BIS Complete 2-Channel Monitor

Added Oct 17, 2012

Manufactured by Covidien

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Reviewed by Avinash Kapoor Reviewed Jan 16, 2013

SpR in Anaesthetics & Intensive Care, Northern Deanery, Newcastle upon Tyne, UK - No Conflict Declared

Editor Rating

The adequate level of anaesthesia is usually determined by anaesthetists based on preoperative assessment and intraoperative monitoring of clinical signs. There are specialised monitors available to prevent or reduce accidental intraoperative awareness1. The limitations and complexity of any such monitoring is further highlighted by Dr. Nesbitt's editorial on the awareness monitors.

Bispectral Index Monitor (Covidien): Review for WhichMedicalDevice

Background

The adequate level of anaesthesia is usually determined by anaesthetists based on preoperative assessment and intraoperative monitoring of clinical signs. There are specialised monitors available to prevent or reduce accidental intraoperative awareness1. The limitations and complexity of any such monitoring is further highlighted by Dr. Nesbitt’s editorial on the awareness monitors.
 

Monitor

The BIS uses a display attached to 3 point sensor which is fixed to patient’s forehead in order to monitor EEG activity. This EEG is analysed and processed to generate a number which indicates the level of brain activity. The scale used is 0-100 with 100 representing fully awake and lower the number means deeper anaesthesia. The target number for BIS during maintenance of general anaesthesia is 40-60 which indicates adequate depth of anaesthesia with minimal risk of awareness.
 

In use:

  • The BIS appears to be a user friendly and easy to use monitor. The instructions available with the monitor are self explanatory to use it. However, the interpretation of data and trouble-shooting requires experience and knowledge of its use. Most of time, a single number generated by the monitor to quantify the depth of anaesthesia is sufficient to alter the amount of anaesthetic agent given to the patient. However, there is a lag which appears to be biggest disadvantage and might be the reason of its failure to prevent awareness completely.
  • The trend seems to be of greater importance than single value at any time, so applying the monitor before start of anaesthetic and continuing of monitoring until patient is fully awake would give better results.
  • The EMG artifacts, due to high muscle tone, can be reduced by use of neuromusclular blockers which can reduce BIS values. The electrical artifacts due to pacemaker, cautery or even forced air warmers can increase BIS values. The situations unrelated to depth of anaesthesia can affect BIS values e.g. cerebral hypoperfusion due to hypotension can reduce BIS value. Similarly, seizures might increase BIS values.
  • BIS doesn’t work similarly with all anaesthetic agents which is unsurprising given the broad spectrum of mechanism of action of general anaesthetic agents. Ketamine, etomidate halothane, ephedrine can give higher BIS values.
  • It might not be feasible to use it in all surgeries e.g. ENT and maxillofacial (as site mightn’t be available for 3 point sensor of BIS).
  • The use of the BIS monitor can lead to reduction in the amount of anaesthetic agent used. If used properly, it can also slightly reduce the time to extubation and discharge from recovery.
 

Results so far:

NICE has produced a draft technology appraisal for awareness monitors in 2012 which recommends BIS as an additional option for selected situation (total intravenous anaesthesia, higher risk of complications from anaesthesia) by the anaesthetists trained in its use. This will be discussed in detail, in Dr. Nesbitt’s editorial on awareness monitors (due to appear on WhichMedicalDevice from 29 January 2013).
 
Avinash Kapoor, SpR in Anaesthetics & Intensive Care, Northern Deanery, Newcastle upon Tyne, UK - No Conflict Declared
 

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