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Efficacy and Risks of Therapeutic Hypothermia after Pediatric Cardiac Arrest: A Systematic Review

Abstract

Background:

Therapeutic hypothermia is used in adults and neonates after cardiac arrest, but its efficiency in children under 18 years old is still uncertain.

Objective:

To evaluate the effectiveness and risks of therapeutic hypothermia after cardiac arrest in children under 18 years of age through a systematic review.

Methods:

A systematic review was performed in January 2022 in the MEDLINE, SciELO, Cochrane, and LILACS databases. Inclusion criteria: randomized controlled trials (RCTs) performed in humans. Articles from other typologies, published more than 10 years ago, or with volunteers over 18 years old were excluded.

Results:

Four studies were identified, of which 3 were analyzed; all of them were of moderate quality according to the Jadad Scale and the Cochrane Collaboration tool. The studies indicated that lowering the temperature did not improve data on mortality and adverse events. Two studies did not identify statistically significant differences (p > 0.05) considering hypothermia in relation to normothermia in terms of survival, safety, and global neurobehavioral and cognitive function. The other study did not show improved serum biomarker concentrations.

Conclusion:

The results found in this review do not support the use of therapeutic hypothermia after pediatric cardiac arrest, as this intervention did not provide any apparent benefits in terms of safety, adverse events, survival, and neurological impact. We recommend the conduction of new RCTs using the measurement of serum biomarkers to better evaluate the effectiveness of the intervention.

Keywords:
Child; Heart Arrest; Induced; Hypothermia; Systematic Review; Meta-Analysis

Introduction

Cardiac arrest (CA) in children offers high risks to survival, neurological function, and quality of life.11 Bistritz JF, Horton LM, Smaldone A. Therapeutic hypothermia in children after cardiac arrest: a systematic review and meta-analysis. Pediatr Emerg Care. 2015;31(4):296-303. doi: 10.1097/PEC.0000000000000407.
https://doi.org/10.1097/PEC.000000000000...
This condition compromises cerebral blood flow, damages neurons, and results in memory and concentration problems, cerebral palsy, seizures and, in extreme cases, vegetative state and death.22 Scholefield B, Duncan H, Davies P, Gao Smith F, Khan K, Perkins GD, et al. Hypothermia for neuroprotection in children after cardiopulmonary arrest. Cochrane Database Syst Rev. 2013;2013(2):CD009442. doi: 10.1002/14651858.CD009442.pub2.
https://doi.org/10.1002/14651858.CD00944...

CA causes ischemia and decreases oxygenation, producing cytotoxic edema due to cellular depolarization and the consequent influx of salt and water, extracellular accumulation of excitatory amino acids, and neuronal death. Therapeutic hypothermia (TH) is able to reduce neuronal metabolism, oxygen consumption, and cerebral blood flow, in addition to controlling depolarization and limiting cell death.33 Harris B, Andrews PJ, Murray GD, Forbes J, Moseley O. Systematic review of head cooling in adults after traumatic brain injury and stroke. Health Technol Assess. 2012;16(45):1-175. doi: 10.3310/hta16450.
https://doi.org/10.3310/hta16450...
66 Drury PP, Gunn ER, Bennet L, Gunn AJ. Mechanisms of hypothermic neuroprotection. Clin Perinatol. 2014;41(1):161-75. doi: 10.1016/j.clp.2013.10.005.
https://doi.org/10.1016/j.clp.2013.10.00...

TH is used in adults and neonates who have suffered CA, but it is not yet indicated for children in the same situation because the cause of arrest in each of these groups is different: in children, CA mainly results from respiratory problems, while in adults it is mostly due to heart disease. This leads to different injury patterns, making it impossible to generalize the effectiveness of TH in these cases.11 Bistritz JF, Horton LM, Smaldone A. Therapeutic hypothermia in children after cardiac arrest: a systematic review and meta-analysis. Pediatr Emerg Care. 2015;31(4):296-303. doi: 10.1097/PEC.0000000000000407.
https://doi.org/10.1097/PEC.000000000000...
, 22 Scholefield B, Duncan H, Davies P, Gao Smith F, Khan K, Perkins GD, et al. Hypothermia for neuroprotection in children after cardiopulmonary arrest. Cochrane Database Syst Rev. 2013;2013(2):CD009442. doi: 10.1002/14651858.CD009442.pub2.
https://doi.org/10.1002/14651858.CD00944...
, 77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
Evidence indicates that this intervention may have a neuroprotective effect, hence it is under research.88 Prajongkit T, Veeravigrom M, Samransamruajkit R. Prognostic value of continuous electroencephalography in children undergoing therapeutic hypothermia after cardiac arrest: A pilot study. Neurophysiol Clin. 2019;49(1):41-7. doi: 10.1016/j.neucli.2018.09.002.
https://doi.org/10.1016/j.neucli.2018.09...

