sturge_weber
Forum Guru
Topics: 77
Posts: 1,042
|
2 hunters,m re found dead in a cabin,a half empty bottle of whiskey is found near,outside the cabin an old birds nest is noted to have blocked the exhaust systemfor a wood stove, that had been used for warmth during the night,u would expect?
1.profound hypooxemia in both hunters
2.an odor in the cabin
3.visible cyanosis in both hunters
4.a normal o2 saturation calculated from the arterial po2
5.that alcohol did not contribute to their death
|
| Doc2378
Forum Guru
Topics: 46
Posts: 688
|
3. Visible cyanosis- its a case of CO poisoning..SaO2 would be markedly decreased leading to Cyanosis
since CO does not affect the PaO2 so it would not produce hypoxemia (rules out 1)...but it would produce tissue hypoxia by left-shifting the curve, decreasing SaO2 (rules out 4), and inhibiting cytochrome oxidase
CO is an odorless gas ('silent killer') -rules out 2
Ethanol acts as an uncoupling agent ( while CO inhibits Cytochrome oxidase)...so both would sequentially affect oxidative phosphorylation in the hunters
Edited by Doc2378 on 09/06/05 - 01:27 AM
___________________
Courage does not always ROAR. Sometimes courage is the quiet voice at the end of the day saying, "I will try again tomorrow" - Mary Anne Radmacher
|
| sturge_weber
Forum Guru
Topics: 77
Posts: 1,042
|
co, gives cherry red colour to the skin and hence the visible cyanosis gets masked..
|
| Doc2378
Forum Guru
Topics: 46
Posts: 688
|
You are right Sturge_Weber...Cyanosis is an infrequently seen sign ...
....but which one would you say is the right answer??
Thanks,
___________________
Courage does not always ROAR. Sometimes courage is the quiet voice at the end of the day saying, "I will try again tomorrow" - Mary Anne Radmacher
|
| p53
Forum Guru
Topics: 51
Posts: 804
|
Because CO does not affect the PaO2 O2 saturation in plasma would be normal. Since CO decreases functional Hb concentration it would produce hypoxemia. Correct answer is 1.
___________________
"Everything should be made as simple as possible, but not simpler." - Albert Einstein
|
| Doc2378
Forum Guru
Topics: 46
Posts: 688
|
but isn't O2 saturation (SaO2) mainly determined by the # of sites occupied by O2 on Hb rather than PaO2 (the dissolved component)?? CO readily displaces O2 from Hb and should decrease that!
___________________
Courage does not always ROAR. Sometimes courage is the quiet voice at the end of the day saying, "I will try again tomorrow" - Mary Anne Radmacher
|
| sturge_weber
Forum Guru
Topics: 77
Posts: 1,042
|
well o2 saturation is determined by the no. of sites occupied on the hb, and definitely the o2 saturation is decreased, but now look closely at the choice no. 4. ... it says normal o2 saturation measured from the po2... now po2 is the o2 dissolved in the blood, not bound to hb, and the po2 will almost be normal, and when u will calculate the sao2 from the po2, it will come out to be normal... as the po2 is normal
well i too got it wrong, its tricky.. but now we know the trick
|
| sturge_weber
Forum Guru
Topics: 77
Posts: 1,042
|
asked an icu doc, and he said, if u have seen a oximeter, it measures ur po2 and then calculates the sao2 from the po2, in that case the sao2 will come normal, but if u attatch the co oximeter, it will measure it correctly
well i personally think, there should be no hypoxemia in co poisonong, because po2 is not affected, but was just reviewing goljan notes and saw co poisonong causes hypoxemia...
but checked kaplan physiology and it says, the po2 remains normal in co poisoning, hence no hypoxemia
Edited by sturge_weber on 09/06/05 - 11:22 AM
|
| p53
Forum Guru
Topics: 51
Posts: 804
|
sturge_weber, you are wrong if you think that because PaO2 remains normal in CO poisoning there would be no hypoxemia. Hypoxemia means decrease in total O2 content of the blood. Total O2 content is O2 dissolved in plasma + O2 bound to Hb. Content of O2 dissolved in plasma is much more small and unimportant than content of O2 bound to Hb.
