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![]() Noninvasive respiratory support can be delivered by several devices, such as large-bore nasal cannulas, a tight face mask, or a helmet while it is indicated to treat patients affected by cardiogenic pulmonary edema or chronic obstructive pulmonary disease exacerbation, it should be used with caution during acute hypoxemic respiratory failure. Noninvasive respiratory support is indicated for respiratory failure treatment when patients do not improve by standard oxygen supplementation (i.e., nasal prongs or oxygen mask) but tracheal intubation is not needed or contraindicated. In vivo data are needed to confirm these findings. Insufficient inflow resulted in tidal volume underestimation. Tidal volume measurement is feasible and accurate during bench continuous-flow helmet CPAP therapy by the analysis of the outflow signal, provided that helmet inflow is adequate to match the patient’s inspiratory efforts. ![]() When the helmet inflow was maintained purposely low, tidal volume underestimation occurred (bias − 93.3 ± 83.9 mL), corresponding to an error of -14.8 ± 6.3%. Tidal volume underestimation correlated with respiratory rate (rho = .411, p = .004) but not with peak inspiratory flow, distress, or PEEP. The Bland‒Altman analysis showed a bias of -3.2 ± 29.3 mL for measured tidal volumes compared to the reference, corresponding to an average relative error of -1 ± 4.4%. The tidal volumes examined herein ranged from 250 to 910 mL. Helmet inflow was increased from 60 to 75 and 90 L/min to match the patient’s peak inspiratory flow an additional subset of tests was conducted under the condition of purposely insufficient inflow (i.e., high respiratory distress and 60 L/min inflow). Tidal volume measurement by the novel technique was based on helmet outflow-trace analysis. MethodsĪ bench model of spontaneously breathing patients undergoing helmet CPAP therapy (three positive end-expiratory pressure levels) at different levels of respiratory distress was used to compare measured and reference tidal volumes. We evaluated a novel technique designed to measure tidal volume during noninvasive continuous-flow helmet CPAP. The total lung capacity (TLC), about 6 L, is the maximum amount of air that can fill the lungs (IRV + TV + ERV + RV).The coronavirus disease 2019 (COVID-19) pandemic has promoted the use of helmet continuous positive airway pressure (CPAP) for noninvasive respiratory support in hypoxic respiratory failure patients, despite the lack of tidal volume monitoring. The vital capacity (VC) is the maximum volume exhaled after maximum inhalation (IRV + TV + ERV). The functional residual capacity (FRC) represents the volume of air remaining in the lungs after expiration of a normal breath (ERV + RV). The inspiratory capacity (IC) is the amount of air that can be inspired from the end-expiratory level (IRV + TV). The residual volume (RV) is the volume of air remaining in the lungs after maximal exhalation. The expiratory reserve volume (ERV) is the additional air that can be forcibly exhaled after the expiration of a normal tidal volume. The air inspired with maximal inspiratory effort in excess of the tidal volume is the inspiratory reserve volume (IRV). The amount of air that moves in and out of the lungs during inspiration and expiration with quiet breathing is called the tidal volume (TV).
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