Hypothermia for neuroprotection after cardiac arrest: systematic review and individual patient data meta-analysis

Therapeutic hypothermia after out-of-hospital cardiac arrest in Finnish intensive care units: the FINNRESUSCI study

PURPOSE

We aimed to evaluate post-resuscitation care, implementation of therapeutic hypothermia (TH) and outcomes of intensive care unit (ICU)-treated out-of-hospital cardiac arrest (OHCA) patients in Finland.

METHODS

We included all adult OHCA patients admitted to 21 ICUs in Finland from March 1, 2010 to February 28, 2011 in this prospective observational study. Patients were followed (mortality and neurological outcome evaluated by Cerebral Performance Categories, CPC) within 1 year after cardiac arrest.

RESULTS

This study included 548 patients treated after OHCA. Of those, 311 patients (56.8%) had a shockable initial rhythm (incidence of 7.4/100,000/year) and 237 patients (43.2%) had a non-shockable rhythm (incidence of 5.6/100,000/year). At ICU admission, 504 (92%) patients were unconscious. TH was given to 241/281 (85.8%) unconscious patients resuscitated from shockable rhythms, with unfavourable 1-year neurological outcome (CPC 3-4-5) in 42.0% with TH versus 77.5% without TH (p < 0.001). TH was given to 70/223 (31.4%) unconscious patients resuscitated from non-shockable rhythms, with 1-year CPC of 3-4-5 in 80.6% (54/70) with TH versus 84.0% (126/153) without TH (p = 0.56). This lack of difference remained after adjustment for propensity to receive TH in patients with non-shockable rhythms.

CONCLUSIONS

One-year unfavourable neurological outcome of patients with shockable rhythms after TH was lower than in previous randomized controlled trials. However, our results do not support use of TH in patients with non-shockable rhythms.

Perioperative hypothermia in the pediatric population: a quality improvement project

There are limited data in the pediatric population regarding the incidence of, risk factors for, and means to prevent perioperative hypothermia. The Institute for Healthcare Improvement Model for quality improvement (QI) methodology was used to bundle the most effective techniques to prevent hypothermia. A multidisciplinary QI team was assembled with the goal to decrease the incidence of perioperative hypothermia by 50%. The baseline incidence of hypothermia was determined and causes identified using a flowchart and a cause-and-effect diagram. Pareto charts were formed and opportunities to decrease the incidence of perioperative hypothermia were trialed. The baseline incidence of hypothermia was 8.9%. Implementation of a standardized temperature management bundle in the operating rooms decreased the incidence to 4.2%. The QI methodology was useful to bundle the most effective techniques to prevent hypothermia, resulting in standardized perioperative care and a sustained reduction in the incidence of perioperative hypothermia.

[Therapeutic hypothermia in acute brain injury]

Induced therapeutic hypothermia (TH) is defined as a controlled reduction of the core body temperature below the physiological range. While TH is neuroprotective in many different models of brain injury, it is only recommended for patients after cardiopulmonary resuscitation and newborns suffering from perinatal hypoxic-ischemic encephalopathy (HIE). Although a strong association exists between elevated body core temperature (fever) and worsening of outcome, TH has so far not been proven to influence outcome after ischemic stroke, intracerebral hemorrhage or subarachnoidal hemorrhage because of insufficient clinical data. This review summarizes the data on TH for different clinical indications and discusses relevant aspects of its use in neurological intensive care units.

Year in review 2011: Critical Care--Out-of-hospital cardiac arrest and trauma

In 2011, numerous studies were published in Critical Care focusing on out-of-hospital cardiac arrest, cardiopulmonary resuscitation, trauma, and some related airway, respiratory, and response time factors. In this review, we summarize several of these studies, including those that brought forth advances in therapies for the post-resuscitative period. These advances involved hypothesis-generating concepts in therapeutic hypothermia as well as the impact of early percutaneous coronary artery interventions and the potential utility of extracorporeal life support after cardiac arrest. There were also articles pertaining to the importance of timing in prehospital airway management, the outcome impact of hyperoxia, and the timing of end-tidal carbon dioxide measurements to predict futility in cardiac arrest resuscitation. In other articles, additional perspectives were provided on the classic correlations between emergency medical service response intervals and outcomes.

[Therapeutic hypothermia and management of sudden death]

Due to its protective effects on the brain and potentially the myocardium, cooling therapy is clearly part of the standard of care of any sudden death especially in the setting of myocardial infarction. Recent guidelines recommend cooling therapy (32 to 34 °C) for 12 to 24 hours in unconscious patients with spontaneous circulation after resuscitated sudden death. We provide here a review of clinical evidence, cooling techniques and potential adverse effects of cooling therapy.

Neurophysiologic responses of peripheral nerve to anoxia: effects of hypothermia and age

OBJECTIVE

Quantify how temperature and age modulate the effects of multiple periods of anoxia on peripheral nerve.

METHODS

Nerve action potentials (NAP) recorded from rat sciatic nerve in vitro. Effects of multiple cycles of anoxia on the NAP are evaluated as functions of temperature and age. In some experiments, the nerve was held at constant temperature and others the nerve was hypothermic only during anoxia and returned to 36°C with restoration of oxygen.

RESULTS

Hypothermia mitigates the effect of anoxia on the NAP, an effect that increases with multiple cycles of anoxia. Preservation of the NAP waveform after 5 cycles of anoxia is best when hypothermia is delivered only during anoxia. Hypothermia reduces the rate at which the NAP disappears during anoxia but has a limited effect on the rate of recovery. With intermittent hypothermia the amplitude of the NAP is best preserved with temperatures of 15-22°C. Velocity and duration are best preserved below 25°C. The loss of the NAP during anoxia is slower in the older nerves.

CONCLUSIONS

Lower temperatures improve the recovery of the NAP from anoxia and increase the time it takes for the NAP to disappear during anoxia as does increasing age.

