Elsevier

Resuscitation

Volume 135, February 2019, Pages 37-44
Resuscitation

Clinical paper
The acute respiratory distress syndrome after out-of-hospital cardiac arrest: Incidence, risk factors, and outcomes

https://doi.org/10.1016/j.resuscitation.2019.01.009Get rights and content

Abstract

Objective

To define the incidence of the acute respiratory distress syndrome (ARDS) following out-of-hospital cardiac arrest (OHCA) and characterize its impact on outcome.

Methods

This was a retrospective cohort study conducted at two urban, tertiary, academic hospitals from 2007 to 2014. We included adults with non-traumatic OHCA and survived for ≥48 h. Patients who received mechanical ventilation for ≥24 h, had 2 consecutive arterial blood gases with a ratio of the partial pressure of oxygen to the fraction of inspired oxygen ≤300, and bilateral radiographic opacities within 48 h of hospital admission were defined as having ARDS. We examined the associations between ARDS and outcome using multivariable analyses and performed sensitivity analyses excluding patients with evidence of cardiac dysfunction.

Results

Of 978 OHCA patients transported to the study hospitals, 600 were mechanically ventilated and survived ≥48 h. A total of 287 (48%, 95% CI 44–52%) met criteria for ARDS within 48 h of admission. There were no differences in demographics, OHCA etiology, or cardiac rhythm according to ARDS status. Patients with ARDS had higher hospital mortality, longer ICU stays, more ventilator days, and were less likely to survive with full neurologic recovery. Upon excluding patients with cardiac dysfunction, the incidence of ARDS was unchanged.

Conclusion

Nearly half of initial OHCA survivors develop ARDS within 48 h of hospital admission. ARDS was associated with poor outcome and increased resource utilization. OHCA should be considered among the traditional ARDS risk factors.

Introduction

Approximately 350,000 persons in the United States suffer out-of-hospital cardiac arrest (OHCA) each year.1 Many who survive the initial event will suffer from the post-cardiac arrest syndrome (PCAS), a highly inflammatory state characterized by reperfusion injury, oxidative stress, and multi organ dysfunction.2, 3, 4, 5, 6

The acute respiratory distress syndrome (ARDS) is defined, according to the Berlin definition, by hypoxemia and bilateral radiographic opacities not fully explained by volume overload, that occur acutely in relation to a clinical insult.7 Cardiac arrest is not listed among the traditional “clinical insults” known to cause ARDS.8 Possible mechanisms of ARDS development in patients with PCAS might include reperfusion injury, oxidative stress, pulmonary contusion from chest compressions, ventilator-induced lung injury, aspiration, and infection. Additionally, there is substantial overlap between the pathophysiology of ARDS and PCAS, including inflammation, leukocyte activation, activation of coagulation pathways, and altered permeability of alveolar endothelial and epithelial barriers.9, 10

The exact incidence of ARDS after OHCA is unknown. One study described an 5% incidence of post-arrest ARDS, while another study reported that 65% of patients had a ratio of the partial pressure of arterial oxygen to fraction of inspired oxygen (PaO2:FIO2)≤ 300, implying a much higher incidence.11, 12 Because prior studies report widely variable incidences, we sought to describe the epidemiology of ARDS in a modern OHCA cohort using the contemporary Berlin definition.7 Further, while ARDS itself is associated with a mortality of up to 40% (depending on severity), the impact of ARDS after OHCA on overall outcome has not been described.13, 14 Our primary aim is to describe the incidence of ARDS in patients who have suffered OHCA. We also test the association between ARDS and survival and favorable neurologic outcome at hospital discharge.

Section snippets

Ethics approval and setting

The University of Washington Human Subjects Division approved this study (Study ID #49480). This study site was Seattle, Washington, a U.S. city with 725,000 residents and 83.9 square miles. The Seattle Fire Department’s emergency medical services system, Seattle Medic One, has been described previously.15

Harborview Medical Center (HMC) is a 413-bed public hospital and trauma center. University of Washington Medical Center (UWMC) is a 450-bed quaternary, University-affiliated hospital. HMC and

Statistical analysis

Baseline demographic characteristics, clinical variables, and outcomes were compared according to ARDS status using two-sample t-tests for means, Mann–Whitney tests for medians, and Chi-squared tests for categorical variables.

Using multivariable logistic regression, we fit models to evaluate the associations between ARDS and hospital mortality and ARDS neurologic outcome at hospital discharge. We adjusted the models for age, Charlson index (coded as binary with a cutoff of 2), and the presence

Sensitivity analyses

We performed a sensitivity analysis to elucidate the relative contribution of cardiac dysfunction to patients’ hypoxemic respiratory failure. We excluded patients with the following markers of cardiac dysfunction: (1) a mechanical circulatory support device (most likely to have the highest severity of heart failure), (2) left ventricular ejection fraction <40% within the first 48 h after ROSC, and (3) percutaneous coronary intervention within the first 24 h after ROSC. We also performed a

Patient characteristics and cardiac arrest care

A total of 978 OHCA patients were transported to the study hospitals from 2007 to 2014 (Fig. 1). Of these, 600 met eligibility criteria and were included. Mean age was 56 ± 16 years, 74% were male, and 69% were white (Table 1). Overall survival to hospital discharge was 60% (95% CI 55–64%), with 328 patients (55%, 95% CI 51–59%) surviving with complete neurologic recovery or mild impairment (CPC 1 or 2).

A total of 45% had an initial shockable cardiac arrest rhythm (ventricular fibrillation or

Discussion

We found that nearly half of OHCA patients surviving for at least 48 h following resuscitation develop ARDS, and that early ARDS is associated with poor outcome and increased healthcare resource utilization. The study results advance our growing understanding of an association between respiratory complications and outcome after cardiac arrest.11, 20, 21, 22, 23, 24 Early recognition of ARDS after OHCA may allow for prompt application of therapies known to improve outcome in ARDS such as low

Limitations

Previous studies in other disease states, such as subarachnoid hemorrhage, documented that longer ICU stay is associated with development of ARDS.47 To reduce the effect of competing risk of death from other causes and to avoid including patients who develop ARDS for reasons other than those directly related to the initial OHCA event, such as ventilator-associated pneumonia, we screened for ARDS within 48 h of admission. It is therefore possible that we underestimate the true incidence of ARDS

Conclusions

Nearly half of all out-of-hospital cardiac arrest survivors develop ARDS within 48 h of hospital admission. Early ARDS is associated with lower survival, worse neurologic outcome, and increased resource utilization in this population. OHCA should be considered among the traditional risk factors for ARDS. Future studies should prospectively evaluate whether specific mechanical ventilation strategies, such as low tidal volume ventilation and avoidance of hyperoxia, might reduce the incidence of

Funding sources/Disclosures

This study was funded by a research grant from the Medic One Foundation. NJ and CTH also receive funding from the National Institutes of Health (U01HL123008-02). The authors have no other disclosures.

Acknowledgements

NJ conceived the study, drafted manuscript, and takes primary responsibility. EC collected and analyzed data. MP, DC, DG, TR, and CLH all reviewed and edited the manuscript. The authors have no conflicts of interest. The study was funded by the Medic One Foundation.

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