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IntroductionHelmet noninvasive support may provide advantages over other noninvasive oxygenation strategies in the management of acute hypoxemic respiratory failure. In this narrative review based on a systematic search of the literature, we summarize the rationale, mechanism of action and technicalities for helmet support in hypoxemic patients.Main resultsIn hypoxemic patients, helmet can facilitate noninvasive application of continuous positive-airway pressure or pressure-support ventilation via a hood interface that seals at the neck and is secured by straps under the arms. Helmet use requires specific settings. Continuous positive-airway pressure is delivered through a high-flow generator or a Venturi system connected to the inspiratory port of the interface, and a positive end-expiratory pressure valve place at the expiratory port of the helmet; alternatively, pressure-support ventilation is delivered by connecting the helmet to a mechanical ventilator through a bi-tube circuit. The helmet interface allows continuous treatments with high positive end-expiratory pressure with good patient comfort. Preliminary data suggest that helmet noninvasive ventilation (NIV) may provide physiological benefits compared to other noninvasive oxygenation strategies (conventional oxygen, facemask NIV, high-flow nasal oxygen) in non-hypercapnic patients with moderate-to-severe hypoxemia (PaO2/FiO2 ≤ 200 mmHg), possibly because higher positive end-expiratory pressure (10–15 cmH2O) can be applied for prolonged periods with good tolerability. This improves oxygenation, limits ventilator inhomogeneities, and may attenuate the potential harm of lung and diaphragm injury caused by vigorous inspiratory effort. The potential superiority of helmet support for reducing the risk of intubation has been hypothesized in small, pilot randomized trials and in a network metanalysis.ConclusionsHelmet noninvasive support represents a promising tool for the initial management of patients with severe hypoxemic respiratory failure. Currently, the lack of confidence with this and technique and the absence of conclusive data regarding its efficacy render helmet use limited to specific settings, with expert and trained personnel. As per other noninvasive oxygenation strategies, careful clinical and physiological monitoring during the treatment is essential to early identify treatment failure and avoid delays in intubation.

Background: Although widely applied, noninvasive ventilatory support (NIVS) efficacy in COVID-19 disease is unknown. Early identification of treatment failure is warranted to avoid delays in endotracheal intubation and protective ventilation. We conducted a study to determine the rate of and factors associated to NIVS failure in critically ill patients with COVID-19 disease, and to compare NIVS failure rate in COVID-19 patients to that of a matched cohort with hypoxemic respiratory failure of other origins. Methods: All consecutive patients receiving first-line treatment NIVS for hypoxemic respiratory failure due to COVID-19 in the ICU of a University Hospital in Italy up to April 20th, 2020, were studied: laboratory data were collected on arrival, 28-day outcome was recorded. After one-to-one propensity score matching based on simplified acute physiology (SAPS) II score, age, PaO2/FiO2 and PaCO2 at arrival, NIVS failure rate in COVID-19 patients was compared to a previously published cohort who received NIVS during hypoxemic respiratory failure from other causes. Results: Eighty-five patients received first-line treatment with NIVS, mainly with helmet noninvasive ventilation and high-flow nasal cannula. Fifty-two patients (61%) needed endotracheal intubation. Independent predictors of NIVS failure were SAPSII score (adjusted hazard ratio 1.039 [1.018-1.061], Conclusions: COVID-19 patients receiving first-line NIVS are burdened by high risk of needing endotracheal intubation: this appears greater than that of patients affected by hypoxemic respiratory failure of other origins. In order to not delay endotracheal intubation, if logistically sustainable, NIVS use in the intensive care unit should be avoided in severe patients (SAPSII score≥33) with serum lactate de-hydrogenase≥405 Units/Liter.