How often do heat moisture exchangers (placed at the circuit wye adapter) for ventilators need to be replaced?

Passive systems using Heat and Moisture Exchangers (HME) trap moisture and prevent it from being lost from the patient.

• Efficacy of these devices drop over time, causing increased resistance. Manufacturers may suggest a change every 24 hours, but studies have shown that an unsoiled device in some circumstances be used for several days or up to 1 week (Ricard et al, AJRCCM 2000; Thomacot et al, CCM, 2002; AARC. Resp Care. 2012).
• Signs of an increase in resistance include an increase in PIP but no change in Plateau pressure or a prolonged expiratory flow time.  
• The most common cause of HME partial occlusion or rise in resistance is from pulmonary edema fluid or blood.  Mucus generally clumps in a dependent portion of the device without increasing resistance appreciably. (Davis et al Crit Care Med. 2000)