Acid base disorders

Question 1

Difference between respiratory and metabolic disturbances.

Answer 1

respiratory acidosis: ↑ CO2
respiratory alkalosis: ↓ CO2

Metabolic acidosis: ↓ HCO3-
Metabolic alkalosis: ↑ HCO3-

Question 2

What direction is compensation?

Answer 2

It is always in the same direction as the primary change and with the corresponding molecule.

Ie: respiratory alkalosis initial change = ↓ PCO2
- compensation is ↓ [HCO3-]

Ie: Metabolic alkalosis initial change = ↑ [HCO3-]
- compensation is ↑ [CO2]

Question 3

In acute respiratory alkalosis, the HCO3- is expected to fall by _____ meq/l for every ___ fall in PCO2-

Answer 3

↓2 HCO3-, ↓ 10 pCO2

2:10

Question 4

In chronic respiratory alkalosis, the HCO3- is expected to fall by _____ meq/l for every ___ fall in PCO2-

Answer 4

↓4 HCO3-, ↓ 10 pCO2

4:10

Question 5

During respiratory alkalosis, how is compensation with ↓ HCO3 achieved?

Answer 5

1. cell H+ release (acute)
2. renal H+ retention (chronic)

• either way, H+ binds to HCO3- which lowers it and drives CO2 formation

Question 6

During respiratory acidosis, how is compensation with ↑ HCO3- achieved?

Answer 6

1. cell buffering (acute)

2. Renal H+ EXCRETION (HCO3- resorption) (Chronic)

Question 7

In acute respiratory ACIDOSIS, the HCO3- is expected to INCREASE by _____ meq/l for every ___ INCREASE in PCO2-

Answer 7

↑ 1 HCO3-, ↑10 pCO2

1:10

Question 8

In chronic respiratory ACIDOSIS, the HCO3- is expected to INCREASE by _____ meq/l for every ___ INCREASE in PCO2-

Answer 8

↑ 4 HCO3-, ↑10 pCO2

4:10

Question 9

Metabolic alkalosis requires generation and maintainance,

How does generation of met alk occur?

Answer 9

1. addition of HCO3-
2. loss of H+
3. Loss of Cl- rich fluids (contraction alkalosis)
4. post hypercapnea
5. hypokalemia

Question 10

Ways that loss of H+ can occur leading to metabolic alkalosis?

Answer 10

1. GI loss
2. Renal loss: loop/thiazide diuretics, mc excess
   - inhibit N+ resorption→ increase Na+ delivery to distal tubule → resorbs Na+ → generates (-) charged tubular lumen → FAVORS H+ SECRETION →metabolic alkalosis

Question 11

maintenance of metabolic alkalosis is ALWAYS due to what?

Answer 11

the inability to excrete excess HCO3-

met alk is due to primary increase in HCO3-

Question 12

How does chloride depletion result in maintaining met alk?

Answer 12

it results in the resorption of HCO3- via Cl-/HCO3- exchanger on basolateral mem.

• note that Cl- depletion is frequently accompanied by volume depletion
  (remember that maintenance of met alk is always due to inability to excrete excess HCO3-)

Question 13

Why does increased mineralocorticoid activity result in maintaining met alk?

Answer 13

They stim the H+-ATPase pump leading to secretion of H+ into the lumen.
This is accompanied by bicarb resorption.

Question 14

Aldosterone and mineralocorticoids effects on H+-ATPase activity. What significance does this have on metabolic disturbances?

Answer 14

Increase H+-ATPase pump, eventually reabsorbing HCO3- and maintaining metabolic alkalosis

Question 15

Metabolic alkalosis is divided into 2 categories:

Answer 15

chloride responsive (saline responsive)
- UCl 20 meq/L

Question 16

causes of Cl- resistant metabolic alkalosis

Answer 16

Excess mineralocorticoids:

• hyperaldosteronism
• cushing syndrome

Question 17

Treatment of metabolic alkalosis is urgent bc?

Answer 17

urgent bc:

1. cardiac arrythmias
   - increases sensitivity to catecholamines
2. hypocalcemia

Question 18

tx for metabolic alkalosis

Answer 18

• mechanical ventilation
• if Cl responsive: infusion of NaCl/KCl
• If Cl resistant: block mineralocorticoid effect with spirinolactone or amiloride