Acid-Base Balance

Question 1

Describe general mechanisms of chemical buffer system regarding pH regulation

Answer 1

Fast conversion. Phosphate and protein (intracellular), bicarbonate (extracellular).

Question 2

Describe general mechanisms of respiratory buffer system regarding pH regulation

Answer 2

Fast control via respiratory center of brain. Metabolic acidosis: compensate by breathing off more acid (CO2); tachypnea. Metabolic alkolosis: compenstate by retaining acid; bradypnea.

Question 3

Describe general mechanisms of liver oxidation of strong acids regarding pH regulation

Answer 3

Slower regulation (hours to days). Produces acid (1/5 of CO2 in body from substrate oxidation) and eliminates acid (utilize acid in lactate oxidation and gluconeogenesis).

Question 4

Describe general mechanisms of renal mechanisms regarding pH regulation

Answer 4

Slow (hours to days). Ultimate regulation - only system that clears non-volatile acids via H+ excretion and NH4 generation. Regulates bicarb: conserves by reabsorbing and generating new bicarb against acidosis. Excretes bicarb to defend alkolosis.

Question 5

Purpose and usefullness of arterial blood gas (ABG)

Answer 5

Calculates: pH, pCO2, PO2, [HCO3]
Essential for determining a pts acidity. When used in conjunction with other bloodwork, status (acidemic, alkalemic), cause (metabolic, respiratory), and compensation can be determined.

Question 6

Significance of anion gap, normal value

Answer 6

Presence of anion gap gives clue to underlying pathologies causing metabolic acidosis. Normal: 12+/-2.
Calculate: Na - (Cl + HCO3)

Question 7

Normal pH

Answer 7

7.35-7.45

Question 8

Normal HCO3

Answer 8

24+/-2

Question 9

Normal pCO2

Answer 9

40+/-2

Question 10

Steps involved in determining acid-base disorder

Answer 10

1. Anticipate disorder
2. Acidemic or alkalemic (pH)
3. Primary process metabolic or respiratory (pCO2 and HCO3 change with pH = met; pCO2 and HCO3 change opposite pH = resp).
4. (Met acid) Calculate anion gap.
5. Compensation appropriate (met - last two digits pH = pCO2; resp - ^HCO3 = .2 x ^pCO2 - acute).
6. Consider mixed acid-base disorder… But not on the test :)