SIGNIFICANCE

Document the effects of hypothermia on the anoxia response as a step toward understanding its nerve protectant effect.

On-line blood viscosity monitoring in vivo with a central venous catheter, using electrical impedance technique

Blood viscosity is an important determinant of microvascular hemodynamics and also reflects systemic inflammation. Viscosity of blood strongly depends on the shear rate and can be characterized by a two parameter power-law model. Other major determinants of blood viscosity are hematocrit, level of inflammatory proteins and temperature. In-vitro studies have shown that these major parameters are related to the electrical impedance of blood. A special central venous catheter was developed to measure electrical impedance of blood in-vivo in the right atrium. Considering that blood viscosity plays an important role in cerebral blood flow, we investigated the feasibility to monitor blood viscosity by electrical bioimpedance in 10 patients during the first 3 days after successful resuscitation from a cardiac arrest. The blood viscosity-shear rate relationship was obtained from arterial blood samples analyzed using a standard viscosity meter. Non-linear regression analysis resulted in the following equation to estimate in-vivo blood viscosity (Viscosity(imp)) from plasma resistance (R(p)), intracellular resistance (R(i)) and blood temperature (T) as obtained from right atrium impedance measurements: Viscosity(imp)=(-15.574+15.576R(p)T)SR ((-.138RpT-.290Ri)). This model explains 89.2% (R(2)=.892) of the blood viscosity-shear rate relationship. The explained variance was similar for the non-linear regression model estimating blood viscosity from its major determinants hematocrit and the level of fibrinogen and C-reactive protein (R(2)=.884). Bland-Altman analysis showed a bias between the in-vitro viscosity measurement and the in-vivo impedance model of .04 mPa s at a shear rate of 5.5s(-1) with limits of agreement between -1.69 mPa s and 1.78 mPa s. In conclusion, this study demonstrates the proof of principle to monitor blood viscosity continuously in the human right atrium by a dedicated central venous catheter equipped with an impedance measuring device. No safety problems occurred and there was good agreement with in-vitro measurements of blood viscosity.

Mild therapeutic hypothermia improves outcomes compared with normothermia in cardiac-arrest patients--a retrospective chart review

OBJECTIVE

Studies showing the effectiveness of therapeutic hypothermia (32-34°C) in postcardiac arrest patients have been criticized because of patients with elevated body temperature (>37.5°C) in the noncooled control group. Thus, the effects of spontaneous normothermia (<37.5°C) compared with mild therapeutic hypothermia were studied.

DESIGN

Retrospective chart review from 1991 to 2010.

PATIENTS

Witnessed out-of-hospital arrest, presumed to be of cardiac origin, aged 18 to 80 yrs and with a Glassgow Coma Scale score of <8 at admission.

INTERVENTIONS

Patients with sustained restoration of spontaneous circulation who did not receive therapeutic hypothermia and never exceeded 37.5°C during the 36 hrs postcardiac arrest were compared with patients who received mild therapeutic hypothermia.

MEASUREMENTS AND MAIN RESULTS

The primary end point was a favorable neurological outcome, defined as Cerebral Performance Categories 1 or 2; the secondary end point was overall survival to 180 days. Significantly more patients in the hypothermia group had Cerebral Performance Categories 1 or 2 (hypothermia: 256 of 467 [55%] vs. normothermia: 69 of 165 [42%]) and survived for >180 days (hypothermia: 315 of 467 [67%] vs. normothermia: 79 of 165 [48%]). The propensity score adjusted risk ratio for good neurological outcome of patients undergoing hypothermia treatment was 1.37 (confidence interval 1.09-1.72, p≤.01) and for dying within 180 days was 0.57 (confidence interval 0.44-0.73, p≤.01) compared to normothermia.

CONCLUSIONS

Therapeutic hypothermia is associated with significantly improved neurological outcome and 180-day survival compared to spontaneous normothermia in cardiac-arrest patients.

Effects of prolonged mild hypothermia on cerebral blood flow after cardiac arrest

OBJECTIVE

The aim of the present study was to assess the cerebral blood flow and cerebral oxygen extraction in adult patients after pulseless electrical activity/asystole or resistant ventricular fibrillation who were treated with mild therapeutic hypothermia for 72 hrs.

DESIGN

Observational study.

SETTING

Tertiary care university hospital.

PATIENTS

Ten comatose patients with return of spontaneous circulation after pulseless electrical activity/asystole or prolonged ventricular fibrillation.

INTERVENTION

Treatment with mild therapeutic hypothermia for 72 hrs.

MEASUREMENTS AND MAIN RESULTS

Mean flow velocity in the middle cerebral artery was measured by transcranial Doppler at 12, 24, 36, 48, 60, 72, 84, 96, and 108 hrs after admission. Jugular bulb oxygenation was measured at the same intervals. Mean flow velocity in the middle cerebral artery was low (26.5 (18.7-48.0) cm/sec) at admission and significantly increased to 63.9 (45.6-65.6) cm/sec at 72 hrs (p=.002). Upon rewarming, the mean flow velocity in the middle cerebral artery remained relatively constant with a mean flow velocity in the middle cerebral artery of 71.5 (56.0-78.5) at 108 hrs (p=.381). Jugular bulb oxygenation at the start of the study was 57.0 (51.0-61.3)% and gradually increased to 81.0 (78.5-88.0)% at 72 hrs (p=.003). Upon rewarming, the jugular bulb oxygenation remained constant with a jugular bulb oxygenation of 84.0 (77.3-86.3)% at 108 hrs (p=.919). There were no differences in mean flow velocity in the middle cerebral artery, pulsatility index, and jugular bulb oxygenation between survivors and nonsurvivors.

