Which inhalant is the most potent and slowest to recover, with up to 50% retention in body tissues?

• A. Nitrous oxide
• B. Methoxyflurane
• C. Sevoflurane
• D. Isoflurane

Answer: (A)

The main idea is that how potent an inhalant is and how slowly you recover from it hinges on how soluble it is in blood and, especially, in body tissues. High solubility means the agent loads into blood and tissues more deeply, so it takes longer to reach the brain and to clear out after anesthesia. Methoxyflurane fits this pattern: it has very high lipid and blood solubility, so it is a potent anesthetic (low MAC) and its recovery is slow because it stays in tissues for a long time. It can accumulate in body fat and other tissues, with substantial retention—often described as up to about half of the absorbed dose stored in tissues during and after anesthesia. By contrast, nitrous oxide has very low blood solubility, so it equilibrates quickly and clears rapidly, leading to fast recovery and minimal tissue storage. Sevoflurane and isoflurane are less soluble than methoxyflurane, so they’re not as slow to recover and don’t accumulate to the same extent. Hence, the description of being the most potent, slowest to recover, with significant tissue retention points to methoxyflurane.