Clinical paperTherapeutic hypothermia is associated with improved neurologic outcome and survival in cardiac arrest survivors of non-shockable rhythms☆
Introduction
An estimated 200,000 cardiac arrests occur out-of-hospital on an annual basis in the United States,1, 2 with limited survival rates of 0–11% depending on the presenting rhythm.3, 4 The true incidence of in-hospital cardiac arrest remains less apparent, but is estimated to be 1–5 events per 1000 hospital admissions.5
Following a cardiac arrest, the brain tolerates anoxia up to 2–4 min6 and thereafter irreversible neuronal damage commences in the absence of re-establishment of circulation. Re-oxygenation with successful return of spontaneous circulation (ROSC), although essential in restoring the energy charge, provokes a deleterious chemical cascade by generating free radicals and other inflammatory mediators which leads to devastating neurologic consequences and death in the form of post-resuscitation syndrome.7 However, these harmful effects of reperfusion injury may be mitigated with the use of hypothermia as demonstrated in case reports and dog models since the 1950s.8, 9, 10, 11, 12, 13, 14, 15
More recently, therapeutic hypothermia has been reported to improve neurologic outcomes and survival of out-of-hospital cardiac arrest patients who have been successfully resuscitated from ventricular fibrillation (VF).16, 17 However, this beneficial effect of hypothermia therapy on outcomes for other rhythms has not been well studied. Approximately 19–32% of patients resuscitated from cardiac arrest who survive to discharge have a poor neurological outcome.18, 19 Moreover, the survival to hospital discharge rate in these patients varies from 0 to 42%, the most common range being between 15% and 20%.5
Advanced Life Support Task Force of the International Liaison Committee on Resuscitation (ILCOR) and the 2010 American Heart Association guidelines for Cardiopulmonary Resuscitation And Emergency Cardiovascular Care states: “unconscious adult patients with ROSC (return of spontaneous circulation) after out-of hospital cardiac arrest should be cooled to 32–34 °C (89.6–93.2 °F) for 12–24 h when the initial rhythm was VF (Class I). Similar therapy may be beneficial for patients with non-VF arrest out of hospital or for in-hospital arrest (Class IIb)”.20
The aim of the present study was to compare therapeutic hypothermia to control (normothermia) in comatose patients with cardiac arrest due to a non-shockable rhythm [pulseless electrical activity (PEA) or asystole].
Section snippets
Study population
Consecutive adult patients who were admitted to the Cardiac Intensive Care Unit (CICU) at Hartford Hospital between January 1, 2004 and November 1, 2010 after successful resuscitation from an out-of-hospital or in-hospital cardiac arrest and who met the inclusion criteria formed the study cohort. The inclusion criteria were:
- 1.
PEA or asystole as the initial cardiac rhythm
- 2.
an age of 18 to 75 years
- 3.
Glasgow Coma Scale ≤ 8 after ROSC
- 4.
an estimated interval of 5–15 min from the patient's collapse to the first
Results
A total of 100 patients were identified who met the inclusion criteria of the study and formed the study cohort. Key follow-up data were available on all of the study patients. Of these, 52 patients (52%) who received therapeutic hypothermia formed the hypothermia group, while 48 patients (48%) who did not receive therapeutic hypothermia formed the control group. Table 1 compares the demographics and clinical characteristics of patients in the hypothermia and control groups. At baseline the
Discussion
Prognosis after resuscitation from cardiac arrest remains poor with post-ischemic brain injury as the leading cause of death.24 Both prospective randomized control trials and retrospective trials have shown that survival with good neurologic outcome is improved by inducing hypothermia in patients with return of spontaneous circulation after ventricular fibrillation cardiac arrest.16, 17, 25 However, this benefit has not been consistently demonstrated in patients with return of spontaneous
Limitations
This is a retrospective study conducted at a single large tertiary center and limits the extent to which the results can be generalized. Retrospective studies are limited by the inability to adjust for confounding factors and referral bias. Though resuscitation protocols may change over time, we do not believe that the resuscitation protocol at our institution has changed substantially during the study time period. Inspite of adjustment for the significant difference seen in number of
Conclusions
The use of therapeutic hypothermia is associated with improved neurologic outcome and survival at discharge in patients that have been successfully resuscitated after cardiac arrest due to a non-shockable rhythm (pulseless electrical activity and asystole) and should be offered to this group of cardiac arrest survivors.
Conflict of interest statement
Financial disclosure: Speaker for ZOLL Temperature Management.
Unlabeled/unapproved use disclosure: ICY Catheter© for induction of Therapeutic Hypothermia.
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A Spanish translated version of the abstract of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2011.08.005.