Therapeutic hypothermia after cardiac arrest: where are we now?:

Changes in Practice of Controlled Hypothermia after Cardiac Arrest in the Past 20 Years: A Critical Care Perspective

For 20 years, induced hypothermia and targeted temperature management have been recommended to mitigate brain injury and increase survival after cardiac arrest. On the basis of animal research and small clinical trials, the International Liaison Committee on Resuscitation strongly advocated hypothermia at 32-34 °C for 12-24 hours for comatose patients with out-of-hospital cardiac arrest with initial rhythm of ventricular fibrillation or nonperfusing ventricular tachycardia. The intervention was implemented worldwide. In the past decade, hypothermia and targeted temperature management have been investigated in larger clinical randomized trials focusing on target temperature depth, target temperature duration, prehospital versus in-hospital initiation, nonshockable rhythms, and in-hospital cardiac arrest. Systematic reviews suggest little or no effect of delivering the intervention on the basis of the summary of evidence, and the International Liaison Committee on Resuscitation today recommends only to treat fever and keep body temperature below 37.5 °C (weak recommendation, low-certainty evidence). Here we describe the evolution of temperature management for patients with cardiac arrest during the past 20 years and how the accrued evidence has influenced not only the recommendations but also the guideline process. We also discuss possible paths forward in this field, bringing up both whether fever management is at all beneficial for patients with cardiac arrest and which knowledge gaps future clinical trials in temperature management should address.

Potential cardiac arrest - an observational study of pre-hospital medical response

OBJECTIVES

A previous study showed that Norwegian GPs on call attended around 40% of out-of-hospital medical emergencies. We wanted to investigate the alarms of prehospital medical resources and the doctors' responses in situations of potential cardiac arrests.

DESIGN AND SETTING

A three-month prospective data collection was undertaken from three emergency medical communication centres, covering a population of 816,000 residents. From all emergency medical events, a sub-group of patients who received resuscitation, or who were later pronounced dead at site, was selected for further analysis.

RESULTS

5,105 medical emergencies involving 5,180 patients were included, of which 193 met the inclusion criteria. The GP on call was alarmed in 59 %, and an anaesthesiologist in 43 % of the cases. When alarmed, a GP attended in 84 % and an anaesthesiologist in 87 % of the cases. Among the patients who died, the GP on call was alarmed most frequently.

CONCLUSION

Events involving patients in need of resuscitation are rare, but medical response in the form of the attendance of prehospital personnel is significant. Norwegian GPs have a higher call-out rate for patients in severe situations where resuscitation was an option of treatment, compared with other "red-response" situations. Key points This study investigates alarms of and call-outs among GPs and anaesthesiologists on call, in the most acute clinical situations: Medical emergencies involving patients in need of resuscitation were rare. The health care contribution by pre-hospital personnel being called out was significant. Compared with other acute situations, the GP had a higher attendance rate to patients in life-threatening situations.

Effect of gender on outcome of out of hospital cardiac arrest in the Resuscitation Outcomes Consortium

INTRODUCTION

This study examined the relationship between gender and outcomes of non-traumatic out-of-hospital cardiac arrest (OHCA).

METHODS

All eligible, consecutive, non-traumatic Emergency Medical Services (EMS) treated OHCA patients in the Resuscitation Outcomes Consortium between December 2005 and May 2007. Patient age was analyzed as a continuous variable and stratified in two age cohorts: 15-45 and >55 years of age (yoa). Unadjusted and adjusted (based on Utstein characteristics) chi square tests and logistic regression models were employed to examine the relationship between gender, age, and survival outcomes.

RESULTS

This study enrolled 14,690 patients: of which 36.4% were women with a mean age of 68.3 and 63.6% of them men with a mean age of 64.2. Women survived to hospital discharge less often than men (6.4% vs. 9.1%, p<0.001); the unadjusted OR was 0.69, 95%CI: 0.60, 0.77 whereas when adjusted for all Utstein predictors the difference was not significant (OR: 1.16, 95%CI: 0.98, 1.36, p=0.07). The adjusted survival rate for younger women (15-45 yoa) was 11.1% vs. 9.8% for younger men (OR: 1.66, 95%CI: 1.04, 2.64, p=0.03) but no difference in discharge rates was observed in the >55 cohort (OR: 0.94, 95%CI: 0.78, 1.15, p=0.57).

CONCLUSIONS

Women who suffer OHCAs have lower rates of survival and have unfavourable Utstein predictors. When survival is adjusted for these predictors survival is similar between men and women except in younger women suggesting that age modifies the association of gender and survival from OHCA; a result that supports a protective hormonal effect among premenopausal women.

