Out of hospital cardiac arrest (OHCA) is a common cause of death. 30 000 people sustain cardiac arrest outside hospital and are treated by emergency medical services (EMS) each year (Nolan et al, 2010). Electrical defibrillation is well established as the only effective therapy for cardiac arrest caused by ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT). Death ensues in the untreated within minutes due to cerebral hypoxia. This provides a very narrow window in which definitive treatment can given by defibrillation, though this window can be prolonged with effective cardiopulmonary resuscitation (CPR) (Wik et al, 2003).
The scientific evidence to support early defibrillation is definitive. The delay from collapse to delivery of the first shock is the single most important determinant of survival. If defibrillation is delivered promptly, survival rates as high as 75% have been reported (Handley et al, 2005). However, the presence of an automated external defibrillator (AED) alone does not increase survival. Box 1 identifies three interventions that, if immediately available, can increase survival.
For every minute delay in defibrillation, the survival rate decreases by 5–10% (Handley et al, 2005). Even in the presence of all three of these elements, outcome can be poor. One recent study identified that of those hospitalised patients who were defibrillated within two minutes of diagnosis, only 39% survived to hospital discharge, and 40% of these had at least moderate neurological disabilities (Chan et al, 2008).
An AED can be used safely and effectively without previous training. Therefore, no inhibitions should be placed on any person willing to use an AED and it should not be restricted to trained rescuers. However, training should be encouraged to help improve the time to shock delivery and correct pad placement (Resuscitation Council UK, 2010).
Placement of AED in busy public places would seem a necessary intervention in the light of its effect on survival. However the decision is a complex one that requires certain factors to be addressed. Firstly, the effectiveness of the placement of the AED requires the local support to be confident in basic life support and the use of the defibrillator.
Secondly, the cost effectiveness of placement and maintenance of the AED and the further cost of local support training must be considered against each individual placement. Therefore a decision on placement of a defibrillator requires identification of the populations most likely to benefit from its use. The personal experience of the authors (Box 2 and 3) identifies individual examples of the contrasting use of AED's in public areas. These experiences form the basis of this review article of AED placement in public areas and workplaces.
Placement of AED's in the workplace
The percentage of OHCA that occurs in the workplace is 1–6% annually (Descatha and Baer, 2008). The majority of those who are at work are fit and well. However, there are certain factors that increase a workforce's potential risk of OHCA, which should be accounted for in the decision to place an AED on site. Workforce age is an important risk factor with those above 55 accounting 96% of cardiac events and strokes that occur in the general population. Automatically, this increases the risk of OHCA (Wald and Law, 2003).
Certain occupational exposures, such as high voltage electricity, are significant risk factors (Descatha and Baer, 2008). Foot-fall on the site from workforce and visitors increases the chances. Additionally, the demographics of this foot-fall will increase this risk factor significantly (for example, if the majority are above the age of 55 years). The site history should also be considered if there have been previous cardiac-arrests on site and the factors involved in that individual event (Descatha and Baer, 2008). The cost effectiveness balance needs to be more closely evaluated for high risk occupational settings, accounting for these factors (Descatha and Baer, 2008).
The legal position for employers in the decision to place and maintain an AED is a precarious one. The Health and Safety (First-Aid) Regulations 1981 do not make provision of an AED a mandatory requirement (Health and Safety Executive, 1981 (revised 2009)). However, employers are open to potential liability due to inadequate provision of workforce safety under common law (Health and Safety Executive, 2009)
The decision to place an AED in the workplace is that of the employer responsible for workforce safety. Overall, the likelihood of an employee having an OHCA is small, therefore the benefit of an AED being available is weighed against the cost of provision and ongoing maintenance (machine and training).In addition to the occupational and legal factors, it should be considered that a proportion of those that have OHCA are young people, therefore the potential benefit in life years of successful use of an AED may be significant (Descatha and Baer, 2008).
