A venous blood gas shows K+ 3.2 mmol/L, pH 7.50, pCO2 28 mmHg, HCO3- 21 mmol/L. The presumptive diagnosis is:

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Multiple Choice

A venous blood gas shows K+ 3.2 mmol/L, pH 7.50, pCO2 28 mmHg, HCO3- 21 mmol/L. The presumptive diagnosis is:

The main idea here is identifying an acid–base disturbance from a blood gas by looking at pH and the primary change in ventilation versus metabolism. The pH is elevated (alkalemia), and the very low pCO2 shows the lungs are driving the alkalosis by blowing off CO2. The bicarbonate is mildly reduced (21 mmol/L), which is the kidneys’ compensatory response to a respiratory alkalosis: they excrete more bicarbonate to counteract the alkalemia. The degree of bicarbonate fall is consistent with a modest compensatory response to the CO2 drop seen here (from around 40 to 28 mmHg). The low potassium (3.2) fits with alkalemia, where potassium shifts out of cells and total body potassium may be reduced. So, the pattern fits respiratory alkalosis with metabolic (renal) compensation.

The main idea here is identifying an acid–base disturbance from a blood gas by looking at pH and the primary change in ventilation versus metabolism. The pH is elevated (alkalemia), and the very low pCO2 shows the lungs are driving the alkalosis by blowing off CO2. The bicarbonate is mildly reduced (21 mmol/L), which is the kidneys’ compensatory response to a respiratory alkalosis: they excrete more bicarbonate to counteract the alkalemia. The degree of bicarbonate fall is consistent with a modest compensatory response to the CO2 drop seen here (from around 40 to 28 mmHg). The low potassium (3.2) fits with alkalemia, where potassium shifts out of cells and total body potassium may be reduced.

So, the pattern fits respiratory alkalosis with metabolic (renal) compensation.

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