Acidosis/Alkalosis

Question 1

4 Causes of Hyperchlroemic Acidosis

Answer 1

• Impaired renal acid excretion (renal failure, distal renal tubule acidosis)
• Renal bicarb loss (CA inhibitors, proximal renal tubule acidosis)
• GI bicarb loss (diarrhea, pancreatic drainage, ureteral diversion)
• Acid gain (tpa, ammonium Cl ingestion)

Question 2

8 Causes of High Anion Gap Acidosis

Answer 2

• M - methanol ingestion (formate and lactate)
• U -uremia (renal failure –> phosphate, sulfate, organic acids)
• D diabetic ketoacidosis (beta- hydroxybutyrate or acetoacetate)
• P - propylene glycol, paraldehyde
• I - infection, iron, isonazid, inborn errors
• L - lactic acidosis
• E - ethylene glycol ingestion (ocylate, glycolate)
• S - salicylates (aspirin –> ketoacids, lactate, salicylate)

Question 3

Anion Gap Equation

Answer 3

AG = [Na] - [Cl-] - [bicarb]

normal is 10 +/- 2

Question 4

Urinary Anion Gap Equation (+ what does it tell us?)

Answer 4

UAG = [Na] + [K] - [Cl] (no bicarb in urine normally)

• UAG <0 - non-renal cause of acidosis b/c make up for acidosis by ammonium production in kidney (+ charge so negative anion gap)
• UAG > 0 - renal cause of acidosis b/c no ammonium present

Question 5

What kind of acidosis is present in chronic kidney disease?

Answer 5

BOTH

it can start as hypercholermic acidosis and later become high anion gap

Question 6

Winter’s Formula

Answer 6

• Predicts the respiratory comp for metabolic acidosis

PCO2 = 1.5 x [bicarb] + 8 +/-2

• If actual meas PCO2 is > prediction by formula… compensatory
• If actual meas PCO2 is < prediction by formula … primary respiratory acidosis

Question 7

What is the risk of chronic metabolic acidosis?

Answer 7

• Bone disease/rickets/growth fail in kids

- Osteoporosis in adults

Question 8

Type I RTA

Answer 8

Classic distal RTA

• Defective distal nephron H+ pumps or back leak of H+ into tubular lumen
• Can be… impaired H-ATPase, bicarb/Cl exchanger, carbonic anhydrase

Question 9

Type II RTA

Answer 9

Proximal RTA

• If congenital defect or proximal tube damage –> impaired H+ secretion –> lower threshold for bicarb reclamation (start spilling bicarb into urine at much lower threshold)
• Can be part of Fanconi Syndrome (mult prox tube defects - glycosuria, phosphate wasting, aminoaciduria and hypouricemia)

Question 10

Type IV RTA

Answer 10

Hyperkalemic distal RTA

• Either aldosterone def/resistance
• OR voltage-dep defect in H+ excretion; if dec Na+ reabsorption then this dec gradient for H+ secretion

Question 11

What 2 things must occur for metabolic alkalosis to take place?

Answer 11

• Generation (acid loss of alkali gain)

- Maintenance (why is alkalosis not being corrected by body?)

Question 12

Generation of Metabolic Alkalosis

Answer 12

• Acid Loss
  - In kidney - diuretics, mineralocorticoid excess, Cushing’s (steroid), severe K+ depletion, Bartter’s, Gitelman’s, Liddle’s
  - In GI - vomiting, nasogastric drainage, chloride diarrhea
• Alkali Gain
  - Bicarb admin
  - Milk-alkali syndrome
  - Infusion of organic anions that are metabolized to bicarb (ex- citrate in blood transfusion; lactate; acetate)

Question 13

Maintenance of Metabolic Alkalosis

Answer 13

• Dec GFR –> less bicarb filtered load; from either dec EABV or renal insufficiency
• Inc proximal tube bicarb reclamation; from dec EABV or chloride depletion
• Inc H+ excretion; from mineralocorticoid excess or hypokalemia

Question 14

2 Classes of Metabolic Alkalosis Tx

Answer 14

1- Responds to saline (vol or Cl- depletion)

- This will enhance EABV and Cl- delivery to dec proximal bicarb reclamation
- Can also give KCl in saline if hypokalemia is severe and contributing
- Also give if GI losses or diuretic use

2- Resistant to saline (PT NOT VOL OR CL- DEPLETED)

- So due to mineralocorticoid excess; give aldosterone antagonist instead
- Also due to severe hypokalemia (Barrters, Gitelmans, Liddles); give K-sparing diuretic instead