CONCLUSIONS

Temperature by itself is probably not a major determinant in regulation of cerebral blood flow after cardiac arrest. The relatively low mean flow velocity in the middle cerebral artery in combination with normal jugular bulb oxygenation values suggests a reduction in cerebral metabolic activity that may contribute to the neuroprotective effect of (prolonged) mild therapeutic hypothermia in the delayed hypoperfusion phase.

Hypothermia for neuroprotection in adults after cardiopulmonary resuscitation

BACKGROUND

Good neurologic outcome after cardiac arrest is hard to achieve. Interventions during the resuscitation phase and treatment within the first hours after the event are critical. Experimental evidence suggests that therapeutic hypothermia is beneficial, and a number of clinical studies on this subject have been published. This review was originally published in 2009.

OBJECTIVES

We performed a systematic review and meta-analysis to assess the effectiveness of therapeutic hypothermia in patients after cardiac arrest. Neurologic outcome, survival and adverse events were our main outcomes. We aimed to perform individual patient data analysis, if data were available, and to form subgroups according to the cardiac arrest situation.

SEARCH METHODS

We searched the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2001, Issue 7); MEDLINE (1971 to July 2011); EMBASE (1987 to July 2011); CINAHL (1988 to July 2011); PASCAL (2000 to July 2011); and BIOSIS (1989 to July 2011). The original search was performed in January 2007.

SELECTION CRITERIA

We included all randomized controlled trials assessing the effectiveness of therapeutic hypothermia in patients after cardiac arrest, without language restrictions. Studies were restricted to adult populations cooled with any cooling method, applied within six hours of cardiac arrest.

DATA COLLECTION AND ANALYSIS

Validity measures, the intervention, outcomes and additional baseline variables were entered into a database. Meta-analysis was only done for a subset of comparable studies with negligible heterogeneity. For these studies, individual patient data were available.

MAIN RESULTS

We included four trials and one abstract reporting on 481 patients in the systematic review. The updated search resulted in no new studies to include. Quality of the included studies was good in three out of five studies. For the three comparable studies on conventional cooling methods all authors provided individual patient data. With conventional cooling methods, patients in the hypothermia group were more likely to reach a best cerebral performance categories (CPC) score of one or two (five point scale: 1 = good cerebral performance, to 5 = brain death) during the hospital stay (individual patient data; RR 1.55; 95% CI 1.22 to 1.96) and were more likely to survive to hospital discharge (individual patient data; RR 1.35; 95% CI 1.10 to 1.65) compared to standard post-resuscitation care. Across all studies, there was no significant difference in reported adverse events between hypothermia and control.

AUTHORS' CONCLUSIONS

Conventional cooling methods to induce mild therapeutic hypothermia seem to improve survival and neurologic outcome after cardiac arrest. Our review supports the current best medical practice as recommended by the International Resuscitation Guidelines.

The implementation of therapeutic hypothermia in the emergency department: a multi-institution case review

BACKGROUND

The use of therapeutic hypothermia (TH) is a burgeoning treatment modality for post-cardiac arrest patients.

OBJECTIVES

We performed a retrospective chart review of patients who underwent post-cardiac arrest TH at eight different institutions across the United States. Our objectives were to assess how TH is currently being implemented in emergency departments and to examine the feasibility of conducting TH research using multi-institution prospective data.

METHODS

A total of 94 cases were identified in a 3-year period and submitted for review by participating institutions of the Peri-Resuscitation Consortium. Of those, seven charts were excluded for missing data. Two independent reviewers performed the data abstraction. Results were subsequently compared, and discrepancies were resolved by a third reviewer. We assessed patient demographics, initial presenting rhythm, time until TH initiation, duration of TH, cooling methods and temperature reached, survival to hospital discharge, and neurological status on discharged.

RESULTS

The majority of cases had initial cardiac rhythms of asystole or pulseless electrical activity (55.2%), followed by ventricular tachycardia or fibrillation (34.5%). The inciting cardiac rhythm was unknown in 10.3% of cases. Time to initiation of TH ranged from 0 to 783 minutes with a mean time of 99 minutes (SD=132). Length of TH ranged from 25 to 2,171 minutes with a mean time of 1,191 minutes (SD=536). The average minimum temperature achieved was 32.5°C, with a range from 27.6°C to 36.7°C (SD=1.5°C). Of the 87 charts reviewed, 29 (33.3%) of the patients survived to hospital discharge.

CONCLUSION

The implementation of TH across the country is extremely varied with no universally accepted treatment. While our study is limited by sample size, it illustrates some compelling trends. A large, prospective, multicenter trial or registry is necessary to elucidate further the optimal parameters for TH and its benefit in various population subsets.

Mild therapeutic hypothermia in cardiogenic shock syndrome

OBJECTIVE

Mortality in patients with cardiogenic shock after out-of-hospital cardiac arrest remains high despite advances in resuscitation and early revascularization strategies. Recent studies suggest a reduced mortality in survivors of cardiac arrest subjected to mild therapeutic hypothermia, but the underlying mechanisms are not yet clear. Because positive hemodynamic effects of mild therapeutic hypothermia have been suggested, we aimed at testing the hypothesis that patients in cardiogenic shock might benefit from mild therapeutic hypothermia.

METHODS

Hemodynamic effects of mild therapeutic hypothermia in 20 consecutive patients admitted in cardiogenic shock after successful resuscitation from out-of-hospital cardiac arrest were investigated. A historic normothermic control group was matched (one-to-one) by means of a propensity score. Patients were cooled to 33°C for 24 hrs using an endovascular cooling device and hemodynamic variables were continuously recorded by means of pulse contour analysis. Cardiac performance was determined by echocardiography.

RESULTS

Mild therapeutic hypothermia induced a significant decrease in heart rate from 74 to 64 beats per minute. Despite the reduction in heart rate, cardiac index remained unchanged under mild therapeutic hypothermia likely due to an increase in ejection fraction from 43 ± 4% to 55 ± 4%. Mean arterial pressure increased rapidly from 75 ± 2 mm Hg to 84 ± 3 mm Hg (p = .001) upon induction of hypothermia paralleled by an initial increase in systemic vascular resistance. Accordingly, patients with mild therapeutic hypothermia required lower cumulative doses of vasopressors and inotropes.

