Thermogard XP for therapeutic hypothermia after cardiac arrest

Introduction

Cardiac arrest is caused by a loss of heart function. The heart stops pumping blood around the body, leading to loss of consciousness and death unless emergency resuscitation is given and the heart can be restarted to achieve the return of spontaneous circulation (ROSC). Post‑cardiac arrest syndrome can occur after ROSC and involves multiple systems. It reflects a state of whole‑body ischaemia (restricted blood supply) and subsequent reperfusion. Its severity depends on the duration and cause of cardiac arrest, often reflecting the underlying condition, pre‑existing co‑morbidities and other complications of resuscitation. It can encompass post‑cardiac arrest myocardial dysfunction and post‑cardiac‑arrest brain injury (Resuscitation Council (UK) 2010). Post‑cardiac arrest brain injury can be manifested as any or all of the following: coma, seizures, involuntary muscle twitching, varying degrees of neurocognitive dysfunction and brain death. Cardiovascular instability can result in early mortality. Late mortality and morbidity can result from brain injury (the most common cause of death following ROSC), multi‑organ failure and sepsis.

A recent analysis of the UK National Cardiac Arrest Audit database reported an overall incidence of adult in‑hospital cardiac arrest of 1.6 per 1000 hospital admissions. Incidence varied seasonally, peaking in winter. Overall unadjusted survival to hospital discharge was 18.4%. The presenting rhythm was shockable (ventricular fibrillation or pulseless ventricular tachycardia) in 16.9% of cases and non‑shockable (asystole or pulseless electrical activity) in 72.3%. The remaining 10.8% comprised non‑shockable bradycardia, unknown rhythms (non‑shockable and shockable) and some cases where the presenting rhythm was never determined or unknown. Rates of survival to hospital discharge associated with these rhythms were 49.0% and 10.5% respectively, but varied substantially across hospitals (Nolan 2014).

Published data for the out‑of‑hospital setting suggests that there are 38 all‑rhythm cardiac arrests per 100,000 person‑years in Europe that are attended by emergency medical services (EMS; Atwood 2005). In the NICE medical technologies innovation briefing on the RhinoChill intranasal cooling system for reducing temperature after cardiac arrest, these estimates were translated into 20,140 all‑rhythm cardiac arrests occurring annually out‑of‑hospital and receiving emergency medical services care in England. A recent consensus paper from the British Heart Foundation, NHS England and Resuscitation Council UK (2014) highlights that the emergency medical services attempted to resuscitate approximately 28,000 cases of out‑of‑hospital cardiac arrest in England in 2013.

The impact of cardiac arrest on NHS resources in intensive care may be represented by the treatment of unconscious survivors, which accounts for 5.6% of the total UK adult general intensive care unit (ICU) bed days in the Intensive Care National Audit and Research Centre Case Mix Programme Database (ICNARC CMPD; Nolan 2007).

Therapeutic hypothermia (also called targeted temperature management) has gained support as a method to counteract the destructive mechanisms of cardiac arrest, although there is some uncertainty both about the benefits of this approach compared with normothermia and about the optimal target temperature for hypothermia. A Cochrane Review (Arrich et al. 2012) of hypothermia for neuroprotection in adults after cardiopulmonary resuscitation concluded that conventional cooling methods to induce mild therapeutic hypothermia improved survival and neurological outcomes. A more recent review of clinical trial data concluded that mild hypothermia, defined as a reduction of core temperature to 32–34°C, is the only proven way to improve survival and neurological outcomes after sudden cardiac arrest (Weng 2012). Regarding the optimum target temperature for therapeutic hypothermia, 1 large, high quality randomised controlled trial concluded that, in unconscious survivors of out‑of‑hospital cardiac arrest of presumed cardiac cause, hypothermia at a target temperature of 33°C did not confer any benefit over maintaining a target temperature of normothermia at 36°C (Nielsen 2013). Updated guidelines from the UK Resuscitation Council on the place in management of therapeutic hypothermia are planned to publish during 2015.

This briefing focuses on the Thermogard XP temperature management system for achieving therapeutic hypothermia after cardiac arrest.