A preliminary study of BIS and AEPex in patients with altered mental state

 

Hoon Kang¹,  G.N.C. Kenny²

 ¹Department of Anesthesiology and Pain Medicine, School of Medicine,
Chungbuk National University, Cheongju, Korea
²Glasgow University Department of Anaesthesia, Royal Infirmary, 8-16 Alexandra Parade, Glasgow G31 2ER, UK

 

Background: Very little is known about the effects of neurological injury on the BIS and AEPex which have been proposed as measures of depth of anesthesia. This preliminary and observational study was performed with the aim of determining if these measures are significantly changed in patients with neurological injuries, and in broad terms whether there is any correlation between these measures and the severity of injury, as assessed by Glasgow Coma Scale (GCS).

Methods:  Fifteen patients with a focal neurological injury (e.g. intracerebral hematoma) or a more global injury (e.g. traumatic diffuse axonal injury), who have been admitted to the neuro-intensive care unit, have not received any sedative medication for over 48 hours, and score E1or E2 on the GCS, were studied. The BIS and AEPex were measured every one minute during a-30-minute period, and physiological data were measured every five minutes: heart rate, arterial blood pressure, respiratory rate, oxygen saturation, intracranial pressure (ICP) and GCS.

Results: The BIS and AEPex in the 10 patients with E₁ on the GCS were maintained very low mostly between 0-50 and 25-45, respectively, for BIS and AEPex, with some abrupt high values of both electrophysiological variables in some patients during a 30 minute period. Of the 10 patients with E_1, patients with a more global brain injury were seen with extremely low BIS (nearly “0”). Some patients with E₂ had a little higher AEPex and BIS values and both values were more fluctuating than other patients with E₁. In the comatose patients with M₄ and M₅ (E₂V_TM_4, E₁V_TM₅ and E₁V_TM₄), the BIS values were maintained very high, ranging 60-95, normally considered awake, in most of monitoring period. The BIS and AEPex did not appear to be correlated with ICP.

Conclusions: Both BIS and AEPex were maintained very low in comatose patients with a more global brain injury than patients with a focal neurological injury, with some inter-patient variability. It was presumed that motor activity of GCS greatly affected the BIS being kept extremely high, while AEPex was not considerably influenced by motor response.

 

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