Nasal Cannula, CPAP, and High-Flow Nasal Cannula: Effect of Flow on Temperature, Humidity, Pressure, and Resistance

Background: Delivery of warm, humidified, supplemental oxygen via high-flow nasal cannula has several potential benefits; however, the high-flow range may not maintain humidification and temperature and in some cases may cause excessive expiratory pressure loading. Objective: To compare the effect of flow on temperature, humidity, pressure, and resistance in nasal cannula (NC), continuous positive airway pressure (CPAP), and high-flow nasal cannula (HFNC) in a clinical setting. Methods: The three delivery systems were tested in the nursery using each instrument's recommended specifications and flow ranges (0–3 L/min and 0–8 L/min). Flow, pressure, temperature, and humidity were measured, and resistance was calculated. Results: For all devices at 0–3 L/min, there was a difference (p<0.01) in temperature (NC 35.9°C > CPAP 34.5°C > HFNC 34.0°C), humidity (HFNC 82% > CPAP 77% > NC 57%), pressure (HFNC 22 cmH2O > NC 4 cmH2O > CPAP 3 cmH2O), and resistance (HFNC 636 cmH2O/L/sec > NC 270 cmH2O/L/sec > CPAP 93 cmH2O/L/sec) as a function of flow. For HFNC and CPAP at 0–8 L/min, there was a difference (p<0.01) in temperature (CPAP 34.5°C > HFNC 34.0°C) in humidity (HFNC 83 % > CPAP 76 %), pressure (HFNC 56 cmH2O > CPAP 14 cmH2O) and resistance (HFNC 783 cmH2O/L/sec > CPAP 280 cmH2O/L/sec) as a function of flow. Conclusions: Gas delivered by HFNC was more humid than NC and CPAP. However, the higher pressure and resistance delivered by the HFNC system may have clinical relevance, such as increased work of breathing, and warrants further in vivo studies.