Humidification in Intensive Care Medicine: General Approach to Selected Humidification Devices and Complications of Mechanical Ventilation

When the tracheal mucosa is bypassed via endotracheal tube (ETT) intubation or from a surgically placed tracheostomy, humidification is essential to preserve tracheobronchial mucosal integrity [1]. Without humidification, the tracheal mucosa will lose ciliary function, develop inspissated secretions, and the underlying connective tissue will undergo structural changes [2–5]. Williams et al. performed a meta-analysis evaluating the relationship between the humidity and temperature of inspired gas and airway mucosal function [6]. They developed a model suggesting above or below optimal temperature, and humidity conditions can lead to impaired airway mucosal dysfunction, or, vice versa, that adequate mucociliary function is an indicator of ideal humidification. Oostdam et al. showed animals that inspired dried air demonstrated a significant reduction of extravascular water of the loose connective tissue of the airways and an increase in airways resistance to histamine [2]. ETT occlusion secondary to thickened or dried secretions is also strongly linked to suboptimal humidification [5, 7]. The most common way to avoid these and other potential complications (Box 1) is accomplished by applying humidification from non-­heated-wire humidifiers, heated-wire humidifiers, or a heat and moisture exchanger (HME) [4, 8]. The goal of each of these humidification devices is to provide tracheal humidification consisting of heat and moisture to the inspired gas with a minimum of 30 mgH2O/l or 100% relative humidity with a delivered gas at 30°C [4, 5].