Original ContributionsSerial Bispectral index scores in patients undergoing observation for sedative overdose in the emergency department☆
Introduction
Of all patients who attend EDs, 2% to 3% present for accidental or deliberate poisoning [1]. Patients presenting after an acute overdose frequently have a depressed level of consciousness. MacNamara et al [1] studied 326 cases of deliberate self-poisoning and found 406 different substances were ingested; 23.7% of the substances caused decreased level of consciousness. In 2002, there were 100 141 exposures to sedatives/hypnotics/antipsychotics reported to US poison control centers. Of these exposures, 4692 resulted in major toxicity and 266 resulted in death [2].
There are many potential management problems when patients present to the ED after an overdose. As many as 50% of patients provide inaccurate histories, either intentionally or unintentionally [3]. The time of ingestion, substances ingested, or quantity/volume of ingestion are often uncertain. In most cases of poisoning, multiple drugs are ingested, making ED treatment more challenging. For example, in a study of acute opiate overdosed patients, 90% reported regular use of other drugs [4].
Many overdosed patients are awake at the time of presentation but then become obtunded. Others present in a state of lethargy but seem to maintain a patent airway. In either case, subtle changes in the level of consciousness of these patients are difficult to objectively assess. Regardless of their initial level of consciousness, as patients become more sedated, they are at an increased risk of losing protective airway reflexes and have the subsequent risk of aspiration or hypoxic/anoxic brain injury. This risk is especially important if activated charcoal is administered as part of the ED management.
The BIS monitor consists of an electroencephalogram (EEG) monitor that displays an analog score of 1 to 100, representing a patient's level of awareness [5], [6], [7], [8], [9], [10], [11]. In addition to the level of awareness, changes in BIS scores have been associated with the administration of sedatives and the dose given [9]. As larger doses are given, the BIS scores decrease; and as the sedative dose wears off, the score increases. Based on this information, we sought to determine if changes in the BIS scores early in a patient's ED treatment course will predict whether patients were likely to require airway intervention while being observed in the ED. We reasoned that at the time of presentation to the ED after ingestion of a sedative, the patient's serum drug level, relative to the occurrence of its peak effect, is not known. As the drug approaches its peak effect, the patient will become increasingly sedated, and the serial BIS score will decrease, indicating a worsening clinical condition. However, if on presentation the drug is at or beyond its peak effect, the patient's BIS score would increase over time as the drug's effects subside.
Section snippets
Methods
This was a prospective, observational study of a convenience sample of patients who presented to the Hennepin County Medical Center ED with an acute overdose between June and November 2002. The Institutional Review Board of Hennepin County Medical Center approved the study. This study used data from a noninvasive monitor with well-established use in the critical care and operating room environments. The institutional review board therefore deemed consent before application of the monitor
Results
Seventy-six patients (mean age, 29 years; 46% men) who were being observed in the ED for suspected overdose were enrolled in the study. The mean time from ED presentation until BIS monitor placement was 48.0 minutes (95% CI, 0-97 minutes; range, 1-480 minutes). All 76 patients had an initial and 20-minute BIS score measured and recorded. Of the 76 patients enrolled, 48 were discharged home and 28 were admitted, 11 of whom were intubated in the ED. The mean time to intubation after study
Discussion
Only 2 of 11 overdosed patients who were intubated in the ED had AMS scores that changed during the 20-minute observation period, but BIS scores decreased in 7 of 11 intubated patients. For patients with an initial BIS score above 70 who eventually required intubation, all 5 demonstrated declining BIS scores. Patients whose presenting BIS score was below 70 had a median AMS of −3, and the changes in the BIS monitor did not appear to predict their eventual need for intubation any more than their
Limitations
The primary limitations of this study are the small sample size and the lack of control of the substances ingested by our patients. Furthermore, our outcome parameter of intubation, although clinically relevant, was based on the clinical decision of the treating physician. The criteria for intubation were not otherwise defined. Because of these limitations, we can only make general conclusions from our data, and we cannot yet make specific clinical recommendations based on this study.
A further
Conclusions
This study suggests that serial bedside BIS monitoring may be useful to predict the need for intubation in overdosed patients, especially in patients who initially arrive in the ED alert. We conclude that BIS monitoring may be useful for earlier treatment and decision making regarding overdosed patients in the ED.
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None of the authors have financial or other interests in the medications used in this study.