Breath-dependent pressure fluctuations in various constant- and variable-flow neonatal CPAP devices.

Objective: In continuous positive airway pressure (CPAP) devices, pressure can be generated by two different mechanisms: either via an expiratory valve or by one or more jets. Valved CPAP devices are referred to as constant-flow devices, and jet devices are called variable-flow devices. Constant-flow CPAP devices are said to reduce the imposed work of breathing due to lower breath-dependent pressure fluctuations. The present study investigates the performance of various constant- and variable-flow CPAP devices in relation to breath-dependent pressure fluctuations.

Design: Experimental study comparing the pressure fluctuations incurred by seven neonatal CPAP devices attached to an active neonatal lung model.

Methodology: Spontaneous breathing was simulated using a tidal volume of 6 ml at pressure levels of 5, 7, and 9 mbar. The main outcomes were respiratory pressure fluctuations, tidal volume, and end-expiratory pressure.

Results: All CPAP devices tested showed respiratory pressure fluctuations, varying from 0.631 to 3.466 mbar. The generated tidal volume correlated significantly with the pressure fluctuations (r = -0.947; p = 0.001) and varied between 5.550 and 6.316 ml. CPAP devices with jets showed no advantage over CPAP devices with expiratory valves. End-expiratory pressure in the nose deviated from the set pressure between -1.305 and 0.644 mbar and varied depending on whether the pressure was measured in the device or in the tube extending to the nose.

Conclusion: During standard spontaneous breathing, breath-dependent pressure fluctuations in constant- and variable-flow devices are comparable. Pressure measurements taken in the tubing system can lead to a considerable deviation of the applied pressure.