Acid Base Flashcards
What is the primary mechanism behind normal anion gap metabolic acidosis (NAGMA)?
NAGMA occurs due to loss of bicarbonate or failure of the kidneys to excrete hydrogen ions, with normal chloride retention to maintain electroneutrality.
What lab finding distinguishes normal anion gap metabolic acidosis from high anion gap metabolic acidosis?
The serum anion gap is normal (<12 mEq/L), with a hyperchloremic state due to compensatory chloride retention.
the serum anion gap is calculated by:
AG = (+ charges) minus (- charges) = Na - (Cl + Bicarb) = Na - Cl - Bicarb
How do you calculate the expected anion gap?
2.5 x albumin
What are the major types of normal anion gap metabolic acidosis (NAGMA) ?
renal tubular acidosis
GI loss of bicarb from chronic diarrhea or fistula
infusion of bicarb or free fluids
acetazolamine
post-hypocapnia
renal failure in the early stages
What is the most common gastrointestinal cause of normal anion gap metabolic acidosis?
Diarrhea, which causes excessive bicarbonate loss from the gastrointestinal tract.
What type of fistulas are associated with bicarbonate loss and normal anion gap metabolic acidosis?
Pancreatic, ileostomy, or biliary fistulas, which result in loss of bicarbonate-rich fluids.
What renal condition causes normal anion gap metabolic acidosis due to a defect in bicarbonate reabsorption in the proximal tubule?
Proximal renal tubular acidosis (Type 2 RTA).
What is the mechanism of Type 1 (distal) renal tubular acidosis in causing NAGMA?
Type 1 RTA results from the inability to excrete hydrogen ions in the distal nephron, leading to acid retention and a metabolic acidosis.
How does acetazolamide cause normal anion gap metabolic acidosis?
Acetazolamide inhibits carbonic anhydrase, impairing bicarbonate reabsorption in the proximal tubule and leading to bicarbonate loss in the urine.
What is the mechanism of post-hypocapnia-induced normal anion gap metabolic acidosis?
After chronic hypocapnia (e.g., from prolonged hyperventilation), the kidneys adapt by decreasing bicarbonate reabsorption, causing a temporary metabolic acidosis when PaCO₂ normalizes.
How can the infusion of free fluids or bicarbonate precursors lead to NAGMA?
Infusion of fluids like normal saline or ammonium chloride can cause hyperchloremic acidosis due to dilutional bicarbonate loss or chloride overload.
How does early-stage renal failure contribute to normal anion gap metabolic acidosis?
In early renal failure, the kidneys fail to adequately excrete hydrogen ions and regenerate bicarbonate, leading to acid retention and acidosis.
What equation helps to determine if the kidneys has appropriately compensated for the metabolic acidosis?
Winter’s Formula:
1.5 x [Bicarb] + 8 (+/- 2)
