Acid-Base Disorders
Andrei Brateanu
Craig Nielsen
RAPID BOARD REVIEW—KEY POINTS TO REMEMBER:
Steps in analyzing acid-base disorders:
Verify the internal consistency of the data:
Calculated [H+] = 24 · × PCO2/[
] should equal the estimated [H+] = 40 + (7.4 – pHmeasured) 100.
Determine the arterial blood pH:
In the presence of a normal pH:
Normal [
] indicates normal arterial blood gases.
Decreased [
] indicates a mixed metabolic acidosis and respiratory alkalosis.
Elevated [
] indicates a mixed metabolic alkalosis and respiratory acidosis.
If pH < 7.35 patient has acidemia.
If pH > 7.45 patient has alkalemia.
Determine if the primary disorder is:
metabolic, when pH and [
] are moving in the same direction;
respiratory when pH and [
] are moving in opposite directions.
In metabolic acidosis:
The expected decrease in ΔPCO2 = 1.2 × Δ[
]:
if CO2 is higher, a respiratory acidosis is also present;
if CO2 is lower, a respiratory alkalosis is also present.
Calculate the anion gap (AG) = Na+ – Cl– –
(normal 10 to 12 mEq/L).
When the patient has normal AG (hyperchloremic) metabolic acidosis, calculate the urine anion gap (UAG) = urine Na+ + urine K+ – urine Cl–:
if negative, it suggests gastrointestinal loss of
;
if positive, it suggests renal loss of
as in renal tubular acidosis.
When the patient has high AG metabolic acidosis, calculate the osmolal gap = osmolalitymeasured – (2·[Na+] + glucose/18 + BUN/2.8) and measure toxins if poisoning suspected, or osmolal gap is high (N < 10 mOsm/L).
When the patient has a high AG metabolic acidosis calculate “Delta Delta”
ΔAG = [(Na+ – Cl– –
) – 12] andRelated posts:
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