Blood pH is controlled by concenrration of H₂CO₃ and ${\mathrm{HCO}}_3^{-}$. In the presence of NaHCO₃, pH of blood is

Acidic buffer solution is prepared by mixing a weak acid and its salt with a strong base.
Thus, a mixture of H_2​CO₃​ and ${\mathrm{HCO}}_3^{-}$​ acts as an acidic buffer solution.
The expression for the p^H of the acidic buffer solution is as given below:
$\mathrm{pH}={\mathrm{pK}}_{\mathrm{a}}+\log \frac{\left[\mathrm{salt}\right]}{\left[\mathrm{Acid}\right]}$
In the presence of NaHCO₃​, the concentration of salt increases. Hence, the term log[salt]​/[Acid] increases. This increases the p^H of blood.