Entropy of the electroencephalogram as applied in the M-Entropy S/5™ Module (GE Healthcare) during increases in nitrous oxide and constant sevoflurane concentrations

Abstract

Background: It has been suggested that spectral entropy of the electroencephalogram as applied in the M-Entropy S/5 TM Module (GE Healthcare) does not detect the effects of nitrous oxide (N 2 O). The aim of this study was to investigate the effect on entropy by graded increases in N 2 O concentrations in the presence of a constant concentration of sevo urane, in the absence of surgical stimulation. Method: This single-blind, randomised study was conducted at an altitude of approximately 1 400 m. Patients received sevo urane 2% (1.7% at sea level) and N 2 O, 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 N 2 O 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. Results: None of the entropy variables differed signi cantly within and between groups before and after N 2 O administration. Within-group analysis revealed that entropy during N 2 O administration was signi cantly lower than before or after N 2 O administration (P < 0.007). While a minor clinical but statistically signi cant linear relationship was observed between increasing N 2 O concentration and decreasing entropy from N 2 O 0% to 60%, a steeper and clinically important decrease (relative change > 20%) was noted at N 2 O > 60% (> 51% at sea level). Conclusions: The M-Entropy Module S/5TM responds to increasing concentrations of N 2 O in the presence of 2% (1.7% at sea level) sevo urane, in the absence of surgical stimulation. There is a linear relationship between increasing N 2 O concentrations and decreasing entropy with a steep and clinically important decrease at N 2 O > 60% (> 51% at sea level). The in uence of ambient pressure on the partial pressures, which determine the effects of anaesthetic agents, must be taken into account.

Calculation of comparative utilisation and cost: a South African perspective on intravenous vs. inhalational anaesthesia for procedures of differing duration

“…Apart from any disadvantages, the reduced effectiveness of N 2 O at altitude may negate the perceived main advantage of its use: reduced awareness while under general anaesthesia. 13,29 Our calculations also showed an increased cost when N 2 O was added to commonly used inhalational agents (isoflurane and sevoflurane). If the cost to the environment is added to this, as a consequence of venting scavenged gas into the atmosphere, the following should be considered: is this adjuvant finally becoming too costly to justify its continued use?…”

Multiparametric Monitoring of Hypnosis and Nociception-Antinociception Balance During General Anesthesia - A New Era in Patient Safety Standards and Healthcare Management

“…The sum of these values results in the numerical values called Spectral Entropy. The first algorithm ever to be used in the clinical practice has been defined and applied in the M-Entropy modules S/5 (GE Healthcare, Helsinki, Finland) [10,[31][32][33]. The EEG data are collected through an adhesive sensor made of three electrodes applied on the fronto-temporal region.…”