A base excess of +4 indicates which acid-base disturbance?

• A. Metabolic alkalosis
• B. Respiratory acidosis
• C. Metabolic acidosis
• D. Bicarbonate toxicity

Answer: (A)

A positive base excess means there is an excess of buffering base, most often bicarbonate, in the blood. That points to a metabolic rather than a respiratory problem. When base excess is +4, the body has too much base or too little acid, which is characteristic of metabolic alkalosis. This pattern typically accompanies conditions that cause loss of hydrogen ions or gain of bicarbonate (for example, vomiting, diuretic use, or mineralocorticoid excess). The respiratory system may compensate by hypoventilating to raise CO2 and lower pH toward normal, but such compensation is limited. A positive base excess is not consistent with metabolic acidosis or primary respiratory acidosis, which would show negative base excess or different compensatory patterns.