# Why does CO2 Lead to Acidosis?

#### justadream

7+ Year Member
I get that

H2O + CO2 <=> H2CO3 <=> HCO3- and H+

So if you add more CO2, the entire equilibrium shifts to the right (producing more H+).

But doesn't this also produce an equal amount of HCO3- (a base)?

So why is there a net acidic effect of adding CO2?

#### Cawolf

##### Medical Student
5+ Year Member
The buffer system is dependent on the ratio of H2CO3 to HCO3-.

So adding CO2 or H+ that drives the reaction to the middle (carbonic acid) will cause the ratio of acid to base to increase - decreasing the pH.

pH = pka (H2CO3) + log ([HCO3-]/[H2CO3])

OP

#### justadream

7+ Year Member
@Cawolf

But how does that equation "account for" the fact that whenever you generate HCO3-, you make a H+ as well?

In other words, is the [H+] irrelevant?

#### Cawolf

##### Medical Student
5+ Year Member
Sort of.

Free H+ would rapidly combine with present bicarbonate to form H2CO3.

It is in equilibrium based on the amount of bicarbonate present in the blood.

So if the pCO2 or H+ concentration is too high for the bicarbonate load to handle, then the pH will decrease.

It isn't irrelevant, but it is best to look at the buffer system as a whole.

That is why if I have a patient who is highly acidotic, I give IV NaHCO3 to support the buffer system.

kraskadva

#### kraskadva

##### ...
7+ Year Member
LeChatlier's principle.
If you've got more of the reactant on one side, it will drive the reaction to the other side.
The soluble anion does not cancel out the H+, but driving the reaction back towards the middle by increasing the amount of the anion (by giving NaHCO3) will remove the H+.