Internal cardiac massage was employed to resuscitate the arrested heart from the late 19th century. This technique was largely confined to intraoperative cardiac arrest in anesthetized patients. If the abdomen was open, the surgeon would attempt subdiaphragmatic compression, a technique later found to be largely ineffective. Hence, if spontaneous cardiac activity did not occur, the diaphragm was incised, and direct compression of the heart was carried out. In their treatise of 1952, Bost et al. described a success rate of one-third with this technique (1).
The adequacy of external chest compression had been evaluated in animals much earlier, followed by several reports in humans. However, by the early 20th century, external compressions had been all but given up in favor of direct massage through an open chest or abdomen. The efficacy of external compressions was rediscovered by William Kouwenhoven, an electrical engineer, during his experiments with defibrillation techniques at the Johns Hopkins University in Baltimore. He had placed heavy paddles on the chest of a dog while investigating external defibrillation. The sheer weight of the paddles increased the blood pressure. Furthermore, rhythmic pressure applied to the sternum seemed to maintain adequate circulation to the brain. It was evident that compression of the chest resulted in forward flow from the heart while relaxation enabled refilling. William Kouwenhoven, with his colleagues James Jude and Guy Knickerbocker, reported a series of five patients who suffered cardiac arrest followed by successful resuscitation with external cardiac compressions (2). They affirmed, “Anyone, anywhere, can now initiate cardiac resuscitative procedures. All that is needed are two hands”. This report marked the rebirth of the era of external cardiac compressions as we know it today.
The importance of early initiation of cardiopulmonary resuscitation (CPR) was clearly the need of the hour. By the 1980s, telephonic instructions to provide CPR were provided to bystanders who sought assistance for out-of-hospital cardiac arrest, while emergency personnel were on the way. By the turn of the new millennium, dispatcher-assisted CPR was established in many emergency medical systems across the world.
Background to the study
Historically, recommendations for out-of-hospital CPR by lay public comprised of chest compressions combined with rescue breathing. A compression-only strategy avoided interruptions, and had the potential to offer enhanced circulatory support (3); besides, it may be more acceptable among the lay public (4). Attempts at rescue breathing during CPR may also lead to a rise in the intrathoracic pressure, reduction in the venous return, cardiac output, and impaired coronary flow. While a compression-only strategy may be advantageous if the underlying etiology is of cardiac origin, a primary respiratory cause clearly requires expeditious respiratory support. Animal studies suggested the efficacy of a tailored strategy based on the etiology of cardiac arrest (5). Observational studies comparing a compression-only strategy with conventional CPR had revealed similar survival rates, although the findings were limited by confounders (6,7). A randomized controlled trial (RCT) that compared chest compression-only CPR with compressions interspersed with mouth-to-mouth respiration revealed improved survival to hospital discharge. Bystanders performed CPR based on instructions provided telephonically by dispatchers. Survival to hospital discharge was higher among those who received compression-only CPR, although the difference was not statistically significant (14.6% vs. 10.4%) (8).
The Dispatcher-Assisted Resuscitation Trial (DART) RCT compared two CPR approaches – chest compression-only vs. compressions combined with rescue breathing, carried out based on dispatcher instructions.
Population and design
Three emergency services – two in the US (Washington state) and one in the UK (the London Ambulance Service) participated in the trial, conducted between 2004–2008. The trial considered emergency calls from bystanders for adult patients (>18 years) who had sustained out-of-hospital cardiac arrest. Patients who were determined to be unconscious and not breathing normally by the dispatcher were eligible if CPR had not already been initiated. Randomization was carried out to one of two groups – compression-only CPR, or standard CPR with chest compression combined with rescue breathing. Randomization was stratified according to the dispatch center and carried out in blocks of 10.
Cardiac arrest due to trauma, drowning, asphyxiation, and those with a do-not-resuscitate order were excluded upon evaluation by the dispatcher. Patients could be excluded post-randomization; final eligibility required basic and advanced care from the EMS. Patients who were judged to be not in cardiac arrest by the dispatcher, and those who were considered irreversible by the EMS were also excluded.
The dispatcher provided instructions to perform 50 consecutive compressions (one cycle). After completion of one cycle, the dispatcher enquired about signs of life; instructions were provided to continue compressions as appropriate.
Compressions with rescue breathing (standard CPR group)
Fifteen chest compressions were followed by two rescue breaths, with subsequent cycles in the same ratio. The dispatcher assessed the situation telephonically and provided instructions to continue CPR as appropriate.
The investigators designed the trial to identify a difference in survival by 3.5 percentage points between the two groups, at a two-sided alpha level of 0.05 with 80% power.
A total of 5525 patients were presumed to be in cardiac arrest and randomization envelopes opened. Among these patients, 1941 fulfilled the inclusion criteria – 981 in the compression-only group and 960 in the conventional group. An underlying cardiac cause was present in 70%; less than half were witnessed arrests, and about one-third presented with a shockable rhythm. The average time from dispatch to arrival of EMS personnel was 6.5 minutes. Baseline characteristics were similar in both groups. The location of the arrest – whether residential, nursing home, or at a public location was also similar.