CONCLUSIONS

We conclude that in cardiogenic shock mild therapeutic hypothermia provides circulatory support and an increase in systemic vascular resistance that leads to reduced vasopressor use and may result in lower oxygen consumption. These findings suggest that mild therapeutic hypothermia could be a therapeutic option in hemodynamically unstable patients independent of cardiac arrest and further randomized clinical studies are needed.

The Benefit of Hypothermia in Experimental Ischemic Stroke is Not Affected by Pethidine

Background

Hypothermia is a promising experimental treatment for acute ischemic stroke. Human trials are still at an early stage, with the focus now on using hypothermia in awake patients. Pethidine (meperidine) is the principle agent used to control shivering in humans; however, whether it has any modulating effects on the neuroprotective efficacy of hypothermia is unknown.

Aim

The aim of this study was to determine if pethidine influences the neuroprotective effect of hypothermia in experimental stroke.

Methods

Seventy-two male spontaneously hypertensive rats were anesthetized with isoflurane and randomly assigned to either normothermia (37·4°C rectal temperature); hypothermia (33°C maintained for 130 mins); normothermia plus pethidine (2·5 mg/kg); or hypothermia plus pethidine. Temporary (90 mins) endovascular occlusion of the middle cerebral artery was induced blinded to treatment allocation and was confirmed with laser Doppler flowmetry. Pethidine and cooling were started immediately after vessel occlusion. Animals in the normothermia group had active temperature management using a heat lamp and fan. Assessments of outcome were carried out 24 after the induction of injury.

Results

Thirteen animals met our prespecified criteria for exclusion, and data for 59 rats were presented here. Hypothermia was associated with a 63% reduction in infarct size, and pethidine had no significant impact on the efficacy of hypothermia. No effects were observed in neurobehavioral outcome or edema volume across experimental groups.

Conclusions

The effects of hypothermia in a model of focal ischemia are not affected by administration of pethidine.

Nitrotyrosine and nitrate/nitrite levels in cardiac arrest survivors treated with endovascular hypothermia

The protective effect of therapeutic hypothermia in cardiac arrest survivors (CAS) has been previously well documented. Animal studies have indicated that attenuation of tissue oxidative stress (OS) may be involved in the mechanisms that lead to the beneficial effect of hypothermia. The extent of OS and nitric oxide (NO) production in adult CAS treated with endovascular hypothermia is, however, unknown. A total of 11 adult patients who experienced cardiac arrest out of hospital were included in the present study, and all were treated with mild hypothermia using the Thermogard XP (Alsius, USA) endovascular system. A target core temperature of 33 °C was maintained for 24 hours, with a subsequent rewarming rate of 0.15 °C per hour, followed by normothermia at 36.8 °C. Blood samples for the measurement of nitrotyrosine and nitrate/nitrite levels were drawn at admission and every 6 hours thereafter for two days. During the hypothermic period, the levels of nitrotyrosine and nitrates/nitrites were comparable with baseline values. During the rewarming period, serum levels of both parameters gradually increased and, during the normothermic period, the levels were significantly higher compared with hypothermic levels (nitrotyrosine, P<0.001; nitrates/nitrites, P<0.05). In our study, significantly lower levels of nitrotyrosine and nitrates/nitrites were demonstrated during hypothermia compared with levels during the normothermic period in adult CAS. These data suggest that attenuation of OS and NO production may be involved in the protective effect of hypothermia in adult CAS.

Combining xenon and mild therapeutic hypothermia preserves neurological function after prolonged cardiac arrest in pigs

OBJECTIVE

Despite the introduction of mild therapeutic hypothermia into postcardiac arrest care, cerebral and myocardial injuries represent the limiting factors for survival after cardiac arrest. Administering xenon may confer an additional neuroprotective effect after successful cardiopulmonary resuscitation due to its ability to stabilize cellular calcium homeostasis via N-methyl-D-aspartate-receptor antagonism.

DESIGN

In a porcine model, we evaluated effects of xenon treatment in addition to therapeutic hypothermia on neuropathologic and functional outcomes after cardiopulmonary resuscitation.

SETTING

Prospective, randomized, laboratory animal study.

SUBJECTS

Fifteen male pigs.

INTERVENTIONS

Following 10 mins of cardiac arrest and 6 mins of cardiopulmonary resuscitation, ten pigs were randomized to receive either mild therapeutic hypothermia (33°C for 16 hrs) or mild therapeutic hypothermia 1 xenon (70% for 1 hr). Five animals served as normothermic controls.

MEASUREMENTS AND MAIN RESULTS

Gross hemodynamic variables were measured using right-heart catheterization. Neurocognitive performance was evaluated for 5 days after cardiopulmonary resuscitation using a neurologic deficit score before the brains were harvested for histopathological analysis. All animals survived the observation period in the mild therapeutic hypothermia 1 xenon group while one animal in each of the other two groups died. Mild therapeutic hypothermia 1 xenon preserved cardiac output during the induction of mild therapeutic hypothermia significantly better than did mild therapeutic hypothermia alone (4.6 6 0.6 L/min vs. 3.2 6 1.6 L/min, p # .05). Both treatment groups showed significantly fewer necrotic lesions in the cerebral cortex, caudate nucleus, putamen, and in hippocampal sectors CA1 and CA3/4. However, only the combination of mild therapeutic hypothermia and xenon resulted in reduced astrogliosis in the CA1 sector and diminished microgliosis and perivascular inflammation in the putamen. Clinically, only the mild therapeutic hypothermia 1 xenon-treated animals showed significantly improved neurologic deficit scores over time (day 1 = 59.0 6 27.0 vs. day 5 = 4.0 6 5.5, p ø .05) as well as in comparison to the untreated controls on days 3 through 5 after cardiopulmonary resuscitation.

