Therapeutic hypothermia after cardiac arrest in clinical practice: Review and compilation of recent experiences:

Therapeutic hypothermia after out-of-hospital cardiac arrest: evaluation of a regional system to increase access to cooling

BACKGROUND

Therapeutic hypothermia (TH) improves survival and confers neuroprotection in out-of-hospital cardiac arrest (OHCA), but TH is underutilized, and regional systems of care for OHCA that include TH are needed.

METHODS AND RESULTS

The Cool It protocol has established TH as the standard of care for OHCA across a regional network of hospitals transferring patients to a central TH-capable hospital. Between February 2006 and August 2009, 140 OHCA patients who remained unresponsive after return of spontaneous circulation were cooled and rewarmed with the use of an automated, noninvasive cooling device. Three quarters of the patients (n=107) were transferred to the TH-capable hospital from referring network hospitals. Positive neurological outcome was defined as Cerebral Performance Category 1 or 2 at discharge. Patients with non-ventricular fibrillation arrest or cardiogenic shock were included, and patients with concurrent ST-segment elevation myocardial infarction (n=68) received cardiac intervention and cooling simultaneously. Overall survival to hospital discharge was 56%, and 92% of survivors were discharged with a positive neurological outcome. Survival was similar in transferred and nontransferred patients. Non-ventricular fibrillation arrest and presence of cardiogenic shock were associated strongly with mortality, but survivors with these event characteristics had high rates of positive neurological recovery (100% and 89%, respectively). A 20% increase in the risk of death (95% confidence interval, 4% to 39%) was observed for every hour of delay to initiation of cooling.

CONCLUSIONS

A comprehensive TH protocol can be integrated into a regional ST-segment elevation myocardial infarction network and achieves broad dispersion of this essential therapy for OHCA.

Usefulness of mild therapeutic hypothermia for hospitalized comatose patients having out-of-hospital cardiac arrest

Mild therapeutic hypothermia has proved beneficial after out-of-hospital cardiac arrest in the adult population, when the initial rhythm is ventricular fibrillation (VF). In this study, data from 110 consecutive patients with out-of-hospital cardiac arrest due to VF (n = 86) or to non-VF rhythm (n = 24), admitted to an intensive cardiac care unit with restoration of spontaneous circulation and who remained unconscious on admission, were analyzed. Patients were cooled using an external cooling system. Of the patients with VF, 66% had favorable outcomes (Glasgow-Pittsburgh Cerebral Performance Category 1 or 2), and 30% died. Of the patients with non-VF, 8% had favorable outcomes (p <0.001 vs VF), and 63% died (p = 0.004 vs VF). In patients with VF, those with poor outcomes were older than those with favorable outcomes (odds ratio [OR] 1.61, 95% confidence interval [CI] 1.03 to 2.7, p = 0.001) and had previous ejection fractions <35% (OR 7.72, 95% CI 1.8 to 33, p = 0.002). Outcomes were also worse when patients presented to the emergency room with seizures (OR 20.96, 95% CI 2.48 to 177.42, p = 0.003) or hemodynamic instability (OR 14.4, 95% CI 3.47 to 60, p <0.0001). In the non-VF group, the 2 patients with good outcomes were younger than those with unfavorable outcomes (39 ± 16 vs 65 ± 12 years, respectively, p = 0.04), with good left ventricular function on presentation (100% vs 4.5%, p = 0.0001) and with short asystole and/or short time from collapse to restoration of spontaneous circulation. In conclusion, mild therapeutic hypothermia in the adult population is more effective in patients with VF compared to those with non-VF. Good prognostic factors for patients with non-VF could be young age, good left ventricular function, and short anoxic time.

Therapeutic hypothermia after cardiac arrest: experience at an academically affiliated community-based veterans affairs medical center

At laboratory and clinical levels, therapeutic hypothermia has been shown to improve neurologic outcomes and mortality following cardiac arrest. We reviewed each cardiac arrest in our community-based Veterans Affairs Medical Center over a three-year period. The majority of cases were in-hospital arrests associated with initial pulseless electrical activity or asystole. Of a total of 100 patients suffering 118 cardiac arrests, 29 arrests involved comatose survivors, with eight patients completing therapeutic cooling. Cerebral performance category scores at discharge and six months were significantly better in the cooled cohort versus the noncooled cohort, and, in every case except for one, cooling was offered for appropriate reasons. Mean time to initiation of cooling protocol was 3.7 hours and mean time to goal temperature of 33°C was 8.8 hours, and few complications clearly related to cooling were noted in our case series. While in-patient hospital mortality of cardiac arrest was high at 65% mortality during hospital admission, therapeutic hypothermia was safe and feasible at our center. Our cooling times and incidence of favorable outcomes are comparable to previously published reports. This study demonstrates the feasibility of implementing, a cooling protocol a community setting, and the role of neurologists in ensuring effective hospital-wide implementation.

