Isoflurane supply issue

13 December 2018

BSAVA members will likely be aware of the reported short-fall in supply of isoflurane to the UK market, which has been suggested could continue until February/March 2019. The BSAVA is currently working in association with relevant organisations and government to ascertain if alternative supplies can be made available as quickly as possible.

The VMD have provided this update.

In the meantime, Ian Self, Clinical Associate Professor and European & RCVS Specialist in Veterinary Anaesthesia and Analgesia at the School of Veterinary Medicine and Surgery, University of Nottingham and incoming Chair of BSAVA Scientific Committee has provided the following advice to support BSAVA members who may need to consider alternative options. This is intended as general advice only and it will be for individual practitioners to assess suitability of use in each instance on a case-by-case basis taking into consideration the experience of the practitioner and patient suitability.

Alternative general anaesthesia options for consideration:

Use low flow anaesthesia
Providing you have a capnograph then you can reduce oxygen flows until just at the point where the capnograph doesn’t reach baseline ie it is at lowest flow possible. As a rule of thumb with non-rebreathing systems, flow rates should be turned down until the point where the patient would start rebreathing (seen on capnograph) and with some circle systems the flows should be turned down once the patient is ‘stable’, always ensuring the reservoir bag maintains a suitable residual volume.
Consider sevoflurane as an alternative (MAC 2.3). Note however that you need a specific vaporiser for this.
Use full mu opioid agonists (such as methadone, fentanyl or pethidine) in the pre-medication (if appropriate) as this allows a reduction in the required gaseous anaesthesia doses.
Consider closer monitoring to allow the delivered anaesthetic concentration to be turned down. With potent analgesia it is often possible to reduce the delivered isoflurane concentration to very low levels while maintaining an adequate plane of anaesthesia.
Use Total Intravenous Anaesthesia (TIVA) combinations
Following suitable premedication, induction and endotracheal intubation (to protect the airway and allow provision of oxygen via a suitable breathing system) it is acceptable to maintain anaesthesia with intravenous agents using infusions OR intermittent boluses.

Suitable single agents include propofol, alfaxalone, ketamine OR combinations of these with opioids/alpha-2 agonists/benzodiazepines. An intravenous cannula should be placed in all patients.

For short procedures, intermittent bolus maintenance is suitable using small incremental doses of the induction agent (approximately 1/4th of the induction dose) whenever the depth of anaesthesia appears inadequate, or approximately every 10 to 15 minutes. For longer procedures a constant rate infusion using a suitably calibrated syringe driver, or similar device, can be used. The patient should be carefully monitored as respiratory depression may occur during TIVA and intermittent positive pressure ventilation (IPPV) may be required. The duration and quality of recovery may be different following TIVA, but these effects are minimised by the administration of robust premedication.

Examples of suitable protocols include the following:

• Propofol: 0.1-0.4mg/kg/minute IV in dogs and cats (less evidence in cats).  In dogs, this has been combined with fentanyl at rates of 0.1 – 0.2µg/kg/minute IV, in which case the lower propofol dose should be used.

• Alfaxalone: 7-9 mg/kg/hour (0.1 – 0.15mg/kg/minute) IV in dogs and 7-11mg/kg/hour IV in cats.  In dogs, this has been combined with fentanyl at rates of 0.1 – 0.2µg/kg/minute IV, in which case the lower alfaxalone dose should be used.

• Ketamine: induce anaesthesia with 5 to 10mg/kg IV (usually combined with a benzodiazepine) in dogs and cats then maintain with intermittent boluses (around 2mg/kg IV) given every 10-20 minutes to effect. It may be necessary to augment the ketamine anaesthesia with suitable agents, such as medetomidine/dexmedetomidine or benzodiazepines given every 30 to 40 minutes to offset the poor muscle relaxation observed when using ketamine alone. The frequency of administration will depend on the agent used and the clinical signs observed.

Remember, all these rates are suggestions only and will be affected by the pre-medication used. In particular, the use of alpha-2 agonists such as medetomidine and dexmedetomidine will reduce the requirement for all subsequent agents.

Download Injectable Anaesthetics Chapter

To support all veterinary professionals working with small animals during the isoflurane shortage, the BSAVA is providing free access to the chapter on ‘Injectable anaesthetics’ from the BSAVA Manual of Canine and Feline Anaesthesia and Analgesia, 3rd edition.

Members and non-members can download the chapter from the BSAVA Library.