CONCLUSIONS

These results demonstrate that even a short exposure to xenon during induction of mild therapeutic hypothermia results in significant improvements in functional recovery and ameliorated myocardial dysfunction.

The hospital's role in improving survival of patients with out-of-hospital cardiac arrest

Out-of-hospital cardiac arrest (OHCA) is a major public health problem. Unfortunately, in spite of recurring updated guidelines, survival of patients with OHCA had been unchanged for decades. Recently, new approaches to patients with OHCA during the community and prehospital phases of therapy for cardiac arrest have resulted in a dramatic improvement in survival. Further improvement in survival has resulted from hospitals designated as Cardiac Receiving Centers. These centers are committed to the treatment of post-cardiac arrest syndrome by providing 24/7 therapeutic mild hypothermia, urgent cardiac catheterization and percutaneous coronary intervention, evidence-based termination of resuscitation protocols that limit premature withdrawal of care, protocol to address organ donation, commitment of cardiocerebral resuscitation training in their community, and a commitment and proven ability of data collection to assure that instituted changes result in improved survival. This newer aspect of hospital practice is an aspect that needs to be embraced by either becoming a Cardiac Receiving Center or partnering with other hospitals that can provide this critically important service.

The "Refrige-a-RAT-or": an accurate, inexpensive, and clinically relevant small animal model of therapeutic hypothermia

BACKGROUND

Physical and molecular mechanisms for the neuroprotective effect of therapeutic hypothermia are not completely understood, and new therapeutic applications incorporating hypothermia remain to be developed and tested. Clinically relevant animal models of therapeutic hypothermia are not well established or consistent.

OBJECTIVES

The objective was to develop and test an inexpensive small animal therapeutic hypothermia system that models those in widespread clinical use and verify that such a system confers neuroprotection in a rat model of global brain ischemia.

METHODS

A water-cooled extracorporeal system and attendant anesthesia/sedation protocol were developed and tested. In Stage 1, animals were instrumented for brain, temporalis, and rectal temperature monitoring, and the system was tested for its effect on temperature and hemodynamics. In Stage 2, animals were instrumented for rectal temperature only, subjected to global brain ischemia by two-vessel occlusion and hypotension for 8 minutes, and given either sham therapy (37°C) or hypothermia (32°C) for 4 hours. Viable CA1 neurons were counted at 7 days.

RESULTS

The system was well tolerated, provided exquisite control of animal core and brain temperatures, and conferred robust neuroprotection at 7 days. The median and interquartile ranges (IQRs) of viable neurons per 300-μm field were 130 (IQR = 128 to 135) for sham control, 19 (IQR = 15 to 30) for untreated ischemic animals, and 101 (IQR = 94 to 113) for ischemic animals treated with hypothermia (p < 0.05 for comparison between all groups).

CONCLUSIONS

Like human protocols, this model incorporates sedation and analgesia, results in robust neuroprotection, is well tolerated, and offers exquisite temperature control. The system is noninvasive and inexpensive and offers a model that is similar to methods used in clinical practice. This system will be of interest to investigators using small animal models to examine neuroprotective mechanisms of hypothermia and translational strategies that combine hypothermia with targeted pharmacotherapy.

Target Temperature Management after out-of-hospital cardiac arrest--a randomized, parallel-group, assessor-blinded clinical trial--rationale and design

BACKGROUND

Experimental animal studies and previous randomized trials suggest an improvement in mortality and neurologic function with induced hypothermia after cardiac arrest. International guidelines advocate the use of a target temperature management of 32°C to 34°C for 12 to 24 hours after resuscitation from out-of-hospital cardiac arrest. A systematic review indicates that the evidence for recommending this intervention is inconclusive, and the GRADE level of evidence is low. Previous trials were small, with high risk of bias, evaluated select populations, and did not treat hyperthermia in the control groups. The optimal target temperature management strategy is not known.

METHODS

The TTM trial is an investigator-initiated, international, randomized, parallel-group, and assessor-blinded clinical trial designed to enroll at least 850 adult, unconscious patients resuscitated after out-of-hospital cardiac arrest of a presumed cardiac cause. The patients will be randomized to a target temperature management of either 33°C or 36°C after return of spontaneous circulation. In both groups, the intervention will last 36 hours. The primary outcome is all-cause mortality at maximal follow-up. The main secondary outcomes are the composite outcome of all-cause mortality and poor neurologic function (cerebral performance categories 3 and 4) at hospital discharge and at 180 days, cognitive status and quality of life at 180 days, assessment of safety and harm.

DISCUSSION

The TTM trial will investigate potential benefit and harm of 2 target temperature strategies, both avoiding hyperthermia in a large proportion of the out-of-hospital cardiac arrest population.

Therapeutic hypothermia for the management of intracranial hypertension in severe traumatic brain injury: a systematic review

BACKGROUND

Traumatic brain injury (TBI) is a major source of death and severe disability worldwide. Raised Intracranial pressure (ICP) is an important predictor of mortality in patients with severe TBI and aggressive treatment of elevated ICP has been shown to reduce mortality and improve outcome. The acute post-injury period in TBI is characterized by several pathophysiologic processes that start in the minutes to hours following injury. All of these processes are temperature-dependent; they are all aggravated by fever and inhibited by hypothermia.

METHODS

This study reviewed the current clinical evidence in support of the use of therapeutic hypothermia (TH) for the treatment of intracranial hypertension (ICH) in patients with severe TBI.

RESULTS

This study identified a total of 18 studies involving hypothermia for control of ICP; 13 were randomized controlled trials (RCT) and five were observational studies. TH (32-34°C) was effective in controlling ICH in all studies. In the 13 RCT, ICP in the TH group was always significantly lower than ICP in the normothermia group. In the five observational studies, ICP during TH was always significantly lower than prior to inducing TH.

