Gasbag Anaesthesia Forums

I use a lot of LMA's. Occassionally I get a patient who just wont breath well and their ETCO₂ starts to creep up. Breathing spontaneously I commonly let the CO₂ get into the 50's and the 60's. But for some of these patients (often young and otherwise well!) they are in the 70's. I have found that if they wake up with the CO₂ this high, they complain of a severe headache, but are otherwise OK.

How high do people let their CO₂'s go? Does the acidosis worry them? Surely this respiratory acidosis will be quickly blown off as soon as they are awake. Or is the cerebral vasodilation a concern in the non-neuro patient? Is the duration a factor?

It was all highlighted for me when a resident came in during an otherwise normal anesthetic and commented on how I was unconcerned about the ETCO₂ being in the 60's/ Should I be more concerned???

I commonly have my CO2 in the 50s and occassionally in the (low) 60's. Rarely higher and then only for short periods (ie I take over and ventilate).

I'm not too worried about high CO₂'s for short periods. As you say, they will blow off the CO₂ after and in the otherwise well patient, hte cerebral vasodilation is not an issue.

But what about the converse? What happens to the cerebral vasculature with prolonged severely overventilated patients with ETCO₂ in the 20's? I was once told by an older collegue that he had a patient have multiple CVAs for no known cause except that her CO₂s were very low. Could such low CO₂ cause so much cerebral vasoconstriction as to cause ischemia????  :o

After about 30 minutes of hyper or hypo ventilation, the cerebral vessels tend to lose their responsiveness and drift back to their baseline level of dilation. This is why hyperventilation for long periods is no longer recommended for neuro cases and keeping the CO₂ at about 35 is now the objective. For this reason, I find it hard to believe that anyone could get an ischemic CVA from prolonged hyperventilation.

Just because u like and use LMA a lot.u cant cross the limit.BE sure to be concerned as soon as ETCO2 enters in 50s.If not satisfied INTUBATE and hyperventilate.GET BLOOD GASES FOR SAFETY OF PATIENT

Quote from: naveen laiker on January 15, 2005, 09:03:33 AM
Just because u like and use LMA a lot.u cant cross the limit.BE sure to be concerned as soon as ETCO2 enters in 50s.If not satisfied INTUBATE and hyperventilate.GET BLOOD GASES FOR SAFETY OF PATIENT

Yes, but WHY? What harm will it do? IS there any evidence of harm to aptients when CO₂'s get high for short (or long) periods?

Happens alot, and doesn't seem a problem.
If it reaches the high 60's i tend to assume the circle is ineffective for whatever4 reason oin that case and turn up the FGF...works to stop the climb. ::)

I respectfully disagree with Naveen's post. High 50s, low 60s in healthy patients having knee scopes, etc in my humble opinion is of no concern. In an 80 year old lady I'd be more vigilant, assist ventilations, turn the gas down, no more opioids, maybe 40mcg naloxone if you thought opioids were a factor, etc. It'd have to be pretty bad for me to pull a patent, well functioning LMA in a case to intubate. I think thats overkill. Of course I wouldnt've said that on my oral boards! haha