The use of head helmets to deliver noninvasive ventilatory support: a comprehensive review of technical aspects and clinical findings

Abstract

A helmet, comprising a transparent hood and a soft collar, surrounding the patient's head can be used to deliver noninvasive ventilatory support, both as continuous positive airway pressure and noninvasive positive pressure ventilation (NPPV), the latter providing active support for inspiration. In this review, we summarize the technical aspects relevant to this device, particularly how to prevent CO₂ rebreathing and improve patient-ventilator synchrony during NPPV. Clinical studies describe the application of helmets in cardiogenic pulmonary oedema, pneumonia, COVID-19, postextubation and immune suppression. A section is dedicated to paediatric use. In summary, helmet therapy can be used safely and effectively to provide NIV during hypoxemic respiratory failure, improving oxygenation and possibly leading to better patient-centred outcomes than other interfaces.

Keywords: Acute respiratory distress syndrome; COVID-19; Continuous positive airway pressure; Helmets; Noninvasive ventilation.

Fig. 1

Schematic drawings of the main helmet circuit configuration possibilities. For free-flow continuous positive airway pressure (CPAP, A), the gas mixture may be generated with either a Venturi system empowered by an oxygen source or an oxygen/air blender. The gas mixture flows through the helmet and is dispersed through a PEEP valve, which maintains a constant positive pressure backwards. An alternative configuration involves the connection of the helmet with a mechanical ventilator to provide noninvasive positive pressure ventilation, typically with the pressure support mode (NPPV) by either a single port (B) connected to the circuit Y piece (condition associated with a higher risk of CO₂ rebreathing, see text) or two separate ports (C)

Fig. 2

Helmet CPAP therapy markedly improves oxygenation in COVID-19 patients (PaO₂/FiO₂ nearly doubles compared to standard oxygen therapy, P < 0.001 for CPAP effect at ANOVA RM). The oxygenation increase was more pronounced in patients who could be successfully treated with helmet CPAP without escalation to intubation (white boxes, P = 0.002 for interaction between the CPAP effect and outcome). Reproduced under Creative Common licence from [40]

Fig. 3

The amount of "fresh" gas flowing through the helmet (MVtotal) determines the average CO₂ concentration within the helmet (hCO₂). Circles represent measured data, while lines are the theoretical curves obtained by the equation reported in the graph at different levels of CO₂ production. Reproduced from [59]