Utility of electroencephalogram in altered states of consciousness in intensive care unit patients

BACKGROUND: EEG is an investigative tool for assessing cerebral activity. Although certain EEG patterns may have a specific diagnostic or prognostic inference, they may not be precise for any sole etiology in majority of cases and may need clinical correlation.
OBJECTIVE: Aim of this study was to assess the severity and prognosis of cerebral dysfunction in patients admitted to Intensive Care Unit (ICU) and to evaluate the incidence of non-convulsive status epilepticus (NCSE).
DESIGN: A prospective study, wherein we analyzed EEG characteristics in a series of 70 patients.
SETTING: A tertiary care hospital in Mumbai, India.
PATIENTS: EEG characteristics of 70 patients admitted in ICU over a period of 9 months were comprehensively analyzed. These patients were clinically examined and a questionnaire was completed without knowledge of the EEG findings. EEGs were requested for by neurologist or intensivist and our inclusion criteria were (i) patients with altered sensorium of varying etiology, (ii) unconscious patients at risk for non-convulsive status epilepticus (those with a history of epilepsy), and (iii) unconscious patients with involuntary jerky eye movements.
RESULTS: Of the various clinical presentations on ICU admission, there were 20 patients with seizures, 15 with metabolic disorders, 13 with infective causes, 9 with hypoxia, 9 with cerebro-vascular accident on presentation, 1 patient with alcohol/drug overdose, 2 with intra-cerebral space occupying lesion and 1 with ambiguous etiology on admission (there being an overlap among the presentation). Mean duration from presentation to performing EEG was 13 hours. 64 (91.42%) patients had abnormal EEGs. 32(50%) patients had EEG slowing and 4(6.25%) patient had electro cerebral inactivity. Eleven (21.87%) patients had epileptiform activity on the EEG of which seven did not have overt seizures (NCSE). Follow-up EEGs of these patients showed resolution of the epileptiform activity.
CONCLUSIONS: EEG is useful in patients admitted to ICU in diagnosing NCSE and various other conditions. Emergent EEG study in obtunded patients provides valuable diagnostic and prognostic information.