Performances of heated humidifiers in mechanical ventilation: A preliminary intra-breath analysis

A correct humidification of gases delivered to mechanically ventilated patients is essential to avoid some complications. Heated Humidifiers (HHs) are widely used in long lasting ventilation to treat gases delivered to patients. Their performances depend on some parameters, such as environmental conditions and ventilatory settings. The aim of this work is to experimentally assess the influence of minute volume (MV), respiratory frequency (f) and the ratio between duration of inspiration and expiration (I:E) on HHs performances in terms of relative humidity (RH) at the humidification chamber outlet. The main novelty of this work is the assessment of RH oscillations during artificial ventilation. Results show marked oscillations of RH during a single breath (ripple of 20% in the worst case); oscillations decrease if f and I:E increase, on the other hand they increase with MV. Since the variation of gas temperature during a respiratory act can be neglected, the RH oscillations are related to the vapour content in the delivered gases. These results further support the hypothesis which asserts that HHs performances could be improved by using a control strategy taking into account ventilatory settings.