Placement of AED's in public areas
Logically, it would seem sensible given the potential benefit of AED in OHCA to place AED's in all public areas. This approach would not be cost effective and the potential life years saved would be minimal.
Seventy two percent of sudden cardiac deaths occur in the home (Muller et al. 2006). We cannot, as a health service, put an AED into every house on this basis, as the potential benefit would never be achieved. However, implantable cardioverter– defibrillator's (ICD's) can be placed in certain high risk patients, who have a significant spontaneous chance of developing a shockable arrhythmia.
Therefore, would targeted AED deployment be a more cost effective measure to achieve the most benefit? One study looked into home defibrillation as a possible method of increasing survival in high risk patients with previous anterior-wall myocardial infarction who were not candidates for an ICD. They were divided into two responses to OHCA: either the control response (calling 999 and performing cardiopulmonary resuscitation) or the interventional response (use of an AED followed by calling 999 and performing CPR). Results showed access to a home AED did not significantly improve overall survival (Bardy et al, 2008).
Similar to workplace legislation, there is no statutory law that states public areas need to provide AED's. The Health and Safety Executive (HSE) stated in the revised 1981 legislation:
‘[We] will continue to strongly recommend that employers should consider the public when conducting their first aid needs assessment and provide first aid for them, but will not be seeking to make provision of first aid for the public a compulsory requirement’
Interestingly, the HSE goes on to mention that special consideration must be given to a ‘workplace that has a large public presence such as educational establishments, places of entertainment, fairgrounds and shops’ (Health and Safety Executive, 2009).
Furthermore, the Resuscitation Council UK has no additional legal standing for AED's to be provided in public areas (Nolan et al, 2010). However, under common law the management of the public area may carry liability for not adequately providing for public safety. Becker et al (1998) retrospectively analyzed previous cardiac arrests at high profile sites by collecting data regarding two areas (Seattle and Kings County, Washington) over five years (1990–1994).
Cardiac arrests in public locations were tallied and sites were given an annual incidence. One hundred and seventy two sites were classified as a high incidence of OHCA (> or = 0.03 per year per site). The study extrapolated that placement of 276 AED's in the 172 higher-incidence sites would have provided treatment for 134 cardiac arrest patients in a 5-year period, 60% of whom were in ventricular fibrillation. The further extrapolation was that this could have potentially saved between 8 to 32 lives (Becker et al, 1998). Identifying that targeted placement of AED's to certain sites would be far more cost effective than blindly allocating AED's to all public areas.
Resuscitation Council guidelines
The Resuscitation Council UK 2005 guidelines state that an AED should be considered in sites with large concentrations of people over the age of 50, or where more than 10 000 people gather. Provision is likely to benefit when the items in Box 4 are present.
For the AED to be maximally effective, OHCA must be recognized, communication made for help, trained first aiders available and co-ordination with local emergency services. Within the new 2010 guidelines, there is a suggestion that video/ computer self-instruction courses, with minimal or no instructor coaching, along with hands-on practice can be considered as an effective alternative to instructor-led BLS and AED courses. (Resuscitation Council UK, 2010).
UK National Defibrillator Programme
The Department of Health initiated the UK National Defibrillator Programme in February 2000 (DH, 2000). Initially, 681 AED's were deployed to public sites for use by lay people (Figure 1). The analysis of success shows that of the first 250 uses of AED's, survival was increased by 25% compared with those having cardiac arrests in ‘conventional’ settings. The majority (146) of the time, the AED's were used correctly in confirmed cardiac arrest. Interestingly half of these events were in airports (Whitfield et al, 2005; Colquhoun et al, 2008). Several thousand AED's are now deployed in public areas with a return of spontaneous circulation (ROSC) being achieved in 39% of those shocked (Colquhoun et al, 2008).
US studies
The American experience in the Chicago HeartSave programme and the North America public access defibrillation trial indentified a smaller, but modest, improvement in survival rates in those treated by lay people trained in CPR and AED use (Caffrey et al, 2002; Hallstrom et al, 2004).