The aim of this study thus was to verify, via a systematic review, the efficacy and risks of TH after CA in children under 18 years old.99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

Methods

This systematic review was conducted based on the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) methodology.1111 Moher D, Liberati A, Tetzlaff J, Altman DG; PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. PLoS Med. 2009;6(7):e1000097. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

Literature search strategy

The search and selection of studies happened between July 2020 and January 2022, without language restrictions. The Medical Literature Analysis and Retrieval System Online (MEDLINE/PubMed), Scientific Electronic Library Online (SciELO), Cochrane, and Latin American and Caribbean Literature in Health Sciences (LILACS) databases were used in our search. The following descriptors and their synonyms, according to the Medical Subject Headings (MeSH), were used in the search phrase: “hypothermia, induced,” “heart arrest,” and “child.”

Item 4 of the PRISMA methodology refers to the PICO (patient/population, intervention, comparison, outcomes) strategy to guide systematic reviews, and it is presented in Chart 1 .1111 Moher D, Liberati A, Tetzlaff J, Altman DG; PRISMA Group. Preferred reporting items for systematic reviews and meta-analyses: the PRISMA statement. PLoS Med. 2009;6(7):e1000097. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

Chart 1
PICO strategy used in this study.

Inclusion and exclusion criteria

Aiming at the scientific value of the analyzed studies, only randomized controlled trials (RCTs) were selected. Inclusion criteria were: studies with humans that investigated the use of TH after CA in people under 18 years old (using the MEDLINE filters “infant,” “preschool child,” “child,” and “adolescent”). Other types of articles, published more than 10 years ago, with volunteers aged 18 years or older, not directly related to the subject, and duplicates of articles found in more than one database were excluded.

Data extraction

The articles found with the search phrase were analyzed by two independent researchers in the following stages: 1) title analysis; 2) abstract analysis; 3) full article reading when the abstract was related to the topic or when the reading was not sufficient to define its eligibility. Divergences were solved by a third independent author.

Assessment of the quality of information and risk of bias

Two independent authors used the Jadad scale and the Cochrane Collaboration tool for randomized clinical trials to assess the quality of information and risk of bias.1212 Araujo V. Assessment of quality of scientific evidence on musical interventions in caring for cancer patients. Interface (Botucatu). 2014;18:479-92. , 1313 Carvalho AP, Silva V, Grande AJ. Avaliação do risco de viés de ensaios clínicos randomizados pela ferramenta da colaboração Cochrane. Diagn Tratamento. 2013;18:38-44. The Jadad scale assesses whether the research was adequately randomized and described as double-blind, identifying sample losses and exclusions to quantify study quality1212 Araujo V. Assessment of quality of scientific evidence on musical interventions in caring for cancer patients. Interface (Botucatu). 2014;18:479-92. . On the other hand, the Cochrane risk-of-bias tool for randomized trials assesses risks involving allocation, selection, outcome analysis, and other biases.1313 Carvalho AP, Silva V, Grande AJ. Avaliação do risco de viés de ensaios clínicos randomizados pela ferramenta da colaboração Cochrane. Diagn Tratamento. 2013;18:38-44.

Results

Characteristics of the selected studies

Using our search phrase, 446 studies were identified in the databases. When applying the inclusion and exclusion criteria, 22 studies were obtained. After reading the full texts and eliminating those that were not directly related to the topic or that were secondary analyses of the studies by Moler et al.77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
and Moler et al.,99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
3 studies were selected, as shown in Figure 1 .77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

Figure 1
Flowchart of the study selection process.

