Association of intra-arrest transport vs continued on-scene resuscitation with survival to hospital discharge among patients with out-of-hospital cardiac arrest (OHCA)

Selected in JAMA by L. Biasco , G. Tersalvi

This multicentre time-dependent propensity score–matched cohort study was designed to evaluate the impact of intra-arrest transport as compared to continued on-scene resuscitationon survival to hospital discharge among patients experiencing out-of-hospital cardiac arrest.

Reviewers

Luigi Biasco

@BiascoDr

Interventional cardiologist / Cardiologist

OSPEDALE CIRIÈ - Ciriè, Italy

Gregorio Tersalvi

@GTersalvi

Interventional cardiologist / Cardiologist

Cardiocentro Ticino-Lugano - Cardiologia - Lugano, Switzerland

Our Comment

Why this study? – the rationale/objective

The management of out-of-hospital cardiac arrest (OHCA) can be provided following two models: rapidly transporting the patient to a hospital during CPR (“scoop and run”) or treating the patient at the scene (“stay and play”). Among emergency medical systems (EMS) all over the world, there is wide variability with respect of the model used, since the benefit of intra-arrest transport during resuscitation is still unclear.

The present study was designed to evaluate the impact of intra-arrest transport as compared to continued on-scene resuscitationon survival to hospital discharge among patients experiencing OHCA

How was it executed? – the methodology

This is a multicentre time-dependent propensity score–matched cohort study, using data from the Resuscitation Outcomes Consortium which involved 10 sites and 192 EMS agencies in the US and Canada. This prospective population-based registry included consecutive EMS-assessed nontraumatic OHCAs between 2005 and 2015.

The registry collected data regarding patient characteristics and time-stamped treatments, interventions, events, hospital discharge outcomes of survival and neurological status. All medical care was carried out per local protocols, including decisions of hospital transport and termination of resuscitation.

In the primary analysis, authors used a time-dependent propensity score in order to overcome resuscitation time bias in which those eligible for intra-arrest transport have already failed initial resuscitative efforts, which is a predictor of poor outcomes. As a result, patients treated with intra-arrest transport were matched with patients in refractory arrest (at risk of intra-arrest transport) at that same time. Potential confounders of the treatment-outcome relationship (such as age, sex, episode location, witnessed status, bystander CPR performed, interval from 911 call to EMS arrival, initial recorded rhythm, presumed aetiology and treatment region) were included in the model. The primary endpoint of the study was survival to hospital discharge.

The secondary endpoint was survival with favourable neurological outcome, defined as a modified Rankin scale of <3, at hospital discharge.

What is the main result?

• Of 43’969 patients with OHCAs treated by EMS in the study regions between April 2011 and June 2015in this study, 11 625 (26%) underwent intra-arrest transport and 32 344 (74%) were treated with on-scene resuscitation until ROSC or termination.
• In the propensity-matched cohort, survival to hospital discharge occurred in 4.0% of the 9’406 patients who underwent intra-arrest transport, versus 8.5% of the 18’299 who were resuscitated on-scene (risk difference, 4.6% [95% CI, 4.0%-5.1%]).
• Among the 15’383 propensity-matched patients with available neurological outcome data, patients undergoing intra-arrest transport demonstrated lower survival with favourable neurological outcome, compared to the on-scene resuscitation group (risk difference, 4.2% [95% CI, 3.5%- 4.9%]).
• The adverse association between intra-arrest transport and outcomes was confirmed also after examining subgroups for which early hospital transport might be considered advantageous (e.g. shockable rhythms of witnessed arrests).

Critical reading and the relevance for clinical practice:

The results of the current study show that intra-arrest transport to the hospital of patients with OHCA compared with continued on-scene resuscitation was associated with lower probability of survival to hospital discharge and lower survival with favourable neurological outcome.

The results raise questions about the hospital-based contributions to intra-arrest transport survivors. Interestingly, the majority of survivors treated with intra-arrest transport achieved ROSC prior to arriving at the hospital. The vast majority of these patients had a presumed cardiac aetiology (93.7%), but the study did not contain data on hospital-based invasive resuscitative techniques such as ECMO, intra-arrest coronary angiography, or advanced monitoring techniques. However, the authors hypothesize that it is likely that only a small number of patients with ongoing resuscitation at the hospital would have been considered eligible for novel invasive treatments, resulting in a modest advantage at the price of a likely loss of CPR quality due to patient’s transport. The latter might also explain the worse neurological outcomes of these patients.

In a secondary analysis, the association of intra-arrest transport and survival to hospital discharge varied within differing times of matched exposure. Within the first 15 minutes, intra-arrest transport was associated with significantly decreased survival, but the greater than 30-minute strata showed a significant association with improved survival. However, this may be biased by the fact that patients receiving CPR for more than 30 minutes were either transported to the hospital or declared dead soon after (given the mean CPR duration of 26 minutes).

This study supports a strategy dedicating effort and expertise on scene rather than prioritizing transport to hospital. However, it focuses on EMS without out-of-hospital physicians, with mainly manual chest compressions. For this reason, authors warn about external validity not being generalizable to systems with different patients’ characteristics and EMS. Furthermore, analysing data from 2011 to 2015, it remains uncertain whether these results are fully applicable to today’s practice. Finally, the observational design limits the study results to association, not causation. It would require validation in randomized controlled trials, although those can be difficult to execute properly and very expensive to conduct in the pre-hospital setting and might require large patients’ cohorts. Therefore, this study might represent a good compromise to evaluate the best management of OHCA.

Because the incidence of OHCA will increase with the anticipated aging of the population, the organisation of new resuscitation models based on other trials is mandatory for the needs of our community. Furthermore, as hospitals are increasingly getting congested by the COVID-19 pandemic, out-of-hospital resuscitation procedures might be reorganised following the “stay and play” model as supported by this study.