Spine surgery presents a set of challenges, including prolonged procedures, prone positioning, fluid shifts, and manipulations adjacent to nerves and blood vessels. Although most patients undergo elective procedures, a significant number present with acute injuries and neurologic compromise that require emergent interventions. Spinal conditions treated with surgical intervention include intervertebral disc disease, spinal stenosis, scoliosis, spondylosis, tumors, and trauma.

1. Acute spinal cord injury can present with neurogenic shock, usually with lesions above T6, characterized by hemodynamic instability secondary to the resultant sympathectomy. Resulting vasodilation causes hypotension and increased heat loss. After the acute phase of spinal shock, autonomic dysreflexia predominates, with hypertension and bradycardia, myocardial ischemia, retinal/cerebral hemorrhage, and seizures.

2. Cervical spine injury is commonly associated with head trauma. Notable lesions are C5 injury presenting with deltoid, biceps, brachialis, and brachioradialis weakness, partial diaphragmatic paralysis, and C4 lesions, which necessitate artificial respiration to be survivable.

3. Prolonged immobility secondary to paraplegia/quadriplegia results in increased extrajunctional receptors at the neuromuscular junction. Succinylcholine is therefore contraindicated after 48 hours after spinal cord injury secondary to risk of hyperkalemia.

1. In addition to the standard concerns for securing an airway, additional caution is needed for patients with cervical spine injuries to prevent or not worsen damage to the spinal cord.

2. For severely unstable cervical spines, awake fiberoptic intubation and positioning should be considered. The process is explained to the patient in advance. A neurologic exam is done immediately before intubation. With minimal or no sedation and adequate topicalization of the airway with local anesthetic, the patient is intubated. The patient is then asked to move their fingers and toes as a method to confirm that no changes in the neurologic examination have occurred. With assistance, the patient then moves to the OR table in the desired position. Once a postposition neurologic examination is made, the patient is then anesthetized.

3. Manual inline stabilization is assumed to limit cervical range of motion by a second provider holding the shoulders and head to limit motion of the neck. Although this technique has traditionally been used and is a component of Advanced Trauma Life Support (1), it has been questioned since it may potentially increase craniocervical motion and worsen the laryngoscopic view (2).

4. In emergency situations where there is no evidence of facial/basal skull fractures, blind nasotracheal intubation is an acceptable option.

1. The physiologic changes associated with prone positioning include depressed cardiac index, inferior vena cava obstruction, increased
functional residual capacity, and pulmonary blood flow and lung ventilation redistribution to dependent areas (3).

2. The eyes, abdomen, genitalia, and breasts should be free of pressure, and the stomach and bladder should be decompressed with an orogastric tube and urinary catheter. Malpositioning of the arms can result in vascular and brachial plexus injury, specifically increased pressure within the cubital tunnel with elbow flexion greater than 130 degrees. Complications such as shoulder dislocation, facial edema, eye injuries, and peripheral nerve palsy have been reported. The greatest risk for cord compromise is when the patient is turned from supine to prone after intubation, while attempting to maintain spinal cord alignment with cervical spine injury. Intraoperative neurologic monitoring is useful for such positional changes.

1. Intraoperative monitoring of the integrity of the spinal cord involves electrophysiologic monitors that detect changes suggestive of ischemia. The different methods of monitoring include epidural electrodes, somatosensory-evoked potentials (SSEPs), motor-evoked potentials (MEPs), electromyography, transcranial electrodes, electrical stimulation of screws, neuromuscular junction monitoring, electrical impedance testing, stimulation of motor spinal roots, F-responses, H-reflexes, and testing specific reflexes. It is recommended to combine methods when risk of ischemia is increased (4). The use of monitoring has been demonstrated to reduce postoperative neurologic morbidity and even identify real-time compromise with surgical manipulation (i.e., retractor placement) (5)

2. Somatosensory- (SSEPs) and motor-evoked (MEPs) potentials are two important modalities for neural monitoring where the amplitude and latency are measured. Peripheral nerves at distal sites are stimulated to obtain SSEPs, and the blood supply for these nerves is largely the posterior spinal arteries. MEPs monitor spinal cord pathways, and the corresponding blood supply is the single anterior spinal artery.

3. The intraoperative “wake-up test” assesses motor function. After the patient has received appropriate narcotic analgesia and the neuromuscular blockade is reversed, the anesthetic is reduced enough for the patient to respond to the commands to move hands and feet.

4. Confounders that may artificially increase latency or decrease amplitude of transmission that may be suggestive of ischemia include nonspecific physiologic changes and dose-dependent effect of inhaled anesthetics, including nitrous oxide. Desflurane and N₂O will still allow some degree of intraoperative monitoring (6,7). Propofol, remifentanil, ketamine, midazolam, and etomidate are recommended to allow successful MEP monitoring (8). For more details on neural monitoring, see the chapter titled Neural Monitoring.

Decortication during instrumentation and fusion of the vertebral column accounts for the majority of blood loss during spinal surgery. The factors predicting increased blood loss and the need for transfusion include surgical technique, type of surgery (fusion versus laminectomy), low preoperative hemoglobin, tumor surgery, increased number of levels fused, and underlying pulmonary disease (9). Factors likely to decrease blood loss include acute normovolemic hemodilution, use of the Jackson table, hypotensive techniques, and the use of cell saver. Monitoring for development of intraoperative coagulopathy includes testing PT/INR and PTT.