Ralf B. Lukner MD PhD

When your blood becomes “too basic,” your body scrambles to restore its delicate pH balance, but knowing why it happened is key: is it the lungs or the kidneys to blame? - Metabolic alkalosis arises when the body loses acid or gains too much base. Common causes include prolonged vomiting (loss of gastric HCl), diuretic use, or excessive bicarbonate intake. In this case, the primary disturbance is a rise in plasma bicarbonate (HCO₃⁻). The respiratory system compensates by slowing breathing (hypoventilation) to retain CO₂, shifting the pH back toward normal. - Respiratory alkalosis, on the other hand, results from excessive CO₂ loss due to hyperventilation — think of anxiety attacks, fever, high altitude, or mechanical overventilation. Here, the primary problem is a drop in arterial CO₂ (PaCO₂), which reduces carbonic acid levels. The kidneys compensate more slowly by excreting bicarbonate, lowering plasma HCO₃⁻ to restore balance. In short: - Metabolic alkalosis: ↑HCO₃⁻ → compensatory ↑PaCO₂ (hypoventilation) - Respiratory alkalosis: ↓PaCO₂ → compensatory ↓HCO₃⁻ (renal excretion) The difference lies in which organ started the imbalance — lungs or kidneys — and which one is struggling to fix it.