Association between rewarming duration and neurological outcome in out-of-hospital cardiac arrest patients receiving therapeutic hypothermia

Temperature Control in the Era of Personalized Medicine: Knowledge Gaps, Research Priorities, and Future Directions

Hypoxic-ischemic brain injury (HIBI) is the leading cause of death and disability after cardiac arrest. To date, temperature control is the only intervention shown to improve neurologic outcomes in patients with HIBI. Despite robust preclinical evidence supporting hypothermia as neuroprotective therapy after cardiac arrest, there remains clinical equipoise regarding optimal core temperature, therapeutic window, and duration of therapy. Current guidelines recommend continuous temperature monitoring and active fever prevention for at least 72 h and additionally note insufficient evidence regarding temperature control targeting 32 °C-36 °C. However, population-based thresholds may be inadequate to support the metabolic demands of ischemic, reperfused, and dysregulated tissue. Promoting a more personalized approach with individualized targets has the potential to further improve outcomes. This review will analyze current knowledge and evidence, address research priorities, explore the components of high-quality temperature control, and define critical future steps that are needed to advance patient-centered care for cardiac arrest survivors.

Randomized comparison between a forced air system and warm water bath for resuscitation of neonatal hypothermic calves with or without oral administration of caffeine

BACKGROUND

Hypothermia is a cause of neonatal calf death in cold climates. Practical and effective rewarming methods are important for bovine health within affected regions.

HYPOTHESIS/OBJECTIVES

To compare the rewarming rate and blood analytes (glucose, lactate, and cortisol) of calves resuscitated with forced air with warm water bath, with or without oral administration of caffeine.

ANIMALS

Twenty healthy neonatal Holstein bull calves.

METHODS

In this randomized, prospective study, calves born healthy and without history of dystocia were cooled to 32°C rectal temperature then thermally resuscitated using either forced air rewarming or warm water bath (40°C) with or without oral administration of caffeine. Rectal temperatures were used to quantify recovery rate. Measurements of glucose, lactate, and cortisol were recorded for every 2°C change in rectal temperature.

RESULTS

Rectal temperature decline (0.03°C per minute) and total cooling time (191.0 ± 33.3 minutes) did not significantly differ among treatment groups. Calves were successfully resuscitated to 38°C by either method. Time required to euthermia using warm water was significantly faster (0.1°C per minute; 64.3 ± 17.8 minute; P < .05) than forced air (0.05°C per minute; 123.1 ± 20.0 minutes). Caffeine had no significant effect on resuscitation rate (P = .14; 95% CI, -0.002 to 0.024) in either treatment; however, caffeine was associated with reduced time to euthermia by 8.3 and 10.8 minutes, respectively. Changes in metabolic variables (glucose, lactate, and cortisol), were inversely related to rectal temperature with no statistical significance among rewarming methods.

CONCLUSIONS AND CLINICAL IMPORTANCE

Although warm water submersion is faster, forced air rewarming is an effective alternative for restoration of euthermia.

Characterizing the impact of thermoregulation in patients after cardiac arrest: a retrospective cohort study

PURPOSE

Core body temperature has been extensively investigated as a thereuptic target in care after cardiac arrest. Nevertheless, the integrity of thermoregulation in patients after cardiac arrest has not been well studied. We sought to evaluate whether low spontaneous body temperature after cardiac arrest is associated with increased death and a worse neurologic outcome, and whether patients with low spontaneous body temperature exhibit features suggestive of impaired thermoregulation.

METHODS

We conducted a single-centre retrospective cohort study. We included all adult patients who underwent temperature control with hypothermia after cardiac arrest between 1 January 2014 and 30 June 2020. The primary exposure was low spontaneous core body temperature (< 35 °C) at initiation of hypothermia therapy. The primary outcome was in-hospital death and the secondary outcome was poor neurologic outcomes at discharge.

RESULTS

Five hundred and ninety-seven adult patients, comprising both in- and out-of-hospital cardiac arrests, were included. Patients with low spontaneous body temperature also had slightly lower average temperature, and more frequent transient but controlled breakthrough fever episodes in the first 24 hr. In the multivariable logistic regression analysis, low spontaneous body temperature was associated with higher odds of in-hospital death (odds ratio, 2.9; 95% confidence interval, 1.9 to 4.2; P < 0.001).

CONCLUSION

In this single-centre retrospective cohort study, low spontaneous core body temperature was associated with poor outcomes in patients after cardiac arrest. Patients with low spontaneous body temperature also exhibited features suggestive of impaired thermoregulation. Further research is needed to determine whether body temperature upon presentation reflects the robustness of the patient's underlying physiology and severity of brain insult after a cardiac arrest.

