NM-299
Hourly 'wake-up tests' for severe idiopathic scoliosis: an anesthetic challenge.
Ausubel G, Liao B
Long Island Jewish Medical Center, New Hyde Park, NY, U.s.a.
Posterior spinal fusion is a common procedure for adolescent scoliosis. Due to the proximity of the surgical site to the spinal cord, intraoperative monitoring methods are used for recognition of neurological complications. Wake up tests require the anesthesiologist to reverse general anesthesia to see the response of the patient. Due to the inherent risks in waking up a prone patient during major surgery, this test is not commonly used.
This is a case of a 17-year-old female requiring posterior spinal fusion for severe scoliosis T4-T10 (133°), T11-L4 (83°). She presented to the emergency department with back pain and leg numbness. In the first two attempts, somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) were lost soon after the start time. During the second attempt, she was unable to move her lower extremities with a wake up test. The surgery was aborted twice.
In the third attempt she received an intravenous induction of general anesthesia. Arterial and central lines were placed. The anesthetic was unchanged from the two previous surgeries. Total intravenous anesthesia was maintained with propofol and remifentanil. A phenylephrine infusion was also started. The operating room was kept warm and two forced air warming devices were used. After prone positioning, SSEPs and MEPs diminished. The patient was placed in a fetal position which brought signals to baseline. Thirty minutes into the procedure, signals were lost and a wake up test was performed. The patient received dexamethasone and lidocaine, and the surgeon removed screws. The patient was able to move all extremities and the surgery proceeded. Two hours later, signals were lost and a wake up test was repeated. The patient moved all extremities. The phenylephrine infusion was increased to maintain the mean arterial pressure above 90. The surgery proceeded with the surgical and anesthesia teams immediately addressing any small change in the SSEP and MEP data. The patient was extubated and moved all extremities. She had an uneventful recovery with no recall of her wake-up tests.
Loss of signals during neuromonitoring is common. Studies report signal changes requiring intervention range from 21% to 1.5%. These authors conclude that most signal changes are false-positives; confirmed by wake-up tests. In cases with true injury, neuromonitoring enabled the team to intervene early, and most patients had full recovery within 18 months. In a high-risk spinal fusion patient, attention to detail is imperative to minimize risk of injury. Careful positioning of the patient, close titration of anesthetic, and constant discussion between specialists are essential to ensure a good outcome.
Cheh G., Lenke LG, Padberg AM, et al. Loss of spinal cord monitoring signals in children during thoracic kyphosis correction with spinal osteotomy - why does it occur and what should you do? Spine. 2008 (10)1:33.
Eager M, Jahangiri F, Shimer A, et al. Intraoperative neuromonitoring: lessons learned from 32 case events in 2095 spine cases. Evidence-Based Spine Care Journal. 2010 (2): 58-61.
Noonan KJ, Walker T, Feingberg JR, et al. Factors related to false-versus true-positive neuromonitoring changes in adolescent idiopathic scoliosis surgery. Spine. 2002 (8):825-30.
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