Why is HCO3 low in DKA?

[Knicks]

In DKA, the patient is acidotic, right? So why would the body decrease bicarbonate (a base)? Wouldn't you want to keep the bicarbonate high so as to neutralize the acid?

Too tired to think straight at the moment.

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[generic]

The HCO3 derangement is not a compensation--it is the primary problem.

DKA patients have a metabolic acidosis, I think it's mostly caused by the formation of tons and tons of ketone bodies (acidic). These are formed because despite high circulating levels of glucose, the cells can't use the glucose without insulin-->turn to ketone formation instead.

The metabolic acidosis may cause respiratory compensation, which would give Kussmaul breathing, for example.

 

[treva]

In DKA, the patient is acidotic, right? So why would the body decrease bicarbonate (a base)? Wouldn't you want to keep the bicarbonate high so as to neutralize the acid?

Too tired to think straight at the moment.

Remember the kidney takes days to compensate for acidodic state by producing more bicarb. Acutely, the bicarb is used to buffer the extra acid, so it drops.

This also explains why DKA pts have increased RR:

CO2 + H20 <--> H2CO3 <--> HCO3- + H+

If you blow off extra CO2 (ie by upping RR) you shift the above equation to the left, and promote the formation of H2CO3 via CA, helping to mop up the H+.

 

[Knicks]

The HCO3 derangement is not a compensation--it is the primary problem.

DKA patients have a metabolic acidosis, I think it's mostly caused by the formation of tons and tons of ketone bodies (acidic). These are formed because despite high circulating levels of glucose, the cells can't use the glucose without insulin-->turn to ketone formation instead.

The metabolic acidosis may cause respiratory compensation, which would give Kussmaul breathing, for example.

Remember the kidney takes days to compensate for acidodic state by producing more bicarb. Acutely, the bicarb is used to buffer the extra acid, so it drops.

This also explains why DKA pts have increased RR:

CO2 + H20 <--> H2CO3 <--> HCO3- + H+

If you blow off extra CO2 (ie by upping RR) you shift the above equation to the left, and promote the formation of H2CO3 via CA, helping to mop up the H+.

Thanks for the clarification guys. Much appreciated.

I was just confused when a UW explanation said that the bicarbonate is low/decreased to counter the acidosis (didn't make sense to me).

Thanks again.