The effects of propofol, small-dose isoflurane, and nitrous oxide on cortical somatosensory evoked potential and bispectral index monitoring in adolescents undergoing spinal fusion

In this study we compared the effects of propofol, small-dose isoflurane, and nitrous oxide (N2O) on cortical somatosensory evoked potentials (SSEP) and bispectral index (BIS) monitoring in adolescents undergoing spinal fusion. Twelve patients received the following anesthetic maintenance combinations in a randomly determined order: treatment #1: isoflurane 0.4% + N2O 70% + O-2 30%; treatment #2: isoflurane 0.6% + N2O 70% + O-2 30%; treatment #3: isoflurane 0.6% + air + O-2 30%; treatment #4: propofol 120 mug (.) kg (.) mm(-1) + air + O-2 30%. Cortical SSEP amplitudes measured during anesthesia maintenance with treatment #3 (isoflurane 0.6%/air) were more than those measured during maintenance with treatment #1 (isoflurane 0.4%/N2O 70%) (P < 0.0001) and treatment #2 (isoflurane 0.6%/N2O 70%) (P < 0.0052). Cortical SSEP amplitudes measured during treatment #4 (propofol 120 mug (.) kg(-1) (.) min(-1)/air) were more than treatment #1 (isoflurane 0.4%/N2O 70%) (P < 0.0001), treatment #2 (Iso 0.6%/N2O 70%) (P < 0.0007), and treatment #3 (isoflurane 0.6%/air) (P < 0.0191). In addition, average BIS values measured during treatments 1, 2, 3 and 4 were 62, 62, 61, and 44 respectively. Only treatment #4 (propofol 120 mug (.) kg(-1) (.) min(-1)/air) uniformly maintained BIS values less than 60. Our study demonstrates that propofol better preserves cortical SSEP amplitude measurement and provides a deeper level of hypnosis as measured by BIS values than combinations of small-dose isoflurane/N2O or small-dose isoflurane alone.