Circle flow rates please

Re: Circle flow rates please

Tracey Annison — Thu, 19 Apr 2012 14:57:08 GMT

Give us a call.... Advanced Anaesthesia Specialists 01491 681974. We can help with flow rates. If you call tomorrow (Friday 20th) you can speak to Vet anaesthetist Colin Dunlop. He will help.

Re: Circle flow rates please

Juliet Drummond DAVN (med) RVN D32/33 — Mon, 26 Mar 2012 23:13:52 GMT

I wrote my last post in a hurry, I would not base my flow rate for the circle solely on capnography. As i said this is not an exact science. According to hall & clark - veterinary anaesthesia, when using a rebreathing system the inspired gases should not contain more than 0.1 to 1% inspired carbon dioxide, significant increases indicate exahusted sodalime; falsely low etco2 measurements can occur when using non-rebreathing systems' I suppose alot depends on whether you use the circle as a truly closed system, or as a semi-open system. I use it as a semi-open system, hence the high denitrogenisation rates, and my minimum of 1-2 L/min maintenance rate. I leave the valve half open, i 'sigh' the patient every 5-10 mins, if i change the vaporiser setting i empty the bag to speed the change in anaesthetic concentration. The original poster wanted to know flow rates for the circle, as i said i woild use 10ml/kg/min as a baseline guide, i also consider the metbolic status of the patient concerned, e.g. temp, age, pre-existing disease etc etc.

Re: Circle flow rates please

emvn80 — Mon, 26 Mar 2012 20:29:15 GMT

Re: Circle flow rates please

Claire Bloor — Mon, 26 Mar 2012 19:04:23 GMT

I think perhaps I have confused you with my first post by not starting my last sentence as a new paragraph...i.e. the comment about titrating FGF according to capnography. That wasn't linked directly to the prior circle flow rate comment. I shall ensure I unequivocally differentiate between two such comments in future posts. And the second comment was again not relating to circles. I was merely pointing out that capnography is essential for assessing ventilatory efficiency (or inefficiency potentially due to low FGF rates - again not specifically related to a circle), as opposed to pulse ox which is only useful for indicating the saturation of haemoglobin with oxygen. Hope this clarifies my comments for you!

Re: Circle flow rates please

emvn80 — Mon, 26 Mar 2012 09:08:45 GMT

[quote user="Claire Bloor"]

I'm sure all VNs know you shouldn't just change your FGF based on a capnograph reading...there are a plethora of other physiological parameters to take into consideration. As an ETCO2 reading, your capnograph can indicate inadequate ventilation and ONE of the reasons for this could be inadequate FGF amongst other things and would warrant further investigation. SPO2 is not an accurate indicator of ventilatory status, so should definitely not be relied upon in this manner.

[/quote] You mis-understood what i was saying, I am not talking about using an EtCO2 reading to assess adequacey of fresh gas, i am talking about using your inspired CO2 reading. Inspired CO2 should be zero and te naseline should return to zero so you can use rebreathing on a capnogrpah trace (ie an increased INSPIRED CO2) to indicate inadequate fresh gas flow when using a Non-rebreathing circuit and it is what I do.... I calculate my FGF at the start then say I make it 3 L/min I will start at that but because I am lucky enough to have a capnograph I can lower my fresh gas flow and can go lower until I see rebreathing however with a circle circuit you definitely CANNOT do this to ensure adequacy of fresh gas flow. Rebreathing on a capnograph when using a circle is due to exhausted soda lime, stuck one way valves or excessive dead space not inadequate fresh gas flow. This is because rebreathing systems use fresh gas flow to physically flush out the exhaled CO2 whereas circles obviously use the soda lime to absorb the CO2 so even if you were supplying inadequate fresh gas flow/oxygen the CO2 would still be being removed by the soda lime. I am not talking about using capnographyto assess adequacy of ventilation at all, just using it to assess adequacy of fresh gas flow which is not effected by other things.

