1887

oa Southern African Journal of Anaesthesia and Analgesia - Entropy of the electroencephalogram as applied in the M-Entropy S/5™ Module (GE Healthcare) during increases in nitrous oxide and constant sevoflurane concentrations : original research

 

Abstract

It has been suggested that spectral entropy of the electroencephalogram as applied in the M-Entropy S/5™ Module (GE Healthcare) does not detect the effects of nitrous oxide (NO). The aim of this study was to investigate the effect on entropy by graded increases in NO concentrations in the presence of a constant concentration of sevoflurane, in the absence of surgical stimulation.


This single-blind, randomised study was conducted at an altitude of approximately 1 400 m. Patients received sevoflurane 2% (1.7% at sea level) and NO, at end-tidal concentrations of 0%, 10%, 20%, 30%, 40%, 50%, 60% or 70% (equivalent to 8.5%, 17%, 25.5%, 34%, 42.6%, 51.1% and 59.6% at sea level). Entropy was measured before, during and after NO administration. The absolute changes and ratios o f entropy relative to the baseline were calculated. Between- and within-group comparisons were made using analysis of variance and covariance.
None of the entropy variables differed significantly within and between groups before and after NO administration. Within-group analysis revealed that entropy during NO administration was signicantly lower than before or after NO administration (P < 0.007). While a minor clinical but statistically significant linear relationship was observed between increasing NO concentration and decreasing entropy from NO 0% to 60%, a steeper and clinically important decrease (relative change > 20%) was noted at NO > 60% (&gt; 51% at sea level).
The M-Entropy Module S/5™ responds to increasing concentrations of NO in the presence of 2% (1.7% at sea level) sevoflurane, in the absence of surgical stimulation. There is a linear relationship between increasing NO concentrations and decreasing entropy with a steep and clinically important decrease at NO > 60% (&gt; 51% at sea level). The influence of ambient pressure on the partial pressures, which determine the effects of anaesthetic agents, must be taken into account.

Loading

Article metrics loading...

/content/medsajaa/16/4/EJC73790
2010-07-01
2016-12-08
This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error