Sample characteristics

The selected studies comprised a sample of 658 patients under 18 years old, without gender restrictions77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
. Table 1 summarizes the general characteristics of the included publications.

Table 1
General characteristics of the studies included in this systematic review

Analyzed variables

The 3 selected studies assessed mortality and adverse events. Studies 1 and 2 measured survival rates and survival with favorable neurobehavioral outcomes (Vineland Adaptive Behavior Scale, Second Edition – VABS ≥ 70) 1 year after CA. In addition, the impact on neurobehavior and overall cognitive function were analyzed separately.77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
Study 3, on the other hand, showed serum concentrations of biomarkers, unfavorable outcomes, and compared the duration of TH interventions (24 h or 72 h). Table 2 presents the main results.1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

Table 2
Main results of the studies included in this systematic review

Main tools used in the analyzed studies

The VABS-II scale assesses the impacts of CA on neurobehavioral function by analyzing deficiencies in adaptive behavior and development, in addition to motor, communication, socialization, and daily life skills (self-care, personal hygiene, and feeding).1414 Community-University Partnership for the Study of Children, Youth, and Families (2011). Review of the Vineland Adaptive Behavior Scales-Second Edition (Vineland-II). Edmonton, Alberta, Canada; 2021.

In studies 1 and 2, when VABS-II could not be applied, the Pediatric Overall Performance Category (POPC) and Pediatric Cerebral Performance Category (PCPC) scores were used for sample selection77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
. In order to be eligible, children should score 1 (good overall performance) or 2 (mild disability) on these scales. Study 3 used PCPC to identify cases of unfavorable outcomes.1313 Carvalho AP, Silva V, Grande AJ. Avaliação do risco de viés de ensaios clínicos randomizados pela ferramenta da colaboração Cochrane. Diagn Tratamento. 2013;18:38-44. Both POPC and PCPC are based on the Glasgow scale1515 Pollack MM, Holubkov R, Funai T, Clark A, Moler F, Shanley T, et al. Relationship between the functional status scale and the pediatric overall performance category and pediatric cerebral performance category scales. JAMA Pediatr . 2014;168(7):671-6. doi: 10.1001/jamapediatrics.2013.5316.
https://doi.org/10.1001/jamapediatrics.2...
and quantify the morbidity of patients after critical conditions. While POPC classifies functional morbidity, PCPC evaluates cognitive disorders.1616 Volakli E, Sdougka M, Mantzafleri PE , Tsonidis CH, Kontopoulos E, Tsikoulas I. Functional outcome following pediatric intensive care: Pediatric Cerebral Performance Category (PCPC) and Pediatric Overall Performance Category (POPC) during a prospective two years follow-up period. The Greek E-J Periop Med. 2015;13(a):2- 13(a): 2-15. ISSN: 11096888.

The Wechsler Abbreviated Scale of Intelligence (WASI) and the Mullen Scales of Early Learning were used to analyze global cognitive function. The WASI is applied to people aged from 6 to 89 years and investigates aspects such as verbal knowledge, visual information processing, spatial and non-verbal reasoning, and fluid and crystallized intelligence through the evaluation of vocabulary, block design, similarities, and matrix reasoning.1717 Yates DB, Trentini CM, Tosi SD, Corrêa SK, Poggere LC, Valli F. Apresentação da escala de inteligência Wechsler abreviada: (WASI). Aval Psicol. 2006;5(2): 227-33. ISSN: 1677-0471. Online: 2175-3431. The Mullen Scales are applied to children aged 68 months or older and is used to analyze data such as visual perception, expression, and receptive language, as well as fine and gross motor skills.1818 Mullen, E. Infant Mullen Scales of early learning. Minnesota: Circle Pines; 1995. (American Guidance Service).

