Water content of delivered gases during Helmet Continuous Positive Airway Pressure in healthy subjects.

INTRODUCTION

During Continuous Positive Pressure Ventilation delivered through helmet, the patient inhales high flows of gas without adequate conditioning. However, the need to humidify the inspired gas during Helmet-CPAP, has not been sufficiently explored.

METHODS

Experimental design study. Six healthy individuals underwent High Flow Helmet CPAP with different gas flows (60 and 80 L/min) and FiO2 (0.35, 0.5, 0.7 and 1) generated by a Venturi system, with and without active humidification. The active humidifier setting was 26 ° at the humidification chamber and 28 ° at the helmet gas inlet. At each setting, measurements about temperature and relative humidity inside helmet were taken. Comfort level at each setting was evaluated using a visual analog scale rated from 0 to 10.

RESULTS

Without heated humidification, the mean value of absolute humidity in the eight combinations investigated was 5.9±2.1 mg H2O/L, with a mean  temperature of 25.8±0.9°. With heated  humidification mean absolute humidity was 15.0±3.5 mg H2O/L with mean temperature of 29.0±0.1°. The median comfort scale value was 6 (IQR: 5.25-6.75) during the phase without humidification vs 8 (7.25-8.0 - P<0.01) when active humidification was applied.

CONCLUSIONS

In healthy subjects undergoing High Flow Helmet CPAP, heated humidifiers with heated wires tubes are necessary to avoid the under-humidification inside the helmet. To obtain patient's comfort and airways mucosal humidification during continuous Helmet CPAP, the most desirable conditions are reached by heated humidifiers with a humidifying chamber temperature settled between 26-28°C.