Mild hypothermia induces incomplete left ventricular relaxation despite spontaneous bradycardia in pigs

AIM

Mild hypothermia (MH) decreases left ventricular (LV) end-diastolic capacitance. We sought to clarify whether this results from incomplete relaxation.

METHODS

Ten anaesthetized pigs were cooled from normothermia (NT, 38 °C) to MH (33 °C). LV end-diastolic pressure (LVPed), volume (LVVed) and pressure-volume relationships (EDPVRs) were determined during stepwise right atrial pacing. LV capacitance (i.e. LVVed at LVPed of 10 mmHg, LV VPed10) was derived from the EDPVR. Pacing-induced changes of diastolic indices (LVPed, LVVed and LV VPed10) were analysed as a function of (i) heart rate and (ii) the ratio between diastolic time interval (t-dia) and LV isovolumic relaxation constant τ, which was calculated using a logistic fit (τL ) and monoexponential fit with zero asymptote (τZ ) and nonzero asymptote (τNZ ).

RESULTS

Mild hypothermia decreased heart rate (85 ± 4 to 68 ± 3 bpm), increased τL (22 ± 1 to 57 ± 4 ms), τZ (26 ± 2 to 56 ± 5 ms) and τNZ (41 ± 1 to 96 ± 5 ms), decreased t-dia/τ ratios, and shifted the EDPVR leftwards compared to NT (all P < 0.05). During NT, pacing at ≥140 bpm shifted the EDPVR progressively leftwards. During MH, relationships between diastolic indices and heart rate were shifted towards lower heart rates compared to NT. However, relationships between diastolic indices and t-dia/τ during NT and MH were superimposable.

CONCLUSION

We conclude that the loss of LV end-diastolic capacitance during MH can be explained at least in part by slowed LV relaxation. MH thereby is an example of incomplete LV relaxation at a spontaneous low heart rate. Caution may be advised, when heart rate is increased in patients treated with MH.

Therapeutic hypothermia after in-hospital cardiac arrest: a critique

More than 210,000 in-hospital cardiac arrests occur annually in the United States. Use of moderate therapeutic hypothermia (TH) in comatose survivors after return of spontaneous circulation following out-of-hospital cardiac arrest (OOH-CA) caused by ventricular fibrillation or pulseless ventricular tachycardia is recommended strongly by many professional organizations and societies. The use of TH after cardiac arrest associated with nonshockable rhythms and after in-hospital cardiac arrest (IH-CA) is recommended to be considered by these same organizations and is being applied widely. The use in these latter circumstances is based on an extrapolation of the data supporting its use after out-of-hospital cardiac arrest associated with shockable rhythms. The purpose of this article is to review the limitations of existing data supporting these extended application of TH after cardiac arrest and to suggest approaches to this dilemma. The data supporting its use for OOH-CA appear to this author, and to some others, to be rather weak, and the data supporting the use of TH for IH-CA appear to be even weaker and to include no randomized controlled trials (RCTs) or supportive observational studies. The many reasons why TH might be expected to be less effective following IH-CA are reviewed. The degree of neurologic injury may be more severe in many of these cases and, thus, may not be responsive to TH as currently practiced following OOH-CA. The potential adverse consequences of the routine use of TH for IH-CA are listed and include complications associated with TH, interference with diagnostic and interventional therapy, and use of scarce personnel and financial resources. Most importantly, it inhibits the ability of researchers to conduct needed RCTs. The author believes that the proper method of providing TH in these cases needs to be better defined. Based on this analysis the author concludes that TH should not be used indiscriminantly following most cases of IH-CA, and instead clinicians should concentrate their efforts in conducting high-quality large RCTs or large-scale, well-designed prospective observation studies to determine its benefits and identify appropriate candidates.

Clinical and translational aspects of hypothermia in major trauma patients: from pathophysiology to prevention, prognosis and potential preservation

The human body strives at maintaining homeostasis within fairly tight regulated mechanisms that control vital regulators such as core body temperature, mechanisms of metabolism and endocrine function. While a wide range of medical conditions can influence thermoregulation the most common source of temperature loss in trauma patients includes: exposure (environmental, as well as cavitary), the administration of i.v. fluids, and anaesthesia/loss of shivering mechanisms, and blood loss per se. Loss of temperature can be classified either according to the aetiology (i.e. accidental/spontaneous versus trauma/haemorrhage-induced temperature loss), or according to an unintended, accidental induction in contrast to a medically intended therapeutic hypothermia. Hypothermia occurs infrequently (prevalence<10% of all injured), but more often (30-50%) in the severely injured. Hypothermia usually come together with and may aggravate acidosis and coagulopathy (the "lethal triad of trauma"), which again may be associated with a high mortality. However, recent studies disagree in the independent predictive role of hypothermia and mortality. Prevention of hypothermia is imperative through all phases of trauma care and must be an interest among all team members. Hypothermia in the trauma setting has attracted focus in the past from a pathophysiological, preventive and prognostic perspective; yet recent focus has shifted towards the potential for using hypothermia for pre-emptive and cellular protective purposes. This paper gives a brief update on some of the clinically relevant aspects of hypothermia in the injured patient.

