Prevalence of discordant elevations of state entropy and bispectral index in patients at amnestic sevoflurane concentrations: a historical cohort study

  • Richard H. Epstein
  • Joni M. Maga
  • Michael E. Mahla
  • Eric S. Schwenk
  • Marc J. Bloom
Reports of Original Investigations

Abstract

Background

Processed electroencephalogram (EEG) monitors help assess the hypnotic state during general anesthesia or sedation. Maintaining the bispectral index (BIS) or state entropy (SE) between 40 and 60 has been recommended to mitigate anesthesia awareness. Nonetheless, SEs > 70 were frequently observed at end-tidal sevoflurane concentrations unlikely to allow awareness. We sought to determine the prevalence of elevated discordant measurements during BIS and SE monitoring.

Methods

Electronic data collected over 11 months at two academic hospitals were retrospectively reviewed. At the hospital using SE, all cases were included with patients ≥ 18 yr and sevoflurane administered for at least 30 min during surgery. A cohort of cases propensity matched by age and American Society of Anesthesiologist Physical Status were selected from the hospital using BIS. Elevated discordant EEG indices were defined as values > 70 occurring during stable end-tidal sevoflurane concentrations > 1.5%. The odds ratio (OR) based on the probability of a case having at least one elevated discordant SE or BIS lasting ≥ two minutes (primary endpoint) was calculated.

Results

At each hospital, 3,690 cases were studied. The mean (95% confidence interval [CI]) incidence of cases with at least one interval of an elevated discordant EEG index lasting at least two minutes was 3.6% (2.8% to 4.4%) for SE compared with 0.24% (0.17% to 0.27%) for BIS (pooled OR, 17.0; 95% CI, 8.3 to 34.7; P < 0.001).

Conclusions

The prevalence of an elevated discordant EEG index is much greater with SE than with BIS. Elevated index values occurring at anesthetic concentrations well above the awareness threshold need to be assessed to determine if they indicate an inadequate depth of anesthesia requiring treatment or if they simply reflect the underlying monitoring algorithm.

Fréquence des élévations discordantes de l’entropie basale et de l’index bispectral chez les patients à des concentrations de sévoflurane provoquant l’amnésie : une étude de cohorte historique

Résumé

Contexte

Les moniteurs d’électroencéphalographie (EEG) dont les données ont été analysées contribuent à évaluer l’état hypnotique pendant l’anesthésie générale ou la sédation. Le maintien de l’index bispectral (BIS) ou de l’entropie basale (SE, pour state entropy) entre 40 et 60 a été recommandé pour réduire l’incidence de l’éveil peropératoire. Toutefois, des entropies basales > 70 ont fréquemment été observées à des concentrations télé-expiratoires de sévoflurane peu susceptibles de permettre un éveil. Nous avons tenté de déterminer la prévalence de mesures discordantes élevées pendant le monitorage du BIS et de l’entropie basale.

Méthode

Les données électroniques colligées sur une période de 11 mois dans deux hôpitaux universitaires ont été rétrospectivement passées en revue. Dans l’hôpital utilisant l’entropie basale comme mesure, tous les cas de patients ≥ 18 ans et auxquels on avait administré du sévoflurane pour un minimum de 30 min pendant la chirurgie ont été inclus. Une cohorte de propension de cas appariés selon l’âge et le système de classification du statut physique de l’American Society of Anesthesiologists (ASA) a été sélectionnée parmi les données colligées dans un autre hôpital utilisant le BIS. On a défini les indices d’EEG discordants élevés tels que des valeurs > 70 survenant durant des concentrations télé-expiratoires stables de sévoflurane > 1,5 %. Le rapport de cotes (RC) fondé sur la probabilité d’un cas ayant au moins une valeur d’entropie basale ou de BIS discordante élevée ≥ deux minutes (critère d’évaluation principal) a été calculé.

Résultats

Au total, 3690 cas ont été étudiés dans chaque hôpital. L’incidence de cas dans l’intervalle de confiance (IC) à 95 % moyen présentant au moins un intervalle d’un indice d’EEG discordant élevé durant au moins deux minutes était de 3,6 % (2,8 % à 4,4 %) lorsque l’entropie basale a été utilisée comme mesure, par rapport à 0,24 % (0,17 % à 0,27 %) lorsqu’on a utilisé le BIS (RC groupé, 17,0; IC à 95 %, 8,3 à 34,7; P < 0,001).

Conclusion

La prévalence d’un indice d’EEG discordant élevé est bien plus importante avec l’entropie basale qu’avec le BIS. Des valeurs d’indice élevées survenant avec des concentrations anesthésiques bien au dessus du seuil d’éveil doivent être évaluées afin de déterminer si elles indiquent une profondeur d’anesthésie inadaptée qui nécessite un traitement ou si elles reflètent simplement l’algorithme de monitorage sous-jacent.

Notes

Conflicts of interest

None declared.

Editorial responsibility

This submission was handled by Dr. Hilary P. Grocott, Editor-in-Chief, Canadian Journal of Anesthesia.

Author contributions

Richard H. Epstein, Joni M. Maga, Michael E. Mahla, Eric S. Schwenk, and Marc J. Bloom contributed substantially to all aspects of this manuscript, including conception and design, acquisition and interpretation of data, and drafting the article.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Supplementary material

12630_2018_1085_MOESM1_ESM.pdf (574 kb)
Supplementary material 1 (PDF 573 kb)

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Copyright information

© Canadian Anesthesiologists' Society 2018

Authors and Affiliations

  1. 1.Department of Anesthesiology, Perioperative Medicine and Pain Management, Miller School of MedicineUniversity of MiamiMiamiUSA
  2. 2.Department of Anesthesiology, Sidney Kimmel Medical CollegeThomas Jefferson UniversityPhiladelphiaUSA

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