[Baseline and alert level of somatosensory evoked potential monitoring in scoliosis surgery].

OBJECTIVE:To explore the choice of timing for baseline and alert levels of somatosensory evoked potential (SEP) monitoring during scoliosis surgery. METHODS:From March 2011 to December 2014, a total of 113 patients with kyphoscoliosis deformity were monitored intraoperatively by SEP. There were 52 males and 61 females with a mean age of (20 ± 15) years. All the patients were recorded preoperativeandintraoperative SEPs on double lower limbs. Latency and amplitude of SEPs were recorded after anesthesia and vertebral laminae exposure respectively and compared with each other. Intraoperative SEPs were compared to baseline as SEP after exposure and divided into 4 groups of A (<40%), B (40%-50%), C (50%-60%) and D (>60%) according to the reduced amplitude. Nerve functions were recorded during follow-ups. RESULTS:Significant statistical difference existed between SEPs post-anesthesia and SEPs after vertebral laminae exposure (P < 0.01). Compared with SEP post-anesthesia, the latency of SEP after exposure was prolonged with (3.28 ± 1.72) ms (left lower limb) and (3.30 ± 2.09) ms (right lower limb) and amplitude decreased with 0.17(0.39) µV (left lower limb) and 0.19(0.40) µV (right lower limb). There was a positive relationship of impaired nerve function between groups C and D (P < 0.05). CONCLUSION:Adopting SEP waveform after exposure as a baseline can improve the accuracy of SEP monitoring during scoliosis surgery. Intraoperative alarm with a reduced amplitude over 50% as the standard may be too sensitive. Alert with a reduced amplitude of over 60% reduces the false positive rate of alarm.