Article

Awareness detection during caesarean section under general anaesthesia using EEG spectrum analysis.

Department of Anesthesiology, Bnai-Zion Medical Centre, Haifa, Israel.
Canadian Journal of Anaesthesia (Impact Factor: 2.5). 06/1995; 42(5 Pt 1):377-81. DOI: 10.1007/BF03015480
Source: PubMed

ABSTRACT This study examined the relationship between the EEG (spectral edge frequency 90-SEF90) and the occurrence of awareness defined for the purpose of this study as responsiveness to verbal commands. Fifty women undergoing general anaesthesia for elective Caesarean section were examined. Responsiveness to verbal commands was detected every minute in the period from the induction of anaesthesia to the delivery of the newborn using the Tunstall isolated forearm technique and correlated with the SEF90 value. The patients were assigned by a randomized code to receive either thiopentone (4 mg.kg-1) or ketamine (1 mg.kg-1) for induction of anaesthesia. Before the administration of succinylcholine a tourniquet was applied to the free arm, and inflated to 200 mmHg, to maintain motor function to one arm. The EEG recordings started five minutes before induction and were recorded throughout anaesthesia. The incidence of responsiveness to verbal commands was lower in the ketamine group (24%) where the average SEF90 was 12.0 +/- 3 Hz, than in the thiopentone group (52%), where the average SEF90 was 18.09 +/- 3 Hz (P = 0.01). The results suggest that SEF values of < or = 8.6 Hz were sufficient to avoid responsiveness to verbal commands.

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    ABSTRACT: Intraoperative monitoring of electroencephalograms (EEGs) is becoming more commonplace as the technology advances,7 and 39 making it easier and less costly to apply.48 Although the cardiovascular status and systemic perfusion are routinely monitored during anesthesia, the brain, which is the target organ of general anesthesia, is generally not monitored. Instead, it is generally assumed that without prior known pathology, adequate cerebral perfusion can be assumed by maintaining adequate mean arterial pressure.72 Cerebral blood flow is not only dependent on adequate cerebral perfusion pressure, which is decreased by elevations in intracranial pressure, but also by changes in cerebral vascular resistance and cerebral vascular pathology.74 Monitoring for cerebral perfusion, however, is not the only application for intraoperative EEG monitoring. EEG can also be used to monitor the depth of sedation and the degree of burst suppression produced by barbiturate infusion, as well as monitoring for the occurrence of seizures while the patients are under the influence of muscle relaxants.20 Each of these applications are discussed in this article, but for intraoperative EEG to be most effectively applied, a number of fundamental principles must first be addressed.
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