Bicarbonate Need in Metabolic Acidosis

 

The general formula used to estimate the dosage required is:

 

mEq HCO3 required =

= (((desired HCO3-) - (measured HCO3-)) * (f) * (lean body weight in kg))

 

where:

• f = fraction of the total body weight in which the administered material is distributed; for HCO3 it is in the range 0.5 - 0.6

 

The calculated base excess may be erroneous in the presence of respiratory acidosis. It also does not account for intracellular bicarbonate stores.

 

Since overalkalinization can result in problems such as tetany, seizures, and cardiac arrhythmias, in practice about half of the calculated dose is given initially, after which the patient is monitored by subsequent blood gases for response. Potassium and calcium are monitored for hypokalemia and hypocalcemia which may occur as the acidosis is corrected.

 

Alternative Equation (Pincus et al)

 

The amount of bicarbonate required to return an acidotic patient's pH to 7.4 is:

 

amount of bicarbonate to administer =

= ((((initial bicarbonate) + (0.03 * (PaCO2))) * (20 - (10 ^ ((initial pH) - 6.1)))) / (1 + (10 ^ ((initial pH) - 6.1))))

 

This gives a value that is about half of the in vivo and in vitro base excesses (see below). The source of the equation is not given in the text.