Absolute Humidity 44 mg/L — FRCA Primary MCQ

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ModeratePhysics & Clinical MeasurementAbsolute Humidity 44 mg/LFRCA Primary

Regarding humidity in the breathing circuit the normal absolute humidity of inspired gas at the carina is approximately:

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Correct answer: C — 44 mg/L

At body temperature (37°C) and 100% relative humidity the absolute humidity is 44 mg/L of water vapour. This represents the maximum water content of gas at body temperature. Anaesthetic gases from the machine are dry and cold. Prolonged delivery of dry gas damages respiratory epithelium / increases mucus viscosity / and impairs mucociliary clearance.

Reference: Al-Shaikh Stacey 2019 Essentials of Anaesthetic Equipment