Part 7.5: Postresuscitation Support

Targeted Temperature Management for Cardiac Arrest Due to Non-shockable Rhythm: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Background

Targeted temperature management (TTM) is recommended in adult patients following cardiac arrest (CA) with any rhythm. However, as to non-shockable (NSR) CA, high-quality evidence of TTM supporting its practices remains uncertain. Thus, we aimed to conduct a systematic review and meta-analysis with randomized controlled trials (RCTs) to explore the efficacy and safety of TTM in this population.

Methods

We searched PubMed, Embase, and Cochrane library databases for potential trials from inception through Aug 25, 2021. RCTs evaluating TTM for CA adults due to NSR were included, regardless of the timing of cooling initiation. Outcome measurements were mortality and good neurological function. We used the Cochrane bias tools to evaluate the quality of the included studies. Heterogeneity, subgroup analyses, and sensitivity analysis were investigated to test the robustness of the primary outcomes.

Results

A total of 14 RCTs with 4,009 adults were eligible for the final analysis. All trials had a low to moderate risk of bias. Of the included trials, six compared NSR patients with or without TTM, while eight compared pre-hospital to in-hospital TTM. Pooled data showed that TTM was not associated with improved mortality (Risk ratio [RR] 1.00; 95% CI, 0.944–1.05; P = 0.89, I² = 0%) and good neurological outcome (RR 1.18; 95% CI 0.90–1.55; P = 0.22, I² = 8%). Similarly, use of pre-hospital TTM resulted in neither an improved mortality (RR 0.99, 95% CI 0.97–1.03; I² = 0%, P = 0.32) nor favorable neurological outcome (RR 1.13, 95% CI 0.93–1.38; I² = 0%, P = 0.22). These results were further confirmed in the sensitivity analyses and subgroup analyses.

Conclusions

Our results showed that using the TTM strategy did not significantly affect the mortality and neurologic outcomes in CA survival presenting initial NSR.

Targeted temperature management in adult cardiac arrest: Systematic review and meta-analysis

AIM

To perform a systematic review and meta-analysis on targeted temperature management in adult cardiac arrest patients.

METHODS

PubMed, Embase, and the Cochrane Central Register of Controlled Trials were searched on June 17, 2021 for clinical trials. The population included adult patients with cardiac arrest. The review included all aspects of targeted temperature management including timing, temperature, duration, method of induction and maintenance, and rewarming. Two investigators reviewed trials for relevance, extracted data, and assessed risk of bias. Data were pooled using random-effects models. Certainty of evidence was evaluated using GRADE.

RESULTS

The systematic search identified 32 trials. Risk of bias was assessed as intermediate for most of the outcomes. For targeted temperature management with a target of 32-34 °C vs. normothermia (which often required active cooling), 9 trials were identified, with six trials included in meta-analyses. Targeted temperature management with a target of 32-34 °C did not result in an improvement in survival (risk ratio: 1.08 [95%CI: 0.89, 1.30]) or favorable neurologic outcome (risk ratio: 1.21 [95%CI: 0.91, 1.61]) at 90 to 180 days after the cardiac arrest (low certainty of evidence). Three trials assessed different hypothermic temperature targets and found no difference in outcomes (low certainty of evidence). Ten trials were identified comparing prehospital cooling vs. no prehospital cooling with no improvement in survival (risk ratio: 1.01 [95%CI: 0.92, 1.11]) or favorable neurologic outcome (risk ratio: 1.00 [95%CI: 0.90, 1.11]) at hospital discharge (moderate certainty of evidence).

CONCLUSIONS

Among adult patients with cardiac arrest, the use of targeted temperature management at 32-34 °C, when compared to normothermia, did not result in improved outcomes in this meta-analysis. There was no effect of initiating targeted temperature management prior to hospital arrival. These findings warrant an update of international cardiac arrest guidelines.

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.

Enhanced dispersion of repolarization explains increased arrhythmogenesis in severe versus therapeutic hypothermia

BACKGROUND

Hypothermia is proarrhythmic, and, as the use of therapeutic hypothermia (TH) increases, it is critically important to understand the electrophysiological effects of hypothermia on cardiac myocytes and arrhythmia substrates. We tested the hypothesis that hypothermia-enhanced transmural dispersion of repolarization (DOR) is a mechanism of arrhythmogenesis in hypothermia. In addition, we investigated whether the degree of hypothermia, the rate of temperature change, and cooling versus rewarming would alter hypothermia-induced arrhythmia substrates.

