Which of the following statements is false of heat and moisture exchangers (HMEs)?

a. Moisture output falls at high volumes and rates of breathing.
b. High inspiratory flows and high FiO2 val-ues can decrease HME efficiency.
c. In-use HMEs have little effect on flow resistance to breathing.
d. HMEs reduce bacterial colonization of ventilator circuits.

ANS: C
As shown in Table 38-3, the moisture output of HMEs tends to fall at high volumes and rates of breathing. In addition, high inspiratory flows and high FiO2 levels can decrease HME efficiency. Flow resistance through the HME also is important. When an HME is dry, resistance across most devices is minimal. However, because of water absorption, HME flow resistance increases after several hours' use. For some patients, the increased resistance imposed by the HME may not be well tolerated, particularly if the underlying lung disease already causes increased work of breathing. Because HMEs eliminate the problem of breathing-circuit condensation, many consid-er these devices (especially hydrophobic filter HMEs) to be helpful in preventing nosocomial in-fections.