Methods used by the studies

This review focused only on RCTs, and studies 1 and 2 are considered references on the subj v ect.77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
These used the same method and duration of intervention (120 h): volunteers were sedated, paralyzed, and had their central temperatures monitored at 2 sites (esophageal, rectal, or bladder) using the automatic mode of the temperature control unit. Temperature management was conducted in 2 stages: initially, central temperature was maintained at 33 ºC for 48 h using blankets, which were later reheated for 16 h or more up to 36.8 ºC.77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

The other RCT analyzed in this review used a similar intervention, but with different temperature management: it was kept at 33 ± 1 ºC for 24 h or 72 h, then patients were reheated by 0.5 ºC every 4 h up to 37 ºC.1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

Quality and risk of bias

Table 3 shows the Jadad scale, used for evaluating study quality, and the Cochrane Collaboration tool, employed in the analysis of risk of bias.1212 Araujo V. Assessment of quality of scientific evidence on musical interventions in caring for cancer patients. Interface (Botucatu). 2014;18:479-92. , 1313 Carvalho AP, Silva V, Grande AJ. Avaliação do risco de viés de ensaios clínicos randomizados pela ferramenta da colaboração Cochrane. Diagn Tratamento. 2013;18:38-44. All studies scored a 3 (moderate quality) on the Jadad scale, as they were not described as double-blind. As for the Cochrane tool, the aspect with the highest risk of bias in the 3 studies was the blinding of participants, but other variables still presented uncertain risks.

Table 3
Classification of articles according to quality and risk of bias.

Discussion

Evidence from studies 1 and 2 indicates that TH was not more effective than TN for a better prognosis of children and teenagers after CA both in and out of hospital.77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
In-hospital CA had better outcomes, since its numbers of survivors and favorable functional results were higher.77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

The results of the third study suggest some advantages, considering the levels of serum biomarkers when using TH for 72 h compared to 24 h. No significant differences were identified in the occurrence of adverse events between groups.1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

Mortality

In articles 1 and 2, mortality was evaluated after 28 days, and in study 3, after 6 months. None of the studies found a statistically significant difference between groups, thus TH in the 120-, 24-, and 72-h regimens had no significant effects on mortality in people under 18 years old after CA.77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
It is worth mentioning that differences in confidence intervals for this variable can weaken the comparison between findings.

Adverse events

Hypothermia did not significantly alter the occurrence of adverse events, and its duration (24 or 72 h) did not influence this outcome. Seizures were a frequent adverse effect reported in all 3 studies. The main adverse effects are mentioned in Table 2 and these findings are compatible with those of a meta-analysis that showed that TH may be related to changes in coagulation, neurological function, and serum ion concentrations.11 Bistritz JF, Horton LM, Smaldone A. Therapeutic hypothermia in children after cardiac arrest: a systematic review and meta-analysis. Pediatr Emerg Care. 2015;31(4):296-303. doi: 10.1097/PEC.0000000000000407.
https://doi.org/10.1097/PEC.000000000000...

Survival at 12 months

Articles 1 and 2 concluded that there was no significant difference between groups in terms of survival one year after CA,7,9,19-25 so it is not possible to state that TH was able to increase 12-month survival.

Secondary analyses of this evidence point to some risk factors such as: children under 1 year old, serum lactate concentrations ≥ 10 mmol / L, the use of more than 4 doses of adrenaline, and chest compressions performed for more than 30 minutes.21,34 Patients who had CA during the weekends or caused by a condition that threatens life or sudden unexpected death also had lower survival rates as a consequence of prolonged exposure to the absence of blood flow.2121 Meert KL, Telford R, Holubkov R, Slomine BS, Christensen JR, Dean JM, et al. Therapeutic Hypothermia after Pediatric Cardiac Arrest (THAPCA) Trial Investigators. Pediatric Out-of-Hospital Cardiac Arrest Characteristics and Their Association With Survival and Neurobehavioral Outcome. Pediatr Crit Care Med. 2016;17(12):e543-e550. doi: 10.1097/PCC.0000000000000969.
https://doi.org/10.1097/PCC.000000000000...