METHODS AND RESULTS

Optical action potentials were recorded from cells spanning the transmural wall of canine left ventricular wedge preparations at baseline (36°C), during cooling and during rewarming. Electrophysiological parameters were examined while varying the depth of hypothermia. On cooling to 26°C, DOR increased from 26±4 ms to 93±18 ms (P=0.021); conduction velocity decreased from 35±5 cm/s to 22±5 cm/s (P=0.010). On rewarming to 36°C, DOR remained prolonged, whereas conduction velocity returned to baseline. Conduction block and reentry was observed in all severe hypothermia preparations. Ventricular fibrillation/ventricular tachycardia was seen more during rewarming (4/5) versus cooling (2/6). In TH (n=7), cooling to 32°C mildly increased DOR (31±6 to 50±9, P=0.012), with return to baseline on rewarming and was associated with decreased arrhythmia susceptibility. Increased rate of cooling did not further enhance DOR or arrhythmogenesis.

CONCLUSIONS

Hypothermia amplifies DOR and is a mechanism for arrhythmogenesis. DOR is directly dependent on the depth of cooling and rewarming. This provides insight into the clinical observation of a low incidence of arrhythmias in TH and has implications for protocols for the clinical application of TH.

Intra-arrest transnasal evaporative cooling: a randomized, prehospital, multicenter study (PRINCE: Pre-ROSC IntraNasal Cooling Effectiveness)

BACKGROUND

Transnasal evaporative cooling has sufficient heat transfer capacity for effective intra-arrest cooling and improves survival in swine. The aim of this study was to determine the safety, feasibility, and cooling efficacy of prehospital transnasal cooling in humans and to explore its effects on neurologically intact survival to hospital discharge.

METHODS AND RESULTS

Witnessed cardiac arrest patients with a treatment interval <or=20 minutes were randomized to intra-arrest cooling with a RhinoChill device (treatment group, n=96) versus standard care (control group, n=104). The final analysis included 93 versus 101 patients, respectively. Both groups were cooled after hospital arrival. The patients had similar demographics, initial rhythms, rates of bystander cardiopulmonary resuscitation, and intervals to cardiopulmonary resuscitation and arrival of advanced life support personnel. Eighteen device-related adverse events (1 periorbital emphysema, 3 epistaxis, 1 perioral bleed, and 13 nasal discolorations) were reported. Time to target temperature of 34 degrees C was shorter in the treatment group for both tympanic (102 versus 282 minutes, P=0.03) and core (155 versus 284 minutes, P=0.13) temperature. There were no significant differences in rates of return of spontaneous circulation between the groups (38% in treated subjects versus 43% in control subjects, P=0.48), in overall survival of those admitted alive (44% versus 31%, respectively, P=0.26), or in neurologically intact survival to discharge (Pittsburgh cerebral performance category scale 1 to 2, 34% versus 21%, P=0.21), although the study was not adequately powered to detect changes in these outcomes.

CONCLUSIONS

Prehospital intra-arrest transnasal cooling is safe and feasible and is associated with a significant improvement in the time intervals required to cool patients.

Outcome measures utilized in clinical trials of interventions for post-cardiac arrest syndrome: a systematic review

BACKGROUND

The post-cardiac arrest syndrome (period of critical illness following return of spontaneous circulation [ROSC]) is a promising window of opportunity for clinical trials of therapeutic interventions to improve outcome from cardiac arrest. However, the methodological rigor of post-ROSC trials and the ability to compare or pool data on treatment effects across studies requires consistent and appropriate outcome measures. We aimed to determine the current degree of uniformity of outcome measures in clinical trials of post-ROSC interventions.

METHODS

We conducted a systematic review of Cochrane Library, MEDLINE, EMBASE, CINAHL, conference proceedings, and clinical trial registrations using a comprehensive strategy. We identified experimental or quasi-experimental trials testing post-ROSC interventions in adults. Four authors independently extracted data and assessed study quality using standardized instruments.

RESULTS

The search yielded 33 potential studies, of which 13 randomized controlled trials (n=1937) were included in the final analysis. Seven trials tested pharmacologic therapies and six tested non-pharmacologic therapies. Our main finding is that heterogeneity in the selection and reporting of outcomes limited comparability of results across studies. No two trials used exactly the same primary outcome, and timing of measurement varied widely. We found only two commonalities: (1) indices of functional survival were used rather than survival alone, and (2) ordinal scales of neurological function were collapsed into clinically meaningful groups ("good" versus "bad" outcome).

