Current approach on spinal cord monitoring: the point of view of the neurologist, the anesthesiologist and the spine surgeon

Abstract

Optimal outcome in spine surgery is dependent of the coordination of efforts by the surgeon, anesthesiologist, and neurophysiologist. This is perhaps best illustrated by the rising use of intraoperative spinal cord monitoring for complex spine surgery. The challenges presented by neurophysiologic monitoring, in particular the use of somatosensory and motor evoked potentials, requires an understanding by each member for the team of the proposed operative procedure as well as an ability to help differentiate clinically important signal changes from false positive changes. Surgical, anesthetic, and monitoring issues need to be addressed when relying on this form of monitoring to reduce the potential of negative outcomes in spine surgery. This article provides a practical overview from the perspective of the neurophysiologist, the anesthesiologist, and the surgeon on the requirements which must be understood by these participants in order to successfully contribute to a positive outcome when a patient is undergoing complex spine surgery.

Fig. 1

During MEP stimulation, prevention of a tongue bite requires the insertion of three soft bite blocks in the mouth. One is placed between the molars on each side and one is placed centrally. These replace the use of a hard orophayngeal airway (e.g., Guedel oropharyngeal airway)

Fig. 2

Preop lateral X-rays of a 75-year-old patient with thoracolumbar kyphosis above a previous lumbar fusion (a). The planned procedure was a pedicle substraction osteotomy at L2 (dashed lines). Electrophysiology monitoring consists of SSEP, MEP, and EMG. During the closure of the osteotomy, the SSEP and MEP remained perfectly normal; however, on the right side the iliopsoas muscle started to fire with burst activity (b). The foramen containing the L1 and L2 nerve was checked further for possible compression. The foramen was further cleaned of soft tissue and the Iliopsoas decreased its firing with a train of activity for 5 min (c) and returned to baseline thereafter (d). Postoperatively, the patient has no complaints and the strength in the hip flexor was normal. Postoperative X-rays (e). In the oval the pedicle substraction osteotomy

Fig. 3

Patient with cervical myelopathy (a) while being positioned prone on the OR table, he experienced a decrease MEPs on the right side (b) compared to the left side that remained normal. Restoration of normal MEP amplitude was produced by increasing the mean arterial blood pressure (c)

Fig. 4

Triggered EMG: In the case of a polyaxial screw, the cathode should not be positioned on the crown of the screw (a) as it may lead to false negative (increased threshold), but rather on the hexagonal part of the screw itself (b)

Fig. 5

The insertion of EMG needles in the rectus abdominis muscles (in the case of thoracic pedicle screws for scoliosis surgery) will allow for the monitoring of the T6–T12 segmental nerves

Fig. 6

a Twelve-year-old boy with 120° curve will undergo posterior release, concave costoplasties and posterior instrumentation and fusion. b Throughout the surgery the SSEPs remained normal (baseline recordings are represented in blue and the current in purple). c During the insertion of the convex rod, an 80% decrease in the MEP amplitude in left foot was noted (yellow arrow). The baseline recording is in blue; the current recording is in purple. The right side (not shown) remained normal. d Return of baseline MEP in the foot 5 min after decreasing the spine correction. The blue (baseline) and the purple (current) recordings show equal amplitudes. e Postoperatively, the patient was neurologically intact