Bispectral Index Scale alterations in brain death patients

Introduction

Brain death (BD) is defined as the total and irreversible loss of brain function, including the brain stem. According to current Greek guidelines, low BD diagnosis is determined only by clinical criteria, thus electroencephalogram (EEG), cerebral angiography or transcranial Doppler are not considered mandatory for BD confirmation. The Bispectral Index Scale (BIS) is a multifactorial parameter derived from the EEG, which allows monitoring of the hypnotic component of anaesthesia. Furthermore, it has been reported that there is a good correlation between BIS and neurological status in unsedated coma patients. In addition, it has been recently suggested that BIS is associated with the Glasgow Coma Score (GCS) and could serve as a good predictor tool for the outcome after head trauma. Moreover it has been reported that BIS can be used in the early detection of BD. The aim of the present study was to record the BIS alterations in BD patients.

Methods

Thirty brain injury patients (24 males and six females, with a mean age of 48.4 ± 12.3 years) who were considered as being BD according to the standard clinical criteria were included in the study. Eleven of them became organ donors. Continuous BIS monitoring (BIS; Aspect Medical Systems Inc., Natick, MA, USA) was performed for 24 to 32 hours (mean 26.7 hours).

Results

All patients were haemodynamically stable, normothermic and without any electrolytical disturbance. Ten patients showed BIS 0 continuously. In the remaining 20 patients (66.6%) BIS fluctuations over 30 continuing for more than 30 minutes were recorded. These values then dropped to the BIS 0 level after different time periods. These alterations were compatible with EEG activity and not associated with external stimulus such as surgical or other manipulations.

Conclusions

BIS monitoring is a continuous, simple method, easily interpreted. Although it has been suggested to be a good predictor tool of early detection of BD, there is a possibility of increased BIS values in BD patients. The anaesthesiologist should be aware of these situations and in no case should the BIS findings decrease the validity of standard clinical criteria of BD determination.