CONCLUSION

Currently there is a lack of uniformity in selection and reporting of outcome measures among trials of post-ROSC interventions. Achieving consensus would be an important advance for resuscitation science.

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. Acute management of patients with severe hypoxic-ischemic encephalopathy requires rapid and well-coordinated efforts involving emergency medicine, neurology, cardiology, critical care medicine, and palliative care. This effort is complex, and broad implementation of TH has been slow in the United States and Europe. This review summarizes recent developments in the practical application of TH, reviews the role of the neurologist, and suggests an algorithm for coordination of care of cardiac arrest survivors by physicians of divergent subspecialties, with the goals of maximizing neurologic and cardiac recovery.

Changes in cardiovascular beta-adrenoceptor responses during hypothermia

The purpose of this study was to determine cardiovascular beta-adrenergic responses during hypothermia. In the present study, we used isoproterenol (Iso), a nonselective, potent beta-adrenoceptor agonist, well known for its positive chronotropic and inotropic pharmacologic actions at normothermia. Rats were instrumented to measure mean arterial pressure (MAP) and left ventricular (LV) pressure-volume changes using a Millar pressure-volume conductance catheter. Core temperature was manipulated from 37 (normothermia) to 24 degrees C (hypothermia) and back to 37 degrees C (rewarming) using both internal and external heat exchangers. During cooling at each temperature (33, 30, 27, and 24 degrees C), central hemodynamic variables and MAP were measured while intravenously infusing Iso (doses of 1.7, 5, 10, and 20 ng/min). Seven animals underwent all phases of the protocol. At normothermia Iso infusion resulted in a significant, dose-dependent increase in heart rate (HR), stroke volume (SV), cardiac output (CO), LV dP/dt(max) (left ventricular maximum derivative of systolic pressure over time) but no change in MAP. During cooling Iso infusion caused no dose-dependent change in any of the hemodynamic variables. After rewarming, baseline HR and LV dP/dt(max) were increased, whereas SV was significantly reduced when compared with their pre-hypothermic baseline values. This study shows that physiological cardiovascular responses mediated by the beta-adrenoceptor are significantly diminished during core hypothermia.

The impact of prehospital transport interval on survival in out-of-hospital cardiac arrest: implications for regionalization of post-resuscitation care

OBJECTIVE

There is growing evidence that therapeutic hypothermia and other post-resuscitation care improves outcomes in out-of-hospital cardiac arrest (OHCA). Thus, transporting patients with return of spontaneous circulation (ROSC) to specialized facilities may increase survival rates. However, it is unknown whether prolonging transport to reach a designated facility would be detrimental.

METHODS

Data from OHCA patients treated in EMS systems that cover approximately 70% of Arizona's population were evaluated (October 2004-December 2006). We analyzed the association between transport interval (depart scene to ED arrival) and survival to hospital discharge in adult, non-traumatic OHCA patients and in the subgroup who achieved ROSC and remained comatose.

RESULTS

1846 OHCA occurred prior to EMS arrival. Complete transport interval data were available for 1177 (63.8%) patients (study group). 253 patients (21.5%) achieved ROSC and remained comatose making them theoretically eligible for transport to specialized care. Overall, 70 patients (5.9%) survived and 43 (17.0%) comatose ROSC patients survived. Mean transport interval for the study group was 6.9 min (95% CI: 6.7, 7.1). Logistic regression revealed factors that were independently associated with survival: witnessed arrest, bystander CPR, method of CPR, initial rhythm of ventricular fibrillation, and shorter EMS response time interval. There was no significant association between transport interval and outcome in either the overall study group (OR=1.2; 0.77, 1.8) or in the comatose, ROSC subgroup (OR 0.94; 0.51, 1.8).

CONCLUSION

Survival was not significantly impacted by transport interval. This suggests that a modest increase in transport interval from bypassing the closest hospital en route to specialized care is safe and warrants further investigation.