Interactions between oxygen homeostasis, food availability, and hydrogen sulfide signaling

The ability to sense and respond to stressful conditions is essential to maintain organismal homeostasis. It has long been recognized that stress response factors that improve survival in changing conditions can also influence longevity. In this review, we discuss different strategies used by animals in response to decreased O(2) (hypoxia) to maintain O(2) homeostasis, and consider interactions between hypoxia responses, nutritional status, and H(2)S signaling. O(2) is an essential environmental nutrient for almost all metazoans as it plays a fundamental role in development and cellular metabolism. However, the physiological response(s) to hypoxia depend greatly on the amount of O(2) available. Animals must sense declining O(2) availability to coordinate fundamental metabolic and signaling pathways. It is not surprising that factors involved in the response to hypoxia are also involved in responding to other key environmental signals, particularly food availability. Recent studies in mammals have also shown that the small gaseous signaling molecule hydrogen sulfide (H(2)S) protects against cellular damage and death in hypoxia. These results suggest that H(2)S signaling also integrates with hypoxia response(s). Many of the signaling pathways that mediate the effects of hypoxia, food deprivation, and H(2)S signaling have also been implicated in the control of lifespan. Understanding how these pathways are coordinated therefore has the potential to reveal new cellular and organismal homeostatic mechanisms that contribute to longevity assurance in animals.

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.

RECOVER evidence and knowledge gap analysis on veterinary CPR. Part 7: Clinical guidelines

OBJECTIVE

To present a series of evidence-based, consensus guidelines for veterinary CPR in dogs and cats.

DESIGN

Standardized, systematic evaluation of the literature, categorization of relevant articles according to level of evidence and quality, and development of consensus on conclusions for application of the concepts to clinical practice. Questions in five domains were examined: Preparedness and Prevention, Basic Life Support, Advanced Life Support, Monitoring, and Post-Cardiac Arrest Care. Standardized worksheet templates were used for each question, and the results reviewed by the domain members, by the RECOVER committee, and opened for comments by veterinary professionals for 4 weeks. Clinical guidelines were devised from these findings and again reviewed and commented on by the different entities within RECOVER as well as by veterinary professionals.

SETTING

Academia, referral practice and general practice.

RESULTS

A total of 74 worksheets were prepared to evaluate questions across the five domains. A series of 101 individual clinical guidelines were generated. In addition, a CPR algorithm, resuscitation drug-dosing scheme, and postcardiac arrest care algorithm were developed.

CONCLUSIONS

Although many knowledge gaps were identified, specific clinical guidelines for small animal veterinary CPR were generated from this evidence-based process. Future work is needed to objectively evaluate the effects of these new clinical guidelines on CPR outcome, and to address the knowledge gaps identified through this process.

Mortality in out-of-hospital cardiac arrest patients has decreased in the era of therapeutic hypothermia

BACKGROUND

Mild therapeutic hypothermia (TH) improves survival after out-of-hospital cardiac arrest (OHCA). This treatment was implemented in most Finnish intensive care units (ICUs) in 2003. The aim of this study was to find out whether hospital mortality of ICU-treated OHCA patients has changed in the era of TH.

METHODS

This was a retrospective study of data collected prospectively into the database of the Finnish Intensive Care Consortium during the years 2000-2008. The study population consisted of 3958 patients for whom cardiac arrest was registered as the reason for ICU admission and who were transferred to the ICU from the emergency department. We divided the patients into those treated in the pre-hypothermia era (2000-2002) and those treated in the hypothermia era (2003-2008). We investigated whether the treatment period had any impact on hospital mortality.

RESULTS

There were no differences between the periods regarding the age or initial Glasgow Coma Scores of the patients. Mean severity of illness was higher in the latter period. Despite this, mortality decreased: the hospital mortality rate was 57.9% in 2000-2002 and 51.1% in 2003-2008, P < 0.001. In a multivariate logistic regression analysis, treatment in 2003-2008 was associated with a reduced risk of in-hospital death (adjusted odds ratio 0.54, 95% confidence interval 0.45-0.64 and P < 0.001). Survival improved markedly between the years 2002 and 2003. This improvement has persisted, but there has been no further improvement.

CONCLUSION

Concurrently with the implementation of TH, hospital mortality of OHCA patients treated in Finnish ICUs decreased.