Whole-body acid-base balance

Question 1

What are the normal levels of:

a) pH
b) pCO2
c) [HCO3-]

Answer 1

a) 7.35-7.45
b) 23-27mmol/l
c) 35-45mmol/l

Question 2

What is the difference between compensation and correction?

Answer 2

Compensation is restoration of a normal pH; correction is restoration of all normal acid base parameters

Question 3

Answer 3

Question 4

For respiratory acidosis describe:

a) two possible causes
b) why the levels of bicarbonate rise
c) compensation
d) correction

Answer 4

a) COPD, airway restriction, respiratory depression
b) because the equation is shifted to the right, resulting in an increase in both H+ and HCO3-. Also a result of compensatory mechanisms
c) compensation is renal- acid excretion and generation of new bicarb
d) requires restoration of normal ventilation

Question 5

For respiratory alkalosis describe:

a) two possible causes
b) why the levels of bicarbonate fall
c) compensation
d) correction

Answer 5

a) excess CO2 removal as a result of hyperventilation, low inspired PO2
b) removal of CO2 shifts the equilibrium to the left- less H+ and HCO3-. Also renal compensation further lowers HCO3
c) renal compensation- reduced H+ secretion and increased bicarb secretion
d) can only be corrected by restoring proper ventilation

Question 6

For metabolic acidosis state:

a) two possible causes
b) why bicarb is also depleted
c) how compensation occurs

Answer 6

a) diabetic ketoacidosis, lactic acidosis, excessive base loss (e.g. diarrhoea)
b) bicarb is depleted either due to the mechanism (e.g. diarrhoea) or in an attempt to buffer. Also respiratory compensation further reduces bicarb
c) more carbon dioxide is “blown off” to compensate for the acidosis
d) correction is due to excretion at the kidneys- compensation is essential because renal correction doesn’t take place immediately

Question 7

For metabolic alkalosis state:

a) two possible causes
b) how it is compensated. What does compensation also cause?
c) how it is corrected

Answer 7

a) excretion of acid e.g. HCl in vomiting, or ingestion of base
b) respiratory compensation- acid is retained (hypoventilation). Also causes HC03- to rise further
c) bicarb is excreted at the kidney