A further American study analyzed ‘the best case scenario OHCA’. This study benefited from its highly public settings (casino's), strategic placement of defibrillators (to minimize the time to first defibrillation), and operators trained in basic life support and using defibrillators. In this study, arrests were witnessed in 86% of the patients and the mean time to the first shock was 4.4 minutes. Patients who were defibrillated within three minutes of their arrest had a 74% survival rate to hospital discharge. For those who received their first defibrillation after more than three minutes, the survival rate was only 49% (Valenzuela et al, 2000).
Placement of AED's in public areas needs to be targeted to locations that they are going to have the most potential benefit. There is clear guidance on the sites most likely to benefit. Additionally. for the AED to be most effective as the evidence suggests, there needs to be local infrastructure to support the use of AED, otherwise the potential benefit will be minimized.
Public access defibrillation programmes
Public access defibrillation (PAD) programmes may increase the number of people experiencing sudden cardiac arrest who receive bystander cardiopulmonary resuscitation. They can reduce time to defibrillation, and may improve survival from sudden cardiac arrest. These are the facets that are required for AED's to be maximally effective. The programmes require an organized and practiced response with rescuers trained and equipped to recognize emergencies, provide CPR and initiate defibrillation.
Results of studies of lay rescuer AED programmes in airports, casinos and with police officers have demonstrated a 49 to 74% survival rate when immediate bystander CPR is provided and defibrillation occurs within 3 to 5 minutes of collapse. The trials support current American Heart Association recommendations for lay rescuer AED programs and the emphasis on planning, training, practice of CPR, and use of AED's. Following on from this, all US states have passed legislation or regulations that allow lay rescuer AED programmes (Hazinski et al, 2005).
The ongoing success of the UK national defibrillator programme demonstrates the effectiveness of PAD. Two basic strategies are used. In the first, static AEDs are installed permanently in busy public places and used by people working nearby. In a complementary strategy, first responders are dispatched by an ambulance control centre when they might reach a patient more quickly than a conventional ambulance, taking mobile AED's to the patient. Colquhoun et al recently analysed resuscitation attempts by means of both strategies (2008). The survey analysed 1530 OHCA; static AED's resulted in ROSC in 170 (39%), with survival to hospital discharge in 113/437 (26%). Mobile AED's demonstrated significantly lower survival (p<0.001) with ROSC in 110/1093 (10%), with survival to hospital discharge in only 32 (2.9%) (Colquhoun et al, 2008).
The significant difference in survival is due to increased incidence of witnessed OHCA, earlier delivery of CPR and decreased time to attachment of the AED (shock given earlier). Colquhoun et al (2008) suggest, additionally, that the demographics of patients treated at home are generally older, being higher risk and hence less likely to survive. The fact that mobile AED's can be taken to the home, where most OHCA's occur, is a major advance in modern day resuscitation.
Since the initiation of PAD programmes in the UK, there has been increased effectiveness of the use of AED's in public areas. Streamlining of all these factors required for AED's to have maximal effectiveness is delivered by the PAD programmes. Overall, this has increased the survival from OHCA in public areas, however personal experiences (Box 2 and 3) demonstrated individual differences in potential success when these elements are in place or not.
Conclusion
The potential benefits that AED's offer to people that had a spontaneous OHCA in a public area or workplace can be highly significant. The presence of an AED alone does not improve survival. Local support with trained first aiders and effective communication to emergency services, together with publicly available AED's, dramatically improves survival. Even if all these elements are in place at every public area or workplace in the UK, then it would not be cost effective due to the rarity of OHCA occurring.
The evidence clearly identifies targeting AED deployment where there are higher incidences of OHCA, due to frequency of attendance (defined as >10 000), with a large proportion of individuals over the age of 55 and high risk occupational factors.
Once sites are identified, a PAD programme must be implemented ensuring the earliest delivery of CPR and application of AED pads. Together, this approach will continue the success of using AED's in public areas and workplaces, making a significant difference to the people's lives that have a OHCA.