The use of A-CPR resulted in a higher rate of survival to hospital compared with C-CPR, yet a tendency for a lower rate of survival to hospital discharge, however these associations did not reach statistical significance. We matched cases to controls using important predictors of survival (age, gender, response time, presenting cardiac rhythm, bystander CPR and regional setting), and adjusted for potential confounding through conditional multiple regression techniques and adjusting for propensity score. The matching process appeared effective as there was little change in the estimate of association when the propensity score was added to the univariable regression model.
Our findings are consistent with a number of other prehospital studies comparing A-CPR to conventional resuscitation [10, 11, 16, 17]. Ong et al compared manual compressions (N = 499) to A-CPR compressions (N = 284) in OHCA patients and found an improved rate of ROSC (34.5% v 20.2%; AOR = 1.94, 95% CI 1.38-2.72), survival to hospital admission (20.9% v 11.1%; AOR = 1.88, 95% CI 1.23-2.86) and survival to hospital discharge (9.7% v 2.9%; OR = 2.27, 95% CI 1.11-4.77) . In a case–control study reported by Casner et al, the proportion of patients achieving sustained ROSC was also found to be greater in the A-CPR group than the C-CPR group (39% v 29%; p = 0.003) . This study also found that more patients presenting in asystole or agonal rhythms had a sustained ROSC with A-CPR. These findings are consistent with our study. A study by Krep et al found the AutoPulse system to an effective and safe mechanical CPR device and useful in the management of out-of-hospital cardiac arrest .
However, a third study did not find improvement in outcome above C-CPR. Hallstrom et al conducted a large, multicentre randomised controlled trial comparing C-CPR to A-CPR. They reported similar proportions of patients surviving to ED (C-CPR 41.3% v A-CPR 40.4%) but a lower proportion of A-CPR being discharged from hospital alive (9.9% v 5.8%; OR = 0.56; P = 0.06) .
The current European Resuscitation Council Guidelines  identify that clinical trials investigating the role of mechanical devices to date have been conflicting. They conclude that mechanical devices have been used effectively to support patients in special circumstances (i.e. undergoing primary coronary intervention and CT scans, and also for prolonged resuscitation attempts) where rescuer fatigue may impair the effectiveness of manual chest compression. Whilst cautioning that the role of mechanical devices still require further evaluation, they acknowledge that mechanical devices may also have a role in the prehospital environment where extrication of patients, resuscitation in confined spaces and movement of patients on a trolley often preclude effective manual chest compressions .
Several studies have shown that survival from OHCA is much lower in rural areas than urban areas [12, 19]. One study showed Urban patients with bystander-witnessed cardiac arrest were more likely to arrive at an emergency department with a cardiac output (odds ratio [OR], 2.92; 95% CI, 1.65–5.17; P < 0.001), and to be discharged from hospital alive than rural patients (urban, 125/1685 [7.4%]; rural, 2/105 [1.9%]; OR, 4.13; 95% CI, 1.09–34.91) . This disparity is often thought to be solely as a result of longer travel distances and time between collapse and defibrillation, but it is likely to be multifactorial. Often there are fewer prehospital clinicians attending a rural cardiac arrest, compared to urban cardiac arrests, which limit the number of interventions which can be performed concurrently whilst maintaining consistent, high quality chest compressions.
The use of A-CPR has several potential advantages in a rural setting. Chest compressions are able to be provided effectively in the back of a moving vehicle en route to hospital. Without such a device, paramedics are unrestrained and are at risk of injury in a moving vehicle. Furthermore, mechanical devices do not tire, and maintain consistent depth and rate of compressions.
The main disadvantage of A-CPR is the substantial weight of the device (11.6 kg including battery).
This study was potentially limited by the low number of patients enrolled in the A-CPR arm during the study period. Also, treatment was not randomised in this study, however we attempted to minimize bias using a matched case–control design and by the use of propensity scores to adjust for known and unknown confounding factors.
Finally, survival rates are lower in rural areas when compared to urban centres , making it difficult to recruit sufficient numbers to detect a difference in outcome and therefore evaluate the true utility of A-CPR in the rural and regional prehospital setting.