Background: Patients with cardiac arrest, either with a shockable or non-shockable rhythm, are at high risk of death and neurological impairment. Hypoxic-anoxic brain injury is a major cause of morbidity and mortality in these patients. (1) International Liaison Committee on Resuscitation (ILCOR) recommends moderate therapeutic hypothermia (32°C to 36°C) for patients who achieve return of spontaneous circulation (ROSC) after a cardiac arrest to improve neurological outcome. (2,3) However, the evidence regarding the use of therapeutic hypothermia (TH) is conflicting and inconsistent.

Methods: Relevant electronic databases were queried up till September 21, 2021 using appropriate search criteria. A total of 10 randomized controlled studies (RCTs) comparing TH (32°C to 34°C) with controls (normothermia or temperature≥36°C) in comatose post cardiac arrest patients were included. (4-13)

Results: The study included a total of 3,988 subjects with 1,999 in the TH arm, and 1989 in the control arm. For the outcome of all-cause mortality, there was no statistically significant difference between TH and control (OR 0.83; 95% confidence interval [CI]: 0.66 to 1.05; p = 0.08; I2 = 41%). Similarly, there was no significant difference on neurological outcomes between the two groups (OR 0.78; 95% CI: 0.61 to 1.01; p= 0.07; I2 = 43%). Subgroup analysis was done according to initial cardiac rhythm, shockable and non-shockable. In the shockable rhythm group, there was a decrease in the incidence of all-cause mortality among TH group compared to control group (OR 0.55; 95% CI: 0.37 to 0.80; p = 1.00; I2 = 0%). Similarly, there was a decrease in the incidence of poor neurological outcomes in TH compared to control groups (OR 0.48; 95% CI 0.32 to 0.72; p = 0.92; I2 = 0%). There was no difference in the outcomes among the two groups in patients with non-shockable rhythm.

Conclusions: Therapeutic Hypothermia is associated with improved survival and better neurological outcomes in comatose post-cardiac arrest patients with an initial shockable rhythm. Trials with comprehensive data are needed to confirm the effect of therapeutic hypothermia.

IMAGE 1: Forrest Plot showing Odds Ratio of All-Cause Mortality Among Patients With Shockable and Non-Shockable Rhythm

IMAGE 2: Forrest Plot showing Odds Ratio of Poor Neurological Outcomes Among Patients With Shockable and Non-Shockable Rhythm