Induction of mild hypothermia in cardiac arrest survivors presenting with cardiogenic shock syndrome

BACKGROUND

Induction of mild hypothermia (MH) in patients resuscitated from cardiac arrest improves their outcome. However, benefits and risks of MH in patients who remain in cardiogenic shock after the return of spontaneous circulation (ROSC) are unclear. We analysed all cardiac arrest survivors who were treated with MH in our intensive coronary care unit (CCU) and compared the outcome of patients with cardiogenic shock syndrome (CSS) with those who were circulatory stable.

METHODS

We performed retrospective analysis of all consecutive cardiac arrest survivors treated by MH in our CCU from November 2002 to August 2006. They were classified into two groups, according to whether they met the criteria for cardiogenic shock or not before MH initiation.

RESULTS

Out of 56 consecutive patients, 28 fulfilled criteria of cardiogenic shock before MH initiation (group A) and 28 were relatively stable (group B). In-hospital mortality was 57.1% in group A and 21.4% in group B patients (P=0.013). Favourable neurological outcome anytime during hospitalization was found in 67.9% of group A patients and in 82.1% of group B subjects (P=0.355). Favourable discharge neurological outcome was reached in 39.3% in group A and in 71.4% in group B (P=0.031). The complication rate in both groups did not differ.

CONCLUSION

While in-hospital mortality in cardiac arrest survivors treated by MH was expectably higher in those with cardiogenic shock than in stable patients, the favourable neurological outcome during hospitalization was comparable in both groups. Therefore, induction of MH should be considered in cardiac arrest survivors with CSS after ROSC.

Keeping Cool: A Case for Hypothermia After Cardiopulmonary Resuscitation

Cessation of circulation during cardiac arrest causes critical end-organ ischemia. Although the neurological consequences of cardiopulmonary arrest can be catastrophic, an aggressive “push fast and push hard” resuscitation technique maintains blood flow until the return of spontaneous circulation. However, reperfusion to the cerebrum leads to cellular chaos and further neurological injury. Use of moderate hypothermia after cardiac arrest mediates these cellular and chemical processes, reducing the impact of the arrest and reperfusion phenomena. A 43-year-old man had 2 asystolic arrests with 20 minutes of cardiopulmonary resuscitation as a result of massive, multiple pulmonary emboli. After the cardiac arrest, the patient was comatose and posturing. The 2005 American Heart Association guidelines for cardiopulmonary resuscitation were used along with moderate hypothermia in an attempt to minimize the neurological consequences of the cardiopulmonary arrest and to optimize the patient’s outcome.

Manipulations of core temperatures in ischemia-reperfusion lung injury in rabbits

The present study was designed to determine the effect of various core temperatures on acute lung injury induced by ischemia-reperfusion (I/R) in our isolated rabbit lung model. Typical acute lung injury was successfully induced by 30 min of ischemia followed by 90 min of reperfusion observation. The I/R elicited a significant increase in pulmonary arterial pressure, microvascular permeability (measured by using the capillary filtration coefficient, Kfc), Delta Kfc ratio, lung weight gain and the protein concentration of the bronchoalveolar lavage fluid. Mild hypothermia significantly attenuated acute lung injury induced by I/R, all parameters having decreased significantly (p<0.05); conversely, mild hyperthermia did not further exacerbate acute lung injury. These experimental data suggest that mild hypothermia significantly ameliorated acute lung injury induced by ischemia-reperfusion in rabbits.

[The new 2005 resuscitation guidelines of the European Resuscitation Council: comments and supplements]

