At each flow setting, F IO 2 was titrated to maintain SpO 2 of 90–97%.Īn adult manikin (Laerdal adult airway management trainer, Stavanger, Norway) with size-appropriate airway anatomy was attached to one chamber of a model lung (TTL, Michigan Instruments, Grand Rapids, USA), while the other chamber was connected to a critical care ventilator (Drager Evita XL, Drager, Lubeck, Germany) to simulate respiratory drive. Then the HFNC flow was progressively increased by 10 L/min every 5–10 min up to 60 L/min or the highest flow the patient could tolerate. Once breathing parameters were acquired, patients were returned to HFNC with the previous flow setting if it was lower than PTIF or with flow set at the PTIF level. A minimum of five breathing cycles were recorded and average values of PTIF, Ti, RR, and Vt were calculated. Breathing profiles were recorded when patient breathing appeared to be stable. Patients were instructed to breathe normally with the mask for at least 2 min. This setup allowed patients to breathe fresh gas with a constant F IO 2 during measurement to truly reflect their breathing profiles at a constant F IO 2.
#JIM FINK CHIEF INVESTMENT STRATEGIST REVIEWS FULL#
Blender gas flow was adjusted to maintain reservoir bag inflation of 1/2 to 3/4 full while patients were breathing, with F IO 2 titrated to maintain SpO 2 of 90–97%. The Y-piece was attached to two one-way valves, with one that allowed exhalation and the other enabled inhalation from a reservoir bag, which was connected to a back pressure compensated flowmeter from an oxygen-air blender (Additional file 1: Fig. The flow sensor was connected to a monitor (NICO2, Respironics, Murrysville, USA) to measure patient PTIF, Ti, RR, and Vt. After giving verbal approval, patients were disconnected from HFNC and placed on a properly fitting full-face mask (Airlife mask, Carefusion, San Diego, USA), which was connected to a flow sensor and a Y-piece. Finally, we performed an in vitro study that used the breathing patterns acquired from the clinical study to analyze tracheal F IO 2 and airway pressures changes that are associated with different HFNC flow settings.Įligible patients were approached by study investigators to thoroughly explain the study, using a written information sheet. We hypothesized that patient oxygenation would improve as the ratio of HFNC gas flow to PTIF increased. We also assessed patient clinical response and changes in comfort with different HFNC flows that matched or exceeded the measured PTIF. Therefore, in this clinical study, we studied breathing patterns of patients with AHRF treated by HFNC and measured their PTIF. Moreover, breathing patterns, including PTIF, tidal volume (Vt), inspiratory time (Ti), and respiratory rate (RR), of patients with AHRF who are treated by HFNC have not been well characterized and there is little guidance on optimal HFNC flow settings based on patient’s breathing patterns. HFNC flows used in many studies and real-life clinical practice also vary widely, from 20 to 60 L/min. The PTIF in adults varies greatly by disease and may be high in the presence of respiratory distress. In vitro studies have reported that the measured fraction of inspired oxygen (F IO 2) at the nose level is lower than the set F IO 2 when HFNC flow is set lower than PTIF.
When the HFNC flow is set to match or exceed patient peak tidal inspiratory flow (PTIF), positive end-expiratory pressure (PEEP) begins to be generated, and a linear increase in PEEP occurs with an incremental increase in gas flow while breathing with the mouth closed. This has led many clinicians to arbitrarily initiate HFNC at the higher flow settings, such as 60 L/min for adults however, higher flows may not be well tolerated or associated with optimal oxygenation in all patients. The higher the flow, the greater is the improvement in inspiratory effort and dynamic lung compliance. įlow settings play a critical role when using HFNC, as the physiological effects of HFNC are flow-dependent. Additionally, a recent clinical practice guideline provides a strong recommendation for use of HFNC in patients with acute hypoxemic respiratory failure (AHRF). Numerous randomized controlled trials and meta-analyses have shown that HFNC improves oxygenation and reduces the need for intubation in hypoxemic patients compared with conventional oxygen therapy. During high-flow nasal cannula (HFNC) therapy, oxygenation is improved by delivering supplemental oxygen at a flow that exceeds the patient’s peak inspiratory flow.
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