RE: ADE circuit

James Colver Cert. Ed, RVN — Tue, 05 Apr 2016 09:18:13 GMT

faq on ADE website -

Q. Induction seems to be slower with the ADE in the semi-closed mode than the T-piece and/or

Q. I have to use high flows to get the patient anaesthetized.

A. Yes, both observations are true. The ADE requires a different approach compared to the T-piece and Bain where the reservoir is on the expiratory . Firstly, with the reservoir bag on the inspiratory limb the ADE system must be primed with vapour at the normal % for induction BEFORE connecting to the patient. With the canister in the system the volume to be pre-filled is significantly greater at about 3 litres so priming needs to be longer using higher flows for 2-3 minutes to ensure that the air is removed. If the system is properly primed induction is much quicker, much as with the T-piece.

What happens if you don’t prime the system is that the patient will initially just re-breathe the air in the inspiratory limb. The reservoir bag will only fill up slowly with the low flows recommended and thus it will take some time for the inspired vapour tension to rise to that set. Thus, not surprising, induction is slow – and with propofol induction the animal may wake up before any significant amount of vapour is inhaled.

Thus it is important that the reservoir bag be pre-filled with the vapour at that normally used for induction – often 2-3% for halothane and 3-4% for isoflurane. Remember nothing goes to waste as the gas is stored on inspiratory side of the system. So at induction fill the bag fast by turning the oxygen flowmeter up – but don’t use the oxygen flush as this bypasses the vaporizer (breathing 0% vapour gets nowhere)! Once the bag is full, turn down the flows to those recommended for induction – and only reduce flows to maintenance flows once the animal is at or near the required degree of anaesthesia.

Another reason why induction may be slow is using too low vaporizer settings. If isoflurane is being used compared with halothane, remember that isoflurane is not as potent as halothane – 2% halothane is the equivalent of about 3% isoflurane. With larger animals who may take up significant amounts of anaesthetic into their tissues it may be necessary to induce with even higher dial settings for a short while. As a general rule, if induction is going too slowly, it is better to increase the vapour % rather than the flow which is just wasteful. As depth of anaesthesia can alter quickly, it is important to monitor the patient and adjust the vapour setting as required.

RE: ADE circuit

James Colver Cert. Ed, RVN — Tue, 05 Apr 2016 09:06:54 GMT

There is another thread on this from very recently - can't seem to add the link but have a look. Yes, do prime the circuit before you connect to the patient - after induction we would usually prime it with just oxygen if the patient was suitably asleep post induction - when we are ready to transfer the patient to theatre another nurse will wait in theatre and prime the circuit with whatever mix the patient was on in the prep room (keeping the end covered) - if not, the patient will likely start to wake up and it is important to make sure all the nitrogen / room air is expelled from the circuit before use.

Personally I would always prime a circuit with such low flow rates :)