Overview of inhaled analgesics

The inhaled anaesthetics methoxyflurane and nitrous oxide are used to provide analgesia for acute pain presentations and to facilitate painful procedures. The relative advantages and disadvantages of methoxyflurane and nitrous oxide may influence drug choice.

• Methoxyflurane is available in a single-use, handheld delivery device.
• Methoxyflurane is self-administered, which requires the patient to be conscious and cooperative. Nitrous oxide administration can be controlled by the patient or a healthcare practitioner.
• Nitrous oxide is more easily titrated because the amount delivered (ie the relative concentrations of nitrous oxide and oxygen) can be adjusted according to patient response.
• Once administration is stopped, the effects of nitrous oxide wear off more rapidly than the effects of methoxyflurane.
• Nitrous oxide must not be used in patients with a condition in which air is trapped in a body cavity (eg pneumothorax, bowel obstruction) because of its potential to increase volume and pressure within the space.