Background The nasal cannula is considered a trusted and effective means of administering low-flow oxygen and is widely used for neonates and infants requiring oxygen therapy, despite an understanding that oxygen concentrations delivered to patients are variable. Methods In the present study, realistic nasal airway replicas derived from medical scans of children less than 3 months old were used to measure the fraction of oxygen inhaled (FiO2) through nasal cannulas during low-flow oxygen delivery. Parameters influencing variability in FiO2 were evaluated, as was the hypothesis that measured FiO2 values could be predicted using a simple, flow-weighted calculation that assumes ideal mixing of oxygen with entrained room air. Tidal breathing through neonatal and infant nasal airway replicas was controlled using a lung simulator. Parameters for nasal cannula oxygen flow rate, nasal airway geometry, tidal volume, respiratory rate, inhalation/exhalation, or I:E ratio (ti/te), breath waveform, and cannula prong insertion position were varied to determine their effect on measured FiO2. In total, FiO2 was measured for 384 different parameter combinations, with each combination repeated in triplicate. Analysis of variance (ANOVA) was used to assess the influence of parameters on measured FiO2. Results Measured FiO2 was not appreciably affected by the breath waveform shape, the replica geometry, or the cannula position but was significantly influenced by the tidal volume, the inhalation time, and the nasal cannula flow rate. Conclusions The flow-weighted calculation overpredicted FiO2 for measured values above 60%, but an empirical correction to the calculation provided good agreement with measured FiO2 across the full range of experimental data.

Portable oxygen concentrators (POCs) are widely used to administer long-term oxygen therapy (LTOT) and employ pulsed delivery modes to conserve oxygen. Efficient pulsed delivery requires that POCs are triggered by patient inhalation. Triggering is known to fail for some patients during periods of quite breathing, as occurs during sleep. The present article describes a new nasal interface designed to improve triggering of pulsed oxygen delivery from portable oxygen concentrators (POCs). In vitro experiments incorporating realistic nasal airway replicas and simulated breathing were conducted. The pressure monitored via oxygen supply tubing (the signal pressure) was measured over a range of constant inhalation flow rates with the nasal interface inserted into the nares of the nasal airway replicas, and compared with signal pressures measured for standard and flared nasal cannulas. Triggering efficiency and the fraction of inhaled oxygen (FiO2) were then evaluated for the nasal interface and cannulas used with a commercial POC during simulated tidal breathing through the replicas. Higher signal pressures were achieved for the nasal interface than for nasal cannulas at all flow rates studied. The nasal interface triggered pulsed delivery from the POC in cases where nasal cannulas failed to trigger. FiO2 was significantly higher for successful triggering cases than for failed triggering cases. The nasal interface improved triggering of pulsed oxygen delivery from a POC and presents a simple solution that could be used with commercially-available POCs to reliably supply oxygen during periods of quiet breathing.

Long-term oxygen therapy prolongs life in patients with COPD and severe daytime hypoxemia. Portable delivery systems, including portable oxygen concentrators (POCs), frequently incorporate delivery of short bursts, or pulses, of oxygen triggered by patient inspiration. In order to trigger a pulse of oxygen from a POC, a patient must generate a sufficiently high signal pressure to exceed the trigger threshold of the device. For standard nasal cannulas, signal pressure varies with inspiratory flow rate, cannula prong geometry, and patient nasal airway geometry. Triggering pulse delivery from POCs is frequently compromised when inspiratory flow rates are low, as occurs during sleep. The present work presents a new pillows-type nasal interface designed to improve inspiratory triggering when used with POCs. Methods: Realistic adult nasal airway replicas described previously in the study of continuous and pulsed oxygen delivery (Chen et al., 2017) were employed. Replicas previously identified as generating high (Subject 2) and low (Subjects 6 and 9) signal pressures were selected from a larger set consisting of 15 replicas. Signal pressures monitored through a single-lumen straight nasal cannula, a flared nasal cannula, and the new nasal interface were measured at inspiratory flow rates ranging from 10 to 40 L/min. The nasal interface includes adjustable channels for entrainment of room air, here referred to as settings A and B. Subsequent in vitro experiments were conducted during simulated breathing to assess oxygen delivered from a POC (SimplyGo Mini; Philips Respironics) using the new nasal interface versus straight and flared nasal cannulas. In vitro methods were consistent with those previously reported by Chen et al. (2019). Results: The new nasal interface produced higher signal pressures compared with the straight and flared cannulas. In addition, variability in signal pressure between replicas was greatly reduced when using the new nasal interface. For example, measured signal pressures for each replica at an inspiratory flow rate of 20 L/min are shown in Table 1. In vitro experiments demonstrated higher fractions of inhaled oxygen for the new nasal interface than for the straight or flared nasal cannula in circumstances where triggering was ineffective for the two nasal cannula types. Conclusion: The new nasal interface provided higher and more consistent signal pressures compared to the straight or flared nasal cannula across the airway replicas and flow rates tested. This translated into improved in vitro oxygen delivery in circumstances where triggering was ineffective for the straight and flared nasal cannula.

No abstract

No abstract