Interpreting the results of the targeted temperature management trial in cardiac arrest

Temperature Control in Acute Brain Injury: An Update

Temperature control in severe acute brain injury (SABI) is a key component of acute management. This manuscript delves into the complex role of temperature management in SABI, encompassing conditions like traumatic brain injury (TBI), acute ischemic stroke (AIS), intracerebral hemorrhage (ICH), aneurysmal subarachnoid hemorrhage (aSAH), and hypoxemic/ischemic brain injury following cardiac arrest. Fever is a common complication in SABI and is linked to worse neurological outcomes due to increased inflammatory responses and intracranial pressure (ICP). Temperature management, particularly hypothermic temperature control (HTC), appears to mitigate these adverse effects primarily by reducing cerebral metabolic demand and dampening inflammatory pathways. However, the effectiveness of HTC varies across different SABI conditions. In the context of post-cardiac arrest, the impact of HTC on neurological outcomes has shown inconsistent results. In cases of TBI, HTC seems promising for reducing ICP, but its influence on long-term outcomes remains uncertain. For AIS, clinical trials have yet to conclusively demonstrate the benefits of HTC, despite encouraging preclinical evidence. This variability in efficacy is also observed in ICH, aSAH, bacterial meningitis, and status epilepticus. In pediatric and neonatal populations, while HTC shows significant benefits in hypoxic-ischemic encephalopathy, its effectiveness in other brain injuries is mixed. Although the theoretical basis for employing temperature control, especially HTC, is strong, the clinical outcomes differ among various SABI subtypes. The current consensus indicates that fever prevention is beneficial across the board, but the application and effectiveness of HTC are more nuanced, underscoring the need for further research to establish optimal temperature management strategies. Here we provide an overview of the clinical evidence surrounding the use of temperature control in various types of SABI.

The Effects of Temperature Management on Brain Microcirculation, Oxygenation and Metabolism

Purpose: Target temperature management (TTM) is often used in patients after cardiac arrest, but the effects of cooling on cerebral microcirculation, oxygenation and metabolism are poorly understood. We studied the time course of these variables in a healthy swine model.Methods: Fifteen invasively monitored, mechanically ventilated pigs were allocated to sham procedure (normothermia, NT; n = 5), cooling (hypothermia, HT, n = 5) or cooling with controlled oxygenation (HT-Oxy, n = 5). Cooling was induced by cold intravenous saline infusion, ice packs and nasal cooling to achieve a body temperature of 33–35 °C. After 6 h, animals were rewarmed to baseline temperature (within 5 h). The cerebral microvascular network was evaluated (at baseline and 2, 7 and 12 h thereafter) using sidestream dark-field (SDF) video-microscopy. Cerebral blood flow (laser Doppler MNP100XP, Oxyflow, Oxford Optronix, Oxford, UK), oxygenation (PbtO₂, Licox catheter, Integra Lifesciences, USA) and lactate/pyruvate ratio (LPR) using brain microdialysis (CMA, Stockholm, Sweden) were measured hourly. Results: In HT animals, cerebral functional capillary density (FCD) and proportion of small-perfused vessels (PSPV) significantly decreased over time during the cooling phase; concomitantly, PbtO₂ increased and LPR decreased. After rewarming, all microcirculatory variables returned to normal values, except LPR, which increased during the rewarming phase in the two groups subjected to HT when compared to the group maintained at normothermia. Conclusions: In healthy animals, TTM can be associated with alterations in cerebral microcirculation during cooling and altered metabolism at rewarming.

Targeted Temperature Management at 33 Versus 36 Degrees: A Retrospective Cohort Study

OBJECTIVES

To determine the association between targeted temperature management goal temperature of 33°C versus 36°C and neurologic outcome after out-of-hospital cardiac arrest.

DESIGN

This was a retrospective, before-and-after, cohort study.

SETTING

Urban, academic, level 1 trauma center from 2010 to 2017.

PATIENTS

Adults with nontraumatic out-of-hospital cardiac arrest who received targeted temperature management.

