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Journal ArticleDOI

33 Systematic review of the effectiveness of prehospital critical care following out-of-hospital cardiac arrest

01 Dec 2017-Emergency Medicine Journal (BMJ Publishing Group Ltd and the British Association for Accident & Emergency Medicine)-Vol. 34, Iss: 12

TL;DR: Current evidence to support prehospital critical care for OHCA is limited by the logistic difficulties of undertaking high quality research in this area, and further research needs an appropriate sample size with adjustments for confounding factors in observational research design.

AbstractBackground Improving survival after out-of-hospital cardiac arrest (OHCA) is a priority for modern emergency medical services (EMS) and prehospital research. Advanced life support (ALS) is now the standard of care in most EMS. In some EMS, prehospital critical care providers are also dispatched to attend OHCA. This systematic review presents the evidence for prehospital critical care for OHCA, when compared to standard ALS care. Methods We searched the following electronic databases: PubMed, EmBASE, CINAHL Plus and AMED (viaEBSCO), Cochrane Database of Systematic Reviews, DARE, Cochrane Central Register of Controlled Trials, NHS Economic Evaluation Database, NIHR Health Technology Assessment Database, Google Scholar and ClinicalTrials.gov. Search terms related to cardiac arrest and prehospital critical care. All studies that compared patient-centred outcomes between prehospital critical care and ALS for OHCA were included. Results The review identified six full text publications that matched the inclusion criteria, all of which are observational studies. Three studies showed no benefit from prehospital critical care but were under-powered with sample sizes of 1028–1851. The other three publications showed benefit from prehospital critical care delivered by physicians. However, an imbalance of prognostic factors and hospital treatment in these studies systematically favoured the prehospital critical care group. Conclusion Current evidence to support prehospital critical care for OHCA is limited by the logistic difficulties of undertaking high quality research in this area. Further research needs an appropriate sample size with adjustments for confounding factors in observational research design.

Summary (2 min read)

Jump to: [INTRODUCTION][METHODS][RESULTS][EVIDENCE REVIEW][DISCUSSION][LIMITATIONS] and [CONCLUSIONS]

INTRODUCTION

  • Improving survival after out-of-hospital cardiac arrest (OHCA) is a priority for many modern emergency medical services (EMS) and prehospital research.
  • 1,2 Reported survival rates vary widely, ranging from 4.4% to 25%3,4 and there is great interest in the influence of prehospital treatments on outcomes from OHCA.
  • 6,7 Research examining ALS as a concept, rather than its individual components, has produced conflicting results.
  • 14,15 Without research to support the attendance of critical care teams at OHCA,16,17 there is a large variation in the dispatch of prehospital critical care services in the UK and worldwide.
  • This review aims to identify and present existing evidence regarding prehospital critical care for OHCA, when compared to standard ALS care.

METHODS

  • The review was carried out in accordance with the International Liaison Committee on Resuscitation 2015 evidence evaluation process18 and was registered with the International Prospective Register of Systematic Reviews , registration number CRD42016039995.
  • The authors searched the following electronic databases between April and June 2016: PubMed, EmBASE, CINAHL Plus and AMED (via EBSCO), Cochrane Database of Systematic Reviews, DARE, Cochrane Central Register of Controlled Trials, NHS Economic Evaluation Database, NIHR Health Technology Assessment Database, Google Scholar and ClinicalTrials.gov.
  • The search strategy reflects the fact that prehospital critical care is often provided by physicians or helicopter medical services (HEMS).
  • Also included were all cited and citing articles of publications which were retrieved for full text analysis during the review process.
  • If there were discrepancies in step three, consensus was sought between the two researchers.

RESULTS

  • The search identified a total of 4,554 publications.
  • Two conference abstracts also fulfilled the inclusion criteria and are presented in table 3.25,26.
  • The remaining study was excluded after a consensus decision within the research group.
  • Based on their best interpretation of the information provided and their knowledge of the EMS studied, the authors considered it unlikely that this publication from Taiwan compared prehospital critical care with ALS care.
  • Two studies reported ROSC as the only outcome, one was a secondary review of previous research, and a further study examined the effect of inhospital emergency physicians.

EVIDENCE REVIEW

  • Only limited information is available from the conference abstracts summarised in table 3.25,26.
  • After adjusting for this imbalance, using multiple logistic regression, no significant difference in the rate of discharge from hospital with CPC 1 or 2 was observed between the physician and paramedic groups (OR 1.35, 95% CI 0.71-2.60).
  • The authors also describe a group of 155 patients where prehospital physicians were requested as second responders.
  • ALS-paramedics and nurse anaesthetists were able to administer intravenous drugs under standing orders, nurse anaesthetists were also able to intubate.
  • The standard EMS response to OHCA is ALS-trained paramedics, but during the study period a prehospital critical care service also attended about 9% of OHCAs.