Other risk factors for survival are preexisting health conditions and the requirement for renal replacement therapy. Renal impairment before or after CA decreases survival rates by intensifying electrolyte and blood pH changes caused by the arrest.2424 Meert K, Telford R, Holubkov R, Slomine BS, Christensen JR, Berger J, et al. Paediatric in-hospital cardiac arrest: Factors associated with survival and neurobehavioural outcome one year later. Resuscitation. 2018;124:96-105. doi: 10.1016/j.resuscitation.2018.01.013.
https://doi.org/10.1016/j.resuscitation....
, 2525 Meert KL, Delius R, Slomine BS, Christensen JR, Page K, Holubkov R, et al. One-Year Survival and Neurologic Outcomes After Pediatric Open-Chest Cardiopulmonary Resuscitation. Ann Thorac Surg. 2019;107(5):1441-6. doi: 10.1016/j.athoracsur.2018.11.028.
https://doi.org/10.1016/j.athoracsur.201...

Protective factors are: administration of low doses of adrenaline, heart rate before CA with ventricular tachycardia and ventricular fibrillation, cardiac etiology, CA occurring during the week and the day, and in-hospital CA. Patients who had in-hospital CA were twice as likely to survive when compared to those who had out-of-hospital CA.21,22

Survival with favorable neurobehavior

Articles 1 and 2 defined survival with favorable neurobehavior as scoring at least 70 points on the VASB II scale in the first year after CA. Both studies reported that there was no statistically significant difference between groups.77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 1919 Moler FW, Hutchison JS, Nadkarni VM, Silverstein FS, Meert KL, Holubkov R, et al. Therapeutic hypothermia after pediatric cardiac arrest out-of-hospital Trial Investigators. Targeted temperature management after pediatric cardiac arrest due to drowning: outcomes and complications. Pediatr Crit Care Med. 2016;17(8):712-20. doi: 10.1097/PCC.0000000000000763.
https://doi.org/10.1097/PCC.000000000000...
2222 Scholefield BR, Silverstein FS, Telford R, Holubkov R, Slomine BS, Meert KL, et al. Therapeutic hypothermia after paediatric cardiac arrest: Pooled randomized controlled trials. Resuscitation. 2018;133:101-7. doi: 10.1016/j.resuscitation.2018.09.011.
https://doi.org/10.1016/j.resuscitation....
,24-26

Secondary analyses suggest some risk factors: children under 1 year old or 5–12 years old, CA caused by a life-threatening condition or by sudden unexpected infant death , low blood pH and platelet count, serum lactate concentrations ≥ 10 mmol / L, and obesity.2121 Meert KL, Telford R, Holubkov R, Slomine BS, Christensen JR, Dean JM, et al. Therapeutic Hypothermia after Pediatric Cardiac Arrest (THAPCA) Trial Investigators. Pediatric Out-of-Hospital Cardiac Arrest Characteristics and Their Association With Survival and Neurobehavioral Outcome. Pediatr Crit Care Med. 2016;17(12):e543-e550. doi: 10.1097/PCC.0000000000000969.
https://doi.org/10.1097/PCC.000000000000...
, 2222 Scholefield BR, Silverstein FS, Telford R, Holubkov R, Slomine BS, Meert KL, et al. Therapeutic hypothermia after paediatric cardiac arrest: Pooled randomized controlled trials. Resuscitation. 2018;133:101-7. doi: 10.1016/j.resuscitation.2018.09.011.
https://doi.org/10.1016/j.resuscitation....

Factors such as CA , the administration of a lower dose of adrenaline, and underweight children were listed as protective. In-hospital CA was considered a protective factor, and patients with this condition were 3 times more likely to survive with favorable neurobehavior when compared to those who had out-of-hospital arrests.21,22 Obesity influences this variable because it compromises the precision of the concentration of drugs administered for resuscitation and the correct energy for defibrillation, which require the patient’s weight for their calculations. In addition, the quality of cardiopulmonary resuscitation is affected in obese patients.21

It is thus not possible to state that TH was effective in guaranteeing a good neurobehavioral outcome in 1-year CA survivors, as it is not the only factor that influences survival with favorable neurobehavior.

Adverse outcome

An adverse outcome was established by article 3 as a PCPC score of 4, 5, or 6, or an increase > 1. Eleven children in the 24-h TH group (65%) and 10 in the 72-h TH group (59%) had an adverse outcome, with no difference between groups 6 months later. It is noteworthy that S100b levels were increased in participants who underwent 24-h therapy before this change could have a direct relationship with the intervention. Since these levels are linked to brain damage , it cannot be said that the interventions were the sole responsible for the observed results.1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

While studies 1 and 2 prioritized the use of VABS-II, study 3 used exclusively PCPC to analyze the impact of TH on neurobehavioral outcome, impairing the analysis of this variable.

