Acid-Base Balance and ABG Interpretation Practice Test

In high anion gap metabolic acidosis, the body accumulates organic acids (like lactate or ketone bodies). These acids donate H+, and bicarbonate (the buffer) is used up to neutralize them, so the bicarbonate level falls and the blood becomes more acidic. Because those acids add unmeasured anions to the plasma, the anion gap increases. The respiratory system tries to compensate by blowing off CO2, so the PaCO2 drops as ventilation rises, helping to raise pH a bit but not eliminating the acidosis.

So the typical ABG pattern is acidemia with low bicarbonate and an elevated anion gap, often with a reduced PaCO2 due to respiratory compensation. Patterns with high pH or normal pH/bicarbonate don’t fit this scenario.