INTERVENTIONS

Our primary exposure was targeted temperature management goal temperature, which was changed from 33°C to 36°C in April of 2014 at the study hospital. Primary outcome was neurologically intact survival to discharge. Secondary outcomes included hospital mortality and care processes.

MEASUREMENTS AND MAIN RESULTS

Of 782 out-of-hospital cardiac arrest patients transported to the study hospital, 453 (58%) received targeted temperature management. Of these, 258 (57%) were treated during the 33°C period (targeted temperature management 33°C) and 195 (43%) were treated during the 36°C period (targeted temperature management 36°C). Patients treated during targeted temperature management 33°C were older (57 vs 52 yr; p < 0.05) and had more arrests of cardiac etiology (45% vs 35%; p < 0.05), but otherwise had similar baseline characteristics, including initial cardiac rhythm. A total of 40% of patients treated during targeted temperature management 33°C survived with favorable neurologic outcome, compared with 30% in the targeted temperature management 36°C group (p < 0.05). After adjustment for demographic and cardiac arrest characteristics, targeted temperature management 33°C was associated with increased odds of neurologically intact survival to discharge (odds ratio, 1.79; 95% CI, 1.09-2.94). Targeted temperature management 33°C was not associated with significantly improved hospital mortality. Targeted temperature management was implemented faster (1.9 vs 3.5 hr from 911 call; p < 0.001) and more frequently in the emergency department during the targeted temperature management 33°C period (87% vs 55%; p < 0.001).

CONCLUSIONS

Comatose, adult out-of-hospital cardiac arrest patients treated during the targeted temperature management 33°C period had higher odds of neurologically intact survival to hospital discharge compared with those treated during the targeted temperature management 36°C period. There was no significant difference in hospital mortality.

Optimizing the Early Resuscitation After Out-of-Hospital Cardiac Arrest

Resuscitation after out-of-hospital cardiac arrest can be one of the most challenging scenarios in acute-care medicine. The devastating effects of postcardiac arrest syndrome carry a substantial morbidity and mortality that persist long after return of spontaneous circulation. Management of these patients requires the clinician to simultaneously address multiple emergent priorities including the resuscitation of the patient and the efficient diagnosis and management of the underlying etiology. This review provides a concise evidence-based overview of the core concepts involved in the early postcardiac arrest resuscitation. It will highlight the components of an effective management strategy including addressing hemodynamic, oxygenation, and ventilation goals as well as carefully considering cardiac catheterization and targeted temperature management. An organized approach is paramount to providing effective care to patients in this vulnerable time period.

Ischemic Brain Injury Leads to Brain Edema via Hyperthermia-Induced TRPV4 Activation

Brain edema is characterized by an increase in net brain water content, which results in an increase in brain volume. Although brain edema is associated with a high fatality rate, the cellular and molecular processes of edema remain largely unclear. Here, we developed an in vitro model of ischemic stroke-induced edema in which male mouse brain slices were treated with oxygen-glucose deprivation (OGD) to mimic ischemia. We continuously measured the cross-sectional area of the brain slice for 150 min under macroscopic microscopy, finding that OGD induces swelling of brain slices. OGD-induced swelling was prevented by pharmacologically blocking or genetically knocking out the transient receptor potential vanilloid 4 (TRPV4), a member of the thermosensitive TRP channel family. Because TRPV4 is activated at around body temperature and its activation is enhanced by heating, we next elevated the temperature of the perfusate in the recording chamber, finding that hyperthermia induces swelling via TRPV4 activation. Furthermore, using the temperature-dependent fluorescence lifetime of a fluorescent-thermosensitive probe, we confirmed that OGD treatment increases the temperature of brain slices through the activation of glutamate receptors. Finally, we found that brain edema following traumatic brain injury was suppressed in TRPV4-deficient male mice in vivo Thus, our study proposes a novel mechanism: hyperthermia activates TRPV4 and induces brain edema after ischemia.SIGNIFICANCE STATEMENT Brain edema is characterized by an increase in net brain water content, which results in an increase in brain volume. Although brain edema is associated with a high fatality rate, the cellular and molecular processes of edema remain unclear. Here, we developed an in vitro model of ischemic stroke-induced edema in which mouse brain slices were treated with oxygen-glucose deprivation. Using this system, we showed that the increase in brain temperature and the following activation of the thermosensitive cation channel TRPV4 (transient receptor potential vanilloid 4) are involved in the pathology of edema. Finally, we confirmed that TRPV4 is involved in brain edema in vivo using TRPV4-deficient mice, concluding that hyperthermia activates TRPV4 and induces brain edema after ischemia.

