Inhaled Nitric Oxide: In Vitro Analysis of Continuous Flow Noninvasive Delivery via Nasal Cannula

Variability in low-flow oxygen delivery by nasal cannula evaluated in neonatal and infant airway replicas

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 (t_i/t_e), 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.

In Vitro Evaluation of a Nasal Interface Used to Improve Delivery from a Portable Oxygen Concentrator

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.