Therapeutic hypothermia in cardiac arrest

In the UK, out of hospital cardiac arrest (OHCA) in which resuscitation was attempted, accounted for approximately 28 000 call outs for the emergency medical services in 2013. However, the survival to hospital discharge was only 8.6% — far lower than in other developed countries (British Heart Foundation, NHS England and Resuscitation Council UK 2015). Of the patients that do survive, ensuring a positive neurological outcome is difficult to attain (Arrich et al, 2012). These poor outcomes have led to research into how the prognosis of these patients can be improved and one of the ways to achieve this could be with the implementation of therapeutic hypothermia (TH) (Soar and Nolan, 2007) with a particular focus on implementation in the prehospital setting (Hunter et al, 2014).

The role of TH either during or after cardiac arrest is by no means a new phenomenon; its uses were initially investigated in the 1950s but not pursued again until the 1980's when potential benefits of the treatment were explored (Marion et al, 1996). In 2002, two ground breaking human studies noted the value of TH after cardiac arrest and from these positive indications, both the International Liaison Committee on Resuscitation (ILCOR) and the American Heart Association (AHA) recommended the use of TH in adults with a return of spontaneous circulation (ROSC) in OHCA, when the presenting rhythm was ventricular fibrillation (VF) (Lee and Asare 2010). A separate review of four clinical trials in 2004 by the Canadian Association of Emergency Physicians Critical Care Committee reviewed further evidence and concluded that TH should be initiated not only in patients presenting in VF, but also when ROSC was achieved and the presenting rhythm was asystole or pulseless electrical activity (PEA) (Howes et al, 2006). However, Arrich et al (2013) recognise that there are conflicting views around the value of TH for the patient. The large international, multicentre randomised controlled trial (RCT) of 950 in-hospital patients by Neilson et al (2013) shed doubt on the perceived benefits of TH, as there was no clinical benefit of lowering temperature to 33°C compared to maintaining a body temperature of 36°C. The National Institute for Health and Care Excellence (NICE 2011) agree that while TH proves effective for some patients, the outcomes can be unpredictable and variable.