Humidification during Invasive and Non-Invasive Ventilation: A Starting Tool Kit for Correct Setting

Abstract

The humidification process of medical gases plays a crucial role in both invasive and non-invasive ventilation, aiming to mitigate the complications arising from bronchial dryness. While passive humidification systems (HME) and active humidification systems are prevalent in routine clinical practice, there is a pressing need for further evaluation of their significance. Additionally, there is often an incomplete understanding of the operational mechanisms of these devices. The current review explores the historical evolution of gas conditioning in clinical practice, from early prototypes to contemporary active and passive humidification systems. It also discusses the physiological principles underlying humidity regulation and provides practical guidance for optimizing humidification parameters in both invasive and non-invasive ventilation modalities. The aim of this review is to elucidate the intricate interplay between temperature, humidity, and patient comfort, emphasizing the importance of individualized approaches to gas conditioning.

Keywords: HME; ICU; active humidification; heated humidifier; pass-over humidifier; passive humidification.

Figure 1

The direct impact of temperature on the air’s ability to carry water vapor. For details, see text below. AH, absolute humidity; RH, relative humidity; T, temperature.

Figure 2

Hydrophobic HME (Panel (A)) and hygroscopic HME (Panel (B)). HME, heat moisture exchanger.

Figure 3

The passover membrane humidifier is integrated into an older ventilatory circuit with condensation collected on both ventilation limbs. This configuration allows for a humidifier setting at 35 °C with zero gradient.

Figure 4

The passover free water humidifier is integrated into a ventilatory circuit without condensation collection. This is possible thank to the high-performance heated inspiratory and expiratory tubes. In this configuration, a humidifier setting of 37 °C with a negative gradient is required.

Figure 5

Absolute humidity (mg/L), Temperature (°C) and relative humidity (%) in ventilatory circuit. Heated tubes reduce relative humidity while maintaining the absolute humidity. This allows for an additional increase in humidity from the natural patient airways.

Figure 6

Operative algorithm to set up a passover humidifier.