Evidence-Based Medicine Analysis of Mechanical Insufflation-Exsufflation Devices

To the Editor:

Evidence-based medicine has become the accepted standard¹ for validating treatments. However, although evidence-based medicine purports to consider the best available evidence, whether that be randomized double-blind placebo-controlled trials or not, treatments not justified by randomized double-blind placebo-controlled trials are largely denigrated, as in the recent paper by Auger et al.² Most importantly, however, evidence-based medicine grounded in randomized double-blind placebo-controlled trials is irrelevant when the intervention takes the place of a life-preserving function or vital organ and use of a placebo would result in certain morbidity or death. This would be the case by withdrawing continuous noninvasive ventilatory support from patients who have little to no measurable vital capacity^3,4 or when pulmonary morbidity is otherwise inevitable by not clearing congested airways due to ineffective cough flows.⁵ Remarkably, this stark limitation of randomized double-blind placebo-controlled trials has been ignored. For example, for renal failure, no placebo control is possible for dialysis or organ transplantation, nor is one possible for parachutes that essentially substitute for wings.⁶ Anyone with profuse airway secretions who cannot generate effective cough flows will develop acute respiratory failure and, if intubated, will fail extubation. Whereas controlled studies can compare different methods of augmenting cough flows, those with placebo controls (augmenting vs nothing) cannot be ethically subject to meta-analysis for high-quality randomized double-blind placebo-controlled trials.

In 2011, we reported 101 continuous noninvasive ventilatory support-dependent subjects with Duchenne muscular dystrophy. They had “… a mean [vital capacity] 176 ± 102 mL, or 3% of predicted normal, which is not compatible with survival without continuous ventilator support … [and] 31 consecutive intubated Duchenne muscular dystrophy subjects who failed extubation at other institutions and/or failed ventilator weaning parameters and spontaneous breathing trials were successfully extubated …” to continuous noninvasive ventilatory support thanks, in large part, to mechanical insufflation-exsufflation, despite vital capacities as low as 80 mL.⁵ In the paper by Auger et al,² the authors did not even consider the study worth citing, although it is certain that our continuous noninvasive ventilatory support-dependent subjects with respiratory infections could not possibly have survived without a tracheostomy tube without the effective airway clearance by mechanical insufflation-exsufflation.

Randomized double-blind placebo-controlled trials are certainly necessary to demonstrate minor evidence-based medicine-supported improvements on major life-preserving breakthroughs, but they cannot be used when those breakthrough interventions substitute for critical life-preserving functions, as does mechanical insufflation-exsufflation for any population with inadequate strength to clear airways by coughing. It must also be pointed out that in all of the controlled studies cited by Auger et al,² mechanical insufflation-exsufflation was used at grossly inadequate pressures, since the 40 cm H₂O of currently available devices is not equivalent to the 40 mm Hg pressures at which mechanical insufflation-exsufflation was studied and used effectively in the 1950s.³

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