by Maia Dorsett, MD PhD (@maiadorsett)

Recap of the Case:

A 64 yo male is having dinner with his family when he begins to feel lightheaded and nauseated. As he stands up to leave the table, he collapses to the ground. His family calls 911. As he is unresponsive with agonal respirations, the call is dispatched as a cardiac arrest and the patient's family is instructed to perform CPR via pre-arrival instructions.

On EMS arrival, the patient is found to be pulseless. Compressions are continued while the patient is connected to the monitor. The EMS supervisor arrives on scene shortly after with a newly purchased mechanical CPR device.

Should the mechanical CPR device be used? If so, when should it be applied?

Do you have a protocol dedicated to use of mechanical CPR? If you utilize mechanical CPR, how do you integrate it into your cardiac arrest resuscitation so as to minimize interruption of chest compressions?

Review:

High quality compressions of adequate depth, rate, recoil and with minimal interruption are crucial to neurologically-intact survival from out of hospital cardiac arrest (OHCA). Quality compressions require considerable physical effort on the part of providers leading to decreased compression quality over time. A number of mechanical CPR devices have been developed with the goal of maintaining compression consistency and off-loading the work of compressions [1]. However, when applied to all patients with cardiac arrest, mechanical CPR is equivalent or inferior to manual CPR in achieving neurologically-intact survival.

The first large trial to examine the effect of mechanical CPR on cardiac arrest outcomes was a multicenter randomized control trial in the United States and Canada [2]. The trial enrolled patients from 2004 to 2005. Individual stations within each site were randomized to manual CPR or mechanical CPR with an AutoPulse band device, with subsequent alternation between intervention and control groups. They found no difference in the primary outcome of 4 hr survival between manual and mechanical CPR (N=1071; 29.5% vs 28.5%; P=.74), but found that an overall lower rate of neurologically-intact survival among those patients who received mechanical CPR (3.1 % for mechanical CPR vs. 7.5% for manual CPR , p=.006). The study was terminated early because of poorer neurologic outcomes in the mechanical CPR group.

Following this, three randomized control trials (CIRC, LINC and PARAMEDIC) found that mechanical CPR was non-inferior to manual CPR.

The CIRC trial was a randomized control trial of mechanical CPR using the Autopulse band device versus standard CPR [3]. It included all 4231 patients with arrests of presumed cardiac origin. Patients were randomized by sealed envelopes opened after manual compressions were initiated. They found no difference in survival to hospital discharge between mechanical and manual CPR (OR for mechanical compared with manual: 1.06, 95% CI 0.83-1.37). For the secondary outcome of good neurologic outcome (defined as a modified Rankin score of < 3 at discharge from the hospital), there was no difference between mechanical and manual CPR (OR for mechanical compared with manual; aOR 0.80, 95% CI 0.47–1.37).

Unlike the CIRC trial, the LINC trial (Lucas IN Cardiac arrest) used the plunger-type Lucas device. 2593 patients were randomized using a sealed envelope after initiation of manual compressions [4]. The mechanical compression arm of the study varied more than just the mode of CPR. In the Lucas arm, the first defibrillation shock was delivered during ongoing compressions without pausing to check the heart rhythm and CPR cycles were extended to 3 minutes between subsequent rhythm checks. When comparing the two arms, the authors found no difference between 4 hr survival (307/1300 [23.6%] vs 305/1289 [23.7%]; risk difference, −0.05%; 95% CI, –3.3% to 3.2%; P<.99) and neurologic outcome at hospital discharge (108/1300(8.3 %) vs. 100/1289 (7.8%), risk difference, 0.55; 95% CI−1.5% to 2.6%; p = 0.61). Mechanical and manual CPR groups were similar in the proportion of patients with witnessed arrest, bystander CPR and shockable rhythm.

The PARAMEDIC trial also compared mechanical CPR with a LUCAS device to manual compressions [5]. Randomization was done with a computer-generated randomization sequence that assigned particular vehicles to carry the device. The study enrolled 4471 patients with similar baseline characteristics. Manual compressions were initiated until the device could be placed. During pauses, if a shockable rhythm was found, the LUCAS was turned back on and defibrillation took place with ongoing mechanical CPR. The study found no significant difference in the primary outcome of survival to 30 days (aOR 0.86, 95% CI 0.64-1.15). Survival with favorable neurologic outcome at 3 months was lower in the group receiving mechanical CPR (aOR 0.72, 95% CI 0.52-0.99).

Two subsequent meta-analyses found no difference between manual and mechanical CPR on favorable neurologic outcome [6,7].

In an effort to compare outcomes for patients receiving manual versus mechanical CPR in the “real world” outside of the well-trained and monitored randomized control trials, two recently published studies retrospectively evaluated outcomes from patients in the CARES registry.

First, an observational cohort study of all cardiac arrests treated in the state of Utah from May 2012 through June 2015 tracked via the CARES registry was published in January 2016 [8]. This included adult patients with non-traumatic arrest who were either defibrillated with an AED or received chest compressions from a prehospital provider. They analyzed 2600 resuscitation attempts. Overall, mechanical CPR (predominantly with the AutoPulse device) was used in only 16% of all arrests. Patients who received mechanical CPR also were more likely to have several poor prognostic factors; their arrests were less likely to be witnessed, more likely to present with asystole and require more interventions (ACLS medications, advanced airway placement). The authors therefore used a regression model with weighted propensity to scores in order to control for possible confounders/selection bias – witnessed arrest, bystander CPR, deliver of bystander AED shock, initial shockable rhythm. Using this approach, the authors found that the adjusted relative risk for neurologically-intact survival with mechanical CPR compared to manual CPR was 0.41 (95% CI, 0.24 – 0.70, p=0.001). In a subgroup analysis, mechanical CPR was still associated decreased likelihood of neurologically-intact survival in patients with a shockable rhythm on initial check (aRR 0.47, 95% CI 0.25 – 0.86, p=0.001) and EMS-witnessed arrests (RR 0.18, 95% CI 0.08-0.40), p< 0.0001).

More recently, the analysis of the CARES registry and been expanded to a national scale [9]. A retrospective study of CARES registry data from January 2013 to December 2015 included an evaluation of outcomes in 80,861 patients. Using a multivariable regression model to control for arrest characteristics – age, arrest location, bystander CPR, AED use, initial rhythm, witnessed arrest, post-arrest targeted temperature management, successful placement of an advanced airway – they found that patients who received mechanical CPR were less likely to survive to hospital discharge (7.0% vs. 11.3%, p < 0.001) or have neurologically-intact survival (5.6% vs. 9.5%, P < 0.0001).