Therapeutic hypothermia and targeted temperature management for traumatic brain injury: Experimental and clinical experience

Traumatic brain injury (TBI) is a worldwide medical problem, and currently, there are few therapeutic interventions that can protect the brain and improve functional outcomes in patients. Over the last several decades, experimental studies have investigated the pathophysiology of TBI and tested various pharmacological treatment interventions targeting specific mechanisms of secondary damage. Although many preclinical treatment studies have been encouraging, there remains a lack of successful translation to the clinic and no therapeutic treatments have shown benefit in phase 3 multicenter trials. Therapeutic hypothermia and targeted temperature management protocols over the last several decades have demonstrated successful reduction of secondary injury mechanisms and, in some selective cases, improved outcomes in specific TBI patient populations. However, the benefits of therapeutic hypothermia have not been demonstrated in multicenter randomized trials to significantly improve neurological outcomes. Although the exact reasons underlying the inability to translate therapeutic hypothermia into a larger clinical population are unknown, this failure may reflect the suboptimal use of this potentially powerful therapeutic in potentially treatable severe trauma patients. It is known that multiple factors including patient recruitment, clinical treatment variables, and cooling methodologies are all important in yielding beneficial effects. High-quality multicenter randomized controlled trials that incorporate these factors are required to maximize the benefits of this experimental therapy. This article therefore summarizes several factors that are important in enhancing the beneficial effects of therapeutic hypothermia in TBI. The current failures of hypothermic TBI clinical trials in terms of clinical protocol design, patient section, and other considerations are discussed and future directions are emphasized.

Efficacy of different cooling technologies for therapeutic temperature management: A prospective intervention study

BACKGROUND

Mild therapeutic hypothermia (32-36 °C) is associated with improved outcomes in patients with brain injury after cardiac arrest (CA). Various devices are available to induce and maintain hypothermia, but few studies have compared the performance of these devices. We performed a prospective study to compare four frequently used cooling systems in inducing and maintaining hypothermia followed by controlled rewarming.

METHODS

We performed a prospective multi-centered study in ten ICU's in three hospitals within the UPMC health system. Four different cooling technologies (seven cooling methods in total) were studied: two external water-circulating cooling blankets (Meditherm® and Blanketrol®), gel-coated adhesive cooling pads (Arctic Sun®), and endovascular cooling catheters with balloons circulating ice-cold saline (Thermogard®). For the latter system we studied three different types of catheter with two, three or four water-circulating balloons, respectively. In contrast to previous studies, we not only studied the cooling rate (i.e., time to target temperature) in the induction phase, but also the percentage of the time during the maintenance phase that temperature was on target ±0.5 °C, and the efficacy of devices to control rewarming. We believe that these are more important indicators of device performance than induction speed alone.

RESULTS

129 consecutive patients admitted after CA and treated with hypothermia were screened, and 120 were enrolled in the study. Two researchers dedicated fulltime to this study monitored TH treatment in all patients, including antishivering measures, additional cooling measures used (e.g. icepacks and cold fluid infusion), and all other issues related to temperature management. Baseline characteristics were similar for all groups. Cooling rates were 2.06 ± 1.12 °C/h for endovascular cooling, 1.49 ± 0.82 for Arctic sun, 0.61 ± 0.36 for Meditherm and 1.22 ± 1.12 for Blanketrol. Time within target range ±0.5 °C was 97.3 ± 6.0% for Thermogard, 81.8 ± 25.2% for Arctic Sun, 57.4 ± 29.3% for Meditherm, and 64.5 ± 20.1% for Blanketrol. The following differences were significant: Thermogard vs. Meditherm (p < 0.01), Thermogard vs. Blanketrol (p < 0.01), and Arctic Sun vs. Meditherm (p < 0.02). No major complications occurred with any device.

