Date: September 21st, 2018

Reference: Kawano et al. Intraosseous Vascular Access Is Associated With Lower Survival and Neurologic Recovery Among Patients With Out-of-Hospital Cardiac Arrest. Annals of EM May 2018

Guest Skeptic: Andrew Merelman is a critical care paramedic and first year medical student at Rocky Vista University in Colorado. His primary interests are resuscitation, prehospital critical care, airway management, and point-of-care ultrasound.

Case: A 46-year-old man has a cardiac arrest at home, witnessed by family. Bystander CPR is initiated prior to EMS arrival. EMS arrives on scene and initiates high quality basic life support (BLS). One defibrillation for ventricular fibrillation (VF) is provided but the patient remains in VF. As part of their protocol, they attempt vascular access to administer epinephrine and an antidysrhythmic. They wonder whether it would be better to attempt a peripheral intravenous (IV) line or intraosseous access first?

Background: Cardiac arrest care has evolved drastically over the past couple of decades, but not in the way many may have expected. We now know that an emphasis on the basics (high quality chest compressions and defibrillation) are the most important aspects of resuscitation. More advanced skills such as airway management, vascular access, and cardiac medications are being de-emphasized.

It was the classic OPALS paper covered on SGEM#64 by the Legend of Emergency Medicine Dr. Ian Stiell that demonstrated no advantage to ACLS vs. BLS for out-of-hospital cardiac arrest (OHCA).

There have been other SGEM episodes that question the efficacy of various interventions:

The resuscitation science community has been struggling to find advanced interventions that can show a benefit in mortality and, most importantly survival with good neurological outcome.

Intraosseous access has become a mainstay of cardiac arrest care due to its speed and reliability. However, no randomized trial has compared intravenous access to intraosseous access with a primary outcome of good neurologic function.

Clinical Question: Is intraosseous vascular access in the pre-hospital setting for OHCA associated with better neurologic outcomes compared to intravenous vascular access?

Reference: Kawano et al.Intraosseous Vascular Access Is Associated With Lower Survival and Neurologic Recovery Among Patients With Out-of-Hospital Cardiac Arrest. Annals of EM May 2018

  • Population: Out-of-hospital, non-traumatic, adult cardiac arrest patients
    • Excluded: Unsuccessful attempt or more than one access site. Patients were also excluded if incarcerated or pregnant, those with DNR orders, and those with arrests presumed to be the result of exsanguination or severe burns.
  • Intervention: Primary intraosseous vascular access
  • Comparison: Primary intravenous vascular access
  • Outcome:
    • Primary Outcome: Favourable neurological outcome (modified Rankin Scale [mRS] score 3)
    • Secondary Outcomes: Return of spontaneous circulation (ROSC) and survival to hospital discharge.

Authors’ Conclusions: “In adult out-of-hospital cardiac arrest patients, intraosseous vascular access was associated with poorer neurologic outcomes than intravenous access.”

Quality Checklist for A Chart Review:

  1. Were the abstractors trained before the data collection? Unsure
  2. Were the inclusion and exclusion criteria for case selection defined? Yes
  3. Were the variables defined? Yes
  4. Did the abstractors use data abstraction forms? Unsure
  5. Was the abstractors’ performance monitored? N/A
  6. Were the abstractors aware of the hypothesis/study objectives? No
  7. Was the interobserver reliability discussed? No
  8. Was the interobserver reliability tested or measured? No
  9. Was the medical record database identified or described? Yes
  10. Was the method of sampling described? N/A 
  11. Was the statistical management of missing data described? Yes
  12. Was the study approved by the institutional or ethics review board? Yes

Quality Checklist for Observational Study:

  1. Did the study address a clearly focused issue? Yes
  2. Did the authors use an appropriate method to answer their question? Yes
  3. Was the cohort recruited in an acceptable way? Yes
  4. Was the exposure accurately measured to minimize bias? Yes
  5. Was the outcome accurately measured to minimize bias? Unsure
  6. Have the authors identified all-important confounding factors? No
  7. Was the follow up of subjects complete enough? Yes
  8. How precise are the results? The 95% CI around the point estimate for the primary and secondary outcomes was fairly wide.
  9. Do you believe the results? No
  10. Can the results be applied to the local population? No
  11. Do the results of this study fit with other available evidence? No

