In the alveolar ventilation context, what does HME refer to in the dead-space term?

• A. Heat and Moisture Exchange
• B. Pulse Oximeter
• C. Capnograph
• D. Ventilator

Answer: (A)

In the dead-space term, HME stands for Heat and Moisture Exchange. It’s a device placed in the ventilator circuit that humidifies inspired gas by capturing heat and moisture from exhaled air and returning it on the next breath. This adds a small volume to the airway, which becomes part of the mechanical dead space—gas that is inhaled but doesn’t participate in gas exchange. So for a given tidal volume and respiratory rate, alveolar (ventilated) gas exchange can be reduced unless you compensate by increasing ventilation. The other options aren’t correct here: a pulse oximeter measures oxygen saturation, a capnograph monitors expired CO2, and a ventilator is the machine delivering breaths.