Isoflurane out of stock time to practise low flow anaesthesia

Updated: Dec 14, 2018

We have pretty much all heard by now that the VMD has been informed of a short-term supply problem with isoflurane; whilst this is sending many of us into panic, I like to look on the bright side and think how this potential catastrophe can enhance our anaesthesia knowledge.


I need to ask myself “how can I reduce my isoflurane usage without putting my patients at risk”


  • Some of us may have the luxury of being able to use sevoflurane instead and I am sure this short-term supply issue will be seen as a great opportunity to introduce sevoflurane into many new practices.


  • We may be able to look into the option of administering total intravenous anaesthesia (TIVA) which has been discussed by our good friends at Jurox in their article "TIVA or not to TIVA" . The BSAVA have also given free access to the chapter on TIVAs in their manual of Canine and Feline Anaesthesia and Analgesia 3rd edition. This will be available until the end of March 2019 and can be accessed here.


  • We can all work on improving our multi-modal analgesia techniques to help us reduce our vaporiser settings. The addition of alpha2s where appropriate and local analgesia techniques are an extremely economical and effective way of achieving gold standard analgesia whilst having a positive impact on our vaporiser settings. Zero pain philosophy have published a great blog discussing how analgesia can impact your volatile agent setting, which you can access here


  • We should remind ourselves what the minimum alveolar concentration (MAC) of isoflurane is and check that we aren't inclined to pop our patients on 2% and leave them there. MAC is the number on a vaporiser dial that keeps 50% of patients asleep to a painful stimuli and is 1.2-1.3% in dogs and 1.6% in cats


  • Finally we e can look into the benefits and techniques of using low flow anaesthesia.


  • What is low flow anaesthesia?

Low flow anaesthesia is a technique which uses a fresh gas flow lower than the patients minute volume


  • What are the benefits of low flow anaesthesia?

  1. Anaesthesia with low fresh gas flow helps maintain body temperature and reduce fluid loss

  2. Results in a reduction of anaesthetic gas consumption which has a significant cost saving

  3. Reduction in environmental contamination reducing exposure to operating room personnel

  • How do I perform low flow anaesthesia

Initially once the patient is induced they should be attached to the breathing system

When using a non-rebreathing circuit such as a t-piece or a Bain you should use a flow rate that meets the patient’s minute volume. Once the patient has reach a stable plane of anaesthesia the fresh gas flow (FGF) can start to be reduced until you can see re-breathing on the capnograph trace. Rebreathing indicates that the FGF is insufficient to efficiently remove the patients exhaled carbon dioxide and the FGF should be adjusted to ensure carbon dioxide removal is achieved without being excessive.



Capnograph trace showing re-breathing. The base line does not return to zero either due to a low FGF or exhausted soda lime.

Re-breathing systems such as circle systems are perfect for achieving low flow anaesthesia and low resistance tubing can enable us to use them safely in smaller patients. When using a circle circuit, you should start at 3l/minute for the first 5-10 minutes to ensure adequate oxygenation, and faster anaesthetic uptake. With a circle system, the soda lime is responsible for removing the carbon dioxide so fresh gas can be reduced between 0.5-1litre/minute always ensuring that the reservoir bag is still filling.


TOP TIP 1: It may help to turn your scavenging down to prevent it sucking out the gas from the bag.

TOP TIP 2: When using low flow anaesthesia, you must remember to increase the flow rate if you require a rapid change in anaesthetic delivery.


What monitoring equipment will I need?

For low flow anaesthesia to be performed safely the patient should have oxygen saturation monitored (pulse oximetry) and end tidal and inspired carbon dioxide monitored (capnography)


If you would like any more help on achieving low flow anaesthesia, please feel free to contact us


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