Temperature Control After Cardiac Arrest: A Narrative Review

Cardiac arrest (CA) is a critical public health issue affecting more than half a million Americans annually. The main determinant of outcome post-CA is hypoxic-ischemic brain injury (HIBI), and temperature control is currently the only evidence-based, guideline-recommended intervention targeting secondary brain injury. Temperature control is a key component of a post-CA care bundle; however, conflicting evidence challenges its wide implementation across the vastly heterogeneous population of CA survivors. Here, we critically appraise the available literature on temperature control in HIBI, detail how the evidence has been integrated into clinical practice, and highlight the complications associated with its use and the timing of neuroprognostication after CA. Future clinical trials evaluating different temperature targets, rates of rewarming, duration of cooling, and identifying which patient phenotype benefits from different temperature control methods are needed to address these prevailing knowledge gaps.

Rapid rewarming rate associated with favorable neurological outcomes in patients with post-cardiac arrest syndrome patients treated with targeted temperature management

Aim

To determine whether the rewarming rate is associated with neurological outcomes in patients with post-cardiac arrest syndrome treated with targeted temperature management (TTM) at 34°C.

Methods

We conducted a retrospective analysis of a nationwide cohort study of out-of-hospital cardiac arrest in Japan. Adult patients who experienced a return of spontaneous circulation and completed TTM at 34°C between June 2014 and December 2019 were divided equally into three groups (slow, moderate, and rapid) according to their rewarming rates from 34°C to 36°C. The rates of favorable neurological outcomes (Cerebral Performance Category of 1-2 after 30 days) were compared among the groups, and the adjusted odds ratios for a favorable neurological outcome were calculated for the groups.

Results

We analyzed 348, 357, and 358 patients in the slow, moderate, and rapid groups, respectively. The periods of rewarming from 34°C to 36°C were 41.9 ± 10.5, 22.4 ± 1.8, and 12.2 ± 3.6 h, respectively. The number of favorable neurological outcomes after 30 days was 121 (34.8%), 125 (35.0%), and 147 (41.1%), respectively, with no significant differences among the three groups (p = 0.145). Rapid rewarming was independently associated with a favorable neurological outcome compared with slow rewarming (adjusted odds ratio 1.57 [95% confidence interval 1.04-2.37]; p = 0.031).

Conclusions

Rapid rewarming after TTM at 34°C was associated with a more favorable neurological outcome than slow rewarming.

Globally, GDP Per Capita Correlates Strongly with Rates of Bystander CPR

Introduction:

Bystander CPR is vital in improving outcomes for out-of-hospital cardiac arrest. There has been ample literature describing disparities in bystander CPR within specific countries, such as the United States, Australia, and the Netherlands. However, there has not been significant literature describing such disparities between countries.

Methods:

We examined various studies published between 2000 and 2021 that reported rates of bystander CPR in various countries. These bystander CPR rates were correlated with the GDP per capita of that country during the time the study was conducted. The correlation between GDP per capita and rates of bystander CPR was assessed.

Results:

A total of 29 studies in 35 communities across 25 countries were examined. Reported rates of bystander CPR ranged from 1.3% to 72%. From this, a strong and significant correlation between GDP per capita and rates of bystander CPR was apparent; 0.772 (p < .01), r² = 0.596.

Conclusions:

GDP per capita can be thought of as a composite endpoint that takes into account various aspects of a country’s social and economic well-being. Socioeconomically-advantaged communities likely have a better ability to provide CPR education to community members, and our findings mirror localized analyses comparing socioeconomic status and rates of bystander CPR. Future studies should continue to elucidate transnational disparities in cardiac arrest, and efforts should be directed at providing CPR education to communities with low rates of bystander CPR; low-and-middle-income countries may represent attractive targets for such interventions. However, it may be possible that rates of bystander CPR may not improve unless significant upstream improvements to socioeconomic factors take place.

Impact of rewarming rate on interleukin-6 levels in patients with shockable cardiac arrest receiving targeted temperature management at 33 °C: the ISOCRATE pilot randomized controlled trial

Purpose

While targeted temperature management (TTM) has been recommended in patients with shockable cardiac arrest (CA) and suggested in patients with non-shockable rhythms, few data exist regarding the impact of the rewarming rate on systemic inflammation. We compared serum levels of the proinflammatory cytokine interleukin-6 (IL6) measured with two rewarming rates after TTM at 33 °C in patients with shockable out-of-hospital cardiac arrest (OHCA).

Methods

ISOCRATE was a single-center randomized controlled trial comparing rewarming at 0.50 °C/h versus 0.25 °C/h in patients coma after shockable OHCA in 2016–2020. The primary outcome was serum IL6 level 24–48 h after reaching 33 °C. Secondary outcomes included the day-90 Cerebral Performance Category (CPC) and the 48-h serum neurofilament light-chain (NF-L) level.