CONCLUSIONS

Endovascular cooling and gel-adhesive pads provide more rapid hypothermia induction and more effective temperature maintenance compared to water-circulating cooling blankets. This applied to induction speed, but (more importantly) also to time within target range during maintenance.

Changes in cardiac arrest patients' temperature management after the publication of 2015 AHA guidelines for resuscitation in China

A survey was performed to assess the current management of targeted temperature management (TTM) in patients following cardiac arrest (CA) and whether healthcare providers will change target temperature after publication of 2015 American Heart Association guidelines for resuscitation in China. 52 hospitals were selected from whole of China between August to November 2016. All healthcare providers in EMs and/or ICUs of selected hospitals participated in the study. 1952 respondents fulfilled the survey (86.8%). TTM in CA patients was declared by 14.5% of physicians and 6.7% of the nurses. Only 4 of 64 departments, 7.8% of physicians and 5.7% of the nurses had implemented TH for CA patients. Since the publication of 2015 AHA guidelines, 33.6% of respondents declared no modification of target temperature, whereas 51.5% declared a target temperature's change in future practice. Respondents were more likely to choose 35∼36 °C-TTM (54.7%) after guidelines publication, as compared to that before guidelines publication they preferred 32∼34 °C-TTM (54.0%). TTM for CA patients was still in the early stage in China. Publication of 2015 resuscitation guidelines did have impact on choice of target temperature among healthcare providers. They preferred 35∼36 °C-TTM after guidelines publication.

Target temperature 34 vs. 36°C after out-of-hospital cardiac arrest - a retrospective observational study

BACKGROUND

Intensive care for comatose survivors of cardiac arrest includes targeted temperature management (TTM) to attenuate cerebral reperfusion injury. A recent multi-center clinical trial did not show any difference in mortality or neurological outcome between TTM targeting 33°C or 36°C after out-of-hospital-cardiac-arrest (OHCA). In our institution, the TTM target was changed accordingly from 34 to 36°C. The aim of this retrospective study was to analyze if this change had affected patient outcome.

METHODS

Intensive care registry and medical record data from 79 adult patients treated for OHCA with TTM during 2010 (n = 38; 34°C) and 2014 (n = 41; 36°C) were analyzed for mortality and neurological outcome were assessed as cerebral performance category. Student's t-test was used for continuous data and Fischer's exact test for categorical data, and multivariable logistic regression was applied to detect influence from patient factors differing between the groups.

RESULTS

Witnessed arrest was more common in 2010 (95%) vs. 2014 (76%) (P = 0.03) and coronary angiography was more common in 2014 (95%) vs. 2010 (76%) (P = 0.02). The number of patients awakening later than 72 h after the arrest did not differ. After adjusting for gender, hypertension, and witnessed arrest, neither 1-year mortality (P = 0.77), nor 1-year good neurological outcome (P = 0.85) differed between the groups.

CONCLUSION

Our results, showing no difference between TTM at 34°C and TTM at 36°C as to mortality or neurological outcome after OHCA, are in line with the previous TTM-trial results, supporting the use of either target temperature in our institution.

