conversion to an open procedure to control bleeding.
- Venous gas embolism is rare but may occur on induction of pneumoperitoneum if the needle or trocar is placed into a vessel or an abdominal organ or if gas is trapped in the portal circulation. The high capacity of blood to absorb CO2 and its rapid elimination in the lungs increases the margin of safety in case of accidental IV injection of CO2. Insufflation of gas under high pressure can lead to a “gas lock” in the vena cava and right atrium; this will decrease venous return and cardiac output and produce circulatory collapse. Embolization of gas into the pulmonary circulation leads to increased dead space, ventilation/perfusion mismatch, and hypoxemia. Systemic gas embolization (with occasionally devastating effects on cerebral and coronary circulation) can occur with massive gas entrainment or via a patent foramen ovale. Treatment consists of immediately stopping gas insufflation, placing the patient on 100% O2 to relieve hypoxemia, and positioning the patient in steep head-down left lateral decubitus to displace gas from the right ventricular outflow tract (see Chapter 19), open up IV fluid and inotropic RV support.
- Anesthetic management. Although laparoscopy procedures have been performed under neuraxial techniques, GA is usually required for laparoscopy. Creation of pneumoperitoneum and steep Trendelenburg positioning can compromise ventilatory function and is not tolerated in an awake patient. A urinary bladder catheter and a gastric tube are inserted (usually after induction of GA) to improve visualization and reduce the risk of trauma to bladder and stomach with trocar insertion.