Efficacy of parachute use questioned
Dear editor, With even greater interest we have reread the systematic review ‘Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials’ by Smith et al.. In this groundbreaking review, efficacy of parachutes use as a successful intervention was questioned because evidence for efficacy was based on anecdotal evidence only. Systematic reviews are generally thought to prevent redundant research, although sometimes they lead to increased trial activity [2 3]. Results from two recent studies may shed new light on efficacy of parachute use.
The first was a single blind randomized controlled trial (RCT); the intervention group used a parachute and subjects in the control group fell from great height without a parachute . The placebo group had significantly and relevantly more head injuries, cervical trauma, thoracic trauma, lumbar trauma, pelvic trauma and more hepatic, spleen and bladder injures. Unfortunately, only study subjects were blinded for having a parachute, limiting the methodological quality of the trial. We acknowledge that this is only one randomized trial and replication is needed. Another limitation of this study was that instead of human volunteers, rag dolls were used, further limiting generalizability.
The second study involved a human volunteer. The results of this study are the first in an ’all or nothing case series’ and could potentially lead to a level of evidence 1c. The inclusion concerned a 42 year old male subject who intentionally jumped out of an airplane form a height of 25,000 ft (7,600 m) without using a parachute. By aiming at a net placed just above earth level the subject survived the jump without injuries. He even felt very great right after the jump, suggesting that this intervention could potentially increase quality of life. The report did not state whether the jump was approved by a local medical ethical committee.
So how to put this new treatment option into perspective? There is only anecdotal evidence for efficacy of parachute use and parachute use is highly association with serious injuries and even death. Availability of this scientifically pretty sound intervention, albeit based on a non-randomized trial, questions whether new studies that establish efficacy and safety of parachute use are necessary. An ‘all or nothing case series’ has the potential to become level 1c evidence for net use when jumping out of a plane. Which is substantially higher than parachute use as argued by Smitt et at. .
A new RCT with parachute use as active comparator would be unnecessary with arguments opposite to reasons mentioned by Smith et al., and possibly unethical, even for rag dolls. The review by Smith et al., retrospectively was also subject to flaws. Non-randomized studies were excluded and Smitt et al. incorrectly concluded their review with a statement that there were only two options for future research; either common sense should be applied when considering risks and benefits of parachute use or that parachute use were to be used outside the context of properly conducted trials. This statement, viewed by Smitt et al. as the only two options, reminds us that a prerequisite for progress is to keep an open mind. Smitt et al. did emphasize the importance of generalizability.
Indeed, safety of net use has only been investigated in men, not women. Generalization based on representative study populations could be called a fundamental research aim on itself. The concept of generalization simply means making a correct statement about how nature works in an individual, although extrapolating can be tricky and lead to wrong assumptions. For example, results from spill risk in women during supine versus sitting micturition can possibly be extrapolated to men. However, when standing versus sitting positions in women were to be investigated, extrapolation of results to men could lead to wrong assumptions.
The implications of this new evidence could be that individuals who intentionally jump out of a plane, should not be advised to use a parachute. Given the scarcity of data, recommendations for jumping out of a plane without parachute use should be restrained in subgroups, especially in the subgroup of women. For the sake of science, for the sake of generalizability, it would be very welcome if several women jump out of a plane without using a parachute. Unfortunately, we authors are both men, so we dare and call upon female readers to volunteer.
1. Smith GC, Pell JP. Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials. BMJ 2003;327(7429):1459-61 doi: 10.1136/bmj.327.7429.1459[published Online First: Epub Date]|.
2. Habre C, Tramer MR, Popping DM, et al. Ability of a meta-analysis to prevent redundant research: systematic review of studies on pain from propofol injection. BMJ 2014;348:g5219 doi: 10.1136/bmj.g5219[published Online First: Epub Date]|.
3. Ker K, Roberts I. Exploring redundant research into the effect of tranexamic acid on surgical bleeding: further analysis of a systematic review of randomised controlled trials. BMJ open 2015;5(8):e009460 doi: 10.1136/bmjopen-2015-009460[published Online First: Epub Date]|.
4. Czorlich P, Burkhardt T, Buhk JH, et al. Does usage of a parachute in contrast to free fall prevent major trauma?: a prospective randomised-controlled trial in rag dolls. European spine journal : official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society 2016;25(5):1349-54 doi: 10.1007/s00586-016-4381-z[published Online First: Epub Date]|.
Competing interests: No competing interests