Re: Circle flow rates please

emvn80 — Mon, 26 Mar 2012 08:45:09 GMT

Sorry, I think you misunderstood what I was saying in regards to using capnography to assess adequacy of fresh gas flow rate , I wasn't talking about adequacy of ventilation! capnography definitely does NOT indequate adequacy of fresh gas flow when using a circle, like it does when using a non-rebreathing system. The only way you can tell you are supplying enough fresh gas using a circle is to look at the rebreathing bag and check it is not empty... The pulse oximeter will also help reassure you that you are supplying adequate oxygen in your fresh gas, especially if you are using nitrous, but I agree it is a late change (again I wa talking about how to assess adequacy of fresh gas flow NOT adequacy of ventilation which are completely separate) I was worried that from the previous posts people would be looking for rebreathing on the capnograph as a sign of inadequate fresh gas flow with te circle like you can with non- rebreathing systems so I was just trying to clarify it.

Re: Circle flow rates please

Claire Bloor — Sun, 25 Mar 2012 22:39:04 GMT

Re: Circle flow rates please

emvn80 — Sat, 24 Mar 2012 15:55:28 GMT

Sorry for the typos- my phone was trying to be clever! X

Re: Circle flow rates please

emvn80 — Sat, 24 Mar 2012 15:54:37 GMT

Remember you CANNOT use the capnograph to help guide your fresh gas flow rates with a circle (rebreathing) circuit like you can with non-rebreathing systems like t-pieces and Bains. This is because in circle circuits it is the sodalime removing the CO2 from the system NOT the fresh gas flow so with a T-piece you will get rebreathing of CO2 if the fresh gas flow is inadequate (easily seen on the capnograph trace). With a circle circuit you won't see rebreathing if you are jot supplying enough oxygen as the sofa lime will still e absorbing the CO2, instead the only way to check is to check the rebreathing bag is not empty and the Spo2 is normal. You will see rebreathing on the capnograph trace with a circle if the sodalime is exhausted, or the one way valves are stuck (or exess dead space) For circle circuits (irrespective of manufacturer) you only need to supply the metabolic oxygen requirement which as previously said is roughly 10 mL/kg/hr although if you are using a sidestream capnograph you must add on the amount (ml/min) that is drawn from the circuit for sampling (between 50-250 mL/min). If you are nervous, for safety I wouldn't recommend going below 0.5L/min for a 5-30kg dog and 1L/min for a giant breed >30-40kg. Also use a higher fresh gas flow for the first 5 min to denitrogenate as previously said (I generally use 2L/min for all dogs to start! Hope this helps, just wanted to emphasise the capnograph fact with circles- a capnograph will not tell you if the fresh gas flow is inadequate in circles

Re: Circle flow rates please

Claire Bloor — Fri, 23 Mar 2012 13:47:36 GMT

You need to have a quick word with the manufacturers to check what flow rates they recommend. Some say 10 minutes on 4L/min for denitrogenation and then down to 2L/min for the rest of the anaesthetic. Some say 3 for denitrogenation then down to 1 etc etc. And I agree with someone's previous comment about titrating the fresh gas flow according to capnography readings...good practice.

Re: Circle flow rates please

Juliet Drummond DAVN (med) RVN D32/33 — Wed, 21 Mar 2012 22:08:53 GMT

i always start on high rates for 10 mins (6-8 litres) to allow denitrogenisation to occur. after this i use between 1-2 litres, these figures equate approximately to 100ml/kg/min for denitrogenisation, and 10ml/kg/min maintenance (as pp said) this is not an exact science, and if using a capnograph you can get flow rates down quite low, with out capno, best to overestimate gas requirements.

Re: Circle flow rates please

Alison Clare Hickman — Wed, 21 Mar 2012 21:03:59 GMT

Cheers Wispa! This will really help my student nurse.

Re: Circle flow rates please

Wispa — Wed, 21 Mar 2012 20:24:52 GMT

Hi,

try this link and see if it helps, if you have one from burtons...

http://www.veterinarytechnics.com/assets/files/Manual%20Burtons%20Cycloflo.pdf

Re: Circle flow rates please

Ju_xx — Wed, 21 Mar 2012 19:47:50 GMT

We use 10ml/kg