Mapleson D breathing circuits are not circle systems and do not preserve which of the following?

Mapleson D breathing circuits are not circle systems and do not preserve which of the following?

• A. Heat
• B. Moisture
• C. Both Heat and Moisture
• D. Nothing; they preserve both

Answer: (C)

Preservation of heat and humidity is what distinguishes circle systems from many Mapleson circuits. Circle systems recycle exhaled gas after humidification and warming, so the next breath starts with warm, moist gas. Mapleson D is a non-circle, semi-open setup where most of the exhaled gas is vented to the atmosphere and not recaptured for subsequent breaths. Because there’s little opportunity for the inspired gas to be warmed or humidified by the returning breath or a humidifier, heat and moisture are not preserved. To ensure humidified, warmed gas with this circuit, you’d need an external humidification/heat exchange method. That’s why both heat and moisture are not preserved in Mapleson D.

Preservation of heat and humidity is what distinguishes circle systems from many Mapleson circuits. Circle systems recycle exhaled gas after humidification and warming, so the next breath starts with warm, moist gas. Mapleson D is a non-circle, semi-open setup where most of the exhaled gas is vented to the atmosphere and not recaptured for subsequent breaths. Because there’s little opportunity for the inspired gas to be warmed or humidified by the returning breath or a humidifier, heat and moisture are not preserved. To ensure humidified, warmed gas with this circuit, you’d need an external humidification/heat exchange method. That’s why both heat and moisture are not preserved in Mapleson D.