Effects of High-Flow Nasal Cannula and Helmet Continuous Positive Airway Pressure in Acute Hypoxemic Respiratory Failure

Headings: The effects of high-flow nasal cannula (HFNC) and continuous positive airway pressure (CPAP) in patients with acute hypoxemic respiratory failure (AHRF) on respiratory mechanics and inspiratory efforts are not entirely understood. Objectives: To compare the physiologic effects of HFNC and helmet CPAP with respect to conventional oxygen therapy (COT) in terms of respiratory mechanics, inspiratory effort, gas exchange, and hemodynamics during AHRF. Design: Crossover study. Setting: General surgical-medical ICU of San Paolo University Hospital, Milan, Italy. Patients: Thirty-three adult patients with AHRF, defined as an Pa o 2 less than 60 mm Hg or an Pa o 2 /F io 2 less than 300 with a positive end-expiratory pressure (PEEP) level greater than or equal to 5 cm H 2 O, along with an Pa co 2 less than 45 mm Hg. Interventions: After support with COT, three types of respiratory support were applied in random order: HFNC with 60 L/min of flow and helmet CPAP with 5 or 10 cm H 2 O of PEEP. Measurements and Main Results: Tidal volume, respiratory rate, inspiratory esophageal (ΔPes), and airway pressure swings were measured and an arterial blood gas analysis, along with hemodynamic data, was obtained after 20 minutes from the application of each respiratory support device. The application of HFNC and helmet CPAP at both 5 and 10 cm H 2 O of PEEP reduced minute ventilation (9.2 ± 3.2, 8.8 ± 2.3, and 9.3 ± 2.7 vs. 10.9 ± 3.3 L/min; p < 0.001) and ΔPes (–6.0 cm H 2 O [–7.8 to –4.0 cm H 2 O], –5.8 cm H 2 O [–7.2 to –4.5 cm H 2 O], and –5.9 cm H 2 O [–8.0 to –4.0 cm H 2 O] vs. –7.5 cm H 2 O [–10.8 to –6.5 cm H 2 O]; p < 0.001) while increasing Pa o 2 /F io 2 (188 ± 57, 208 ± 62, and 213 ± 69 vs. 129 ± 32; p < 0.001) with respect to COT; the application of 10 cm H 2 O of PEEP with helmet CPAP did not reduce inspiratory effort indices or increased oxygenation, but worsened mechanical power compared with HFNC and helmet CPAP with 5 cm H 2 O of PEEP. Conclusions: In patients with mild and moderate AHRF, HFNC and helmet CPAP ameliorated minute ventilation and respiratory rate, reduced inspiratory effort, and increased oxygenation compared with COT; the application of 10 cm H 2 O of PEEP during CPAP support worsened mechanical power.