On a Monday morning, the first patient receives desflurane through an anaesthesia machine whose soda lime canister was left connected with continuous fresh gas flow over the weekend, leaving the absorbent completely desiccated. Midway through the case the arterial sample shows a carboxyhaemoglobin of 18%. The toxic compound generated by the interaction of desflurane with desiccated absorbent is:

• A Compound A
• B Carbon monoxide ✓
• C Formaldehyde
• D Hydrogen fluoride

Explanation

Desiccated strong base absorbents, classically Baralyme and dry soda lime, cleave the difluoromethoxy group of desflurane and isoflurane to liberate carbon monoxide, the so-called Monday morning hazard. Carboxyhaemoglobin is dangerous precisely because pulse oximetry cannot distinguish it from oxyhaemoglobin and reads falsely reassuring values. Compound A arises from sevoflurane with wet absorbent at low flows, an entirely separate reaction requiring moist, warm absorbent.

Reference: Miller's Anesthesia, 9th ed.

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Written and medically reviewed by the StethoPrep medical team.