Objective: At this moment, a wake-up test needs to be done when amplitudes of TES-MEP monitoring decrease irreversible during scoliosis surgery, what mostly turns out to be a false-positive. To make TES-MEP measurements more reliable, we need to know what causes variability in TES-MEP amplitudes and how to diminish this variability. There is an in- dication that MAP is related to these variability’s. The aim of this study was to improve IONM during scoliosis surgery by examining change in blood pressure in relation to cerebral oxygenation, measured with NIRS, as a possible cause of change in cortical excitability and therefore, vari- ability in TES-MEP amplitudes. Methods: Seven healthy subjects participated in a pilot study. MAP and NIRS were measured during this. Four interventions were executed to vary MAP of each subject: 1) valsalva manoeuvre, 2) handgrip exercise, 3) hip anteversion and 4) tilttable test. EtCO2 is also measured to monitor its influence on cerebral oxygenation. Data of MAP, oxygenation and EtCO2 were analysed by Microsoft Excel, Matlab 2014a and IBM SPSS Statistics 21. Results: The results of the handgrip exercise show a significant cor- relation between MAP and oxygenation (rs = 0.893, P<0.01). There was no significant differ in MAP and oxygenation. Hip anteversion shows no significant correlation between MAP and oxygenation (rs = -0.107, P<0.05). There was also no significant differ in MAP and oxygenation. The tilttable test and valsalva manoeuvre were excluded. Conclusion: Blood pressure is related to cerebral oxygenation, but further research needs to be done to correlate oxygenation to the variabil- ity in TES-MEP