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Date: February 11th, 2020

Reference: Yeh et al. Parachute use to prevent death and major trauma when jumping from aircraft: randomized controlled trial. BMJ 2018.

Guest Skeptic: Marcus Prescott is a nurse in Norway. He is also now a third-year medical student.

Case: A 32-year-old woman with no previous medical history calls you while a passenger on a crashing plane. She has been offered a parachute by the flight attendant but is unsure whether jumping from the plane is wise. You quickly scour the literature for evidence to inform her decision.

Background: The parachute– an umbrella term for devices to slow the motion of an object through an atmosphere by creating drag – was first deployed in China roughly 4,000 years age. The modern versions reached widespread use with the invention of heavier than air flight early last century.

Different variants of parachutes have been used both for recreational and safety purposes; in either case aiming to avoid death in people falling from heights presumed to be lethal. Despite the near universal application, a systematic review from 2003 (Smith and Pell, BMJ) found no RCTs of parachute intervention.

That systematic review published in the BMJ is a classic paper and part of their annual holiday edition. It stated that there was observational data showing parachutes failed at times to prevent morbidity and mortality. There are also case reports of free falls that did not result in 100% mortality.

The authors suggested taking evidence-based medicine advocates up in a plane for a double blinded randomized control trial. The intervention would be a parachute and the control arm would be a sham parachute (backpack). To make it more rigorous, anyone who survived the first jump would cross over into the other arm of the study and jump again. Only then would we have definitive evidence that a parachute was effective in preventing death and major trauma related to gravitational challenges.

After years of trying to organize a trial, researchers were finally able to recruit some volunteers to jump out of a plane with a parachute or backpack.

Clinical Question: Do parachutes reduce death or major injury when jumping from aircraft?

Reference: Yeh et al. Parachute use to prevent death and major trauma when jumping from aircraft: randomized controlled trial. BMJ 2018.

  • Population: Adults 18 years of age and older, seated on aircraft and deemed rational decision makers.
  • Intervention: Jumping from aircraft with parachute
  • Comparison: Jumping from aircraft with backpack
  • Outcome:
    • Primary Outcome: Composite of death and major traumatic injury (ISS>15) within five minutes of impact or at 30 days.
    • Secondary Outcomes: Health status and subgroup analysis based on type of aircraft or previous parachute use.

Authors’ Conclusions: “Parachute use did not significantly reduce death or major injury when jumping from aircraft in the first randomized evaluation of this intervention. However, the trial was only able to enroll participants on small stationary aircraft on the ground, suggestion cautious extrapolation to high altitude jumps. When beliefs regarding the effectiveness of an intervention exists in the community, randomized trials might selectively enroll individuals with a lower perceived likelihood of benefit, thus diminishing the applicability of the results to clinical practice.”

Quality Checklist for Randomized Clinical Trials:

  1. The study population included or focused on those in the emergency department. No
  2. The patients were adequately randomized. Yes
  3. The randomization process was concealed. Yes
  4. The patients were analyzed in the groups to which they were randomized. Yes
  5. The study patients were recruited consecutively (i.e. no selection bias). No
  6. The patients in both groups were similar with respect to prognostic factors. Unsure
  7. All participants (patients, clinicians, outcome assessors) were unaware of group allocation. No
  8. All groups were treated equally except for the intervention. Yes
  9. Follow-up was complete (i.e. at least 80% for both groups). Yes
  10. All patient-important outcomes were considered. Yes
  11. The treatment effect was large enough and precise enough to be clinically significant. No

Key Results: They screened 92 adults with only 23 agreeing to be in the trial. The median age was 38 years and 43% were female.

Parachutes did not reduce death or major injury

  • Primary Outcome:
    • Composite of death and major traumatic injury (ISS>15) within five minutes of impact was 0% vs. 0% with p>0.9
    • Composite of death and major traumatic injury (ISS>15) within 30 days was 0% vs. 0% with p>0.9
  • Secondary Outcomes:
    • No statistical difference in health status
    • No statistical differences when stratified by type of aircraft or previous parachute use.

Talk Nerdy: There were many limitations to this study including a composite outcome for the primary outcome. However, we will only discuss five things that threaten the validity and interpretation of this trial.

  1. Convenience Sample: These were not consecutive adults sitting on an airplane. Participants were selected from those seated next to the recruiter. This could have introduced some selection bias into the study population. When we use the term “bias” we are not talking about random noise in the data but rather something that systematically moves us away from the true point estimate.
  2. Lack of Blinding: Allocation to parachute or backpack was not concealed to the investigator who assigned the treatment. This too could have led to some selection bias. The groups were unbalanced with more frequent fliers in the control (backpack) group. This may or may not have impacted the results.
  3. Ikea Bias: Most of the participants who were randomized were study investigators. They would be unblinded to the study hypothesis and could be more invested in the results because they helped design the study. Whether or not this would have a significant impact on the results is unclear.
  4. Lack of Deployment: In the intervention arm none of the12 participants had their parachute open. This makes the trial very difficult to interpret. If the parachute did deploy properly would it have provided a benefit? However, none of the 12 participants died or were injured because the parachute did not open during the jump.
  5. Fatal Flaw: There was a difference between participants and non-participants. Participants jumped from a mean altitude of 0.6m traveling at a velocity of 0km/hr. This is in comparison to the non-participants who were at a mean altitude of 9,000m and traveling at a velocity of 800km/hr.

Comment on Authors’ Conclusion Compared to SGEM Conclusion: We generally agree with the authors’ conclusions.

SGEM Bottom Line: Wear a parachute if jumping out of a moving aircraft in the air to prevent morbidity and mortality.

Case Resolution: Despite the lack of high-quality evidence demonstrating the efficacy of parachutes, you advise your friend to use the parachute being offered by the flight attendant.

Marcus Prescott

Clinical Application: Based on your understanding of physics and reality, you would recommend people use parachutes if jumping out of an aircraft that is flying. While it does not guarantee you will not be injured or die it is the best evidence we have on the topic. In addition, more research is not needed to determine if parachutes prevent morbidity or mortality due to gravitational challenges.

What Do I Tell the Passenger? Accept the parachute being provided by the flight attendant. 

Keener Kontest: Last weeks’ winner was Jonathan Carter. He knew Kingston was the first capital of Canada.

Listen to the podcast to hear this weeks’ question. Send your answer to TheSGEM@gmail.com with “keener” in the subject line. The first correct answer will receive a cool skeptical prize.

Other FOAMed:

  • Hayes et al. Most medical practices are not parachutes: a citation analysis of practices felt by biomedical authors to be analogous to parachutes. CMAJ 2018
  • Potts and Grossman. Parachute approach to evidence based medicine. BMJ 2006
  • Mamas. What a Parachute Study Tells Us About RCTs. Medscape 2018
  • First10EM: Finally, an RCT of parachutes

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