CONCLUSIONS

Pending results from large multi-centre studies evaluating the effect of TH on ICH and outcome, TH should be included as a therapeutic option to control ICP in patients with severe TBI.

Therapeutic hypothermia and prevention of acute kidney injury: a meta-analysis of randomized controlled trials

BACKGROUND

Therapeutic hypothermia has been shown to reduce neurological morbidity and mortality in the setting of out-of-hospital cardiac arrest and may be beneficial following brain injury and cardiopulmonary bypass. We conducted a systematic review to ascertain the effect of therapeutic hypothermia on development of acute kidney injury (AKI) and mortality.

METHODS

We searched for randomized controlled trials in MEDLINE through February 2011. We included trials comparing hypothermia to normothermia that reported kidney-related outcomes including, development of AKI, dialysis requirement, changes in serum creatinine, and mortality. We performed Peto fixed-effect and random-effects model meta-analyses, and meta-regressions.

RESULTS

Nineteen trials reporting on 2218 patients were included; in the normothermia group, the weighted rate of AKI was 4.2%, dialysis requirement 3.7%, and mortality 10.8%. By meta-analysis, hypothermia was not associated with a lower odds of AKI (odds ratio [OR] 1.01, 95% confidence interval [CI] 0.68, 1.51; P=0.95) or dialysis requirement (OR 0.81; 95% CI 0.30, 2.19; P=0.68); however, by meta-regression, a lower target cooling temperature was associated with a lower odds of AKI (P=0.01). Hypothermia was associated with lower mortality (OR 0.69; 95% CI 0.51, 0.92; P=0.01).

CONCLUSIONS

In trials that ascertained kidney endpoints, therapeutic hypothermia prevented neither the development of AKI nor dialysis requirement, but was associated with lower mortality. Different definitions and rates of AKI, differences in mortality rates, and concerns about the optimal target cooling temperature preclude definitive conclusions.

Management of the post-cardiac arrest syndrome

BACKGROUND

Recent advances in resuscitation science have revolutionized care of the cardiac arrest patient. Dramatic departures from time-honored advanced cardiac life support therapies, such as cardiocerebral resuscitation and bundled post-arrest care, have given rise to a new paradigm of resuscitation practices, which has boosted the rate of neurologically intact survival.

OBJECTIVES

This article reviews the pathophysiology of the post-cardiac arrest syndrome, the collective pathophysiology after return of spontaneous circulation, and presents management pearls specifically for the emergency physician. This growing area of scientific inquiry must be managed appropriately to sustain improved outcomes.

DISCUSSION

The emergency physician must understand this pathophysiology, manage resuscitated patients according to the latest evidence, and coordinate with appropriate inpatient resources.

CONCLUSION

The new approach to cardiac arrest care is predicated on a chain of survival that spans the spectrum of care from the prehospital arena through the emergency, intensive, and inpatient settings. The emergency physician is a crucial link in this chain.

Molecular mechanisms of therapeutic hypothermia on neurological function in a swine model of cardiopulmonary resuscitation

OBJECTIVE

To explore the molecular mechanisms by which mild hypothermia following resuscitation improves neurological function in a porcine model of cardiac arrest.

METHODS

Thirty-three inbred Chinese Wuzhishan (WZS) minipigs were used. After 8 min of untreated ventricular fibrillation (VF), the surviving animals (n=29) were randomly divided into two groups including serum group (n=16) and molecular group (n=13). Serum group animals were used to measure porcine-specific tumour necrosis factor-alpha (TNF-α), interleukin (IL-6, IL-10), matrix metalloproteinase (MMP9), Aquaporin-4 (AQP4), tissue inhibitor to metalloproteinase-1 (TIMP1), neuron-specific enolase (NSE) and S100B at 0.5 h, 6 h, 12 h, 24 h and 72h recovery by enzyme-linked immunosorbent assay (ELISA). Molecular group animals were used to measure cerebral cortex messenger RNA (mRNA) and protein expression of nuclear factor-κB (NF-κB), MMP9 and AQP4 by real-time (RT) quantitative polymerase chain reaction (PCR) and Western blotting at 24 h and 72 h recovery. Animals were further divided into either normothermia or hypothermia groups. Hypothermia (33°C) was maintained for 12 h using an endovascular cooling device. Swine neurologic deficit scores (NDS) were used to evaluate neurological function at 24-h and 72-h recovery.

RESULTS

Twenty-nine of the 33 (87.9%) animals were successfully resuscitated. The hypothermia group exhibited higher survival rates at 24 h (75%) and 72 h (62.5%) compared to the normothermia group (37.5% and 25%, respectively). Hypothermia markedly inhibited expression of NF-κB, TNF-α, MMP9 and NSE, and promoted expression of TIMP1 (P<0.01). The mean NDS at 24-h and 72-h recovery was 112.5 and 61, respectively, in the hypothermic group, and 230 and 207.5, respectively, in the normothermia group.

CONCLUSION

Brain protection induced by hypothermia involves inhibition of inflammatory and brain edema pathways.

Thrombocytopenia in the Intensive Care Unit

Thrombocytopenia is a common laboratory finding in critically ill patients admitted to the intensive care unit. Potential etiologies of thrombocytopenia are myriad, ranging from acute disease processes and concomitant conditions to exposures and drugs. The mechanism of decreased platelet counts can also be varied: laboratory measurement may be spurious, platelet production may be decreased, or platelet destruction or sequestration may be increased. In addition to evaluation for the cause of thrombocytopenia, the clinician must also guard against spontaneous bleeding due to thrombocytopenia, prophylax against bleeding resulting from an invasive procedure performed in the setting of thrombocytopenia, and treat active bleeding related to thrombocytopenia.