Results

We randomized 50 patients. The median IL6 area-under-the-curve was similar between the two groups (12,389 [7256–37,200] vs. 8859 [6825–18,088] pg/mL h; P = 0.55). No significant difference was noted in proportions of patients with favorable day-90 CPC scores (13/25 patients at 0.25 °C/h (52.0%; 95% CI 31.3–72.2%) and 13/25 patients at 0.50 °C/h (52.0%; 95% CI 31.3–72.2%; P = 0.99)). Median NF-L levels were not significantly different between the 0.25 °C/h and 0.50 °C/h groups (76.0 pg mL, [25.5–3074.0] vs. 192 pg mL, [33.6–4199.0]; P = 0.43; respectively).

Conclusion

In our RCT, rewarming from 33 °C at 0.25 °C/h, compared to 0.50 °C/h, did not decrease the serum IL6 level after shockable CA. Further RCTs are needed to better define the optimal TTM strategy for patients with CA.

Trial registration ClinicalTrials.gov, NCT02555254. Registered September 14, 2015.

Take-Home Message: Rewarming at a rate of 0.25 °C/h, compared to 0.50 °C, did not result in lower serum IL6 levels after achievement of hypothermia at 33 °C in patients who remained comatose after shockable cardiac arrest. No associations were found between the slower rewarming rate and day-90 functional outcomes or mortality.

140-character Tweet: Rewarming at 0.25 °C versus 0.50 °C did not decrease serum IL6 levels after hypothermia at 33 °C in patients comatose after shockable cardiac arrest.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-021-03842-9.

Brain vulnerability and viability after ischaemia

The susceptibility of the brain to ischaemic injury dramatically limits its viability following interruptions in blood flow. However, data from studies of dissociated cells, tissue specimens, isolated organs and whole bodies have brought into question the temporal limits within which the brain is capable of tolerating prolonged circulatory arrest. This Review assesses cell type-specific mechanisms of global cerebral ischaemia, and examines the circumstances in which the brain exhibits heightened resilience to injury. We suggest strategies for expanding such discoveries to fuel translational research into novel cytoprotective therapies, and describe emerging technologies and experimental concepts. By doing so, we propose a new multimodal framework to investigate brain resuscitation following extended periods of circulatory arrest.

Targeted Temperature Management After Cardiac Arrest

and that reference citations are not used in the synopsis. A devastating complication of cardiac arrest is hypoxic-ischemic injury, which leads to neurologic dysfunction and subsequently high mortality. Post-cardiac arrest care is complex and requires a multimodal approach to manage hemodynamic instability as well as provide neuroprotection. Targeted temperature management is recommended by the American Heart Association as well as the International Liaison Committee on Resuscitation as a class 1 intervention for postarrest neuroprotection in patients who remain unresponsive after cardiac arrest.

Thermoregulation in post-cardiac arrest patients treated with targeted temperature management

OBJECTIVE

Evaluate the relationship between heat generation during rewarming in post-cardiac arrest patients receiving targeted temperature management (TTM) as a surrogate of thermoregulatory ability and clinical outcomes.

METHODS

This is a prospective observational single-centre study conducted at an urban tertiary-care hospital. We included post-cardiac arrest adults who received TTM via surface cooling device between April 2018 and June 2019.

RESULTS

Patient heat generation was calculated by multiplying the inverse of the average machine water temperature with time to rewarm to 37 °C and standardized in two ways to account for target temperature variation: (1) divided by number of degrees between target temperature and 37 °C, and (2) limited to when patient was rewarmed from 36 °C to 37 °C. The primary outcome was poor neurologic status, defined as Cerebral Performance Category (CPC) score 3-5, and the secondary outcome was 30-day survival. Sixty-six patients were included: 45 (68%) had a CPC-score of 3-5 and 23 (35%) were alive at 30 days. Besides initial rhythm and arrest downtime, baseline characteristics were similar between outcomes. Heat generation was not associated with poor neurological outcome (CPC 3-5: 6.6 [IQR: 6.1, 7.4] versus CPC 1-2: 6.6 [IQR: 5.7, 7.6], p = 0.89) or survival at 30 days (non-survivors: 6.6 [IQR: 6.6, 7.4] vs. survivors: 6.6 [IQR: 5.7, 8.0, p = 0.78]).

CONCLUSION

Heat generation during rewarming was not associated with neurologic outcomes. However, there was a relationship between poor neurological outcome and higher median water temperatures. Time to rewarm was prolonged in patients with poor neurological outcome.

Resuscitation highlights in 2020

BACKGROUND

This review is the latest in a series of regular annual reviews undertaken by the editors and aims to highlight some of the key papers published in Resuscitation during 2020. The number of papers submitted to the Journal in 2020 increased by 25% on the previous year.MethodsHand-searching by the editors of all papers published in Resuscitation during 2020. Papers were selected based on then general interest and novelty and were categorised into general themes.ResultsA total of 103 papers were selected for brief mention in this review.ConclusionsResuscitation science continues to evolve rapidly and incorporate all links in the chain of survival.