Hypothalamic or Extrahypothalamic Modulation and Targeted Temperature Management After Brain Injury

Targeted temperature management (TTM) has been recognized to protect tissue function and positively influence neurological outcomes after brain injury. While shivering during hypothermia nullifies the beneficial effect of TTM, traditionally, antishivering drugs or paralyzing agents have been used to reduce the shivering. The hypothalamic area of the brain helps in controlling cerebral temperature and body temperature through interactions between different brain areas. Thus, modulation of different brain areas either pharmacologically or by electrical stimulation may contribute in TTM; although, very few studies have shown that TTM might be achieved by activation and inhibition of neurons in the hypothalamic region. Recent studies have investigated potential pharmacological methods of inducing hypothermia for TTM by aiming to maintain the TTM and reduce the shivering effect without using antiparalytic drugs. Better survival and neurological outcome after brain injury have been reported after pharmacologically induced TTM. This review discusses the mechanisms and modulation of the hypothalamus with other brain areas that are involved in inducing hypothermia through which TTM may be achieved and provides therapeutic strategies for TTM after brain injury.

Establishment of an ideal time window model in hypothermic-targeted temperature management after traumatic brain injury in rats

Although hypothermic-targeted temperature management (HTTM) holds great potential for the treatment of traumatic brain injury (TBI), translation of the efficacy of hypothermia from animal models to TBI patientshas no entire consistency. This study aimed to find an ideal time window model in experimental rats which was more in accordance with clinical practice through the delayed HTTM intervention. Sprague-Dawley rats were subjected to unilateral cortical contusion injury and received therapeutic hypothermia at 15mins, 2 h, 4 h respectively after TBI. The neurological function was evaluated with the modified neurological severity score and Morris water maze test. The brain edema and morphological changes were measured with the water content and H&E staining. Brain sections were immunostained with antibodies against DCX (a neuroblast marker) and GFAP (an astrocyte marker). The apoptosis levels in the ipsilateral hippocampi and cortex were examined with antibodies against the apoptotic proteins Bcl-2, Bax, and cleaved caspase-3 by the immunofluorescence and western blotting. The results indicated that each hypothermia therapy group could improve neurobehavioral and cognitive function, alleviate brain edema and reduce inflammation. Furthermore, we observed that therapeutic hypothermia increased DCX expression, decreased GFAP expression, upregulated Bcl-2 expression and downregulated Bax and cleaved Caspase-3 expression. The above results suggested that HTTM at 2h or even at 4h post-injury revealed beneficial brain protection similarly, despite the best effect at 15min post-injury. These findings may provide relatively ideal time window models, further making the following experimental results more credible and persuasive.

Time to Cooling Is Associated with Resuscitation Outcomes

Our purpose was to analyze evidence related to timing of cooling from studies of targeted temperature management (TTM) after return of spontaneous circulation (ROSC) after cardiac arrest and to recommend directions for future therapy optimization. We conducted a preliminary review of studies of both animals and patients treated with post-ROSC TTM and hypothesized that a more rapid cooling strategy in the absence of volume-adding cold infusions would provide improved outcomes in comparison with slower cooling. We defined rapid cooling as the achievement of 34°C within 3.5 hours of ROSC without the use of volume-adding cold infusions, with a ≥3.0°C/hour rate of cooling. Using the PubMed database and a previously published systematic review, we identified clinical studies published from 2002 through 2014 related to TTM. Analysis included studies with time from collapse to ROSC of 20–30 minutes, reporting of time from ROSC to target temperature and rate of patients in ventricular tachycardia or ventricular fibrillation, and hypothermia maintained for 20–24 hours. The use of cardiopulmonary bypass as a cooling method was an exclusion criterion for this analysis. We compared all rapid cooling studies with all slower cooling studies of ≥100 patients. Eleven studies were initially identified for analysis, comprising 4091 patients. Two additional studies totaling 609 patients were added based on availability of unpublished data, bringing the total to 13 studies of 4700 patients. Outcomes for patients, dichotomized into faster and slower cooling approaches, were determined using weighted linear regression using IBM SPSS Statistics software. Rapid cooling without volume-adding cold infusions yielded a higher rate of good neurological recovery than slower cooling methods. Attainment of a temperature below 34°C within 3.5 hours of ROSC and using a cooling rate of more than 3°C/hour appear to be beneficial.

