Intraoperative Considerations in the AS Patient
1. Anesthetic Choice: In this patient undergoing repair of a large umbilical hernia, general endotracheal anesthesia (GETA) is likely to be used, as neuromuscular blockade can be given to facilitate relaxation of the abdominal wall for hernia repair. Some surgical procedures can be done under regional anesthesia including spinal anesthesia, combined spinal-epidural anesthesia, or via nerve block. Insertion of needle and/or catheter placement for neuraxial anesthesia in patients with severe spinal deformity such as AS can be challenging. Patients receiving spinal anesthesia for spine surgery must be assessed for ability to tolerate the prone position, as well as range of motion of the neck, shoulders, and arms.
2. Airway Management: Airway management in patients with AS may be complex and must be evaluated and anticipated in advance. Patients with advanced AS may have restricted neck or jaw movement that may make head positioning for endotracheal intubation difficult. Clinically significant subluxation of the atlantoaxial joint (C1-C2) can also occur in AS, and assessing for any signs of instability is crucial in the advanced planning of a safe anesthetic induction and intubation.
3. Operative Positioning Positioning for surgery is important to avoid excessive pressure on any bony prominences or compression of peripheral nerves. Patients with severely anyklosed spines can have asymptomatic vertebral fractures that must be considered vis-à-vis patient positioning. Uveitis is the most common extra-articular complication of AS; therefore, efforts should be made to protect the eyes when patients are under general anesthesia. Additionally, when surgery is done in the prone position, special attention must be given to protecting the eyes from direct pressure.
Special Considerations for Spinal Surgery in the Patient With AS
1. Anesthetic agents and neuromuscular blockade can affect intraoperative neuromonitoring and, as such, total intravenous anesthesia is sometimes used.
2. When estimated blood loss during spinal surgery is high, patients can consider preoperative autologous blood donation. Techniques of induced hypotension to prevent blood loss are generally not recommended due to issues with end-organ ischemia. Patients with spinal stenosis are at further risk for spinal cord anesthesia; therefore, maintenance of blood pressure close to baseline level is usually indicated.
3. A rare complication of spinal fusion surgery is vision loss as a result of ischemic optic neuropathy, central retinal artery occlusion, and retinal vein occlusion.