The Meyer-Overton hypothesis relates anaesthetic potency to which physicochemical property, and which inhalational agent is the principal exception to this rule?

• A Water solubility; halothane
• B Blood:gas partition coefficient; desflurane
• C Molecular weight; xenon
• D Lipid solubility (oil:gas partition coefficient); nitrous oxide (cutoff phenomenon) ✓

Explanation

The Meyer-Overton hypothesis states that anaesthetic potency correlates with lipid solubility measured by the oil:gas partition coefficient — the more lipid soluble, the lower the MAC. N2O and xenon partially defy this through the 'cutoff phenomenon', where compounds beyond a certain chain length lose potency despite high lipid solubility. Nitrous oxide has a relatively low oil:gas coefficient but still provides analgesia and anaesthetic effects. The blood:gas partition coefficient determines speed of onset, not potency.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.