Scenario 1

SITUATION:
Your patient has been positioned for an anterior cervical discectomy, fusion and plating.

• The surgeon is using 15 lbs. of traction connected to the Gardner Wells head tongs.
• A rolled towel was placed under the shoulders to increase the cervical lordotic curve.
• To improve exposure the surgeon has applied 3" tape to the shoulders which is attached to the end of the OR table.

Shortly after positioning is completed you notice a 50% reduction in the amplitude of the cervical and cortical response along with a prolongation of the latencies by greater than 10% on the left side only with bilateral ulnar nerve stimulation. You immediately alert the surgeon.

What is the most likely cause of this change?
A. Excessive traction on the cervical spine
B. The traction caused hyperextension of the neck
C. Excessive traction on the brachial plexus
D. Ischemia as a result of the blood pressure cuff

Scenario 2

SITUATION:
A lateral approach for an L2 vertebrectomy and L1 - L3 stabilization and fusion was performed on a 40 year old female.

• The patient was positioned in a left lateral decubitus with the table jack-knifed.
• The technologist used somatosensory evoked potentials to monitor the tibial and ulnar nerves and electromyography to monitor for spontaneous activity.
• All studies were stable throughout dissection and decompression.
• The anesthetic regime included nitrous oxide 50% and desflurane at 3% end tidal with a propofol infusion

Continued stimulation of the tibial nerves generating cervical and cortical potentials began to show a gradual prolongation of latency exceeding 10% of the baseline studies, the amplitude did not significantly change. Potentials generated with ulnar nerve stimulation, acting as a control, showed no significant deviation from baseline.

What is the most likely cause of this change?
A. Inadequate blood flow to the spinal cord
B. Spinal cord compression
C. Anesthetic variations
D. Hypotension

Scenario 3

SITUATION:
A 46 year old female is positioned supine for an anterior lumbar discectomy and interbody fusion at L4-5.

• Pulse oximeters attached to the great toes bilaterally showed 99% oxygen saturation post induction.
• Blood pressure was maintained around 135/80 and core temperature 35.7 C.

Prior to beginning the discectomy no oxygen saturation could be recorded from the left lower extremity. Bilateral tibial SSEP's recorded from the C7-T1 interspinous space, sagittal and ipsilateral parietal scalp showed no significant baseline deviation.

What is the most likely cause of this change?
A. Anesthetic variations
B. Patient positioning
C. Prolonged exposure
D. Occlusion of the left femoral artery