The primary outcome: survival to hospital discharge
Survival to hospital discharge could not be established in seven patients – three in the compression-only group and four in the conventional group. In the compression-only group, 122/978 (12.5%) patients survived to hospital discharge compared with 105/956 (11.0%) in the conventional group. The difference was not statistically significant (p = 0.31).
On predefined subgroup analysis, there was a trend towards improved survival to hospital discharge with compression-only CPR among patients with an underlying cardiac cause for the arrest (15.5% vs. 12.3%, P=0.09). A similar trend favoring compression-only CPR was also observed among patients who had a shockable rhythm (31.9% vs. 25.7%, p = 0.09).
Return of spontaneous circulation at the end of EMS care was significantly higher in the compression-only compared to the standard group (38.5% vs. 31.3%, p = 0.005). Survival to hospital discharge with a favorable neurological outcome, defined as a Cerebral Performance Category (CPC) score of 1 or 2, was similar between the two groups. However, among patients with an underlying cardiac cause for the arrest, survival to hospital discharge with a good neurological outcome was signficantly higher in the compression-only group (18.9% vs. 13.5%, p = 0.03).
The DART trial compared CPR instructions to the lay public in patients who suffered out-of-hospital cardiac arrest. Instructions were provided to perform chest compressions alone compared with compressions and rescue breathing. The overall survival to hospital discharge, the primary outcome, did not differ significantly between these strategies. However, subgroup analysis revealed that a compression-only strategy may improve survival in patients with an underlying cardiac cause and those with a shockable rhythm. Furthermore, survival to hospital discharge with a favorable neurological outcome was also higher in patients who received compression-only CPR.
Evidence from other studies
Yet another RCT comparing compression-only with standard CPR was published in the same issue of the New England Journal of Medicine. This study was conducted by the Swedish Emergency Medical services, and included 1276 patients – 620 patients were assigned to receive compression-only CPR and 656 to a standard strategy of two ventilations alternating with 15 compressions (9). There was no significant difference in the 30-day survival between the two groups (compression-only vs. standard CPR: 8.7% vs. 7.0%, p = 0.29). Subgroup analysis revealed similar 30-day survival regardless of the location of the arrest, the time to EMS response, and the presenting cardiac rhythm.
A meta-analysis by Cabrini et al. included three RCTs that compared compression-only with standard CPR among patients with witnessed or unwitnessed cardiac arrest (10). The meta-analysis included 3737 patients – 1895 received compression-only CPR, while 1842 received standard CPR. Survival to hospital discharge was higher with compression-only CPR (11.5% vs. 9.4%, p = 0.04). These findings were echoed in the meta-analysis by Hüpfl et al. The primary meta-analysis of RCTs revealed that dispatcher-assisted compression-only CPR by lay public resulted in a 22% improvement in survival compared with standard CPR (11).
The outcomes from out-of-hospital cardiac arrest have remained abysmal. CPR by the lay public may is of crucial importance in improving outcomes. The DART RCT addressed a simplified, compression-only approach to out-of-hospital CPR by the untrained. This large RCT involved three EMS providers and addressed clinically meaningful outcomes. The study offered sound evidence that compression-only CPR is at least equally effective compared with the standard approach of rescue breathing interspersed with compressions. Furthermore, a simplified approach may curtail fears of transmission of infection during rescue breathing. The study design and its systematic conduct, including validation of randomization by audio review enabled tenability across a wider community.
Although a large RCT, the study may still have lacked the requisite power to evaluate survival with favorable neurological outcomes. The neurological status was evaluated in only two of the three centers that participated in the study. The efficacy of interventions – including the depth of chest compression – was not objectively assessed. The study excluded patients with asphyxia, drowning, and trauma. Hence, the results cannot be generalized to heterogeneous causes of cardiac arrest. The compression to ventilation ratio followed was 15:2 although the American Heart Association (AHA) currently recommends a 30:2 ratio. Needless to emphasize, the efficacy of compression-only CPR in out-of-hospital cardiac arrest does not apply to trained rescuers.
Standard CPR – with compressions interspersed with rescue breathing may have limitations when performed by the lay public. The efficacy of mouth-to-mouth respiration is questionable; besides, attempts at rescue breathing leads to undesirable interruption to compressions, likely to adversely impact the quality of CPR. Rescue breaths may also be detrimental during the early phase of CPR due increased intrathoracic pressures, leading to reduced venous return. The lay public may also be reluctant to perform mouth-to-mouth rescue breathing on an unidentified victim, thereby exposing themselves to the possibility of transmission of infections. The concept of compression-only CPR had already been in vogue at the time of publication of the DART trial. This large RCT cemented the feasibility and efficacy of compression-only CPR, with the likelihood of improved outcomes, particularly among patients with an underlying cardiac cause for arrest. The authors suggested that attempts at rescue breathing by the lay public would likely have a deleterious impact emanating from interruption of compressions. The American Heart Association recommends compression-only CPR by the lay public in patients with out-of-hospital cardiac arrest (12). However, trained EMS personnel must continue to practice standard CPR in out-of-hospital cardiac arrest. Ventilation may be crucial with an underlying non-cardiac cause, especially related to primary respiratory failure.
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2. Kouwenhoven WB, Jude JR, Knickerbocker GG. Closed-chest cardiac massage. JAMA. 1960 Jul 9;173:1064–7.
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