Therapeutic hypothermia for acute neurological injuries

Therapeutic hypothermia (TH) is the intentional reduction of core body temperature to 32°C to 35°C, and is increasingly applied by intensivists for a variety of acute neurological injuries to achieve neuroprotection and reduction of elevated intracranial pressure. TH improves outcomes in comatose patients after a cardiac arrest with a shockable rhythm, but other off-label applications exist and are likely to increase in the future. This comprehensive review summarizes the physiology and cellular mechanism of action of TH, as well as different means of TH induction and maintenance with potential side effects. Indications of TH are critically reviewed by disease entity, as reported in the most recent literature, and evidence-based recommendations are provided.

Posttraumatic hypothermia increases doublecortin expressing neurons in the dentate gyrus after traumatic brain injury in the rat

Previous studies have demonstrated that moderate hypothermia reduces histopathological damage and improves behavioral outcome after experimental traumatic brain injury (TBI). Further investigations have clarified the mechanisms underlying the beneficial effects of hypothermia by showing that cooling reduces multiple cell injury cascades. The purpose of this study was to determine whether hypothermia could also enhance endogenous reparative processes following TBI such as neurogenesis and the replacement of lost neurons. Male Sprague-Dawley rats underwent moderate fluid-percussion brain injury and then were randomized into normothermia (37°C) or hypothermia (33°C) treatment. Animals received injections of 5-bromo-2'-deoxyuridine (BrdU) to detect mitotic cells after brain injury. After 3 or 7 days, animals were perfusion-fixed and processed for immunocytochemistry and confocal analysis. Sections were stained for markers selective for cell proliferation (BrdU), neuroblasts and immature neurons (doublecortin), and mature neurons (NeuN) and then analyzed using non-biased stereology to quantify neurogenesis in the dentate gyrus (DG). At 7 days after TBI, both normothermic and hypothermic TBI animals demonstrated a significant increase in the number of BrdU-immunoreactive cells in the DG as compared to sham-operated controls. At 7 days post-injury, hypothermia animals had a greater number of BrdU (ipsilateral cortex) and doublecortin (ipsilateral and contralateral cortex) immunoreactive cells in the DG as compared to normothermia animals. Because adult neurogenesis following injury may be associated with enhanced functional recovery, these data demonstrate that therapeutic hypothermia sustains the increase in neurogenesis induced by TBI and this may be one of the mechanisms by which hypothermia promotes reparative strategies in the injured nervous system.

The impact of response time reliability on CPR incidence and resuscitation success: a benchmark study from the German Resuscitation Registry

Introduction

Sudden cardiac arrest is one of the most frequent causes of death in the world. In highly qualified emergency medical service (EMS) systems, including well-trained emergency physicians, spontaneous circulation may be restored in up to 53% of patients at least until admission to hospital. Compared with these highly qualified EMS systems, markedly lower success rates are observed in other systems. These data clearly show that there are considerable differences between EMS systems concerning treatment success following cardiac arrest and resuscitation, although in all systems international guidelines for resuscitation are used. In this study, we investigated the impact of response time reliability (RTR) on cardiopulmonary resuscitation (CPR) incidence and resuscitation success by using the return of spontaneous circulation (ROSC) after cardiac arrest (RACA) scores and data from seven German EMS systems participating in the German Resuscitation Registry.

Methods

Anonymised patient data after out-of-hospital cardiac arrest gathered from seven EMS systems in Germany from 2006 to 2009 were analysed with regard to socioeconomic factors (population, area and EMS unit-hours), process quality (RTR, CPR incidence, special CPR measures and prehospital cooling), patient factors (age, gender, cause of cardiac arrest and bystander CPR). End points were defined as ROSC, admission to hospital, 24-hour survival and hospital discharge rate. χ² tests, odds ratios and the Bonferroni correction were used for statistical analyses.

Results

Our present study comprised 2,330 prehospital CPR patients at seven centres. The incidence of sudden cardiac arrest ranged from 36.0 to 65.1/100,000 inhabitants/year. We identified two EMS systems (RTR < 70%) that reached patients within 8 minutes of the call to the dispatch centre 62.0% and 65.6% of the time, respectively. The other five EMS systems (RTR > 70%) reached patients within 8 minutes of the call to the dispatch centre 70.4% up to 95.5% of the time. EMS systems arriving relatively later at the patients side (RTR < 70%) initiate CPR less frequently and admit fewer patients alive to hospital (calculated per 100,000 inhabitants/year) (CPR incidence (1/100,000 inhabitants/year) RTR > 70% = 57.2 vs RTR < 70% = 36.1, OR = 1.586 (99% CI = 1.383 to 1.819); P < 0.01) (admitted to hospital with ROSC (1/100,000 inhabitants/year) RTR > 70% = 24.4 vs RTR < 70% = 15.6, OR = 1.57 (99% CI = 1.274 to 1.935); P < 0.01). Using ROSC rate and the multivariate RACA score to predict outcomes, we found that the two groups did not differ, but ROSC rates were higher than predicted in both groups (ROSC RTR > 70% = 46.6% vs RTR < 70% = 47.3%, OR = 0.971 (95% CI = 0.787 to 1.196); P = n.s.) (ROSC RACA RTR > 70% = 42.4% vs RTR < 70% = 39.5%, OR = 1.127 (95% CI = 0.911 to 1.395); P = n.s.)

Conclusion

This study demonstrates that, on the level of EMS systems, faster ones more often initiate CPR and increase the number of patients admitted to hospital alive. Furthermore, we show that, with very different approaches, all centres that adhere to and are intensely trained according to the 2005 European Resuscitation Council guidelines are superior and, on the basis of international comparisons, achieve excellent success rates following CPR.

Pharmacological postconditioning with sevoflurane after cardiopulmonary resuscitation reduces myocardial dysfunction

Introduction

In this study, we sought to examine whether pharmacological postconditioning with sevoflurane (SEVO) is neuro- and cardioprotective in a pig model of cardiopulmonary resuscitation.