Neurobehavioral evaluation

A neurobehavioral evaluation was performed in studies 1 and 2, based on the difference between VABS-II right after CA and 1 year after the intervention.77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
Patients with good results had a difference in VABS ≥ 15.99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 2323 Moler FW, Silverstein FS, Nadkarni VM, Meert KL, Shah SH, Slomine B, et al. Pediatric out-of-hospital cardiac arrest: Time to goal target temperature and outcomes. Resuscitation. 2019;135:88-97. doi: 10.1016/j.resuscitation.2018.12.012.
https://doi.org/10.1016/j.resuscitation....
Those who died and those who obtained the lowest possible score in VABS-II were classified as having the worst results.99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 2222 Scholefield BR, Silverstein FS, Telford R, Holubkov R, Slomine BS, Meert KL, et al. Therapeutic hypothermia after paediatric cardiac arrest: Pooled randomized controlled trials. Resuscitation. 2018;133:101-7. doi: 10.1016/j.resuscitation.2018.09.011.
https://doi.org/10.1016/j.resuscitation....

The change between baseline scores and scores after 12 months and the difference of less than 15 points were similar between groups in both studies.99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 1919 Moler FW, Hutchison JS, Nadkarni VM, Silverstein FS, Meert KL, Holubkov R, et al. Therapeutic hypothermia after pediatric cardiac arrest out-of-hospital Trial Investigators. Targeted temperature management after pediatric cardiac arrest due to drowning: outcomes and complications. Pediatr Crit Care Med. 2016;17(8):712-20. doi: 10.1097/PCC.0000000000000763.
https://doi.org/10.1097/PCC.000000000000...
, 2222 Scholefield BR, Silverstein FS, Telford R, Holubkov R, Slomine BS, Meert KL, et al. Therapeutic hypothermia after paediatric cardiac arrest: Pooled randomized controlled trials. Resuscitation. 2018;133:101-7. doi: 10.1016/j.resuscitation.2018.09.011.
https://doi.org/10.1016/j.resuscitation....
, 2727 Slomine BS, Silverstein FS, Christensen JR, Page K, Holubkov R, Dean JM, et al. Neuropsychological Outcomes of Children 1 Year After Pediatric Cardiac Arrest: Secondary Analysis of 2 Randomized Clinical Trials. JAMA Neurol. 2018;75(12):1502-10. doi: 10.1001/jamaneurol.2018.2628.
https://doi.org/10.1001/jamaneurol.2018....
3030 Slomine BS, Silverstein FS, Christensen JR, Holubkov R, Page K, Dean JM, et al. THAPCA Trial Group. Neurobehavioral Outcomes in Children After Out-of-Hospital Cardiac Arrest. Pediatrics. 2016;137(4):e20153412. doi: 10.1542/peds.2015-3412.
https://doi.org/10.1542/peds.2015-3412...
Drowning was related to less negative impacts, while respiratory etiologies aggravated the condition.29

Advanced age and high initial VABS-II were related to worse results. According to a secondary analysis, this may be due to the inability of young children to perform the activities measured by the test, causing their initial score to be reduced and the decline after 12 months to be smaller, making the deficit less evident when compared to older children.2929 Slomine BS, Nadkarni VM, Christensen JR, Silverstein FS, Telford R, Topjian A, et al. Therapeutic Hypothermia after Pediatric Cardiac Arrest THAPCA Trial Investigators. Pediatric cardiac arrest due to drowning and other respiratory etiologies: Neurobehavioral outcomes in initially comatose children. Resuscitation. 2017;115:178-84. doi: 10.1016/j.resuscitation.2017.03.007.
https://doi.org/10.1016/j.resuscitation....

The evidence indicates that TH was not beneficial in fighting brain damage from hypoxemia. Intrinsic factors, however, can change VABS-II results, but they do not reflect cognitive deficits themselves.

