metabolic compensation (co2)

this is really just me being a bit nosy as to the biology behind whats going on. I was back in resus last night and my hospital apparantly does have a doc that understands that ABGs are more important that o2 probes, makes a change, and surprise surpirse my co2 was elevated. However, he was explaining to the nurse how to interpret the results and i was listening too, and he was talking about the fact that my pH was normal, and high co2 levels would lower my blood pH, and so that meant i was metabolically compensating. what does that mean? i assumed it would be something to do with the rate of respiration in my cells but i wasnt really sure.

plus, if my co2 was high but pH was normal, would that still explain why i felt really really sick, or is that likely to be die to something else, i think those two are linked, but im not really sure how!

finally, a quick side note, he described high co2 levels in an asthmatic as a 'pre-terminal' sign...that sounds really scary, but i didn't think i was THAT bad, i mean, dont get me wrong i'm not the sort to ring an ambu unless i'm really starting to struggle so i wasnt feeling particularily great, but i've felt worse, and i've felt worse and not had ABGs done - which is kind of more scary. is pre-terminal a poor choice of phrase (like terminal exams lol!) or is high co2 really that bad?

thanks for any info - i find this stuff really quite fascinating, and its always nice to be distracted from breathing by knowing cool stuff my body is trying to do to fix me!

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  • I suspect he was talking about metabolic acidosis. I got this the first time I was almost ventilated in ITU.

    patient.co.uk/doctor/Metabo...

    Lynda :)

  • hmmmm....but he sounded like he was saying my high co2 was making the pH lower, but something my metabolic system was doing was making it higher (and so *just* back within normal range - although interestingly i was still acidotic according to the numbers in that article) so surely that's almost the opposite of what you had? or am i misunderstanding. it was interesting reading though, and if rehydration is what they do for acidosis then i guess that explains why they were doing that! so thanks :-)

  • hmmmm....but he sounded like he was saying my high co2 was making the pH lower, but something my metabolic system was doing was making it higher (and so *just* back within normal range - although interestingly i was still acidotic according to the numbers in that article) so surely that's almost the opposite of what you had? or am i misunderstanding. it was interesting reading though, and if rehydration is what they do for acidosis then i guess that explains why they were doing that! so thanks :-)

    LOL Im confusled now ;) metabolic acidosis (not alkalosis) is when your blood ph is low therefore there your blood is too acidic. Thats what I had. If you think according to those numbers that you were acidotic, how is that different...?

    I cant remember much about my experience as my sats were low 80's and I was acidotic and extremely confused and disorientated. I can remember saying I was tired and wanted to stop breathing and go to sleep :/ Its only from what my hubby remembers happening (he's a doctor and was involved in the conversations as he understood what was happening).

    Lynda :)

  • LOL Im confusled now ;) metabolic acidosis (not alkalosis) is when your blood ph is low therefore there your blood is too acidic. Thats what I had. If you think according to those numbers that you were acidotic, how is that different...?

    its to do with the cause, respiratory acidosis as opposed to metabolic acidosis!

    And i did feel pretty rough, but i've felt worse when they didn't do my blood gases which is a bit scary. i think i was quite tired, so could imagine i was making less effort to work hard than usual, so i guess that could be it. it does make sense, and it helps me coz i do like to understnad whats going on. it helps me feel a bit more in control in a fairly scary situation.

    recently i have had high co2 more often than i used to, could that be something to do with my muscles getting tired faster as im having attacks so frequently? and could the high co2 thing explain why in the ambu the para said i stopped responding to him breifly? or is that just a bit random of my body?

    thanks for the info - sorry if i was at all unclear!

  • Hey,

    As you say, co2 is acidic so if you have high levels in your blood this can give you an acidosis. The body doesn't like being acidic (or alkalotic) so has compensatory mechanisms. In the short term your body tries to increase your resp rate to breathe off the co2 but unfortunately this doesn't work if you are having an asthma attack. The second way to normalise the ph is to metabolically compensate using bicarbonate which is an alkali .... So acid (co2) plus alkali (bicarb) = water (give or take!)

    I'm surprised you weren't feeling that bad if you had a high co2 as its usually a later sign. I often have high normal co2 levels which still isn't great but usually they attack me with lots of ivs and catch it in time! The few times I've had a high co2 I've been completely out of it and ended up in ITU. Though I was also very acidotic as I tend to have a high lactate (partly from masses of salbutamol, partly from being hypoxic) which is also acidic - so I had a respiratory and metabolic acidosis.

    Oh dear, this has turned out a bit of a lecture ... Sorry. I hope this vaguely makes sense, blood gases can get a bit complicated and I tried not to get too tied up in the chemistry behind it!

    B x

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