Cause of Respiratory Alkalosis in ASA tox

[engineeredout]

Okay nobody I've talked to seems to know the answer to this and the professors seem to keep contradicting each other.

So in ASA poisoning there is a metabolic acidosis with respiratory alkalosis. Two questions:

#1) What is the pH going to be? Is it always acidic or can it be anything?
#2) What is the cause of the respiratory alkalosis? Is it just respiratory compensation or is there a direct increase in ventilation due to the salicylates?

Thanks.

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[JelloBrain]

The pH will be low initially due to metabolic acidosis. The body compensates for the acidosis by hyperventilation which causes the respiratory alkalosis by driving the CO2 out. Once respiratory compensation is in effect, the pH might be quite close to normal.

 

[sumyounguy]

I seem to recall that salicylates cause a combination of both a primary respiratory alkalosis (by stimulation of respiratory centers) and a primary metabolic acidosis with the pH falling within either the normal range (7.35-7.45) or slightly on the acidic side.

please correct me if I'm wrong.

 

[Fuzuli]

#1) What is the pH going to be? Is it always acidic or can it be anything?

Depends on the timing and the age group.

• In adults, the first sign will be respiratory alkalosis due to direct stimulation of the respiratory center. Eventually, metabolic acidosis will develop as well due to uncoupling of oxidative phosphorylation and lactate formation. [Increased anion gap metabolic acidosis + primary respiratory alkalosis]
• In children, respiratory alkalosis may be less pronounced, so they can present initially as metabolic acidosis.

#2) What is the cause of the respiratory alkalosis? Is it just respiratory compensation or is there a direct increase in ventilation due to the salicylates?

Aspirin is a weak acid that can directly stimulate the respiratory center. This will result hyperventilation, which will decrease paCO2 and this will cause primary respiratory alkalosis.