Case reportUse of an anesthesia cerebral monitor bispectral index to assess burst-suppression in pentobarbital coma
Introduction
The bispectral index originally was developed to monitor the depth of anesthesia. Additional uses in adult intensive care units are assessment of sedation during mechanical ventilation, neuromuscular blockade, and bedside procedures. Investigations are currently ongoing in pediatric intensive units about the utility of bispectral index in critically ill children [1], [2]. The bispectral index is derived from the electroencephalogram (EEG) using a sophisticated algorithm that uses the advanced signal processing of bispectral and power spectral variables in a multivariate analysis to produce a bispectral index number on a scale from 0 (no brain activity) to 100 (full awake). Artifact and poor signal quality may lead to unreliable bispectral index values. Poor skin contact, muscle activity or rigidity, head and body motion, sustained eye movements, improper sensor placement or skin preparation, and unusual or excessive interference may cause potential artifacts. The authors report on a patient with status epilepticus who was placed in barbiturate coma and monitored simultaneously by a full-channel EEG and the Bispectral Index monitor.
Section snippets
Case report
The patient was a previously healthy 7-year-old male who presented to an outside hospital with a generalized seizure of greater than 30-minute duration where he was given midazolam, diazepam, phenytoin, and phenobarbital intravenously without cessation of the seizure. A computed tomogram of the head without contrast at the referring hospital was unremarkable. On arrival to our pediatric intensive care unit, he was given additional phenobarbital intravenously because rhythmic movements of the
Methods
The patient was monitored by a bispectral index monitor (Aspect Medical Systems, Newton MA) while also undergoing continuous EEG monitoring on days 19 and 20. Three disposable skin electrodes (Zipprep, Aspect Medical Systems, Natick, MA) were placed in a single channel referential montage on the forehead of the patient after a brief skin preparation with isopropyl alcohol. All leads were connected to a portable EEG monitor (A-2000, Aspect Medical Systems) software version 3.11. The bispectral
Results
For our patient with refractory status epilepticus in pentobarbital coma, the bispectral index number and suppression ratio correlated inversely extremely well (r = −984, P <0.01) (Fig 1). The correlation of bursts/min and SR (r = −0.64) (Fig 2) and of bursts/min and bispectral index number (r = 0.59) (Fig 3) was both significant (P < 0.01). The mean hourly bispectral index when bursts ≤ 5/min was 7 (95% confidence interval = 4-10). The mean hourly SR when bursts ≤ 5/min was 85 (95%
Discussion
Occasionally, children and adults are placed in a barbiturate-induced coma for refractory status epilepticus or uncontrollable intracranial hypertension. The physiologic end point of the chemically induced coma is burst suppression or an isoelectric tracing. Suppression duration is used clinically to titrate barbiturate coma and may be quantified by several methods, none of which is definitively accepted. Our objective was 5 to 10 seconds of quiescent EEG. Sigl and Johansen [7] compared
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