Humidification and heating of inhaled gas in patients with artificial airway. A narrative review

Abstract

Instrumentation of the airways in critical patients (endotracheal tube or tracheostomy cannula) prevents them from performing their function of humidify and heating the inhaled gas. In addition, the administration of cold and dry medical gases and the high flows that patients experience during invasive and non-invasive mechanical ventilation generate an even worse condition. For this reason, a device for gas conditioning is needed, even in short-term treatments, to avoid potential damage to the structure and function of the respiratory epithelium. In the field of intensive therapy, the use of heat and moisture exchangers is common for this purpose, as is the use of active humidification systems. Acquiring knowledge about technical specifications and the advantages and disadvantages of each device is needed for proper use since the conditioning of inspired gases is a key intervention in patients with artificial airway and has become routine care. Incorrect selection or inappropriate configuration of a device can have a negative impact on clinical outcomes. The members of the Capítulo de Kinesiología Intensivista of the Sociedad Argentina de Terapia Intensiva conducted a narrative review aiming to show the available evidence regarding conditioning of inhaled gas in patients with artificial airways, going into detail on concepts related to the working principles of each one.

Current Practice of High Flow through Nasal Cannula in Exacerbated COPD Patients

“…In healthy subjects, the upper respiratory tract humidifies the inspired room air to full saturation of water vapor (absolute humidity = 44 mg/L) and heats at 37 °C [ 8 ]. However, the administration of not conditioned medical gases, such as during COT or NIV, affects the ciliary motion, damages the respiratory tract epithelial cell and reduces the water content of the bronchial secretions [ 9 , 10 , 11 ].…”

Cold Bubble Humidification of Oxygen

“…Absolute humidity (expressed in g/m 3 ) is defined as the mass of water vapor present per unit volume of gas at any given temperature and pressure. 9 Relative humidity is a comparative measurement, describing the ratio between the mass of water vapor present in a given volume of air to the mass of water vapor required to completely saturate said volume of air, at a particular temperature. It is expressed in percentage (%).…”

An evaluation of temperature stability and resistance in neonatal ventilator circuits

“…Inadequate gas conditioning may lead to progressive airway dysfunction and systemic effects, depending on the degree of under-humidification and coolness, the exposure time, and the underlying disease [ 1 ]. Delivery of cooled (inspired temperatures less than 31.5°C) humidified inspired gas can negatively affect the isothermal boundary and contribute to airway obstruction, bronchospasm, disruption of the bronchial epithelium, hypothermia, and redirected caloric intake [ 2 , 3 ]. Inadequately humidified gases delivered to intubated preterm infants can impair surfactant activity, decrease functional and residual capacity, and significantly compromise pulmonary mechanics [ 4 ].…”