A low body temperature on arrival at hospital following out-of-hospital-cardiac-arrest is associated with increased mortality in the TTM-study

AIM

To investigate the association of temperature on arrival to hospital after out-of-hospital-cardiac arrest (OHCA) with the primary outcome of mortality, in the targeted temperature management (TTM) trial.

METHODS

The TTM trial randomized 939 patients to TTM at 33 or 36°C for 24h. Patients were categorized according to their recorded body temperature on arrival and also categorized to groups of patients being actively cooled or passively rewarmed.

RESULTS

OHCA patients having a temperature ≤34.0°C on arrival at hospital had a significantly higher mortality compared to the OHCA patients with a higher temperature on arrival. A low body temperature on arrival was associated with a longer time to return of spontaneous circulation (ROSC) and duration of transport time to hospital. Patients who were actively cooled or passively rewarmed during the first 4h had similar mortality. In a multivariate logistic regression model mortality was significantly related to time from OHCA to ROSC, time from OHCA to advanced life support (ALS), age, sex and first registered rhythm. None of the temperature related variables (included the TTM-groups) were significantly related to mortality.

CONCLUSION

OHCA patients with a temperature ≤34.0°C on arrival have a higher mortality than patients with a temperature ≥34.1°C on arrival. A low temperature on arrival is associated with a long time to ROSC. Temperature changes and TTM-groups were not associated with mortality in a regression model.

Combined intra- and post-cardiac arrest hypothermic-targeted temperature management in a rat model of asphyxial cardiac arrest improves survival and neurologic outcome compared to either strategy alone

AIM

Post-cardiac arrest hypothermic-targeted temperature management (HTTM) improves outcomes in preclinical cardiac arrest studies. However, inadequate understanding of the mechanisms and therapeutic windows remains a barrier to optimization. We tested the hypothesis that combined intra- and post-cardiac arrest HTTM provides a synergistic outcome benefit compared to either strategy alone.

METHODS

Rats subjected to 8-min asphyxial cardiac arrest were block randomized to 4 treatment groups (n=12/group): NTTM) normothermic-targeted temperature management; 1-24 HTTM) HTTM initiated 1h post-ROSC and maintained for 24h; Intra-1 HTTM) HTTM initiated at CPR onset and maintained for 1h; and Intra-24 HTTM) HTTM initiated at CPR onset and maintained for 24h. HTTM was induced by nasopharyngeal cooling and maintained using an automated temperature regulation system. Target temperature range was 36.5-37.5°C for NTTM and 32.0-34.0°C for HTTM. Post-arrest neurologic function score (NFS) was measured daily, and rats surviving 72h were euthanized for histological analysis of neurodegeneration.

RESULTS

Target brain temperature was achieved 7.8±3.3min after initiating intra-arrest cooling. The survival rate was 42%, 50%, 50%, and 92% in the NTTM, 1-24 HTTM, Intra-1 HTTM, and Intra-24 HTTM groups, respectively (p<0.05, Intra-24 group vs. all other groups). The rate of survival with good neurologic function (NFS≥450) was 33% in the Intra-24 HTTM group vs. 0% in all other groups (mid p<0.05). Hippocampal CA1 sector neurodegeneration was significantly reduced in the Intra-24 HTTM group compared to all other groups (p<0.05).

CONCLUSION

Combined intra- and post-cardiac arrest HTTM has greater outcome benefits than either strategy alone.

Variability of Post-Cardiac Arrest Care Practices Among Cardiac Arrest Centers: United States and South Korean Dual Network Survey of Emergency Physician Research Principal Investigators

