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

Abstract

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.

High-Flow and Low-Flow Oxygen Delivery by Nasal Cannula Evaluated in Infant and Adult Airway Replicas

“…Therefore, a new empirical correlation was established that yielded good agreement with measured F DO 2 across the full range of experimental data. 30 In the present work, we aimed to unify our findings with previous work conducted on adult 22 and infant 30 airway replicas by extending the range of oxygen flow considered for both age groups. We hypothesize that a single correlation can be developed to accurately predict variation in F DO 2 with breathing pattern in both adult and infant airway replicas for low-and high-flow regimens.…”

“…F DO 2 , measured at the trachea after mixing supplied oxygen with entrained room air, was found to be influenced mainly by the tidal volume (V T ), the inspiratory time (T I ), and the flow of supplied oxygen. 30 A predictive equation previously validated against in vitro experiments conducted by using adult airway replicas 22 was found to overpredict measured F DO 2 in the infant airway replicas at high F DO 2 (>0.60). Therefore, a new empirical correlation was established that yielded good agreement with measured F DO 2 across the full range of experimental data.…”

“…Replicas were constructed by using photopolymers and included the face, nasal vestibule and valve, the turbinate and nasopharynx, and the trachea. 42 These replicas were used by Sabz et al 30 to investigate F DO 2 delivered to young children via nasal cannula. Because it was previously demonstrated that the influence of replica geometry on F DO 2 was not statistically…”

“…[21][22][23][24][25] Variability in F DO 2 is not limited to adults because studies in neonates, infants, and children have illustrated the same trends. [26][27][28][29][30] Fluctuations in F DO 2 during nasal cannula oxygen administration are caused mainly by variations in breathing pattern, which alter the extent of oxygen mixing with entrained room air. Vulnerable patients may be adversely affected by a lack of certainty concerning F DO 2 because either insufficient or excessive F DO 2 can lead to harmful effects.…”

“…[21][22][23][38][39][40] Based on airway geometries segmented from medical images, these airway replicas are more closely representative of human upper airways than are highly simplified geometries previously used for evaluating inhaled concentrations of medical gases. 41 Most recently, Sabz et al 30 conducted an in vitro investigation to evaluate variation in F DO 2 that resulted from lowflow oxygen delivery through nasal cannulas to realistic nasal airway replicas derived from computed tomographies of infants < 3 months old. Tidal breathing through the airway replicas was controlled by using a lung simulator.…”