Abstract
Introduction: Somatosensory evoked potentials are monitored during the surgical treatment of spinal disorders to reduce the risk of cord injury. Whilst studies have examined its role in patients undergoing correction of idiopathic and neuromuscular scoliotic curves, its effectiveness in patients undergoing operative treatment for spinal injury is less certain.
Methods and Results: We reviewed the medical records of patients who underwent surgery for spinal trauma. between 1995 and 2000. There were 82 patients with adequate data for analysis who underwent 83 spinal reconstructive procedures. We recorded the age at injury, diagnosis, time of operation, levels instrumented, systolic and diastolic blood pressures and surgical approach. The intraoperative somatosensory evoked potential (SSEP) traces were examined. The SSEP at insertion of electrode was taken as the control level. The highest and lowest intraoperative somatosensory evoked potentials and SSEP at closure were noted and expressed as a percentage of the control value.
Forty patients (48%) had a pre-operative neurological deficit. Neurological deterioration occurred postoperatively in three patients. Eighty-three traces from 82 patients were available for analysis. Fifty-seven patients had a fall in trace amplitude by more than 25% of the control, 25 by more than 50% and eight by more than 75%.
With an SSEP amplitude loss of 60%, both sensitivity and specificity for the prediction of post-operative neurological injury were optimised at 67 and 81% respectively, with one false negative result.
SSEP rise at completion of spinal reconstruction and highest intraoperative SSEP rise was compared with neurological outcome in the 40 patients with abnormal pre-operative neurology. Neurology improved in all patients in this group who had a trace amplitude more than 60% above the control value at end of operation. None had neurological deterioration. There was no correlation between intraoperative SSEP rise and neurological outcome.
Conclusion: Loss of trace amplitude more than 50% is common during spinal reconstructive surgery after trauma, however a 60% threshold for SSEP fall improves specificity by reducing the rate of false positive results. A trace amplitude 60% above the control value at completion of operation is specific but not sensitive for postoperative neurological improvement.
Abstracts prepared by Mr J. Dorgan. Correspondence should be addressed to him at the Royal Liverpool Children’s Hospital, Alder Hey, Eaton Road, Liverpool L12 2AP, UK
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