Global cognitive function

Global cognitive function was rated in studies 1 and 2 using the Early Learning Composite score from the Mullen Scales of Early Learning, the IQ scored at the WASI, and the combined Mullen and Wechsler tests . The WASI was used in participants aged 6 years or older and the Mullen scales, in children under 6 years old. The results did not differ between groups.77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 99 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic hypothermia after out-of-hospital cardiac arrest in children. N Engl J Med. 2015;372(20):1898-908. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

Secondary analyses investigated the impairment of specific skills due to ischemic injury to identify individual demands in the rehabilitation and education of children and teenagers after CA. Those most affected were: executive function, fine motor skills, visuomotor skills, and visual memory. On the other hand, the IQ did not change significantly.2727 Slomine BS, Silverstein FS, Christensen JR, Page K, Holubkov R, Dean JM, et al. Neuropsychological Outcomes of Children 1 Year After Pediatric Cardiac Arrest: Secondary Analysis of 2 Randomized Clinical Trials. JAMA Neurol. 2018;75(12):1502-10. doi: 10.1001/jamaneurol.2018.2628.
https://doi.org/10.1001/jamaneurol.2018....
3030 Slomine BS, Silverstein FS, Christensen JR, Holubkov R, Page K, Dean JM, et al. THAPCA Trial Group. Neurobehavioral Outcomes in Children After Out-of-Hospital Cardiac Arrest. Pediatrics. 2016;137(4):e20153412. doi: 10.1542/peds.2015-3412.
https://doi.org/10.1542/peds.2015-3412...

Younger children do not have these areas fully developed, so deficiencies may be less noticeable, whereas in older children these changes are easily identified and closely linked to the sites that are most sensitive to hypoxic injury.27 One of the evaluations by VABS-II aimed to discover which cognitive deficits the child already had before the arrest, reporting the effectiveness of the intervention more accurately.2727 Slomine BS, Silverstein FS, Christensen JR, Page K, Holubkov R, Dean JM, et al. Neuropsychological Outcomes of Children 1 Year After Pediatric Cardiac Arrest: Secondary Analysis of 2 Randomized Clinical Trials. JAMA Neurol. 2018;75(12):1502-10. doi: 10.1001/jamaneurol.2018.2628.
https://doi.org/10.1001/jamaneurol.2018....

Studies have not indicated a protective effect of TH on global cognitive function, and the analysis of the impact of this intervention was compromised by the influence of age and preexisting conditions.

Safety

In studies 1 and 2, the incidence of infection, the need for blood products, and the occurrence of severe arrhythmias 7 days after randomization were analyzed as safety measures. The incidence rates of these parameters were similar in both groups.77 Moler FW, Silverstein FS, Holubkov R, Slomine BS, Christensen JR, Nadkarni VM, et al. THAPCA Trial Investigators. Therapeutic Hypothermia after In-Hospital Cardiac Arrest in Children. N Engl J Med. 2017;376(4):318-29. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 1919 Moler FW, Hutchison JS, Nadkarni VM, Silverstein FS, Meert KL, Holubkov R, et al. Therapeutic hypothermia after pediatric cardiac arrest out-of-hospital Trial Investigators. Targeted temperature management after pediatric cardiac arrest due to drowning: outcomes and complications. Pediatr Crit Care Med. 2016;17(8):712-20. doi: 10.1097/PCC.0000000000000763.
https://doi.org/10.1097/PCC.000000000000...
, 2020 Meert K, Telford R, Holubkov R, Slomine BS, Christensen JR, Dean JM, et al. Therapeutic Hypothermia after Paediatric Cardiac Arrest (THAPCA) Trial Investigators. Exploring the safety and efficacy of targeted temperature management amongst infants with out-of-hospital cardiac arrest due to apparent life threatening events. Resuscitation. 2016;109:40-8. doi: 10.1016/j.resuscitation.2016.09.026.
https://doi.org/10.1016/j.resuscitation....
, 2222 Scholefield BR, Silverstein FS, Telford R, Holubkov R, Slomine BS, Meert KL, et al. Therapeutic hypothermia after paediatric cardiac arrest: Pooled randomized controlled trials. Resuscitation. 2018;133:101-7. doi: 10.1016/j.resuscitation.2018.09.011.
https://doi.org/10.1016/j.resuscitation....

