circle circuits

Re: circle circuits

jules007 — Thu, 16 May 2013 16:28:53 GMT

You should be using a higher flow rate of O2 to start with to allow for denitrogenation ( i think this particularly important with circles due to it being a re-breathing circuit). 3L for 10 mins is normally adequate and then reduce down to 1-2Lp/m if using open.

Re: circle circuits

Siobhan Steven — Thu, 16 May 2013 10:07:37 GMT

This link may help:

http://www.abbottanimalhealth.com/static/cms_workspace/pdfs/AAH-318_Recommended_Flow_Rates_for_Anesthesia_Systems.pdf

Of course its in lbs so you need to convert to kgs...

There are flow rates that can be used as a 'low flow' delivery, which essentially entails closing the pop off valve and running the O2 at 7-10 mls per kg, but it should only be used when capnography is monitored and the soda lime can not be exhausted. The O2 flow is so low that what is delivered just continues to be filtered and then recirculated, which explains why capnography needs to be used to ensure the patient doesn't suffer hypercapnia.

Re: circle circuits

Selena Carnell — Wed, 15 May 2013 20:51:08 GMT

Circle can be used open or close, we use ours open and the O2 level depends on the weight of the dog. Never heard the 3 litre O2 thing. I thought the point of an circle system was so it reduced the amount of O2 needed due to the soda lime.

Re: circle circuits

Siobhan Steven — Wed, 15 May 2013 09:42:30 GMT

The percentage of Isoflurane chosen should essentially be based on the effect of your induction agent, and to some extent the effect of your pre med. For example if you have given a extremely boisterous dog 8ug/kg medetomidine and 0.5 mg/kg methadone and achieved a very effective sedation you may only need 0.5-1 mg/kg of propofol or alfaxalone (remember induction agent is given 'to effect' there is no exact dose though 1-2 mg/kg of Alfaxalone and 4-6 mg/kg of propofol is the dose range we draw up...). So, that rather sedate dog could easily go on 1-1.5% iso, you need to be mindful of the fact the the induction agent may a) cause induction apnoea so you need to supplement ventilation to the tune of 3-4 BPM, as you actually want CO2 to build up to stimuate the respiratory drive, but you don't want the patient to become hypoxic or hypoxeamic. And b) your induction agent will metabolise within 10-20 minutes so the patient will 'lighten' if it is not receiving Iso, i.e if its not breathing...you can have the Iso at 5% but if its not breathing it won't stay asleep. So be actively checking your patients depth, titrate the Iso and IPPV to assist your patient to get to a surgical plane/stage of anaesthesia. There are occasions where additional induction agent may be needed to 'top up', especially if the patient is moved or manipulated.

With effective analgesia and protocols you should be able to maintain many patients at 1-1.5% Iso (the MAC of Iso for dogs is 1.2%)

Hope this helps...I can give you info re O2 later if you like?