Metabolic Acidosis B&B Flashcards
for which acid-base disorders should you always check Winter’s Formula?
Winter’s formula tells you expected decrease in pCO2 in the case of metabolic acidosis
pCO2 = 1.5 (HCO3-) + 8 +/- 2
assesses whether there is a concurrent respiratory disorder
what is the use of the delta-delta ratio?
delta-delta tells you whether there is a concurrent metabolic acid-base disorder in the case of metabolic acidosis
ratio of the [measured - normal AG (12)] over the [normal (24) - measured HCO3-]
delta-delta of 1-2 is normal, if low then there is secondary non-AG metabolic acidosis (HCO3- too low), if high there is secondary metabolic alkalosis or pre-existing respiratory acidosis (HCO3- too high)
how do the following cause non-anion gap metabolic acidosis?
a. diarrhea
b. acetazolamide
c. spironolactone
d. Addison’s disease
e. saline infusion
f. hyperalimentation
a. diarrhea: loss of HCO3-
b. acetazolamide: blocks formation/reabsorption of HCO3-
c. spironolactone and d. Addison’s disease: loss of aldosterone, cannot excrete H+ effectively
e. saline infusion: decreased RAAS activity decreases H+ excretion
f. hyperalimentation: metabolism increases HCl, lowering pH
what are the common anion gap metabolic acidoses? (hint, there’s an acronym)
MUDPILES:
Methanol
Uremia
Diabetic ketoacidosis
Propylene glycol
Iron tablets or INH
Lactic acidosis
Ethylene glycol
Salicylates
how does methanol cause anion gap metabolic acidosis?
what is it found in?
how can it be treated?
metabolized to formic acid, which is CNS poison —> visual loss, coma
found in antifreeze, cleaners, fuels
tx: inhibit alcohol dehydrogenase (enzyme it is metabolized by) or give ethanol (competes for binding sites)
how does ethylene glycol cause anion gap metabolic acidosis?
what is it found in?
how can it be treated?
metabolized to glycolate and oxalate, which are kidney toxins (slow excretion) —> flank pain
found in antifreeze, solvents, cleaners
tx: inhibit alcohol dehydrogenase (enzyme it is metabolized by) or give ethanol (competes for binding sites)
how does propylene glycol cause anion gap metabolic acidosis?
what is it found in?
propylene glycol = antifreeze, metabolized to pyruvic acid —> acetic acid —> lactic acid
—> hemolysis, seizures, coma, CNS depression
how does uremia cause anion gap metabolic acidosis?
uremia seen in advanced renal disease (early kidney disease has non-AG gap acidosis due to retained Cl-)
kidneys cannot excrete organic acids —> retention of phosphates, sulfates, urate, others
how does diabetic ketoacidosis cause anion gap metabolic acidosis?
usually type I diabetes, often triggered by infection
insulin requirements rise and cannot be met —> fatty acid metabolism produces ketone bodies (beta-hydroxybutyrate, acetoacetate)
—> polyuria (triggered by high glucose), polydipsia, Kussmaul breathing
how can iron cause anion gap metabolic acidosis?
acute iron poisoning has initial GI phase (direct toxic effects), then disseminated effects in 24h
—> cardio: shock, tachycardia, hypotension
—> anti-coagulation (inhibits thrombin)
—> AG metabolic acidosis from ferric irons and lactate (due to hypoperfusion)
weeks later, bowel obstruction due to scarring
how can isoniazid (INH) cause anion gap metabolic acidosis?
INH: tuberculosis antibiotic
acute overdose causes seizures (status epilepticus) —> lactic acidosis
how can salicylates cause anion gap metabolic acidosis?
salicylates = aspirin
aspirin overdose causes 2 acid-base disorders:
1. immediate respiratory alkalosis (simulated medulla —> hyperventilation)
2. hours: AG metabolic acidosis (decreased lipolysis, uncoupled ox. phosphorylation —> accumulation of pyruvate, lactate, ketoacids)
will see low CO2 (hyperventilation) with low HCO3- (acidosis), and Winter’s formula will predict higher CO2 than actual