Key Results: The study included 13,155 patients with OHCA. The vast majority (95%) had intravenous access with only 5% in theintraosseous group

Significantly fewer patients had a favourable neurologic outcome in the IO group compared to the IV group

  • Primary Outcome: mRS score 3 was 10/660 (1.5%) IO group vs. 945/12,495 (7.6%) IV group
  • Secondary Outcome:
    • IO was associated with poorer survival to hospital discharge and ROSC.
    • Sensitivity analyses revealed similar results.

This was a secondary analysis of the PRIME study NCT00394706

1) Association vs. Causation: The most obvious limitation with this study design is it cannot conclude causation. The vast majority of patients had IVs placed with only 5% getting an IO. There may have been multiple unmeasured confounders responsible for the EMS crews deciding to use an IO. A randomized control trial would need to be conducted to answer whether or not IOs cause poorer neurological outcomes in these patients.

2) Reliability of the mRS: The reliability of the mRS has been questioned (Quinn et al Stroke 2009). Inter-rater reliability was not discussed, tested or measured in the publication.

3) Differences at Baseline: There were multiple differences in the population such as sex, witnessed or not, location, and defibrillation. There was a significant difference in initial rhythm between the two groups. In the IO group, 13.9% had a shockable rhythm while 26.2% in the IV group had a shockable rhythm. We know patients with shockable rhythms are more likely to do well. They attempted to mitigate these issues using various adjustments including propensity score matching.

4) Differences in Treatment: There were also differences in treatment between groups. One example is twice the number of patients in the IV group received interventional cardiac catheterization compared to the IO group. Techniques used to address these issues cannot remove all the potential biases in this type of study design.

5) So What? At the end of the day does it really matter if you have vascular access in an adult patient with an OHCA? We do not have good evidence that the ACLS drugs provide a patient-oriented outcome.

The recent PARAMEDIC2 trial is another excellent example the failure of epinephrine to improve survival with favorable neurologic outcome. Stay tuned, because we will be covering this on future episode of the SGEM.

Comment on Authors’ Conclusion Compared to SGEM Conclusion: We agree with the authors that this data demonstrates an association of worse outcomes in patients with OHCA who had IOs placed compared to IVs.

SGEM Bottom Line: High-quality CPR and early defibrillation for shockable rhythms are more important in OHCA than obtaining vascular access.

Case Resolution: The responding EMS providers choose to initiate IO access as the fastest, most reliable means. They are then able to administer ACLS medications as per their protocol knowing it’s unlikely to make an important patient-oriented difference.

Clinical Application: This secondary analysis should not deter paramedics from obtaining vascular access via IO. They should use the approach they think is best for each individual patient. In cardiac arrest, this is typically IO as it is faster and more reliable than intravenous. Using the fastest method allows more time to focus on the important interventions such as chest compressions and defibrillation.

About 1.5 metres

What Do I Tell My Patient? I would tell the family we are putting in tube directly into the bone. This is faster than starting an IV and we can give him medication quickly if needed. However, the most important things are good CPR and shocking the heart.

Keener Kontest: Last weeks’ winner was Mat Goebel, a 4th year medical student at UC San Diego School of Medicine.  He knew in the movie Top Gun, Maverick claimed to have pulled a 4G inverted dive with a MiG-28 at a distance of about 1.5 metres.

Listen to the SGEM podcast on iTunes to hear this the new keener question. If you know the answer send an email to TheSGEM@gmail.com with “keener” in the subject line. The first correct answer will receive a cool skeptical prize.

Other FOAMed:

  • REBEL EM: IO vs. IV in Out of Hospital Cardiac Arrest (OHCA)

Remember to be skeptical of anything you learn, even if you heard it on the Skeptics’ Guide to Emergency Medicine.