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Background: Slow waves (< 1 Hz) are the most important electroencephalogram signatures of non-rapid eye movement sleep. While considered to have a substantial importance in, for example, providing conditions for single-cell rest and preventing long-term neural damage, a disturbance in this neurophysiological phenomenon is a potential indicator of brain dysfunction. Methods: Since, in healthy individuals, slow waves can be induced with anesthetics, we tested the possible association between hypoxic brain injury and slow wave activity in comatose post-cardiac arrest patients (N = 10) using controlled propofol exposure. The slow wave activity was determined by calculating the low-frequency (< 1 Hz) power of the electroencephalograms recorded approximately 48 h after cardiac arrest. To define the association between the slow waves and the potential brain injury, the patients’ neurological recovery was then followed for six months. Results: In the patients with good neurological outcome (N = 6), the low-frequency power of electroencephalogram representing the slow wave activity was found to substantially increase (190 ± 83%, mean ± SD) due to the administration of propofol. By contrast, the patients with poor neurological outcome (N = 4) were unable to generate propofol-induced slow waves. Conclusions: In this experimental pilot study, the comatose post-cardiac arrest patients with poor neurological outcome were unable to generate normal propofol-induced electroencephalographic slow wave activity 48 h after cardiac arrest. The finding might offer potential for developing a pharmacological test for prognostication of brain injury by measuring the electroencephalographic response to propofol.

Hypoxic ischemic encephalopathy (HIE) is a severe consequence of cardiac arrest (CA) representing a substantial diagnostic challenge. We have recently designed a novel method for the assessment of HIE after CA. The method is based on estimating the severity of the brain injury by analyzing changes in the electroencephalogram (EEG) slow wave activity while the patient is exposed to an anesthetic drug propofol in a controlled manner. In this paper, Hilbert-Huang Transform (HHT) was used to analyze EEG slow wave activity during anesthesia in ten post-CA patients. The recordings were made in the intensive care unit 36–48 hours after the CA in an experiment, during which the propofol infusion rate was incrementally decreased to determine the drug-induced changes in the EEG at different anesthetic levels. HHT was shown to successfully capture the changes in the slow wave activity to the behavior of intrinsic mode functions (IMFs). While, in patients with good neurological outcome defined after a six-month control period, propofol induced a significant increase in the amplitude of IMFs representing the slow wave activity, the patients with poor neurological outcome were unable to produce such a response. Consequently, the proposed method offer substantial prognostic potential by providing a novel approach for early estimation of HIE after CA.