Comparative study of propofol and midazolam effects on somatosensory evoked potentials during surgical treatment of scoliosis

OBJECTIVE: Studies of the effects on lower-limb cortical somatosensory evok ed potentials (CSEP) during total intravenous anesthesia are sparse for pro pofol and ave lacking fbr midazolam. This study was designed to compare the effects of propofol and midazolam on CSEP under total intravenous anesthes ia during intraoperative monitoring for surgical treatment of scoliosis. METHODS: CSEPs weve recorded in two groups of 15 patients during posterior instrumentation for treatment of idiopathic scoliosis. The anesthesia used the combination of atracurium, alfentanil, and an hypnotic agent (propofol for Group I or midazolam for Group II). The main characteristics of the CSE Ps (P40 latency and N34-P40 and P40-N50 amplitudes) were recorded using ank le posterior tibial nerve stimulation. The CSEPs were recorded before induc tion, 10, 70, 100, 130, and 160 minutes after induction, and before the wak e-up test. The statistical analysis involved analysis of variance far repea ted measures. Both groups were homogeneous before induction. RESULTS: Neither CSEP deterioration during risk-associated surgical procedu res nor postoperative clinical abnormalities were observed. Both propofol a nd midazolam induced increases in P40 latencies, with the increases being g reater and more regular for the propofol-treated group. The amplitude value s changed with time for both groups, decreasing mainly after induction; in the midazolam-treated group, the amplitudes were smaller but more stable. P ropofol modified the morphological characteristics of the response by decre asing the late P60 component amplitude; the W-shaped CSEP morphological pat tern was maintained with midazolam. CONCLUSION: This study demonstrates the appropriate use of either propofol or midazolam in scoliosis monitoring. Preoperative small-amplitude CSEPs mi ght favor the use of propofol anesthesia.