Heads Up! There is No Association with Improved Outcomes for Head Up CPR: Why We Must Read Past the Abstract

Background: There are only two interventions that have been proven in the medical literature to improved outcomes in cardiac arrest: high-quality CPR and early defibrillation. Over the years, we as a scientific community have worked extensively to find other interventions that improve outcomes. Some look promising (ie eCPR and application of US) while others have been considerably less effective or inconsistent (ie epinephrine and targeted temperature management). Additionally, there is ongoing research into targeting improvements in the interventions we know work. Examples include mechanical CPR, which hasn’t been shown to be superior to manual CPR but does make running a resuscitation easier, and dual sequence defibrillation, which appears to be useful in certain circumstances. It is imperative that we continue to look at ways to improve cardiac arrest resuscitation.

Head Up (HUP) CPR may be the next critical improvement. Instead of lying the patient flat while administering compressions, HUP CPR requires the head and thorax to be elevated. The physiologic theory is that HUP allows venous blood to drain from the brain to the heart resulting in decreased intracranial pressure (ICP) and improved cerebral perfusion pressure (CPP). Increased CPP, in turn, may lead to improved neurologic outcomes. In order for HUP to be effectively delivered, it is paired with mechanical CPR (mCPR) as well as an impedance threshold device (ITD) which provides active compression-decompression.There is substantial animal data demonstrating improvements in ICP and CPP as well as some data demonstrating better neurologic outcomes. However, human data is sorely lacking.

Article: Moore JC et al. Head and thorax elevation during cardiopulmonary resuscitation using circulatory adjuncts is associated with improved survival. Resuscitation 2022; 179: 9-17. PMID: 35933057

Clinical Question: Does automated controlled elevation CPR (ACE-CPR) with mCPR + ITD improve survival to hospital discharge in comparison to traditional CPR?

Population: Patients > 18 years of age w/ OHCA treated by 10 EMS systems in in the US.

Outcomes: 

  • Primary: Survival to hospital discharge.
  • Secondary: 
    • ROSC at any time
    • Survival to discharge with favorable neurological function (defined as CPC 1 or 2).

Intervention: 

  • Automated controlled elevation of the head (to 22 cm) and thorax (to 9 cm).
  • Mechanical CPR with a commercially available device.
  • Impedance threshold device application.

Control: Standard CPR (patients for control arm obtained from de-identified patient-level data from 3 NIH-funded randomized controlled OHCA resuscitation trials with high quality CPR performance).

Design: Prospective observational study with historic controls with propensity score-matched analysis.

Excluded: Prisoners

Primary Results

    • 409 patients collected from 10 EMS systems using ACE-CPR
      • 4 EMS systems were involved in early implementation phase and their patients excluded from analysis.
      • 227 patients were enrolled from the other 6 EMS systems and 222 were matched and analyzed.

Critical Findings:

Strengths:

  • Looks at the utility of an intervention in a human population where previous data was limited to animal models.
  • Propensity score matching performed to find comparable control population.
  • EMS systems from multiple states in the US increasing external validity.

Limitations:

  • Selection bias: unclear if continuously selected, 4/10 EMS systems were excluded from analysis.
  • There is no blinding or randomization of patients which introduces bias.
  • Comparison to historical controls introduces issue that other variables may have changed in practice that could affect outcomes.
  • Prior to propensity matching there was an imbalance of patients at baseline with more patients in the ACE-CPR group with non-shockable rhythms and less likely to have bystander witnessed CPR both of which would favor the conventional CPR group in terms of outcomes.
  • Patients <35kg and >175kg cannot currently be treated with ACE-CPR and excluded from the study.

Discussion

  • Abstract outcome reporting frankly misleading.
    • The abstract reports benefit of ACE-CPR within specific time windows.
    • These time windows were not the pre-established primary outcomes and don’t appear to be preset subgroup analyses either.
    • This appears to be data dredging or “seeking more information from a data set than it actually contains.”
  • Selection Bias
    • Data from 4 EMS systems (n=165) were excluded as these systems were early in ACE-CPR implementation.
    • Unclear when exclusion of this data occurred (before or after analysis).
  • The conclusion of improved outcomes based on rapid time to initiation of ACE-CPR is based on limited data (just a small subset of the overall dataset). 
  • There is a lot of equipment involved here: Device to elevated head/thorax, mechanical CPR device and ITD. This can add complexity to a stressful situation that can delay application of compressions and electricity. Significant training is necessary to make this occur smoothly.

Authors Conclusions: “Compared with C-CPR controls, rapid initiation of ACE-CPR was associated with a higher likelihood of survival to hospital discharge after OHCA.”

Our Conclusions: This data does not show any evidence of improved outcomes for ACE-CPR vs standard CPR. Data-dredging to find the associations that are highlighted in the abstract can be used to generate hypothesis but have no effect on the delivery of clinical care.

Potential to Impact Current Practice: Anyone involved in cardiac arrest management should keep an eye on this space as future data may (or may not) demonstrate a benefit for ACE-CPR. At this time, ACE-CPR should only be applied within a study setting.

For More on This Topic Checkout:

References:

  1. Moore JC et al. Head and thorax elevation during cardiopulmonary resuscitation using circulatory adjuncts is associated with improved survival. Resuscitation 2022; 179: 9-17. PMID: 35933057

Post Peer Reviewed By: Salim R. Rezaie, MD (Twitter: @srrezaie)

Cite this article as: Anand Swaminathan, "Heads Up! There is No Association with Improved Outcomes for Head Up CPR: Why We Must Read Past the Abstract", REBEL EM blog, September 19, 2022. Available at: https://rebelem.com/heads-up-there-is-no-association-with-improved-outcomes-for-head-up-cpr-why-we-must-read-past-the-abstract/.

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