Source: Gill M, et al. Can the bispectral index monitor quantify altered level of consciousness in emergency department patients? Acad Emerg Med 2003;10:175-179.
Bispectral index (BIS) monitoring makes use of a noninvasive device to measure electroencephalographic (EEG) data. Two sensor patches placed on the forehead transmit EEG data to a small computer. The data is converted to a BIS score, a dimensionless number ranging from zero (absence of brain activity) to 100 (wide awake). The data is updated continuously, and appears as a digital display and via a printout. Its use is well established in the anesthesia arena.
In this prospective, observational, ED study, a convenience sample of patients 8 years of age or older with an altered level of consciousness (ALOC) — defined as a Glasgow Coma Scale (GCS) score of 14 or lower —were included. Excluded were patients with known abnormal baseline mental status, deafness, inability to tolerated the BIS sensors, or those with neuromuscular blockade prior to calculation of the GCS. Patients receiving analgesics, sedative/hypnotics, or anticonvulsants were not excluded.
The GCS was calculated by an emergency physician at the earliest possible time, and was followed by application of the BIS sensors within five minutes. BIS scores were correlated with GCS scores. A target population of 100 patients was truncated to 38 subjects, due to an obvious high discordance in BIS/GCS values.
The correlation between BIS and GCS was "moderate" (Spearman’s rho = 0.387), and displayed wide variability. For example, patients with a GCS of 3-5 had BIS scores ranging from 47 to 98. Similarly, those with relatively high-end GCS scores (12-14) featured BIS values between 56 and 98. The authors concluded that BIS does not reliably correlate with GCS in ED patients with ALOC.
Commentary by Richard A. Harrigan, MD
BIS monitoring has been through a development phase using healthy volunteers, and has been validated using other, well-described, objective measures of sedation. In general, a BIS of 83-89 is consistent with lack of recall, and a BIS of 64-72 is consistent with loss of consciousness.1 Recent studies of the BIS in sedated intensive care patients have shown wide variability in sedation, with 54% of patients over-sedated and 15% under-sedated. Use of the BIS in this setting improved titration of sedation and decreased cost.2
Can BIS find a home in the ED? Probably, although it seems to me that the logical focus of study should be on monitoring level of sedation in the ED — mirroring applications that have been explored in the intensive care unit and the operating room. The authors have attempted to correlate BIS to an old saw in emergency medicine — the GCS score — and it did not work out. That is okay, because we don’t necessarily need to have an apple when an orange works quite well. So many things impact BIS (including cerebral ischemia and motor activity, as well as medication effects — none of which were controlled for in this study) that it is not surprising that the varied population of all comers with ALOC had varied BIS scores. It will be interesting to watch the literature as BIS searches for a niche in the ED.
Dr. Harrigan, Associate Professor of Emergency Medicine, Temple University Hospital and School of Medicine, Philadelphia, PA, is Editor of Emergency Medicine Alert.
1. Iselin-Chaves IA, et al. The effect of the interaction of propofol and alfentanil on recall, loss of consciousness and the bispectral index. Anesth Analges 1998;87:949-955.
2. Kaplan LJ, et al. Bispectral index monitoring of ICU patients on continuous infusion of sedatives and paralytics reduces sedative drug utilization and cost. Crit Care Med 2000; 4:S110.