The new CPR guidelines are based on a scientific consensus which was reached by 281 international experts. Chest compressions (100/min, 4-5 cm deep) should be performed in a ratio of 30:2 with ventilation (tidal volume 500 ml, Ti 1 s, FIO2 if possible 1.0). After a single defibrillation attempt (initially biphasic 150-200 J, monophasic 360 J, subsequently with the respective highest energy), chest compressions are initiated again immediately for 2 min. Endotracheal intubation is the gold standard; other airway devices may be employed as well depending on individual skills. Drug administration routes for adults and children: first choice IV, second choice intraosseous, third choice endobronchial [epinephrine dose 2-3x (adults) or 10x (pediatric patients) higher than IV]. Vasopressors: 1 mg epinephrine every 3-5 min IV. After the third unsuccessful defibrillation attempt amiodarone IV (300 mg); repetition (150 mg) possible. Sodium bicarbonate (1 ml/kg 8.4%) only in excessive hyperkalemia, metabolic acidosis, or intoxication with tricyclic antidepressants. Consider atropine (3 mg) and aminophylline (5 mg/kg). Thrombolysis during spontaneous circulation only in myocardial infarction or massive pulmonary embolism; during CPR only during massive pulmonary embolism. Cardiopulmonary bypass only after cardiac surgery, hypothermia or intoxication. Pediatrics: best improvement in outcome by preventing cardiocirculatory collapse. Alternate chest thumps and chest compression (infants), or abdominal compressions (>1-year-old) in foreign body airway obstruction. Initially five breaths, followed by chest compressions (100/min; approximately 1/3 of chest diameter): ventilation ratio 15:2. Treatment of potentially reversible causes (4 "Hs", "HITS": hypoxia, hypovolemia, hypo- and hyperkaliemia, hypothermia, cardiac tamponade, intoxication, thrombo-embolism, tension pneumothorax). Epinephrine 10 microg/kg IV or intraosseously, or 100 microg (endobronchially) every 3-5 min. Defibrillation (4 J/kg; monophasic oder biphasic) followed by 2 min CPR, then ECG and pulse check. Newborns: inflate the lungs with bag-valve mask ventilation. If heart rate<60/min chest compressions:ventilation ratio 3:1 (120 chest compressions/min). Postresuscitation phase: initiate mild hypothermia [32-34 degrees C for 12-24 h; slow rewarming (<0.5 degrees C/h)]. Prediction of CPR outcome is not possible at the scene; determining neurological outcome within 72 h after cardiac arrest with evoked potentials, biochemical tests and physical examination. Even during low suspicion for an acute coronary syndrome, record a prehospital 12-lead ECG. In parallel to pain therapy, aspirin (160-325 mg PO or IV) and in addition clopidogrel (300 mg PO). As antithrombin, heparin (60 IU/kg, max. 4000 IU) or enoxaparine. In ST-segment elevation myocardial infarction, define reperfusion strategy depending on duration of symptoms until PCI (prevent delay>90 min until PCI). Stroke is an emergency and needs to be treated in a stroke unit. A CT scan is the most important evaluation, MRT may replace a CT scan. After hemorrhage exclusion, thrombolysis within 3 h of symptom onset (0.9 mg/kg rt-PA IV; max 90 mg within 60 min, 10% of the entire dosage as initial bolus, no aspirin, no heparin within the first 24 h). In severe hemorrhagic shock, definite control of bleeding is the most important goal. For successful CPR of trauma patients, a minimal intravascular volume status and management of hypoxia are essential. Aggressive fluid resuscitation, hyperventilation, and excessive ventilation pressure may impair outcome in severe hemorrhagic shock. Despite bad prognosis, CPR in trauma patients may be successful in select cases. Any CPR training is better than nothing; simplification of contents and processes remains important.

Critical time window for intra-arrest cooling with cold saline flush in a dog model of cardiopulmonary resuscitation

BACKGROUND

Mild hypothermia improves outcome when induced after cardiac arrest in humans. Recent studies in both dogs and mice suggest that induction of mild hypothermia during cardiopulmonary resuscitation (CPR) greatly enhances its efficacy. In this study, we evaluate the time window for the beneficial effect of intra-arrest cooling in the setting of prolonged CPR in a clinically relevant large-animal model.

METHODS AND RESULTS

Seventeen dogs had ventricular fibrillation cardiac arrest no flow of 3 minutes, followed by 7 minutes of CPR basic life support and 50 minutes of advanced life support. In the early hypothermia group (n=9), mild hypothermia (34 degrees C) was induced with an intravenous fluid bolus flush and venovenous blood shunt cooling after 10 minutes of ventricular fibrillation. In the delayed hypothermia group (n=8), hypothermia was induced at ventricular fibrillation 20 minutes. After 60 minutes of ventricular fibrillation, restoration of spontaneous circulation was achieved with cardiopulmonary bypass for 4 hours, and intensive care was given for 96 hours. In the early hypothermia group, 7 of 9 dogs survived to 96 hours, 5 with good neurological outcome. In contrast, 7 of 8 dogs in the delayed hypothermia group died within 37 hours with multiple organ failure (P=0.012).

CONCLUSIONS

Early application of mild hypothermia with cold saline during prolonged CPR enables intact survival. Delay in the induction of mild hypothermia in this setting markedly reduces its efficacy. Our data suggest that if mild hypothermia is used during CPR, it should be applied as early as possible.