Improved survival with therapeutic hypothermia after cardiac arrest with cold saline and surfacing cooling: keep it simple

Aim. To evaluate whether the introduction of a therapeutic hypothermia (TH) protocol consisting of cold saline infusion and surface cooling would be effective in targeting mild therapeutic hypothermia (32–34°C). Additionally, to evaluate if TH would improve survival after cardiac arrest. Design. Before-after design. Setting. General Intensive Care Unit (ICU) at an urban general hospital with 470 beds. Patients and Methods. Patients admitted in the ICU after cardiac arrest between 2004 and 2009 were included. Effectiveness of the TH protocol to achieve the targeted temperature was evaluated. Hospital mortality was compared before (October 2004–March 2006) and after (April 2006–September 2009) the protocol implementation. Results. Hundred and thirty patients were included, 75 patients were not submitted to TH (before TH group), and 55 were submitted to TH (TH group). There were no significant differences concerning baseline, ICU, and cardiac arrest characteristics between both groups. There was a significant reduction in hospital mortality from 61% (n = 46) in the before TH group to 40% (n = 22) in the TH group. Conclusion. Our protocol consisting of cold saline infusion and surface cooling might be effective in inducing and maintaining mild therapeutic hypothermia. TH achieved with this protocol was associated with a significant reduction in hospital mortality.

The role of hypothermia in post-cardiac arrest patients with return of spontaneous circulation: a systematic review

OBJECTIVES

To update a comprehensive systematic review of the use of therapeutic hypothermia after cardiac arrest that was undertaken initially as part of the 2010 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science. The specific question addressed was: 'in post-cardiac arrest patients with a return of spontaneous circulation, does the induction of mild hypothermia improve morbidity or mortality when compared with usual care?'

METHODS

Pubmed was searched using ("heart arrest" or "cardiopulmonary resuscitation") AND "hypothermia, induced" using 'Clinical Queries' search strategy; EmBASE was searched using (heart arrest) OR (cardiopulmonary resuscitation) AND hypothermia; The Cochrane database of systematic reviews; ECC EndNote Library for "hypothermia" in abstract OR title. Excluded were animal studies, reviews and editorials, surveys of implementation, analytical models, reports of single cases, pre-arrest or during arrest cooling and group where the intervention was not hypothermia alone.

RESULTS

77 studies met the criteria for further review. Of these, four were meta-analyses (LOE 1); seven were randomised controlled trials (LOE 1), although six of these were from the same set of patients; nine were non-randomised, concurrent controls (LOE 2); 15 were trials with retrospective controls (LOE 3); 40 had no controls (LOE 4); and one was extrapolated from a non-cardiac arrest group (LOE 5).

CONCLUSION

There is evidence supporting the use of mild therapeutic hypothermia to improve neurological outcome in patients who remain comatose following the return of spontaneous circulation after a cardiac arrest; however, much of the evidence is from low-level, observational studies. Of seven randomised controlled trials, six use data from the same patients.

Is hypothermia after cardiac arrest effective in both shockable and nonshockable patients?: insights from a large registry

BACKGROUND

Although the level of evidence of improvement is significant in cardiac arrest patients resuscitated from a shockable rhythm (ventricular fibrillation or pulseless ventricular tachycardia [VF/Vt]), the use of therapeutic mild hypothermia (TMH) is more controversial in nonshockable patients (pulseless electric activity or asystole [PEA/asystole]). We therefore assessed the prognostic value of hypothermia for neurological outcome at hospital discharge according to first-recorded cardiac rhythm in a large cohort.

METHODS AND RESULTS

Between January 2000 and December 2009, data from 1145 consecutive out-of-hospital cardiac arrest patients in whom a successful resuscitation had been achieved were prospectively collected. The association of TMH with a good neurological outcome at hospital discharge (cerebral performance categories level 1 or 2) was quantified by logistic regression analysis. TMH was induced in 457/708 patients (65%) in VF/Vt and in 261/437 patients (60%) in PEA/asystole. Overall, 342/1145 patients (30%) reached a favorable outcome (cerebral performance categories level 1 or 2) at hospital discharge, respectively 274/708 (39%) in VF/Vt and 68/437 (16%) in PEA/asystole (P<0.001). After adjustment, in VF/Vt patients, TMH was associated with increased odds of good neurological outcome (adjusted odds ratio, 1.90; 95% confidence interval, 1.18 to 3.06) whereas in PEA/asystole patients, TMH was not significantly associated with good neurological outcome (adjusted odds ratio, 0.71; 95% confidence interval, 0.37 to 1.36).

CONCLUSIONS

In this large cohort of cardiac arrest patients, hypothermia was independently associated with an improved outcome at hospital discharge in patients presenting with VF/Vt. By contrast, TMH was not associated with good outcome in nonshockable patients. Further investigations are needed to clarify this lack of efficiency in PEA/asystole.

State of the art in therapeutic hypothermia

Historically, hypothermia was induced prior to surgery to enable procedures with prolonged ischemia, such as open heart surgery and organ transplant. Within the past decade, the efficacy of hypothermia to treat emergency cases of ongoing ischemia such as stroke, myocardial infarction, and cardiac arrest has been studied. Although the exact role of ischemia/reperfusion is unclear clinically, hypothermia holds significant promise for improving outcomes for patients suffering from reperfusion after ischemia. Research has elucidated two distinct windows of opportunity for clinical use of hypothermia. In the early intra-ischemia window, hypothermia modulates abnormal cellular free radical production, poor calcium management, and poor pH management. In the more delayed post-reperfusion window, hypothermia modulates the downstream necrotic, apoptotic, and inflammatory pathways that cause delayed cell death. Improved cooling and monitoring technologies are required to realize the full potential of this therapy. Herein we discuss the current state of clinical practice, clinical trials, recommendations for cooling, and ongoing research on therapeutic hypothermia.

