Nonconvulsive status and bispectral index:

Processed EEG from depth of anaesthesia monitors and seizures: A scoping review

PURPOSE

Processed electroencephalogram (EEG) is used peri-operatively for monitoring depth of anaesthesia. Because these utilise EEG data, attempts have been made to investigate their use in diagnosing and monitoring seizures. This is important as formal EEG monitoring can be hard to obtain in many critical care environments. We undertook a scoping review of the evidence for using processed EEG (pEEG) from depth of anaesthesia monitors for this indication.

METHODS

Medline, Psych INFO, and Embase were searched for peer-reviewed journals until 20 March 2021. Data and conclusions taken from the study of pEEG in both critical care and peri-operative settings have been included in a qualitative synthesis about the current evidence for the use of pEEG in the detection and monitoring of seizures.

RESULTS

Searches yielded 8 observational studies, 1 randomised trial and 15 case reports in which the use of pEEG in critical care and peri-operative medicine was described. Most concerned the Bispectral Index (BIS) device. The majority of observational studies reported the use of BIS for optimisation of burst suppression in patients with refractory status-epilepticus (RSE), or in the comparison of pEEG data with conventional EEG during epileptic activity. Multiple case reports describe the application of pEEG in the presence of disorders of consciousness as a tool for detection of non-convulsive status-epilepticus, finding variable trends in the pEEG output.

CONCLUSIONS

Processed EEG may be helpful in monitoring pharmacologically induced burst suppression. Despite this, its use in the diagnosing or monitoring seizure activity is controversial and currently not evidenced, with numerous confounding variables that requires systematic assessment in future studies.

Increasing or fluctuating bispectral index values during post-resuscitation targeted temperature management can predict clinical seizures after rewarming

AIM

To investigate whether an increasing bispectral index (BIS) value during targeted temperature management (TTM) correlates with increased clinical seizures after TTM or worse neurological prognoses after TTM.

METHODS

We performed a retrospective prognostication study of patients who were treated with TTM after recovery of spontaneous circulation from cardiac arrest at a tertiary care hospital. We recorded the BIS regularly during TTM and calculated the correlations of the mean BIS values, standard deviations of the BIS values, and linear regression coefficient of the trend of the BIS values over time as index tests. Study outcomes included the occurrence of clinical seizures after TTM and unfavourable neurological outcomes (defined as a Cerebral Performance Scale score of 3-5). Receiver operating characteristics (ROC) analyses evaluated the predictability of the index tests for the study outcomes.

RESULTS

Of 534 patients with post-cardiac arrest who were admitted to the intensive care unit, 103 were enrolled in this study. Thirty-one patients (30.1%) experienced sequelae in the form of clinical seizures, and 52 (50.5%) had unfavourable neurological outcomes at 30days post-resuscitation. The standard deviation (area under the ROC curve [AUC]=0.763) and the regression coefficient (AUC=0.763) had higher predictability of clinical seizures than the mean BIS value (AUC=0.657); in contrast, the low mean BIS value best predicted unfavourable neurological outcomes (AUC=0.861) compared to the standard deviation (AUC=0.532) and regression coefficient (AUC=0.501).

CONCLUSION

An increase of, or greater fluctuation in, BIS during hypothermia may predict clinical seizures after TTM.

Should we monitor with bispectral index in all patients at high risk for seizures in the operating room?

We report the case of a patient with a cerebral aneurysm, located in the left middle cerebral artery. During the clipping of this aneurysm, the bispectral index (BIS) increased for no apparent reason. This was then interpreted as intraoperative non-convulsive status epilepticus. This clinical condition may have negative impact in the prognosis of the patient, so it is very important to be able to detect this conditions as early as possible. Measuring the BIS while the patient is anaesthetised could be useful in this situation, considering that an increase in values greater than 60, associated with acidosis and without any other peri-anaesthetic explanation, may provide evidence of a convulsive equivalent state, allowing appropriate action to be taken.

Anesthesia and analgesia protocol during therapeutic hypothermia after cardiac arrest: a systematic review

BACKGROUND

Present practice guidelines recommend sedative-analgesic and neuromuscular blocking administration during therapeutic hypothermia in comatose patients after cardiac arrest. However, none suggests the best administration protocol. In this study, we evaluated intensivists' preferences regarding administration.

METHODS

A systematic literature review was conducted to identify clinical studies published between 1997 and July 2009. Selected articles had to meet the following criteria: use of hypothermia to improve neurologic outcome after cardiac arrest, and specific mention of the sedative protocol used. We checked drugs and dose used, the reason for their administration, and the specific type of neurologic and neuromuscular monitoring used.

RESULTS

We identified 44 studies reporting protocols used in 68 intensive care units (ICUs) from various countries. Midazolam, the sedative used most often, was used in 39 ICUs at doses between 5 mg/h and 0.3 mg/kg/h. Propofol was used in 13 ICUs at doses up to 6 mg/kg/h. Eighteen ICUs (26%) did not report using any analgesic. Fentanyl was the analgesic used the most, in 33 ICUs, at doses between 0.5 and 10 microg/kg/h, followed by morphine in 4 ICUs. Neuromuscular blocking drugs were routinely used to prevent shivering in 54 ICUs and to treat shivering in 8; in 1 ICU, their use was discouraged. Pancuronium was used the most, in 24 ICUs, followed by cisatracurium in 14. Four ICUs used neuromuscular blocking drug administration guided by train-of-four monitoring and 3 ICUs used continuous monitoring of cerebral activity.

CONCLUSIONS

There is great variability in the protocols used for anesthesia and analgesia during therapeutic hypothermia. Very often, the drug and the dose used do not seem the most appropriate. Only 3 ICUs routinely used electroencephalographic monitoring during paralysis. It is necessary to reach a consensus on how to treat this critical care population.