Table 1.

Summary of studies

Study Year-1st Author	Study design	Medical setting	Number of patients	Major findings
2019 Nielsen	Prospective Observational	ITU	102 sepsis or septic shock without acute primary CNS disease	The absence of delirium was independently associated with preserved high-frequency beta activity (> 13 Hz) (P < 10 – 7) and cEEG reactivity (P < 0.001). Delirium was associated with low-frequency cEEG activity and absence of high-frequency cEEG activity. cEEG was helpful in distinguishing delirious from non-delirious septic patients.
2018 Velissaris-Pantzaris	Prospective, Observational	Internal Medicine Department	17 sepsis, without primary CNS involvement	EEG helped to identify brain alterations at an early stage in sepsis, before clinical signs of encephalopathy were evident. The presence of EEG abnormalities did not correlate with the sepsis severity prognostic scores SOFA, APACHE II or SAPS II.
2016 Berisavac	Prospective		39 SAE patients	At the time of clinical exacerbation, SAE patients were more likely to have suppression on the EEG and less likely theta activity. Delta waves, TW waves and suppression of EEG activity were the most common findings 24 h before death (P = 0.0004). The lack of EEG reactivity was also associated with death (P = 0.00043).
2015 Azabou	Prospective Observational	ITU	110 Sepsis patients	Absence of EEG reactivity (OR: 4.44; 95% CI [1.37–14.3]), a delta-predominant background (OR: 3.36; 95% CI [1.08–10.4]), periodic discharges (OR: 3.24; 95% CI [1.03–10.2]), Synek grade ≥ 3 (OR: 5.35; 95% CI [1.66–17.2]) and Young grade > 1 (OR: 3.44; 95% CI [1.09–10.8]) at day 1 to 3 following admission were independent predictors of ITU mortality and were also associated with delirium occurrence.
2015 Gilmore	Prospective Observational	Medical ITU	98 severe sepsis patients	Non-convulsive seizures and periodic discharges are common in patients with severe sepsis and altered mental status. They were less frequent among the most severely ill patients. A lack of EEG reactivity was associated with higher 1-year mortality [mean survival time 3.3 (95% CI 1.8–4.9) vs. 7.5 (6.4–8.7) months; P = 0.002] but the presence of periodic discharges or non-convulsive seizures was not [mean survival time 3.3 (95% CI 1.8–4.9) vs. 7.5 (6.4–8.7) months; P = 0.592].
2013 Semmler	Prospective Observational	ITU	25 sepsis vs 19 non-sepsis ITU survivors	Sepsis patients as well as some non-septic ITU patients had more low-frequency EEG activity compared to healthy controls, indicating non-specific brain dysfunction.
2012 Rosengarten	Prospective Observational	Internal Medicine Department	50 CAP patients	EEG showed a significant drop in the relative frequency of the alpha band and increases in the theta and beta bands in pneumonia patients. This was accompanied by a slowing of the peak frequency in the alpha band and fastening of that in the theta band. When compared to the controls, the power in the theta band was significantly higher in the pneumonia groups.
2010 Van den Boogaard	Prospective		15 Experimental induced endotoxemia 10 Healthy controls	Endotoxemia induced no clinically relevant EEG changes except in one subject with a mild encephalopathic episode but without cognitive dysfunction. Quantitative EEG analysis showed a higher state of alertness detected by changes in the central region, and peak frequency in the occipital region witch significantly correlated with cortisol.
2009 Oddo	Retrospective	Medical ITU	201 medical ITU admissions without a primary acute neurological condition	Patients with sepsis had a higher rate of electroencephalographic seizures (ESZs) and periodic epileptiform discharges (PEDs) than those without sepsis (32% vs. 9%, p < 0.001). Seizures were mainly nonconvulsive. Multivariable analysis, sepsis at ITU admission was the only significant predictor of ESZs or PEDs (OR 4.6, 95%, CI 1.9–12.7, P = 0.002) and they were also associated with death or severe disability at hospital discharge (89% with ESZs or PEDs, vs. 39%; OR 19.1, 95% CI 6.3–74.6, P < 0.001) when controlled for age, coma, and organ dysfunction.
1998 Straver	Prospective		14 SAE patients	All EEGs showed decreased fast activity and an increase in slow wave activity. The abnormalities seen in those patients were independent of the sedation level. Neither the APACHE II score, nor the EEG parameters predicted the outcome.
1992 Young		ITU	62 patients with positive blood cultures	The EEG was more sensitive than clinical criteria for encephalopathy. It also had well-defined categories that correlated with mortality.

ITU: intensive treatment unit; SAE: sepsis-associated encephalopathy; CNS: central nervous system; EEG: electroencephalography.