Effects of Imposed Resistance on Tidal Volume With 5 Neonatal Nasal Continuous Positive Airway Pressure Systems

BACKGROUND: Neonates with respiratory distress syndrome are often treated with nasal continuous positive airway pressure (CPAP). Nasal CPAP methods include electronic feedback control, underwater seal, flow opposition, and flow opposition with fluidic flow reversal on expiration. Few studies have compared those modes, and the results have been contradictory.

METHODS: We compared the effect of resistive load on simulated tidal volume (V_T) with 5 neonatal nasal CPAP systems: Fisher and Paykel nasal CPAP tubing with Maquet Servo-i ventilator in NIV CPAP mode; Cardinal Health AirLife nasal CPAP system; Fisher and Paykel nasal CPAP tubing with water-seal pressure generator; AirLife infant nasal CPAP generator kit; and Hamilton Medical Arabella fluidic nasal CPAP generator. The lung simulator settings were: compliance 0.5 mL/cm H₂O, resistance 125 H₂O/L/s, sinusoidal patient-effort range 6.5–26 cm H₂O, rise 25%, hold 0%, release 25%, respiratory rate 65 breaths/min. We compared the mean values from 10 breaths.

RESULTS: The mean inspiratory pressure drop and V_T difference (compared to the simulator alone, unloaded) increased with V_T, respectively, from 0.32 cm H₂O to 1.73 cm H₂O, and from −0.04 mL to −0.40 mL. Flow opposition had the smallest pressure drop (from 0.10 cm H₂O to 0.64 cm H₂O, P < .001). At V_T of ≤ 6 mL, the bubble nasal CPAP's pressure drop was largest (P < .001), whereas at V_T of ≥ 9 mL the electronic nasal CPAP's pressure drop was largest (P < .001). All systems except the ventilator did not have an average end-expiratory pressure of the targeted 5 cm H₂O.

CONCLUSIONS: The differences in these nasal CPAP systems correlate with the differences in unassisted V_T due to loading effects. The ventilator imposed the least load, and the AirLife nasal CPAP system imposed the most.