The alert applying value of somatosensory evoked potential examination in total vertebral osteotomy.

Abstract

Objective To investigate risk factors related to changes in somatosensory evoked poten-tials (SEPs) in total vertebral osteotomy. Methods From April 2002 to December 2007, 118 patients with severe kyphoscoliosis deformity were treated with posterior total vertebral osteotomy. There were 68 males and 50 females with the mean age of 29 years (range, 4-73years). The pre-operative scoliosis Cobb angle was 70° (40°-130°) and kyphosis Cobb angle was 78° (32°-147°). The preoperative and intraoperative SEPs were recorded. The highest, lowest and mean arterial pressure (MAP) were recorded at the beginning, ending, and during the procedure. More than 50% decrease in SEPs amplitudes or more than 10% increase in latency was considered to be the warning threshold. Results The average blood loss volumn was 2000ml (800-6500 ml). The MAPs were less than 60 mm Hg in 14 patients, and 8 of those patients had false-posi-tive readings. There were 100 patients (84.6%) without monitoring changes and no postoperative neurologicdeficit, 1 patient (0.8%) with false-negative reading, 8 patients (6.8%) with true-positive readings, 9 patients (7.6%) had false-positive readings. Nine patients had a postoperative motor or sensory deficit. Higher false-positive rates were seen in patients with greater lability in MAP. In 12 patients, N50 latency increased and the latter two peaks amalgamated to form one slower wave. Conclusion False-positive readings are asso-ciated with high variability in MAP. The concussion, translation, rotation and distraction of the spinal cord and transient ischemia may cause the restrain of the SEPs. N50 latency increased and the latter two peaks a-malgamated to form one slower wave is the alert value possibly. Key words: Spine; Osteotomy; Evoked potentials, somatosensory; Monitoring, intraoperative