Figure 12.2 The frame of survival. Source: Nadarajan GD, Tiah L, Ho AFW, et al. Global resuscitation alliance utstein recommendations for developing emergency care systems. Resuscitation 2018;132:85–8. Used with permission of Elsevier.
When callers do not know CPR, the telecommunicator should provide real‐time instructions over the phone. Most current dispatch protocols include detailed, specific CPR instructions [38]. Growing evidence suggests that properly performed chest compressions are more important than ventilations [39–40]. The AHA recommends that bystanders not trained in CPR and those trained but not confident or willing to perform ventilations should perform chest compression‐only CPR until a defibrillator is ready for use [41]. Many emergency dispatch protocols now favor providing instructions only for chest compressions. Unrecognized fatigue is common after just 1‐2 minutes, so bystanders providing chest compressions should switch frequently [42].
Public‐Access Defibrillation
The most important cardiac arrest interventions for patients in VF or VT are early chest compressions and defibrillation. Although 70‐80% of VF can be successfully converted to a perfusing rhythm if shocked within 3 minutes of VF onset, this success rate deteriorates rapidly with each additional minute [43]. Survival decreases 7‐10% for each minute that passes before defibrillation (Figure 12.3) [36].
AEDs provide lay bystanders with the ability to deliver rescue shocks. These devices were first used clinically in 1979 to recognize and deliver rescue shocks for VF and rapid VT [44]. AEDs are automated and simple to use, with visual and audible instructions for operating the defibrillator and initiating CPR. They are relatively inexpensive and extremely safe; modern AEDs do not allow delivery of inappropriate shocks [45]. Most are equipped with memory modules that can record the entire resuscitation event, including continuous ECG and audio recording.
Figure 12.3 Relation of collapse to CPR and defibrillation to survival: simplified model. Graphical representation of simplified (includes collapse to CPR and collapse to defibrillation only) predictive model of survival after witnessed, out‐of‐hospital cardiac arrest due to VF. Each curve represents change in probability of survival as delay (minutes) to defibrillation increases for a given collapse‐to‐CPR interval (minutes).
Source: Valenzuela TD. Circulation. 1997; 96:3308–13. Reproduced with permission of Lippincott, Williams and Wilkins.
Defibrillators with CPR feedback use accelerometers embedded within chest defibrillation pads to measure depth and rate of compressions, or use variations in chest impedance to reflect chest wall movements [46, 47]. These devices are able to give verbal as well as visual prompts to cue the rescuer to speed up, slow down, or increase the depth of compressions or ventilations [48]. Such devices have been shown to improve the quality of out‐of‐hospital as well as in‐hospital CPR [48, 49].
Many AED models are now available, ranging in sophistication and ruggedness. Some models are designed for minimally trained lay bystanders and are available for consumer purchase without a physician prescription, depending on applicable laws.
There is strong scientific evidence confirming the effectiveness of early first responder, bystander, and public‐access defibrillation. A trial that trained security personnel in casinos to recognize OHCA, start CPR, and use on‐site AEDs achieved 53% survival from VF. Among patients shocked within 3 minutes, survival was 74% [24]. AEDs have also been successfully used on commercial aircraft and in airports [50]. In the multi‐center PAD trial, 993 high‐risk locations were randomized