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Three Part Question

In [adults undergoing prehospital emergency anaesthesia] does [monitoring with bispectral index] reduce [inadequate depth of anaesthesia]

Clinical Scenario

A 72-year-old man is seen in the prehospital setting following an out-of-hospital cardiac arrest with successful return of spontaneous circulation. He has received prehospital emergency anaesthesia (PHEA) for the indication of ventilatory failure / inadequate oxygenation. You wonder whether bispectral index (BIS) monitoring would reduce the risk of inadequate depth of anaesthesia in prehospital care.

Search Strategy

Ovid MEDLINE (R) 1946 (inception) to December 30th 2022 using the OVID interface, and Medline Epub Ahead of Print, In-Process & Other Non-Indexed Citations:

('bispectral index'/exp OR 'bispectral index') AND (‘prehospital’/exp OR ‘prehospital)

Embase 1974 to December 2022 using the OVID interface:

('bispectral index'/exp OR 'bispectral index') AND ('emergency care'/exp OR 'emergency care')

The Cochrane Library and Google Scholar databases were also searched.

Search Outcome

30 papers were identified, 26 which were irrelevant for inclusion were excluded following abstract review by a single author. The remaining four papers are summarised in table 1.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Chollet-Xemard et al 2008 France	92 adult patients in OHCA.	Non-controlled prospective observational study	Primary outcome correlation between BIS and ETCO2 values (to predict ROSC). Secondary outcomes difference in BIS values between ROSC (n=30) and no ROSC (n=62), and difference in BIS between hospital survivors (n=3) and non-survivors (n=27).	Poor correlation between BIS and ETCO2 during advanced life support (r2=0.02, P=0.19). No significant difference in BIS between ROSC and non-ROSC (P=0.78). No significant difference in BIS on admission between hospital survivors and non-survivors (P=0.78).	Convenience sample. Small sample size and in particular small number of ROSC and survivors. BIS monitoring discontinued shortly after hospital admission. Delays in time to advanced life-support. Most patients in asystole (known to be associated with worse prognosis)
Heegaard et al 2009 USA	47 intubated adults undergoing aeromedical transport. 18 healthy adult volunteers undergoing simulated aeromedical transport.	Controlled prospective observational study.	BIS and SQI values during transport.	The median BIS for intubated patients was 54.6 [36.7 – 67.3]. Median SQI 89.3 [67.4 – 94.2]. In comparison the control group had a median BIS of 95.6 [93.1 – 97.3]. Median SQI 61.9 [39.8 – 72.6]. Only 22/708 (3.1%) BIS readings were >85% in the intubated patients and these were from two patients.	Convenience sample. Small sample size. No recall surveys to assess awareness in patients.
Duchateau et al 2014 France	72 intubated adult in OHCA	Non- controlled prospective observational study	Correlation between BIS values and Ramsay score. Correlation between BIS values and ATICE Awakeness Scale.	The correlation between BIS and the Ramsay score is moderate with a low concordance correlation coefficient of 0.54 for repeated measurements and 67% appropriate BIS values. The correlation between BIS and the ATICE Awakeness Scale was also moderate with a low correlation coefficient of 0.45 for repeated measurements and 53% appropriate BIS score.	Convenience sample. Small sample size. No control group. Large proportion of patients had toxic coma (36%) or neurological coma (21%). Small heterogenous cohort.
Soto Garcia et al 2012 Spain	16 adult patients in OHCA	Non-controlled prospective observational study.	Difference in initial and 3 minute mean BIS (SQI >60%). Difference n BIS values in patients with ROSC (n-3) and no ROSC (n=13).	No significant difference between initial BIS (36) and 3 minute BIS (33.6). No significant difference between ROSC and no ROSC groups (P=0.1)	Convenience sample. Small sample size. No control group. Initial heart rhythm shockable in only 3/16 patients (18.7%)

Comment(s)

Bispectral Index Monitoring (BIS) collects electroencephalogram (EEG) data via its sensors and applies an algorithm to generate a numeric value between zero and 100 (without units). BIS monitoring is a surrogate for depth of anaesthesia with values of 85-60 representing amnesia, and <60 accepted as general anaesthesia. Awareness during anaesthesia can lead to severe long-term consequences for patients, including: post-traumatic stress disorder (PTSD) and anxiety disorders, avoiding both over- and under-sedation is therefore important in the delivery of PHEA. However, there are various limitations to using BIS for monitoring depth of anaesthesia. First, it is prone to overestimation due to artefact. These can be generated by multiple factors, including muscle activity, vehicle vibration, chest compressions, defibrillation, hypothermia, and the specific anaesthetic agent used.In particular, ketamine, which is favoured for PHEA, may not produce reliable changes in the BIS due to its dissociative anaesthesic effect. Second, BIS is unreliable for use in patients with neurological impairment, and only reflects activity in cortical (and not subcortical) structures. Finally, the algorithm used to convert raw EEG data into BIS values was developed for patients under anaesthesia without brain injury or acute cerebral impairment. The studies to date on this topic present limited evidence. Few studies have used BIS in the pre-hospital environment. All are observational studies consisting of small convenience samples and most have no control group. Three of the four studies included patients in OHCA which may limit the external validity of the results to other patients undergoing PHEA. Furthermore, the majority of studies’ results seem affected by the aforementioned environmental confounding factors. Unfortunately, these have neither examined specific anaesthetic regimes relevant to PHEA, nor has follow-up included recall surveys to assess the prevalence of awareness. Therefore, the evidence to support a conclusion on the utility of BIS in the prehospital setting is insufficient and further studies are required.

Clinical Bottom Line

There is insufficient evidence to indicate any benefit of BIS monitoring to reduce inadequate depth on anaesthesia in the prehospital setting. Further studies which are adequately powered and controlled to avoid confounding are required to answer this clinical question.

References

1. Chollet-Xémard C, Combes X, Soupizet F, et al. Bispectral index monitoring is useless during cardiac arrest patients' resuscitation. Resuscitation. 2009;80(2):213-216
2. Heegaard W, Fringer RC, Frascone RJ, et al. Bispectral index monitoring in helicopter emergency medical services patients. Prehosp Emerg Care 2009;13(2):193-197
3. Duchateau FX, Saunier M, Larroque B, et al. Use of bispectral index to monitor the depth of sedation in mechanically ventilated patients in the prehospital setting Emerg Med J. 2014;31(8):669-672.
4. Soto Garcia MA, Giraldo Sebastia JM, Carmano Jiminez FJ, et al. . Bispectral index recorded during prehospital cardiopulmonary resuscitation as a predictor of survival Emergencias. 2012; 24: 35-38