Re: Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials
As Christmas approaches and the BMJ is putting its midwinter edition to bed we reflect on 13 years of needless confusion around the parachute analogy.  When is the analogy helpful and when is it not? For example, the analogy works for tension pneumothorax which has a high risk death. Prompt insertion of a needle or tube alleviates the problem with an audible hiss and an immediate, clinically evident, beneficial effect which is mechanistically explicable. We have concerns about the use of the analogy in rebuttal of the need for a randomised controlled trial of lung metastasectomy.
There has now been a randomised trial of parachutes. Researchers dropped rag dolls with and without parachutes in random order from a height of 20.83 metres and then checked to see whether the various air or water filled balloons within them were ruptured. Under their controlled test conditions the dolls with parachutes had fewer ‘organ’ injuries and fractures. Despite this evidence, it is unlikely that commercial airlines would consider it worthwhile to put parachutes under the seats of passengers or crew. One reason might be that the risk of death from this cause is so low that the intervention cannot be justified but more likely is that the efficacy of parachutes under specific circumstances does not translate into general effectiveness in modern civil aviation. General awareness of the analogy is unsurprising: Smith and Pell have been cited 829 times - make that 830 now. Some readers have been misled - perhaps they didn't know it was Christmas. Analogies can be informative but need to be taken in context when making decisions on patient care.
On a radiological “now you see, it now you don’t” basis metastasectomy works but unlike dropping out of a plane, a colorectal lung metastasis is rarely if ever lethal. A carefully selected small minority (≤3%) have a lung metastasectomy but during their ‘cancer journey’ they have multiple other treatments spread over years. It is impossible to distinguish the signal from the noise unlike when a person falling from a plane deploys a parachute.
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Competing interests: No competing interests