Methods

Twenty-two pigs were subjected to cardiac arrest. After 8 minutes of ventricular fibrillation and 2 minutes of basic life support, advanced cardiac life support was started. After successful return of spontaneous circulation (N = 16), animals were randomized to either (1) propofol (CONTROL) anesthesia or (2) SEVO anesthesia for 4 hours. Neurological function was assessed 24 hours after return of spontaneous circulation. The effects on myocardial and cerebral damage, especially on inflammation, apoptosis and tissue remodeling, were studied using cellular and molecular approaches.

Results

Animals treated with SEVO had lower peak troponin T levels (median [IQR]) (CONTROL vs SEVO = 0.31 pg/mL [0.2 to 0.65] vs 0.14 pg/mL [0.09 to 0.25]; P < 0.05) and improved left ventricular systolic and diastolic function compared to the CONTROL group (P < 0.05). SEVO was associated with a reduction in myocardial IL-1β protein concentrations (0.16 pg/μg total protein [0.14 to 0.17] vs 0.12 pg/μg total protein [0.11 to 0.14]; P < 0.01), a reduction in apoptosis (increased procaspase-3 protein levels (0.94 arbitrary units [0.86 to 1.04] vs 1.18 arbitrary units [1.03 to 1.28]; P < 0.05), increased hypoxia-inducible factor (HIF)-1α protein expression (P < 0.05) and increased activity of matrix metalloproteinase 9 (P < 0.05). SEVO did not, however, affect neurological deficit score or cerebral cellular and molecular pathways.

Conclusions

SEVO reduced myocardial damage and dysfunction after cardiopulmonary resuscitation in the early postresuscitation period. The reduction was associated with a reduced rate of myocardial proinflammatory cytokine expression, apoptosis, increased HIF-1α expression and increased activity of matrix metalloproteinase 9. Early administration of SEVO may not, however, improve neurological recovery.

Therapeutic hypothermia after cardiac arrest in a 66-year-old man

Hypoxic-ischaemic brain injury is an important cause of morbidity and mortality following both in- and out-of-hospital cardiac arrest. Despite significant advances in critical care the only intervention proven to increase survival rates after cardiac arrest is mild hypothermia. The authors present a case describing the use of therapeutic hypothermia after ventricular fibrillation cardiac arrest, including its indications and contra-indications, and the techniques that can be used to induce it.

Targeted temperature management in critical care: a report and recommendations from five professional societies

OBJECTIVE

Representatives of five international critical care societies convened topic specialists and a nonexpert jury to review, assess, and report on studies of targeted temperature management and to provide clinical recommendations.

DATA SOURCES

Questions were allocated to experts who reviewed their areas, made formal presentations, and responded to questions. Jurors also performed independent searches. Sources used for consensus derived exclusively from peer-reviewed reports of human and animal studies.

STUDY SELECTION

Question-specific studies were selected from literature searches; jurors independently determined the relevance of each study included in the synthesis.

CONCLUSIONS AND RECOMMENDATIONS

1) The jury opines that the term "targeted temperature management" replace "therapeutic hypothermia." 2) The jury opines that descriptors (e.g., "mild") be replaced with explicit targeted temperature management profiles. 3) The jury opines that each report of a targeted temperature management trial enumerate the physiologic effects anticipated by the investigators and actually observed and/or measured in subjects in each arm of the trial as a strategy for increasing knowledge of the dose/duration/response characteristics of temperature management. This enumeration should be kept separate from the body of the report, be organized by body systems, and be made without assertions about the impact of any specific effect on the clinical outcome. 4) The jury STRONGLY RECOMMENDS targeted temperature management to a target of 32°C-34°C as the preferred treatment (vs. unstructured temperature management) of out-of-hospital adult cardiac arrest victims with a first registered electrocardiography rhythm of ventricular fibrillation or pulseless ventricular tachycardia and still unconscious after restoration of spontaneous circulation (strong recommendation, moderate quality of evidence). 5) The jury WEAKLY RECOMMENDS the use of targeted temperature management to 33°C-35.5°C (vs. less structured management) in the treatment of term newborns who sustained asphyxia and exhibit acidosis and/or encephalopathy (weak recommendation, moderate quality of evidence).

Therapeutic hypothermia for cardiac arrest: a practical approach

Therapeutic hypothermia (TH), which prevents and ameliorates the cascade of secondary neurologic injury after the return of spontaneous circulation, is the most effective neuroprotective therapy for encephalopathic survivors of cardiac arrest. Despite the compelling efficacy of TH, most patients who survive cardiac arrest long enough to be hospitalized will nonetheless suffer a poor neurologic outcome. Attention to the details of therapy and an integrated approach involving emergency medicine, neurology, cardiology, critical care medicine, and palliative care are likely to yield the best results. This effort is complex, and broad implementation of TH has been slow in the United States and Europe. Given that most cardiac arrest mortality in patients who survive long enough to be hospitalized is due to brain injury rather than circulatory collapse, neurologists should recognize their primary role as advocates for neuroprotective therapy at all stages of the evaluation. In the emergency department, hemodynamic stabilization must be achieved and a rapid neurologic and cardiac evaluation performed, with patients efficiently triaged to hypothermia and cardiac revascularization. Cardiologists should be aware that it is safe and desirable to induce TH, even when urgent coronary angiography and percutaneous revascularization procedures are required. In the intensive care unit, cerebral perfusion must be optimized, metabolic homeostasis achieved, and neuromonitoring used during the dangerous decooling phase. Cardiac arrest is always a life-altering event for patients and their families. Even after cardiac arrest survivors have been stabilized and treated, physicians must recogonize and embrace their role in facilitating a variety of difficult transitions: to organ donation, end-of-life care, nursing or rehabilitation placement, or home.