Acid/Base Physiology

Question 1

Normal value for arterial pH

Answer 1

7.35-7.45

Question 2

Normal value for arterial CO2

Answer 2

35-45 mm Hg (use 40 mm Hg in calculations)

Question 3

Normal value for arterial O2

Answer 3

80-100 mm Hg

Question 4

Normal value for arterial bicarb

Answer 4

22-26 (use 24 mEq/L in calculation)

Question 5

What 2 blood gas components may change your pH? What type of disturbance is each of these correlated with?

Answer 5

HCO3 changes in metabolic disturbances

CO2 changes in respiratory disturbances

Question 6

When looking at someone with altered acid/base status, how would you determine that it was due to metabolic causes?

Answer 6

If HCO3 and pH change in same direction = metabolic

[Kidneys and other organs control HCO3; changes in HCO3 will produce metabolic acid-base imbalances]

Question 7

When looking at someone with altered acid/base status, how would you determine that it was due to respiratory causes?

Answer 7

If pH is altered in the setting of CO2 imbalance, it is respiratory (CO2 and pH change in opposite directions)

Question 8

How is respiratory acidosis generated?

Answer 8

Decreased ventilation –> increased blood PCO2 –> increased conversion of H2CO3 to [H+] –> decreased serum pH

Question 9

How is respiratory alkalosis generated?

Answer 9

Increased ventilation –> decreased blood PCO2 –> decreased conversion of H2CO3 to [H+] –> increased serum pH

Question 10

Increased lactic acid, ketoacids in diabetics, etc. would lead to ______ ______

Answer 10

Metabolic acidosis

Question 11

How are respiratory disturbances compensated?

Answer 11

By metabolic system, in this case via reabsorption/secretion of H+ or HCO3 in the kidneys (mainly PCT)

Question 12

How is respiratory acidosis compensated?

Answer 12

Kidney secretes H+ via urine and reabsorbs HCO3 in the blood, thus increasing plasma bicarb

There is increased ammonium production and increased bicarb generation

This is renal buffering!

Question 13

How is respiratory alkalosis compensated?

Answer 13

By decreasing acid filtration: kidney secretes or creates new HCO3 via urine and reabsorbs H+ in the blood, thus decreasing plasma bicarb

Decreased ammonium production and thus decreased acid excretion in urine, along with decreased bicarb regeneration

Question 14

How is metabolic acidosis compensated for?

Answer 14

Acidemia stimulates chemoreceptors in the carotid bodies that produce an immediate increase in ventilation rate (hyperventilation)

More CO2 will be expired to reduce PCO2 and increase arterial pH

Question 15

How is metabolic alkalosis compensated for?

Answer 15

Ventilation decreases to retain more CO2 and decrease arterial pH

Question 16

What are the renal mechanisms for regulating hydrogen and bicarb ion concentrations in the blood?

Answer 16

Reabsorption of virtually all of the filtered HCO3 and excreteion of H+ as titratable acid and ammonium

For each H+ excreted as titratable acid or NH4, one new HCO3 is synthesized and reabsorbed

Question 17

How would you determine that the respiratory acidosis is acute?

Answer 17

If the change in HCO3 = 1 mEq/L for every 10 mm Hg change in CO2

Expected [HCO3] = 24 + (PaCO2 - 40 mm Hg)/10

Question 18

How would you determine that the respiratory acidosis is chronic?

Answer 18

If change in HCO3 = 3-4 mEq/L for every 10 mm Hg change in CO2

Expected [HCO3] = 24 + 4(PCO2 - 40 mm Hg)/10

Question 19

How would you decide that the respiratory alkalosis is acute?

Answer 19

Expected HCO3= 24 -2((PaCO2 - 40 mm Hg)/10

Question 20

How would you decide that the respiratory alkalosis is chronic?

Answer 20

HCO3 = 24-5(PaCO2 - 40 mm Hg)/10

Question 21

How would you decide that the respiratory compensation for metabolic acidosis is adequate?

Answer 21

Expected PaCO2 = 1.5[HCO3] + 8 +/- 2

Question 22

How would you determine if respiratory compensation for metabolic alkalosis is adequate?

Answer 22

Change in PCO2 = (0.5 to 1.0) x change in HCO3

In this case, the change is an increase in CO2

Question 23

How would you calculate predicted osmolarity?

Answer 23

Osmolarity = 2(serum Na) + (BUN/2.8) + (glucose/18)

Normal osmolarity = 290 mOsm/L