A 34-year-old woman with (kypho)sclerosis on medication has dyspnoea. ABG: pH 7.37, PCO2 50, PO2 71, HCO3 31. What is the acid-base disorder?
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الإجابة: B. Chronic respiratory acidosis
pH is low-normal (7.37) with a raised PCO2 (50) = primary respiratory acidosis. PCO2 is up by 10: acute compensation would raise HCO3 by only ~1 (to ~25), chronic renal compensation by ~4 (to ~28). An HCO3 of 31 with a near-normal pH therefore means chronic (compensated) respiratory acidosis, fitting chronic hypoventilation from kyphoscoliosis. Metabolic alkalosis is not primary because the pH sits on the acidic side; the HCO3 is a little above the expected value, which could hint at an added metabolic alkalosis (e.g., diuretics), but B is the best answer.
ليش كل خيار صح أو غلط
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A
ليش غلط
Acute compensation raises HCO3 by only 1 per 10 rise in PCO2. HCO3 of 31 with a PCO2 of 50 is far more than the acute response allows.
✓ ABG & A-a gradient.pdf · p. 2 -
B
ليش صح
Chronic compensation raises HCO3 by 4 per 10 rise in PCO2 (slow renal compensation over days). A raised PCO2 with a high HCO3 and near-normal pH fits chronic respiratory acidosis.
✓ ABG & A-a gradient.pdf · p. 2 -
C
ليش غلط
Metabolic acidosis comes from loss of HCO3 or extra H+, with a low HCO3. Her HCO3 is raised, so it does not fit.
✓ ABG & A-a gradient.pdf · p. 2 -
D
ليش غلط
Here the high HCO3 is the kidney's chronic compensation for CO2 retention (more HCO3 reabsorbed), not a primary metabolic alkalosis.
✓ ABG & A-a gradient.pdf · p. 2
- المصدر
- ABG & A-a gradient.pdf · p. 2
Step Up To Medicine 6th Edition 2024 (Acid-base imbalance).pdf · p. 10 - المحاضرة
- Respiratory Failure & Acid–Base · Pulmonology · Module B
- ظهر في
- MED41 ♂ EOM B