Helmet noninvasive support for acute hypoxemic respiratory failure: rationale, mechanism of action and bedside application

Abstract

Introduction Helmet 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 results In 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. Conclusions Helmet 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.

Non-Invasive Ventilation for Community-Acquired Pneumonia: Outcomes and Predictors of Failure from an ICU Cohort

“…In this single-center retrospective cohort study, we report our use of NIV for patients with ARF secondary to severe CAP. Despite the lack of guidelines, the use of NIV for this purpose is now relatively common [2][3][4], and the most recent literature suggests that NIV may reduce the requirement for IMV and mortality [7][8][9][10]. However, NIV failure is associated with increased mortality [18,20], and it remains unclear which patients are most likely to benefit.…”

“…Although NIV is accepted as the first-line respiratory support for patients with hypercapnic respiratory failure or acute heart failure, its use for CAP remains controversial, and guidelines generally do not support its routine use [5,6]. However, more recently, the use of helmet continuous positive airway pressure (CPAP) and NIV has been shown to be effective in patients with hypoxemic respiratory failure in improving outcomes [7,8].…”

Severe Community-Acquired Pneumonia: Noninvasive Mechanical Ventilation, Intubation, and HFNT

“…In a recent model of helmet, a zip opening ensures patient accessibility without the need to remove the interface, and alternative fastening systems on the top of the helmet avoid skin damage along the braces of the armpits. 51 In most studies and clinical practice, NIV is delivered as a means of biphasic positive airway pressure, mainly pressure support ventilation (PSV) ¼ pressure support (PS) þ positive end-expiratory pressure (PEEP). Although not providing any PS, CPAP is frequently classified as NIV since commonly used in the clinical practice as an alternative to PSV.…”

“…Conversely, during helmet NIV, apart from the limits of no Vt monitoring, a better high PEEP-related alveolar recruitment and homogeneity may be provided along with the prevention of positive P L swings due to the asynchrony of delivered PS. 51 From a practical standpoint, in absence of indications to straightforward intubation, CPAP or NIV, giving the possibility to significantly improve oxygenation, may be preferred in presence of moderate/severe hypoxemia (PaO 2 /FiO 2 ≤150 mm Hg). Indeed, when respiratory effort is deemed to be low (esophageal pressure [Pes] swings <10 cm H 2 O or PaCO 2 > 35 mm Hg in the absence of metabolic acidosis) CPAP noninvasive support may be enough to increase functional residual capacity and improve oxygenation.…”

Effects of CPAP and FiO2 on respiratory effort and lung stress in early COVID-19 pneumonia: a randomized, crossover study

“…Theoretically, CPAP has the potential to alleviate respiratory effort and lung stress in acute respiratory failure (ARF) [ 7 , 8 ], by improving oxygenation [ 9 , 10 ] and lung recruitment [ 11 ]. However, early COVID-19 pneumonia may be characterized by ventilation-perfusion inequalities [ 12 ], with little alveolar collapse and, hence, low recruitability [ 13 , 14 ].…”