Practical considerations for postarrest targeted temperature management

Out-of-hospital cardiac arrest remains a major challenge worldwide, with survival to discharge rates of <20% in the great majority of countries. Advancements in prehospital care, including increasing deployment of automated external defibrillators and improvements in bystander cardiopulmonary resuscitation, have led to more victims achieving return of spontaneous circulation (ROSC), yet the majority of patients with ROSC suffer in-hospital mortality or significant neurologic injuries that persist after discharge. This postarrest morbidity and mortality is largely due to a complex syndrome of mitochondrial dysfunction, inflammatory cascades and cellular injuries known as the postcardiac arrest syndrome (PCAS). The management of PCAS represents a formidable task for emergency and critical care providers. A cornerstone of PCAS treatment is the use of aggressive core body temperature control using thermostatically controlled devices, known as targeted temperature management (TTM). This therapy, demonstrated to be effective in improving both survival and neurologic recovery by several randomized controlled trials nearly 20 years ago, remains a major topic of clinical investigation. Important practical questions about TTM remain: How soon must providers initiate the therapy? What TTM goal temperature maximizes benefit while limiting potential adverse effects? How long should TTM therapy be continued in patients following resuscitation? In this review, we will address these issues and summarize clinical research over the past decade that has added to our fund of knowledge surrounding this important treatment of patients following cardiac arrest.

The association between neuromuscular blockade use during target temperature management and neurological outcomes

BACKGROUND

To date, no study has comprehensively analyzed the association between neuromuscular blockade (NMB) during target temperature management (TTM) and the neurological outcomes after out-of-hospital cardiac arrest (OHCA) using a multicenter dataset. We aimed to examine the association between NMB during TTM after cardiac arrest and neurological outcomes after OHCA.

METHODS

This study was a secondary analysis of the Japanese Population-based Utstein-style study with defibrillation and basic/advanced Life Support Education and implementation-Hypothermia (J-PULSE-HYPO) study registry. The exposure of the current study was the use of NMB during TTM. The primary outcome was favorable neurological outcome, i.e., a cerebral performance category of 1-2, at hospital discharge.

RESULTS

Of the 452 patients with OHCA enrolled in the J-PULSE-HYPO study, 431 were analyzed. NMB was used in 353 patients (81.9%). Multivariable logistic regression analysis revealed that NMB use was not independently associated with favorable outcomes [odds ratio (OR), 0.96; 95% confidence interval (CI), 0.42-2.18; p = .918)] or survival at discharge (OR, 0.83; 95% CI, 0.31-2.02; p = .688). After adjusting the covariates, the predicted probabilities did not reveal significant differences between NMB use and non-NMB use in the respective mean (95% CI) values for favorable neurological outcomes [53.6 (50.2-57.0) % vs. 58.0 (50.4-65.6) %, p = .304], and survival rates [77.1 (74.7-79.5) % vs. 75.8 (70.5-81.0) %, p = .647].

CONCLUSIONS

The NMB use during TTM was not associated with favorable neurological outcomes and survival rate in patients with OHCA.

A practical approach to the use of targeted temperature management after cardiac arrest

Among comatose survivors after cardiac arrest, target temperature management (TTM) is considered the most effective treatment to reduce the consequences of postanoxic brain injury. Several international guidelines have thus incorporated TTM in the management of the postresuscitation phase. However, despite extremely promising results in animal models and in randomized trials including selected patient cohorts, TTM benefits on neurological outcome have been questioned. Moreover, TTM potential side effects have raised some concerns on its wide application in all cardiac arrest patients in different healthcare systems. There is indeed still relatively large uncertainty concerning some practical aspects related to TTM application, such as: A) how to select patients who will benefit the most from TTM; B) the optimal time to initiate TTM; C) the best target temperature; D) the most effective methods to provide TTM; E) the length of the cooling phase; and F) the optimal rewarming rate and fever control strategies. The purpose of this manuscript is to review and discuss the most recent advances in TTM use after cardiac arrest and to give some proposals on how to deal with all these relevant practical questions.

High Quality Targeted Temperature Management (TTM) After Cardiac Arrest

Targeted temperature management (TTM) is a complex intervention used with the aim of minimizing post-anoxic injury and improving neurological outcome after cardiac arrest. There is large variability in the devices used to achieve cooling and in protocols (e.g., for induction, target temperature, maintenance, rewarming, sedation, management of post-TTM fever). This variability can explain the limited benefits of TTM that have sometimes been reported. We therefore propose the concept of “high-quality TTM” as a way to increase the effectiveness of TTM and standardize its use in future interventional studies.