What is the “wake-up test”?
A preoperative discussion should occur with the patient concerning the details of the wake-up test and to dispel any fears of awakening during the surgery and/or experiencing pain.
The wake-up test is used to assess the anterior spinal cord (motor) pathway. This test is not reflective of the posterior spinal cord (sensory) pathway. The wake-up test is performed intraoperatively following spine instrumenta-tion. Adequate notice should be given to the anesthesiologist by the surgeon, so as to coordinate the timing of “lightening the anesthesia” to an appropriate level so that the patient can follow commands. The wake-up test can present a challenge for the anesthesiologist, with regard to the balance that must be maintained between the patient performing some level of activity but without excessive movement.
The wake-up test begins by assessing the level of the patient’s comprehension by asking the patient to squeeze the anesthesiologist’s hand. If the response is acceptable, then the patient is asked to move their feet. If the patient is unable to move their feet, the amount of spinal distraction must be decreased and the test is repeated. Excessive dis-traction can compromise spinal cord blood flow leading to ischemia and may result in postoperative paraplegia. Following completion of the wake-up test, anesthesia is deepened with an intravenous hypnotic agent, benzodi-azepine, and the anesthesiologist’s neuromuscular blocking agent of choice.
The wake-up test has its limitations. It evaluates the patient’s motor function at only one point in time. It has no bearing on the time following the performance of the test, when spinal cord injury remains a possibility. The wake-up test is not appropriate for young children or the cognitively impaired patient. Excessive patient movement may promote self-extubation, bleeding, air embolus, or disruption of the spinal instrumentation. Somatosensory evoked potential (SSEP) monitoring can be used as an adjunct to the wake-up test. SSEP offers the advantage of continuous monitoring.