Managing the isoflurane shortage
With isoflurane availability currently limited and the risk of low supplies how can we manage with less?
We have become extremely reliant on inhalant agents for maintenance of anaesthesia in recent years and the current limited supplies are a good incentive to introduce some new ideas to reduce the use of inhalants.
A sensible alternative to isoflurane is to use sevoflurane. It similar to isoflurane, but less potent and has a slightly faster onset and offset. Sevoflurane is more expensive, and requires a dedicated vaporiser; supply of these is limited. Methods to reduce inhalant agent use are just as relevant to sevoflurane as isoflurane.
Options to reduce inhalational agent use:
- Check anaesthetic machines, vaporisers and breathing circuits are serviced and maintained properly.
- Use appropriate gas flows (e.g. oxygen) for the patient and the breathing system to ensure the lowest quantity of isoflurane is used. Endeavour to use circle systems wherever possible. Once anaesthesia is stable the oxygen flow needs only to supply what the animal is actually metabolising – about 10-20ml/kg/min (Minimum flow 0.5-1.0L/min dependent on your equipment). Higher flows are needed at the start, and when a change in anaesthetic depth is required.
- Consider using a circle breathing system designed for smaller patients. This has low resistance valves and smaller volume tubing/Y-connectors and is suitable for patients less than 7-10kg. This will allow lower gas flows to be used as well as providing warming and humidification.
- Consider using a Mini-Lack breathing system rather than a T-Piece for lower gas flows.
- Ensure the patient is premedicated at an appropriate time before induction of anaesthesia, aiming to maximise the chosen drug effects during the procedure. Remember to take into account both the onset time and duration of action of the chosen drugs.
- Review your analgesic and premedication protocols. Could you improve sedation and analgesia and provide a greater sparing effect on isoflurane? Considerations here include:
- Using an alpha-2 agonist such as medetomidine or dexmedetomidine as part of premedication.
- Selecting a pure mu opioid agonist, e.g. methadone as part of premedication and intra-operatively if required.
- Using local anaesthetic blocks to provide excellent analgesia, improve post-operative patient comfort and minimise inhalational agent requirements.
- For short routine procedures (e.g. neutering) consider triple or quad combinations given IV or IM: ketamine, medetomidine (or dexmedetomidine) and an opioid. Include a benzodiazepine to reduce the alpha-2 dose. Consider tracheal intubation to secure and always supply oxygen.
- Consider the use of partial intravenous anaesthesia (PIVA) e.g. ketamine, or total intravenous anaesthesia (TIVA) if suitable equipment is available (e.g. syringe driver or infusion pump). Always intubate the trachea and supply oxygen.
Please visit the Veterinary Medicines Directorate (VMD) website for further information and regular updates https://www.gov.uk/government/organisations/veterinary-medicines-directorate. Veterinary surgeons may also obtain isoflurane licenced for human use in the UK under the cascade or may apply for an import licence from the VMD to import isoflurane from another country. It is possible that a special licence may be granted for the production of isoflurane in the UK in order to meet the shortfall.