A replacement for methoxyflurane (Metofane) in open-circuit anaesthesia

Area of Science:

• Veterinary Anesthesiology
• Laboratory Animal Science

Background:

• Methoxyflurane was a standard open-circuit anesthetic for small animals.
• Discontinuation of methoxyflurane production created a need for alternatives.
• Its low vapor pressure and high blood solubility facilitated simple delivery systems.

Purpose of the Study:

• To adapt isoflurane for open-circuit drop-chamber/nose-cone anesthesia in small animals.
• To establish an effective and humane anesthetic protocol as a methoxyflurane substitute.

Main Methods:

• Isoflurane was dissolved in propylene glycol to control vapor concentration.
• A 20% isoflurane solution was used in a drop-chamber setup for induction and maintenance.
• Anesthesia efficacy and recovery were assessed in adult and pregnant mice undergoing surgical procedures.

Main Results:

• A 20% isoflurane in propylene glycol solution induced anesthesia in mice within 2 minutes.
• Surgical plane anesthesia was maintained for 10-12 minutes with rapid recovery (within 1 minute).
• Procedures on pregnant mice, including laparotomy and intrauterine injection, were successfully completed with no adverse effects on dams or litters.

Conclusions:

• Isoflurane in propylene glycol provides a simple, effective, and humane alternative to methoxyflurane for small animal anesthesia.
• This method is suitable for routine procedures and complex surgeries in research settings.
• The rapid induction and recovery minimize animal distress and support ethical research practices.