Question

A man suffering from untreated diabetes mellitus is admitted to the hospital. Glucose is present in his urine and he exhibits shallow breathing. Analysis of his blood shows [HCO3-] of 16 mM and [CO2] of .9 mM.

1.) Write a multi-step equilibrium for bicarbonate as a buffer in blood. Your expressions should include carbon dioxide and carbonic acid.

2.) What is the approximate pH of the blood of the patient above? Use carbon dioxide as the acid.

3.) After the patient is treated with insulin his blood pH returns to 7.4. His [HCO3-] increases to 21 mM. What is the [CO2] in the blood?

4.) What is the [H+] at both pH’s measured?

Answer 1

1)

2) Using Henderson-Hasselbalch Equation

pKa = 6.1 [HCO₃^-] = 16mM and [CO₂] = .9mM

3) Again using Henderson equation

4) a. When patients pH = 7.34

[H⁺] = 4.57 * 10^-5mM                                                                   (using [H⁺] = 10^-(pH))

b. When pH = 7.4

[H⁺] = 3.98*10^-5mM