DISCUSSION

  • There is limited evidence to support prehospital critical care for OHCA.
  • 24 However, the authors advise caution when interpreting these results.
  • Another factor that might influence reporting of outcomes in favour of prehospital critical care is in- hospital treatment.
  • While many prehospital critical care procedures require significant training and expertise, others can be integrated into ALS provider care through new equipment or guidelines.10.
  • All of these aspects make it possible that prehospital providers can achieve better outcomes for an individual patient following OHCA.22-24.

LIMITATIONS

  • This review identified only studies with observational research designs, which raises the possibility of bias and confounding.
  • To control for this, one publication presented a subgroup analysis of only witnessed OHCA with a shockable rhythm,20 four studies used regression methods17,21,22,24 and one publication used propensity score matching.
  • The authors attempted to address potential confounding and bias of the full text publications in their review, but were not able to obtain further information for the conference abstracts.
  • Likewise, ALS care will have varied between countries but also has developed and changed significantly over the course of the last 20 years.
  • This limitation applies in particular to EMS where prehospital critical care is delivered by paramedics, as only one publication in this review describes a system of paramedic and physician prehospital critical care17, with the other five studies focusing exclusively on EMS physicians.

CONCLUSIONS

  • Prehospital critical care has the potential to improve survival after OHCA.
  • While there is some observational research to support this, potential sources of bias limit the conclusions that can be drawn.
  • On the other hand, studies that show no benefit from prehospital critical care are limited by inadequate sample sizes.
  • With randomised controlled trials unlikely to gain ethical approval, the benefits of prehospital critical care would need to be proven through the use of large and detailed databases with sophisticated statistical adjustment to control for as many potential confounders as possible.

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TITLE
Systematic review of the effectiveness of prehospital critical care following out-of-hospital cardiac
arrest
AUTHORS
Johannes von Vopelius-Feldt MD, MSc, MCEM
Academic Emergency Department
University Hospitals Bristol NHS Foundation Trust
Upper Maudlin Way
BS2 8HW Bristol
Janet Brandling, MSc, PhD
Research Fellow - Emergency and Critical Care Research
Faculty of Health & Applied Sciences
University of the West of England, Glenside Campus
BS16 1QY Bristol
Jonathan Benger MD, FRCS, FCEM
Professor of Emergency Care, University of the West of England, Bristol
Consultant in Emergency Medicine, University Hospitals Bristol NHS Foundation Trust
Academic Emergency Department
University Hospitals Bristol NHS Foundation Trust
Upper Maudlin Way
BS2 8HW Bristol
Abstract word count: 240
Manuscript word count: 3,827
Number of references: 36
Number of tables: 4

ABSTRACT
Background
Improving survival after out-of-hospital cardiac arrest (OHCA) is a priority for modern emergency
medical services (EMS) and prehospital research. Advanced life support (ALS) is now the standard of
care in most EMS. In some EMS, prehospital critical care providers are also dispatched to attend
OHCA. This systematic review presents the evidence for prehospital critical care for OHCA, when
compared to standard ALS care.
Methods
We searched the following electronic databases: PubMed, EmBASE, CINAHL Plus and AMED (via
EBSCO), Cochrane Database of Systematic Reviews, DARE, Cochrane Central Register of Controlled
Trials, NHS Economic Evaluation Database, NIHR Health Technology Assessment Database, Google
Scholar and ClinicalTrials.gov. Search terms related to cardiac arrest and prehospital critical care. All
studies that compared patient-centred outcomes between prehospital critical care and ALS for
OHCA were included.
Results
The review identified six full text publications that matched the inclusion criteria, all of which are
observational studies. Three studies showed no benefit from prehospital critical care but were
underpowered with sample sizes of 1,028 to 1,851. The other three publications showed benefit
from prehospital critical care delivered by physicians. However, an imbalance of prognostic factors
and hospital treatment in these studies systematically favoured the prehospital critical care group.
Conclusion
Current evidence to support prehospital critical care for OHCA is limited by the logistic difficulties of
undertaking high quality research in this area. Further research needs an appropriate sample size
with adjustments for confounding factors in observational research design.

