Introduction. Triphasic waves in an electroencephalogram (EEG) in patients with decreased alertness traditionally is associated with hepatic encephalopathy. The development of digital technologies and the introduction of systems that allow long-term EEG monitoring of the neurocritical care patients has led to accumulation of significant experience in recording triphasic waves in various metabolic, toxic, and structural brain disorders, as well as in nonconvulsive status epilepticus.

Materials and methods. We present a case of diagnosis and successful treatment of a nonconvulsive status epilepticus, that developed in a female patient after CABG, and that presented electrographically as a triphasic wave pattern.

Results. Description of the patient’s EEG according to the classification of rhythmic and periodic patterns of the American Clinical Neurophysiology Society and the use of clinical and EEG criteria of nonconvulsive status epilepticus of the International League Against Epilepsy enabled us to correctly diagnose the cause of her decreased alertness and other neurological symptoms. Proper selection of the antiepileptic drugs along with monitoring of daily EEG recordings led to a recovery of consciousness in the patient and to normalization of the EEG pattern, which confirmed the clinical hypothesis of a nonconvulsive status epilepticus.

Conclusions. Utilization of the modern clinical and electrographic classifications enables the diagnosis of a nonconvulsive epileptic seizure and status epilepticus when the EEG pattern is ambiguous and traditionally associated with other conditions. EEG monitoring must be performed in patients with a sudden deterioration of consciousness that cannot be explained by brain imaging studies.