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NEUROSURGICAL ANESTHESIOLOGY AND NEUROSCIENCE

The Use of Bispectral Index to Monitor Barbiturate Coma in Severely Brain-Injured Patients with Refractory Intracranial Hypertension

Vincent Cottenceau, MD^*, Laurent Petit, MD^*, Françoise Masson, MD^*, Dominique Guehl, MD, PhD, Julien Asselineau, MS, Jean-François Cochard, MD^*, Catherine Pinaquy, MD^*, Alain Leger, MD^*, and François Sztark, MD, PhD^*

From the *Departments of Anesthesia and Intensive Care Unit, Clinical Neurophysiology, and Clinical Epidemiology Unit, Centre Hospitalo-Universitaire de Bordeaux, Bordeaux, France; Université Victor Segalen Bordeaux 2, Bordeaux, France.

Address correspondence and reprint requests to François Sztark, MD, PhD, Département d’anesthésie réanimation 1. Hôpital Pellegrin, Centre Hospitalo-Universitaire de Bordeaux, 33076 Bordeaux Cedex, France. Address e-mail to francois.sztark{at}chu-bordeaux.fr.

Abstract

BACKGROUND: Barbiturate therapy in severely traumatic brain-injured (TBI) patients is usually monitored by an electroencephalogram (EEG) with burst-suppression pattern as a target. The Bispectral Index (BIS) is derived from EEG and considers cortical silence. We sought to determine whether a BIS range could predict a specific burst-suppression pattern.

METHODS: Eleven TBI patients treated with barbiturate were included prospectively. EEG was recorded daily for 1 h. Every 5 min, the number of bursts and the suppression ratio (suppression ratio from EEG [SR_EEG]: percentage of last 60 s in cortical silence) was calculated for 1 min on the raw EEG and compared to concomitant data from the BIS-XP^TM (BIS and suppression ratio [SR_BIS]). The optimal level of barbiturate coma was defined as 2–5 bursts/min in the EEG. A BIS range predictive of optimal level was determined from all data and its accuracy was studied for each examination.

RESULTS: Agreement between SR_EEG and SR_BIS was high (interclass correlation coefficient 0.94 [95% confidence interval: 0.90–0.96]). There was a significant association between SR_EEG and BIS. Significant disagreements were observed in some examinations. The best accuracy to predict optimal pattern was obtained with a BIS range from 6 to 15.

CONCLUSION: The relationship between BIS and SR_EEG was high in TBI patients treated with barbiturates. The rate of barbiturate infusion might be decreased if BIS is <6 or increased if BIS is >15. Correspondence between BIS and suppression pattern should periodically be checked by observation of the EEG analogical signal (as displayed by BIS-XP^TM).