To assess the correlation between sleep stage and second heart rate variability. We employed polysomnography to decide on sleep stage and assessed visual wave patterns of second heart rate variability which was simultaneously recorded using a fetal heart rate monitor. The fetal heart rate monitor displayed heart rate variability per beat. Subjects were 10 children who had N2, N3, and REM sleep stages lasting more than 15 minutes each. In N2 and N3, variability was poor, second heart rate baseline variability was present with an amplitude of 5–15 bpm and the difference in the nadir of the heart rate curve was within 5 bpm. In REM, variability was remarkable, heart rate baseline was difficult to identify, the variable band was 15–20 bpm and the period was 10–40 seconds. Heart rate at the lower peak on the nadir curve in REM was variable, with differences of 5–30 bpm found. It was possible to distinguish REM from N2, N3 using the wave form in second heart rate variability curves.

The stimulation methods that can elicit motor evoked potential are transcranial stimulation or transpharyngeal stimulation with a nasal tube electrode. Transcranial stimulation elicited compound muscle action potentials more easily in distal muscles than in proximal muscles. On the other hand, transpharyngeal stimulation showed tendency to have large compound muscle action potentials in proximal muscles more than in distal muscles. There is a possibility some different motor tracts are evaluated. Transpharyngeal stimulation has advantage for estimation of C5 palsy. We used mainly better stimulation method in eliciting compound muscle action potentials. Transpharyngeal stimulation are able to elicit compound muscle action potentials with half intensity of transcranial stimulation. Muscle MEP is most reliable for the lower cervical and lumbar spinal cord that have more large gray matter, nerve roots and the cauda equine. About the kind of the operation, muscle MEP is most suitable for correction of deformity and removal of spinal cord tumor. The limits of muscle MEP are so sensitive that positive predictive value is low except removal of intramedullary spinal cord tumor, and muscle twitch following stimulation interferes with the operation procedure, so compound muscle action potentials must be recorded before and after procedures. It is not real time monitoring. Good communication between a surgeon and an examiner is essential in monitoring. It is impossible that monitoring using muscle MEP prevent a risk of nerve damage that an operator does not notice. Descending spinal cord evoked potential is able to be recorded using both stimulations in patients with severe spinal cord damage preoperatively and had no response of compound muscle action potential. Transpharyngeal stimulation showed larger descending spinal cord evoked potential than transranial stimulation. These potentials can be recorded under the muscle relaxation. They does not interfere with surgical procedures, therefore, descending spinal cord evoked potential can evaluate risk of spinal cord damage that an operator can not predict. Descending spinal cord potentials after these stimulations are reliable in monitoring of the upper cervical spinal cord and thoracic spinal cord that evaluation of the gray matter or nerve root are not very important in. Descending SCEP following transpharyngeal stimulation is possible to estimate more axons than transcranial stimulation. A late negative wave in descending spinal cord evoked potential recorded at lumbar enlargement after spinal cord stimulation is most suitable potential in spinal cord ischemia. This wave reflects function of the interneurons in the dorsal horn that is most sensitive to ischemia. We need to select main evoked potential for spinal cord monitoring depending the kind of disease, operation and level of the spinal cord. It is possible to use muscle MEP and descending SCEP properly with muscle relaxant and its reverse sugammadex.