PaO2 determines content of O2 dissolved in plasma and content of O2 dissolved in plasma is O2 saturation of plasma. This value in CO poisoning would be normal. At the same time PaO2 in pulmonary capillaries in normal people is not the major factor determining how much O2 would be bound to Hb. O2 exchange in alveolar capillaries is perfusion-limited, not diffusion limited. This means that red blood cell spends in pulmonary capillary much more (3 times more) time than is needed for maximal saturation of blood plasma with O2 (i.e. establishing equilibrium between alveolar air and pulmonary capillary blood) and then for maximal binding of O2 to Hb. So, no matter how you increase PaO2 total O2 content wouldn't go up - it is already maximal. You have to decrease PaO2 too much than normal if you want that content of O2 bound to Hb even begin to decrease. At the same time, if you decrease Hb content (as in anemia) or number of functional Hb molecules (as in CO poisoning) in red blood cells - total O2 content will decrease, even though there would be normal PO2, i.e. normal content of O2 dissolved in plasma, i.e. normal O2 saturation of plasma.
Edited by p53 on 09/06/05 - 01:23 PM
___________________
"Everything should be made as simple as possible, but not simpler." - Albert Einstein
|
| sturge_weber
Forum Guru
Topics: 77
Posts: 1,042
|
well 3 things i think , p53, u re wrong
po2 is the o2 dissolved in plasma
2.sao2 means amount of o2 bound to hb
3. sao2 is decreased in co poisoning
4. by pulse oximeter, the sao2 will appear normal, but using a co oximeter thesao2 will be decreased
well experts have to help...
|
| p53
Forum Guru
Topics: 51
Posts: 804
|
When we are talking about dissolving gases in liquids, saturation means how much gas is dissolved in liquid. Again, as I already said, O2 saturation of blood (mostly of plasma) isn't decreased in CO poisoning, no matter how you measure it.
___________________
"Everything should be made as simple as possible, but not simpler." - Albert Einstein
|
| ssrpk
Forum Fanatic
Topics: 154
Posts: 2,819
|
well if you are knocking out the binding sites on Hb for O2, how can saturation be normal! (O2 per g Hb)
p53 you must be confusing it with something else! che3ck Ganong! even mentioned in kaplan notes! [CO poisoning : low SaO2, normal PaO2]
nice question sturge!
___________________
life is guud
|
| p53
Forum Guru
Topics: 51
Posts: 804
|
OK, maybe I'm cofusing terminology, I'll check. Anyway, I was talking about O2 saturation of PLASMA, not of Hb!
___________________
"Everything should be made as simple as possible, but not simpler." - Albert Einstein
|
| loschicharos
Forum Newbie
Topics: 1
Posts: 4
|
p53 you are correcto!!!! O2SAT is normal in this case.
|
| ssrpk
Forum Fanatic
Topics: 154
Posts: 2,819
|
well if it's O2 saturation of plasma then it's correct, it will remain normal but O2 saturation of Hb will definitely be decreasd, in general terms you should consider hemoglobin when it's about saturation!
In CO poisoning O2 saturation will decrease!
"loschicharos" - where did u read it from that O2 saturation will be normal!
___________________
life is guud
|
| sturge_weber
Forum Guru
Topics: 77
Posts: 1,042
|
well guys check this article out ...esp page 2
Attached Files:
hkm0003p113.pdf (24 KB, 12 downloads)
|
| gpsbrar
Forum Elite
Topics: 34
Posts: 278
|
ans is 5 alcohol didnot contribute to the death.
___________________
B+
|
|
| |
| | | | | | | | | | | | | | | | | |
