Metabolic Acidosis

Question 1

metabolic acidosis

Answer 1

*any process in which the pH of the body decreases as a result of either: 1) retention of acids; or 2) loss of bicarbonate buffers

*ABG findings:
-low pH
-low bicarbonate
-low PaCO2 (compensation)

Question 2

metabolic acidosis - clinical presentation

Answer 2

*often asymptomatic
*if symptomatic, commonly presents with:
-very deep breathing
-nausea, vomiting, abd pain
-lethargy

Question 3

metabolic acidosis - pathophysiology

Answer 3

*can result from:
1. body making excess nonvolatile metabolic acids (lactic acid, ketoacids)
2. ingestion of substances that are converted to acids (ethylene glycol, methanol)
3. loss of bicarbonate in stool (diarrhea)
4. a diseased kidney that is unable to excrete acid (renal tubular acidosis)

Question 4

anion gap

Answer 4

*represents the calculated difference between the serum concentrations of sodium vs. chloride + bicarbonate
*AG = sodium - (chloride + bicarb)

Question 5

normal anion gap

Answer 5

*8-12 mEq/L
*average is ~ 8 mEq/L
*exists because of the unmeasured anions that we did not include in the calculation (urate, phosphate, sulfate, etc)

Question 6

an elevated anion gap is due to…

Answer 6

*elevated levels of unmeasured anions (presence of unexpected metabolites) in the blood such as:
-lactic acid
-ketoacid
-other

Question 7

elevated anion gap metabolic acidosis is due to

Answer 7

*due to gain of either:
1. ingested nonvolatile acids
2. body-produced nonvolatile acids

Question 8

MUDPILES acronym for causes of elevated anion gap metabolic acidosis

Answer 8

M - methanol, metformin
U - uremia (acute or chronic renal failure)
D - diabetic ketoacidosis
P - propylene glycol
I - isoniazid/iron
L - lactic acidosis
E - ethylene glycol
S - salicylates (aspirin)

Question 9

GOLDMARK acronym for causes of elevated anion gap metabolic acidosis

Answer 9

G - glycols (ethylene + propylene)
O - oxoproline
L - L-lactic acid
D - D-lactic acid
M - methanol, metformin
A - aspirin
R - renal failure
K - ketoacids (diabetic + alcoholic)

Question 10

normal anion gap metabolic acidosis is due to…

Answer 10

*due to either:
1. loss of bicarbonate
2. failure of the kidney to acidify urine

Question 11

causes of normal anion gap metabolic acidosis

Answer 11

*diarrhea
*chronic kidney disease
*renal tubular acidosis

Question 12

pathophysiology of diarrhea → normal anion gap metabolic acidosis

Answer 12

*diarrhea → loss of bicarbonate and potassium in the stool → metabolic acidosis + hypokalemia
*most common cause of normal anion gap metabolic acidosis

Question 13

pathophysiology of chronic kidney disease → normal anion gap metabolic acidosis

Answer 13

*CKD → impaired ammoniagenesis → impaired ability to excrete the daily acid load

Question 14

pathophysiology of renal tubular acidosis → normal anion gap metabolic acidosis

Answer 14

*RTA is a dysfunction in acid handling by various segments of the nephron
*recall: kidneys are responsible for excreting excess metabolic acids + reabsorbing bicarbonate
*failure of either of these tasks (due to disease) results in normal anion gap metabolic acidosis

Question 15

hyperkalemic RTA (type 4)

Answer 15

*characterized by an increased serum potassium level
*caused by defective ammonia production in the proximal tubule → decreased secretion of ammonium → decreased urine buffering and reduced acid excretion
*urine pH should be appropriately acidic (<5.3) in the presence of the systemic acidosis

Question 16

proximal RTA (type 2)

Answer 16

*caused by defective proximal tubule reabsorption of bicarbonate
*results in excess bicarbonate excretion in the urine, along with potassium loss in the urine
*result: hypokalemia + normal AG metabolic acidosis
*urine pH should be appropriately acidic (<5.5)

Question 17

distal RTA (type 1)

Answer 17

*caused by dysfunction of collecting duct alpha-intercalated cells in which they are not able to adequately secrete H+ into the urine
*result: hypokalemia + normal AG metabolic acidosis
*urine pH > 5.5

Question 18

diagnostic clues for high anion gap metabolic acidosis due to: alcoholic ketoacidosis

Answer 18

*history of ethanol abuse
*abdominal pain
*low-normal serum glucose

Question 19

diagnostic clues for high anion gap metabolic acidosis due to: diabetic ketoacidosis

Answer 19

*hyperglycemia
*fruity breath

Question 20

diagnostic clues for high anion gap metabolic acidosis due to: ingestion of ethylene glycol

Answer 20

*urine oxalate crystals
*high serum osmolar gap

Question 21

diagnostic clues for high anion gap metabolic acidosis due to: ingestion of propylene glycol

Answer 21

*hypotension
*high serum osmolar gap

Question 22

diagnostic clues for high anion gap metabolic acidosis due to: ingestion of methanol

Answer 22

*blindness
*renal failure
*high osmolar gap

Question 23

diagnostic clues for high anion gap metabolic acidosis due to: isoniazid toxicity

Answer 23

*liver toxicity
*seizures

Question 24

diagnostic clues for high anion gap metabolic acidosis due to: lactic acidosis

Answer 24

*hypotension
*fever
*seen in sepsis + shock due to anaerobic glycolysis

Question 25

diagnostic clues for high anion gap metabolic acidosis due to: D-lactate

Answer 25

*seen in short-bowel syndrome after surgical resection of small bowel (bacteria overgrow in gut and form d-lactate)
*confusion/headache after surgery

Question 26

diagnostic clues for high anion gap metabolic acidosis due to: oxoproline

Answer 26

*malnourished women after taking acetaminophen or paracetamol
*metabolite of glutamate builds up with glutathione depletion

Question 27

diagnostic clues for high anion gap metabolic acidosis due to: salicylates (aspirin)

Answer 27

*concurrent respiratory alkalosis
*tinnitus
*GI bleeding

Question 28

diagnostic clues for high anion gap metabolic acidosis due to: uremia (renal failure)

Answer 28

*high BUN and creatinine

Question 29

common causes of type 1 RTA (distal)

Answer 29

*chronic tubulointerstitial nephritis
*amphotericin B
*lithium
*lupus
*Sjogren syndrome
*amyloidosis

Question 30

common causes of type 2 RTA (proximal)

Answer 30

*acetazolamide
*heavy metals
*multiple myeloma
*Fanconi syndrome

Question 31

common causes of type 4 RTA (hyperkalemic)

Answer 31

*diabetic kidney disease
*spironolactone
*hypoaldosteronism