It can thus be inferred that TH in the 120-h regimen can be considered a safe intervention, since it did not expose patients to a higher risk of complications when compared to the TN group.

Biomarker concentration

Study 3 evaluated the serum concentrations of biomarkers such as neuron specific enolase (NSE), S100b, and myelin basic protein (MBP). Three mL of blood were collected by a blinded technician for treatment and results, twice a day (every 12 h) for 4 days, and once on the seventh day after spontaneous return of circulation.1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

These biomarkers assist in the prediction of therapeutic characteristics and neurological prognosis, also helping in the choice of treatment.1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...
, 3131 Oliveira Carla de, Ikuta Nilo, Regner Andrea. Biomarcadores prognósticos no traumatismo crânio-encefálico grave. Rev bras ter intensiva. 2008; 20(4): 411-21. PMID: 25307248. Neuronal injuries and worse results were concluded to be related to higher serum concentrations of NSE and S100b.1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

The concentrations of all biomarkers were higher in the 24-h group, except for MBP on day 7, and baseline concentrations were similar in both arms. It is worth mentioning that S100b was increased in the 24-h group in the 12-h to 24-h period, and it is not possible to state that this difference was due to the intervention.1010 Fink EL, Clark RSB, Berger RP, Fabio A, Angus DC, Watson RS, et al. 24 vs. 72 hours of hypothermia for pediatric cardiac arrest: A pilot, randomized controlled trial. Resuscitation. 2018;126:14-20. doi: 10.1056/NEJMoa1610493.
https://doi.org/10.1056/NEJMoa1610493...

Researchers advise that these measurements should be validated for clinical use in pediatric CA, as they complement clinical results and help guide care. Moreover, these concentrations should be inclusion criteria in neuroprotective therapy trials or be used to optimize their duration.10

Although considered efficient in the analysis of neurological injuries, the measurement of these biomarkers has been little addressed in studies on the subject. In this context, more RCTs should be performed associating these biomarkers with clinical aspects to validate them as instruments for assessing TH on post-CA neurological outcomes.

Limitations

Limitations of this study involve the analysis of studies with different methodologies and tools for assessing neurobehavioral state and the impossibility of blinding researchers.

It is worth mentioning that the benefits of TH cannot be totally denied by the observed results, as some statistical data showed confidence intervals that contemplated 1. Therefore, the intervention may or not be a protective factor, requiring further studies with larger samples and longer follow-up periods to reach more definitive results.

In addition, studies had some specific limitations: article 1 was interrupted because of the difficulty in obtaining an adequate sample size, associated with minor benefits. Furthermore, the delay in reaching the desired temperature delayed the return of circulation, which may have caused adverse effects. Study 2 postponed the evaluations of patients with hypothermia, which may cause a false idea of greater survival rates after the intervention. In article 3, a small sample size was used, and the PCPC was not blindly applied.7,9,10

Conclusions

There was no apparent benefit of TH compared to TN after pediatric CA regarding its efficacy and risk prevention, thus it is not possible to recommend this intervention. Other RCTs, involving larger samples, similar tools, and exploring the measurement of serum biomarkers, are necessary to assess this intervention.

  • Sources of funding
    This study was funded by a scholarship for a research internship dissertation from Faculdade de Ciências Médicas e da Saúde de Juiz de Fora.
  • Study association
    This article is part of the research internship dissertation from Faculdade de Ciências Médicas e da Saúde de Juiz de Fora.
  • Ethical approval and consent
    This article does not contain any studies with human participants or animals performed by any of the authors.

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Publication Dates

  • Publication in this collection
    22 Apr 2022
  • Date of issue
    Nov-Dec 2022

History

  • Received
    07 Oct 2021
  • Reviewed
    03 Feb 2022
  • Accepted
    23 Feb 2022
Sociedade Brasileira de Cardiologia Avenida Marechal Câmara, 160, sala: 330, Centro, CEP: 20020-907, (21) 3478-2700 - Rio de Janeiro - RJ - Brazil
E-mail: revistaijcs@cardiol.br