INTRODUCTION
Improving survival after out-of-hospital cardiac arrest (OHCA) is a priority for many modern
emergency medical services (EMS) and prehospital research.
1,2
Reported survival rates vary widely,
ranging from 4.4% to 25%
3,4
and there is great interest in the influence of prehospital treatments on
outcomes from OHCA. While short ambulance response times, coupled with EMS cardio-pulmonary
resuscitation (CPR) and early defibrillation can improve survival after OHCA,
5
there is little evidence
to support advanced life support (ALS) interventions, such as intravenous adrenaline (epinephrine)
and tracheal intubation.
6,7
Research examining ALS as a concept, rather than its individual
components, has produced conflicting results.
2,8,9
Despite this lack of evidence, ALS has become the
standard of care for OHCA in most modern EMS.
10
A number of further interventions, drugs and
treatment modifications have been trialled, but have failed to improve outcomes consistently.
11
Another focus of research has been the impact of the prehospital provider for OHCA, with a number
of studies comparing physician and paramedic care.
12
A recent meta-analysis attributed the
seemingly better outcomes associated with prehospital physician care to a higher quality of ALS
provided.
12
However, we would argue that the quality of ALS is a matter of provider training and
experience, rather than professional background.
13
Nevertheless, prehospital physicians in some
EMS can undertake interventions and make decisions outside of or in addition to ALS algorithms,
thus providing prehospital critical care.
10
In the UK, the availability of prehospital critical care is
gradually increasing and provided by a combination of physicians and paramedics.
14,15
Without
research to support the attendance of critical care teams at OHCA,
16,17
there is a large variation in
the dispatch of prehospital critical care services in the UK and worldwide. This review aims to
identify and present existing evidence regarding prehospital critical care for OHCA, when compared
to standard ALS care.
METHODS
The review was carried out in accordance with the International Liaison Committee on Resuscitation
(ILCOR) 2015 evidence evaluation process
18
and was registered with the International Prospective
Register of Systematic Reviews (PROSPERO), registration number CRD42016039995.
We searched the following electronic databases between April and June 2016: PubMed, EmBASE,
CINAHL Plus and AMED (via EBSCO), Cochrane Database of Systematic Reviews, DARE, Cochrane
Central Register of Controlled Trials, NHS Economic Evaluation Database, NIHR Health Technology
Assessment Database, Google Scholar and ClinicalTrials.gov. We excluded research published prior

to 1990 as it was deemed very unlikely that it would be relevant to modern EMS. The search strategy
reflects the fact that prehospital critical care is often provided by physicians or helicopter medical
services (HEMS). Please see table 1 for a detailed description of the search strategy. Also included
were all cited and citing articles of publications which were retrieved for full text analysis during the
review process. In addition we used social media (Twitter and Research Gate) to identify further grey
literature.
Review of publications identified by the search followed a three-step approach. First, two
independent researchers (JVVF and JBR) reviewed all study titles and remove all publications which
were obviously not related to the study question as well as duplicate results. Next, the two
researchers independently reviewed the abstracts of all remaining publications, removing those that
did not fulfil the inclusion criteria outlined in box 1. Finally, both researchers independently
reviewed the full text of all remaining publications to assess for inclusion in the final analysis. If there
were discrepancies in the researchers’ opinions during step one or two, the publication in question
was moved forward to the next step. If there were discrepancies in step three, consensus was
sought between the two researchers. If no consensus was achieved, a third researcher (JB) was
asked to review the publication. The final full analysis of all included manuscript was undertaken by
one reviewer (JVVF).
All included studies were assessed for methodological quality and the risk of bias, using the STROBE
checklist for observational studies as guidance.
19
Given the anticipated paucity of randomised
controlled trials, we planned for a narrative analysis of the evidence.
RESULTS
The search identified a total of 4,554 publications. After excluding duplicates, 183 abstracts were
reviewed of which 29 manuscripts were retrieved for further assessment. After review of the full
text publications, six eligible papers remained for analysis; see table 2.
17,20-24
Two conference
abstracts also fulfilled the inclusion criteria and are presented in table 3.
25,26
The authors of the
conference abstracts were contacted but we were unable to obtain further information. Six full text
publications did not include enough information to decide if EMS providers were practicing

prehospital critical care and/or ALS. For five publications, we were successful in gaining this
information by contacting the authors, resulting in two exclusions
27,28
and three inclusions in the
review.
21,23,24
The remaining study was excluded after a consensus decision within the research
group. Based on our best interpretation of the information provided and our knowledge of the EMS
studied, we considered it unlikely that this publication from Taiwan compared prehospital critical
care with ALS care.
4
Reasons for exclusion of the other 18 publications were comparison of advanced treatment with
Basic Life Support (4/18), all patients receiving critical care (3/18), non-experimental study designs
such as systematic reviews (3/18) and publications classified as editorials (2/18), comparing
paramedics and physicians providing ALS (2/18). Two studies reported ROSC as the only outcome,
one was a secondary review of previous research, and a further study examined the effect of in-
hospital emergency physicians. All four of these publications were therefore also excluded.
EVIDENCE REVIEW
Only limited information is available from the conference abstracts summarised in table 3.
25,26
We
therefore provide a brief summary of key aspects for each abstract, all of which used observational
study designs. Seki et al. included only cases of OHCA with non-shockable rhythm in their analysis
and found no difference in 1-month survival between patients attended by prehospital physicians or
paramedics.
25
Shiraishi et al. also compared physician and paramedic care in Japan.
26
In their
propensity matched groups of 34 cases (68 patients in total), no difference in outcome was found.
All full text publications in this review are observational studies, four of which used prospective data
collection whilst two were retrospective. Sample sizes ranged from 614 to 95,072 cases. In five
publications, prehospital critical care was provided by physicians; one study describes a model of
physician and paramedic-delivered prehospital critical care. The full text publications are described
in chronological order.
The first publication by Mitchell et al. compares the EMS of Edinburgh (UK) and Milwaukee (USA)

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