Table 1.

Summary of electrophysiological research in post-cardiac arrest (CA) survivors with therapeutic hypothermia (TH) intervention.

Research Group	Background Condition of Subjects	The Timing of the Monitoring	Results
Clinical Study
Rossetti et al., 2010 [16]	111 consecutive comatose post-CA patients and not brain dead within 48 h TH to 33 ± 1 °C for 24 h and passively rewarming to 35 °C	Continuous electroencephalography (cEEG) and SSEPs were recorded within 72 h after CA	Unreactive EEG background was strongly associated with mortality (adjusted odds ratio for death, 15.4). The presence of at least 2 independent predictors out of 4 (incomplete brainstem reflexes, myoclonus, unreactive EEG, and absent cortical SSEP) accurately predicted poor long-term neurological outcome (Positive Predictive Value (PPV) = 1.00).
Rundgren et al., 2010 [17]	111 consecutive comatose post-CA patients with a Glasgow Coma Scale score of less than 7 TH to 33 ± 1 °C for 24 h and rewarm at 0.5 °C/h	Amplitude-Integrated EEG (aEEG) monitoring was stopped if the patients showed signs of awakening, death or persistent comatose and no later than 120 h after CA	aEEG continuous pattern was highly correlated with the recovery of consciousness (29/31 patients at start of registration and 54/62 patients at normothermia). Patients with aEEG suppression-burst pattern remained comatose even dead. The aEEG status epilepticus (Negative Predictive Value (NPV) of 0.92) developing from a continuous background was found in patients who regained consciousness (2/10 patients).
Seder et al., 2010 [18]	97 post-CA patients within 12 h of ROSC TH to 33 ± 1 °C for up to 24 h and rewarm to 36.5 °C within 12 h	Bispectral Index Monitoring (BIS) monitoring was recorded until rewarming was completed	The higher BIS predicted good outcome with likelihood ratio of 14.2 and an area under the curve of 0.91. Supression ratio larger than 48 predicted poor outcome with likelihood ratio of 12.7 and an area under the curve of 0.90.
Tjepkema-Cloostermans et al., 2013 [19]	109 consecutive comatose post-CA patients without addition neurologic injuries TH to 33 °C for 24 h	EEG recordings were started after the patients’ arrival on the ICU and lasted up to 5 days or until discharge	At 24 h after CA, a Cerebral Recovery Index (CRI) < 0.29 predicted poor outcome (sensitivity = 0.55, specificity = 1.00, PPV = 1.00, NPV = 0.71). A CRI > 0.69 predicted good outcome (sensitivity = 0.25, specificity = 1.00, PPV = 0.55, NPV = 1.00).
Noirhomme et al., 2014 [20]	46 postanoxic comatose patients The average time from CA to ROSC was 20 ± 12 min TH to 33 ± 1 °C for 24 h	Video-EEG was performed during TH for at least 20 min and repeated after rewarming	Non-reactive EEG background and discontinuous EEG background were strongly associated with poor outcome and continuous EEG was related with good outcome by automatic analysis of EEG background and reactivity.
Grippo et al., 2013 [21]	60 consecutive comatose post-CA patients (Glasgow Coma Scale < 9) within 60 min from collapse to ROSC TH to 33 ± 1 °C for 24 h	Somatosensory evoked potentials (SSEPs) were recorded during TH and after re-warming	None of patients with the absence of N20 regained consciousness. The patients with the absence of N20 during TH did not get the recovery of N20 after re-warming.
Animal Study
Chen et al., 2013 [22]	20 adult rats under 5-min cardiac arrest TH to 33.5 °C for 2 h and re-warming to 37 °C over 2 h	cEEG was recorded for 6 h	Burst frequency and spectrum entropy of EEG measurement were higher in hypothermia group than normothermia group and they were highly correlated with 96-hr favorable outcome and survival.
Jia et al., 2008 [23]	24 adult rats under 7-min asphyxia-cardiac arrest TH to 33 ± 1 °C for 6 h and re-warming from 33 to 37 °C in 2 h Hyperthermia to 39 ± 0.5 °C and cooling to 37 °C in 2 h	cEEG was recorded hypothermia and re-warming and additon 2-h recovery period Serial 30-min recording was conducted at 24, 48 and 72 h after ROSC	Information Quantities (IQs) in normothermia group and hyperthermia were significantly lower than those in hypothermia group. The cut-off points at 30 min, 60 min, 2 h and 4 h could accurately predict good outcome, especially the cut-off point of 0.523 at 60 min with sensitivity of 81.8% and specificity of 100%.