Heated Humidifier

Abstract

Humidification and warming of the inspired gases during mechanical ventilation require either a heated humidifier (HH) or a heat and moisture exchanger (HME) on the inspiratory limb of the respirator. HH is an active humidifier that adds water vapor and heat to the inspiratory air from temperature-regulated water reservoirs independently of the patient. “Active” HMEs combine an HME with an integrated HH for use at the patient connection port of the breathing circuit. The larger the area of contact between water and gas, the more opportunity there is for evaporation to occur. Cascade humidifiers, where the flow is passed beneath the surface of the water in a heated reservoir, and passover humidifiers, where the airflow is directed over a water surface, are the two main types of HHs. The humidification device must ensure physiologic conditions in the respiratory tract and avoid pulmonary water losses of greater than 7 mg/L due to ventilation with dry gases. There are several potential complications with the use of an HH, including electrical burns, burning of the patient’s airway, hypothermia, under-humidification and mucus plugging, etc. The device should have a temperature alarm and automatic shut down mechanisms to prevent any possible adverse effects to the patient and operator. There is insufficient knowledge among critical care physicians with regard to the optimal inspiratory gas temperature. A permanent default temperature setting of 37°C can simplify this and also increases patient safety. A visual inspection of the humidification device should be done with every patient ventilator system check and condensate removed from the patient circuit as necessary. When mounting a humidifier adjacent to a patient, one must always ensure that the humidifier is positioned lower than the patient. An HH is preferred over an HME in patients with acute respiratory distress syndrome (ARDS), during non-invasive ventilation (NIV), during weaning from mechanical ventilation, in very low birth weight infants and in those with contraindications for HME. There are no contraindications to the use of an HH; however, one should be aware of its potential complications.