There is little consensus regarding many post-cardiac arrest care parameters. Variability in such practices could confound the results and generalizability of post-arrest care research. We sought to characterize the variability in post-cardiac arrest care practice in Korea and the United States. A 54-question survey was sent to investigators participating in one of two research groups in South Korea (Korean Hypothermia Network [KORHN]) and the United States (National Post-Arrest Research Consortium [NPARC]). Single investigators from each site were surveyed (N = 40). Participants answered questions based on local institutional protocols and practice. We calculated descriptive statistics for all variables. Forty surveys were completed during the study period with 30 having greater than 50% of questions completed (75% response rate; 24 KORHN and 6 NPARC). Most centers target either 33°C (N = 16) or vary the target based on patient characteristics (N = 13). Both bolus and continuous infusion dosing of sedation are employed. No single indication was unanimous for cardiac catheterization. Only six investigators reported having an institutional protocol for withdrawal of life-sustaining therapy (WLST). US patients with poor neurological prognosis tended to have WLST with subsequent expiration (N = 5), whereas Korean patients are transferred to a secondary care facility (N = 19). Both electroencephalography modality and duration vary between institutions. Serum biomarkers are commonly employed by Korean, but not US centers. We found significant variability in post-cardiac arrest care practices among US and Korean medical centers. These practice variations must be taken into account in future studies of post-arrest care.

Targeted temperature management in traumatic brain injury

Traumatic brain injury (TBI) is recognized as the significant cause of mortality and morbidity in the world. To reduce unfavorable outcome in TBI patients, many researches have made much efforts for the innovation of TBI treatment. With the results from several basic and clinical studies, targeted temperature management (TTM) including therapeutic hypothermia (TH) have been recognized as the candidate of neuroprotective treatment. However, their evidences are not yet proven in larger randomized controlled trials (RCTs). The main aim of this review is thus to clarify specific pathophysiology which TTM will be effective in TBI. Historically, there were several clinical trials which compare TH and normothermia. Recently, two RCTs were able to demonstrate the significant beneficial effects of TTM in one specific pathology, patients with mass evacuated lesions. These suggested that TTM might be effective especially for the ischemic-reperfusional pathophysiology of TBI, like as acute subdural hematoma which needs to be evacuated. Also, the latest preliminary report of European multicenter trial suggested the promising efficacy of reduction of intracranial pressure in TBI. Conclusively, TTM is still in the center of neuroprotective treatments in TBI. This therapy is expected to mitigate ischemic and reperfusional pathophysiology and to reduce intracranial pressure in TBI. Further results from ongoing clinical RCTs are waited.

Variability in Postarrest Targeted Temperature Management Practice: Implications of the 2015 Guidelines

In 2002 postarrest care was significantly altered when multiple randomized controlled trials found that therapeutic hypothermia at a goal temperature of 32-34°C significantly improved survival and neurologic outcomes. In 2013, targeted temperature management (TTM) was reexamined via a randomized controlled trial between 33°C and 36°C in post-cardiac arrest patients and found similar outcomes in both cohorts. Before the release of the 2015 American Heart Association (AHA) Guidelines, our group found that across hospitals in the United States, and even within the same institution, TTM protocol variability existed. After the 2013 TTM trial, it was anticipated that the 2015 Guidelines would clarify which target temperature should be used during postarrest care. The AHA released their updates for post-cardiac arrest TTM recently and, based on the literature available, have recommended the use of TTM at a goal temperature between 32°C and 36°C. Whether this variability has an effect on TTM implementation or patient outcomes is unknown.

What is the proper target temperature for out-of-hospital cardiac arrest?

The implementation of target temperature management (TTM) or therapeutic hypothermia has been demonstrated in several major studies to be an effective neuroprotective strategy in postresuscitation care after cardiac arrest. Although several landmark studies found the promising results of lower targeted temperature (32-34 °C) in terms of survival and neurological outcomes, recent evidence showed no difference in either survival or long-term neurological outcome when compared with higher targeted temperature (36 °C). Thus, recent data suggest that avoiding hyperpyrexia, rather than cooling "per se," may be considered the main therapeutic target to avoid secondary brain damage after out-of-hospital cardiac arrest. Many questions are still debated about the exact protocol of TTM to be used, including whether temperature control is more beneficial than standard of care without active temperature control, the optimal cooling temperature, patient selection, and duration of cooling. The aim of this review article was to discuss the physiology of hypothermia, available cooling methods, and current evidence about the optimal target temperature and timing of hypothermia.