History and current trends in sudden cardiac arrest and resuscitation in adults

Cardiac arrest occurs when organized cardiac contractility ceases and circulation stops. During cardiac arrest, electrical activity may be abnormal or absent, and the rhythm documented can be ventricular fibrillation, pulseless ventricular tachycardia, pulseless electrical activity, or asystole. It has been estimated that 300 000 sudden cardiac arrests occur each year in the United States, with 75% (225,000) occurring out-of-hospital and 25% (75,000) occurring in-hospital. A similar number occur in Europe each year. The 3-phase model of cardiac arrest, which proposes that a cardiac arrest progresses through distinct phases as time elapses, helps inform research and clinical care by providing a framework for improving outcomes from cardiac arrest. Early in an arrest, during the electrical phase, defibrillation is paramount. The circulatory phase begins after 4 to 5 minutes, and interventions to optimize circulation become of primary importance. When an arrest is prolonged, lasting for ≥10 minutes, the patient passes into the metabolic phase, in which significant metabolic derangements have accrued and start to dominate arrest physiology. If return of spontaneous circulation occurs during this phase, significant injury to diverse organs may have occurred, producing a critical illness known as post-cardiac arrest syndrome. The post-cardiac arrest syndrome has been recognized as a unique entity requiring unique therapies for successful management. Recent advances in cardiac arrest care include cardiocerebral resuscitation and the use of therapeutic hypothermia to treat comatose survivors of cardiac arrest.

Drug-induced mild therapeutic hypothermia obtained by administration of a transient receptor potential vanilloid type 1 agonist

Background

The use of mechanical/physical devices for applying mild therapeutic hypothermia is the only proven neuroprotective treatment for survivors of out of hospital cardiac arrest. However, this type of therapy is cumbersome and associated with several side-effects. We investigated the feasibility of using a transient receptor potential vanilloid type 1 (TRPV1) agonist for obtaining drug-induced sustainable mild hypothermia.

Methods

First, we screened a heterogeneous group of TRPV1 agonists and secondly we tested the hypothermic properties of a selected candidate by dose-response studies. Finally we tested the hypothermic properties in a large animal. The screening was in conscious rats, the dose-response experiments in conscious rats and in cynomologus monkeys, and the finally we tested the hypothermic properties in conscious young cattle (calves with a body weight as an adult human). The investigated TRPV1 agonists were administered by continuous intravenous infusion.

Results

Screening: Dihydrocapsaicin (DHC), a component of chili pepper, displayed a desirable hypothermic profile with regards to the duration, depth and control in conscious rats. Dose-response experiments: In both rats and cynomologus monkeys DHC caused a dose-dependent and immediate decrease in body temperature. Thus in rats, infusion of DHC at doses of 0.125, 0.25, 0.50, and 0.75 mg/kg/h caused a maximal ΔT (°C) as compared to vehicle control of -0.9, -1.5, -2.0, and -4.2 within approximately 1 hour until the 6 hour infusion was stopped. Finally, in calves the intravenous infusion of DHC was able to maintain mild hypothermia with ΔT > -3°C for more than 12 hours.

Conclusions

Our data support the hypothesis that infusion of dihydrocapsaicin is a candidate for testing as a primary or adjunct method of inducing and maintaining therapeutic hypothermia.

Postresuscitation care: entering a new era

PURPOSE OF REVIEW

The purpose of this study is to discuss recent data relating to the treatment of cardiac arrest survivors. This is a rapidly evolving component of resuscitation medicine that impacts significantly on the quality of survival after cardiac arrest.

RECENT FINDINGS

The postcardiac arrest syndrome comprises postcardiac arrest brain injury, postcardiac arrest myocardial dysfunction, the systemic ischaemia/reperfusion response, and the persistent precipitating disease. Primary percutaneous coronary intervention is the preferred method for restoring coronary perfusion when cardiac arrest has been caused by an ST-elevation myocardial infarction. Many cardiac arrest survivors with non-ST-elevation myocardial infarction may also benefit from urgent percutaneous coronary intervention. Comatose cardiac arrest survivors should be managed with a moderate blood glucose target range of below 10 mmol/l (180 mg/dl). Therapeutic hypothermia is now generally accepted as part of a treatment strategy for comatose survivors of cardiac arrest, but its use may render conventional methods of prognostication unreliable.

SUMMARY

Survivors from cardiac arrest develop a postcardiac arrest syndrome. Postresuscitation care, including primary percutaneous coronary intervention, therapeutic hypothermia, and control of blood sugar, improves survival and neurological outcome in cardiac arrest survivors. Completely reliable prognostication in comatose survivors of cardiac arrest is difficult to achieve.