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 < or = 6 mL, the bubble nasal CPAP's pressure drop was largest (P < .001), whereas at V(T) of > or = 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.