renal acid/base

Question 1

how do you calculate the predicted respiratory compensation for a simple metabolic acidosis?

Answer 1

PCO2 should = 1.5[HCO3-] + 8 (plus or minus 2).

if the PCO2 is significantly different from that, then a mixed acid-base disorder is likely present.

Question 2

acidemia vs. acidosis

Answer 2

acidema: the pH of the blood is low
acidosis: the process that could lead to a low pH

Question 3

causes of metabolic acidosis

Answer 3

if you detect a metabolic acidosis, check the ANION GAP.
Anion Gap = [Na+] - ([HCO3-] + [Cl-]). normal is 8-12
Positive anion gap: something is there that shouldn’t be. MUDPILES: methanol, uremia, diabetic ketoacidosis, propylene glycol, iron tablets or isoniazid, lactic acidosis, ethylene glycol, salicylates (late).
Normal anion gap:
HARD-ASS:
hyperalimentation, addison disease, renal tubular acidosis, diarrhea, acetazolamide, spironolactone, saline infusion

Question 4

causes of metabolic alkalosis

Answer 4

loop diuretics, vomiting, antacid use, hyperaldosteronism

Question 5

causes of respiratory acidosis

Answer 5

hypoventilation: airway obstruction, acute or chronic lung disease, opioids, weakened resp. muscles.

Question 6

causes of respiratory alkalosis

Answer 6

hypoxemia (ie high altitude), early salicylates, tumor, pulmonary emobolism

Question 7

renal tubular acidosis

Answer 7

a defect in the renal tubules that leads to a non-anion gap hyperchloremic metabolic acidosis.

Question 8

type I renal tubular acidosis

Answer 8

distal problem; pH > 5.5. I assume this is urine pH?
there is a defect in alpha intercalated cells to secrete H+. new HCO3- is not generated. associated with HYPOKALEMIA. incr. risk of calcium phosphate kidney stones due to incr. urine pH and incr. bone turnover.
causes: amphotericin B toxicity, analgesic nephropathy, multiple myeloma (light chains), congenital obstuctions of the urinary tract

Question 9

type II renal tubular acidosis

Answer 9

urine pH < 5.5.
defect in proximal tubule HCO3- resorption causes an increase in excretion of HCO3- in the urine –> metabolic acidosis. urine is acidified by alpha intercalated cells in collecting tubule. associated with hypokalemia. incr. risk for hypophosphatemic rickets.
causes: Fanconi syndrome (eg. Wilson’s disease), chemicals toxic to the proximal tubule (lead, aminoglycosides), and carbonic anhydrase inhibitors

Question 10

type IV renal tubular acidosis

Answer 10

hypoaldosteronism or aldosterone resistance or K sparing diuretics. resulting hyperkalemia impairs ammoniagenesis in the proximal tubule. decr. buffering capacity and decr. H+ excretion into urine.

Question 11

RBC casts, RBCs in urine

Answer 11

RBCs in urine have many causes, including bladder cancer or kidney stones. however, casts indicates that the hematuria is of renal (vs. bladder) origin. RBC casts are seen in glomerulonephritis, ischemia, or malignant HTN.

Question 12

WBC casts ddx

Answer 12

tubulointerstitial inflammation, acute pyelonephritis, transplant rejection

Question 13

fatty cast ddx

Answer 13

aka oval fat bodies. seen in nephrotic syndrome

Question 14

waxy casts ddx

Answer 14

advanced renal disease/chronic renal failure

Question 15

granular casts

Answer 15

aka muddy brown casts. indicate acute tubular necrosis.