Hypopharyngeal oxygen concentration and pressures delivered by low flow nasal cannula in preterm infants: Relationship with flow, gas mixture, and infant's weight.

Abstract

Low flow nasal cannula (LFNC) are frequently used in preterm infants. However, the delivered inspired oxygen concentration and airway pressures are not well established. To determine the fraction of inspired oxygen (FiO2 ) and hypopharyngeal pressures generated by LFNC at different gas flows, gas mixture concentrations and infant's weight. Serial samples of hypopharyngeal gas were obtained in 33 very low birth weight infants who were receiving oxygen with LFNC. Measurements were obtained with different gas flows and oxygen concentrations. FiO2 was measured using an electrochemical cell analyzer and hypopharyngeal pressures with a pressure transducer. 33 infants with a mean BW of 910 ± 284 g and 27 ± 1.7 weeks gestational age were studied at 36 ± 22 days after birth. FiO2 increased proportionally to gas flow, but with large variability: median (range) FiO 2 were 0.33 (0.23-0.54), 0.44 (0.29-0.67), 0.57 (0.33-0.81), and 0.69 (0.51-0.92) at 0.1, 0.3, 0.5, and 1 L/minute, respectively. Significantly higher mean FiO 2 were observed despite low flows in infants ≤ 1000 g compared to those > 1000 g (0.5 ± 0.1 vs 0.4 ± 0.07 at 0.3 L/minute; 0.66 ± 0.09 vs 0.5 ± 0.08 with 0.5 L/minute, respectively, P < .05). Hypopharyngeal pressures increased proportionally to gas flow with high variability: mean ± standard deviation pressures were 1.5 ± 0.8; 2.8 ± 1.2; 4.6 ± 1.3; 6.1 ± 1.6 cm H 2 O at 0.5, 1, 2, and 3 L/minute of gas flow. Peak pressures > 15 cm H 2 O were frequently observed with gas flows ≥ 2 L/min. Large variability in FiO2 and hypopharyngeal pressures were observed with oxygen administration through LFNC. Very high FiO 2 were observed despite low flows in infants < 1000 g. Excessive peak pressures can be generated with flows ≥ 2 L/minute especially among infants < 1000 g.