Hypothermia for Neuroprotection in Adults After Cardiac Arrest

Abstract

What are the effects of therapeutic hypothermia after cardiac arrest on neurologic outcomes, survival, and adverse events?Cardiac arrest refers to a sustained decrease in function of the heart without evidence of circulation.1 Recent reports indicate that cardiac arrest causes between 15% and 20% of deaths in many countries.2 Those who survive a cardiac arrest have a high risk of neurologic harm due to hypoxia and a resultant decreased quality of life.3 Management strategies for cardiac arrest include early cardiopulmonary resuscitation with defibrillation, circulatory support, and temperature management.4 The use of therapeutic hypothermia, also referred to as targeted temperature management, may help protect against neurologic damage after cardiac arrest through several pathways, including slowing down the inflammation process and reducing cerebral metabolism and edema.5 Although previous studies indicated that induced hypothermia was beneficial, some recent research has shown no benefit from this strategy and a potential risk of harm.6 A recent retrospective analysis of cardiac arrests in US hospitals showed that only 0.85% of patients received targeted temperature management7; therefore, evaluation of this approach is warranted. Exploring recommendations from systematic reviews, the highest form of evidence, can help guide clinical decision-making.This systematic review summary is based on an update to previously published systematic reviews on the topic conducted in 2009, 2012, and 2016.8 As new evidence on a topic becomes available, updates are necessary to account for the results that the new evidence presents. This update, conducted by Arrich et al8 in 2023, included 12 randomized controlled trials comprising 3956 adult participants.The team investigated neurologic outcomes as the main primary outcome, with the main secondary outcomes of survival, pneumonia, hypokalemia, and arrhythmia. These outcomes were assessed by comparing therapeutic hypothermia practices (cooling to 32–34 °C) with standard temperature management practices (>36 °C).Arrich et al8 independently assessed the risk of bias for each study, including selection, performance, detection, attrition, reporting, and publication biases (through visual inspection of funnel plots). Any disagreements were resolved by reviewing the data together and discussing them. The authors used risk ratios (RRs) with 95% CIs as measures of treatment effect between the comparisons and outcomes.8 They used the internationally approved GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach to determine the certainty of evidence—high, moderate, low, or very low—for each outcome9: Low-certainty evidence indicated better neurologic outcomes for the therapeutic hypothermia group (RR, 1.41 [95% CI, 1.12-1.76]; 3914 participants).Low-certainty evidence indicated no significant difference in survival to hospital discharge between the 2 groups (RR, 1.07 [95% CI, 0.95-1.20]; 3871 participants).Low-certainty evidence indicated that pneumonia was more frequent in the therapeutic hypothermia group (RR, 1.09 [95% CI, 1.00-1.18]; 3634 participants).Very-low-certainty evidence indicated that hypokalemia was more frequent in the therapeutic hypothermia group (RR, 1.38 [95% CI, 1.03-1.84]; 975 participants).Low-certainty evidence indicated that arrhythmias were more frequent in the therapeutic hypothermia group (RR, 1.40 [95% CI, 1.19-1.64]; 2163 participants).This systematic review yielded low-certainty evidence that, compared with standard practices (temperature management >36 °C), the use of therapeutic hypothermia after cardiac arrest may improve neurologic outcomes, with no difference found in terms of survival. Given that the therapeutic hypothermia group had an increased frequency of pneumonia, hypokalemia, and arrhythmias, appropriate treatment plans can be anticipated.Although the findings of this review aligned with best practices and current recommendations, the ongoing use of therapeutic hypothermia warrants further investigation and evaluation, and potentially updated guidelines (eg, from the American Heart Association). Other systematic reviews have indicated that the use of therapeutic hypothermia after cardiac arrest did not improve outcomes.10,11 Some of the evidence used to draw those conclusions were also graded as low certainty, which suggests that further research is needed to gain greater clarity. In contrast, a different systematic review conducted earlier this year showed that the use of hypothermia after cardiac arrest was associated with improved neurologic and survival outcomes.12The varying results of these sources of evidence can leave clinical care teams unsure of what approach is best for their patients. Furthermore, even systematic reviews need to be critically appraised for quality, inclusion and exclusion parameters, and relevance to a specific patient population before we can consider basing practice on the results or changing current practice. In evaluating the use of therapeutic hypothermia, a factor to consider is the method of cooling, specifically whether it is intravascular cooling or surface cooling. In 1 study, intravascular cooling was found to be a better therapeutic option than surface cooling.12The evidence from this systematic review and other recent evidence may affect decisions of the clinical care team in the development of treatment plans for patients who have experienced cardiac arrest. An important part of our role as nurses caring for critically ill patients is advocating for the best evidence-based treatment. We must always consider the best available evidence and understand the feasibility, appropriateness, meaningfulness, and effectiveness of any intervention to determine whether to implement it in a given situation.

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