[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Conditions](https://durgical.com/en/conditions/) › Metabolic alkalosis [Conditions](https://durgical.com/en/conditions/) · [Metabolism (biochemistry)](https://durgical.com/en/conditions/) # Metabolic alkalosis Blood bicarbonate rises, usually from vomiting or diuretics; the [kidney](https://durgical.com/en/anatomy/kidney/) will not shed it while volume, chloride or potassium are short. Updated 2026-11-01 ## Structures involved Tap one to see what it is and open it in 3D. - [Kidneys](https://durgical.com/en/anatomy/kidney/) - [Stomach](https://durgical.com/en/anatomy/stomach/) - [Left adrenal gland](https://durgical.com/en/anatomy/suprarenal-gland/) - [Right adrenal gland](https://durgical.com/en/anatomy/suprarenal-gland-abdomen/) ## In biochemistry - [Acid–base interpretation (step by step)](https://durgical.com/en/biochemistry/topics/acid-base-interpretation/) - [Bicarbonate–CO₂ buffer system](https://durgical.com/en/biochemistry/topics/bicarbonate-co-buffer-system/) - [Acid–base compensation rules](https://durgical.com/en/biochemistry/topics/acid-base-compensation-rules/) ## In embryology - [Hypertrophic pyloric stenosis](https://durgical.com/en/embryology/hypertrophic-pyloric-stenosis/) ## In physiology - [Gastric acid secretion](https://durgical.com/en/physiology/gastric-acid-secretion/) - [Gastric motility and emptying](https://durgical.com/en/physiology/gastric-motility-and-emptying/) - [Vomiting and its control](https://durgical.com/en/physiology/vomiting-and-its-control/) - [Transport in the loop of Henle](https://durgical.com/en/physiology/transport-in-the-loop-of-henle/) - [Distal tubule and collecting duct](https://durgical.com/en/physiology/distal-tubule-and-collecting-duct/) - [Reading an arterial blood gas step by step](https://durgical.com/en/physiology/reading-an-arterial-blood-gas-step-by-step/) - [Where and how diuretics act](https://durgical.com/en/physiology/where-and-how-diuretics-act/) - [Renal handling of H⁺ and bicarbonate](https://durgical.com/en/physiology/renal-handling-of-h-and-bicarbonate/) - [Metabolic alkalosis and its compensation](https://durgical.com/en/physiology/metabolic-alkalosis-and-its-compensation/) - [Mixed acid–base disorders](https://durgical.com/en/physiology/mixed-acid-base-disorders/) ## Why it happens - [Cachexia, anorexia nervosa and bulimia](https://durgical.com/en/general-pathology/cachexia-anorexia-nervosa-and-bulimia/) ## What it is A primary rise in plasma bicarbonate with high pH, sustained because the kidney reabsorbs it when volume, chloride or potassium are depleted or mineralocorticoids are in excess. ## Who gets it It is the most common acid–base disorder in hospital patients, mainly from diuretics and gastric aspiration or vomiting. In infants, hypertrophic pyloric stenosis is the classic cause. ## Causes - Loss of gastric acid: vomiting, nasogastric drainage, pyloric stenosis - Loop and thiazide diuretics - Mineralocorticoid excess: primary hyperaldosteronism, Cushing syndrome, liquorice - Bartter and Gitelman syndromes - Alkali load (bicarbonate, citrate in massive transfusion, milk–alkali syndrome) and post-hypercapnic alkalosis ## Risk factors - Prolonged vomiting (gastroenteritis, hyperemesis, bulimia) - Diuretic use - Resistant hypertension with hypokalaemia (aldosteronism) - Ventilation that rapidly corrects chronic hypercapnia ## Pathophysiology Generation: H⁺ is lost ([stomach](https://durgical.com/en/anatomy/stomach/), kidney) or HCO₃⁻ is gained. Maintenance: with volume and chloride depletion, the kidney reabsorbs sodium with bicarbonate in the proximal tubule; aldosterone drives H⁺ and K⁺ secretion in the collecting duct, so paradoxical aciduria and hypokalaemia appear, and hypokalaemia in turn increases HCO₃⁻ reabsorption. Urine chloride separates the causes: low in saline-responsive ones (vomiting, diuretics already stopped) and high in unresponsive ones (mineralocorticoid excess, Bartter, Gitelman, current diuretic). Respiratory compensation (hypoventilation) is limited. Alkalaemia lowers ionised calcium and favours arrhythmias. ## Classification - Low urine chloride: chloride/volume-responsive (vomiting, gastric drainage, past diuretic, post-hypercapnic) - High urine chloride: unresponsive (hyperaldosteronism, Cushing, Bartter, Gitelman, current diuretic, severe hypokalaemia) ## Symptoms and signs - Symptoms of the cause (vomiting, dehydration) - Cramps, weakness and paraesthesia - Tetany or carpopedal spasm from low ionised calcium - Palpitations - Confusion in severe cases ## Red flags - Very high pH with arrhythmias - Severe hypokalaemia - Infant with projectile vomiting and hypochloraemic alkalosis (pyloric stenosis) ## Diagnosis **Clinical** History of vomiting, tubes, diuretics or hypertension; assessment of volume status and blood pressure. **Tests** Gases with high HCO₃⁻ and pH, electrolytes (low chloride and potassium), urine chloride, renin and aldosterone if hypertensive, magnesium. **Imaging** Pyloric ultrasound in a vomiting infant; adrenal CT if primary aldosteronism is confirmed. ## Treatment **Medical** In the chloride-responsive form: saline to restore volume and chloride, plus potassium **Medical** Correct hypokalaemia and hypomagnesaemia, which sustain the alkalosis **Medical** In the unresponsive form: treat mineralocorticoid excess (aldosterone antagonists, surgery for an adenoma) and adjust diuretics; acetazolamide in selected cases **Follow-up** Monitoring of gases, electrolytes and heart rhythm ## Complications - Arrhythmias - Tetany and seizures - Hypoventilation with hypoxaemia - Severe hypokalaemia ## Prognosis Good once the cause is corrected; severe alkalaemia (very high pH) is linked to higher mortality in critically ill patients. ## Test yourself Think of the answer, then tap the question to see it. ## Why does vomiting cause metabolic alkalosis? Gastric HCl is lost, bicarbonate is left in the blood, and volume and chloride depletion make the kidney reabsorb it instead of excreting it. ## Which test separates saline-responsive from unresponsive alkalosis? Urine chloride: low in responsive cases (vomiting) and high in unresponsive ones (mineralocorticoid excess, Bartter, Gitelman). ## What is paradoxical aciduria? Acid urine despite alkalosis, because aldosterone and hypokalaemia force the kidney to secrete H⁺ to retain sodium. ## Why can alkalosis cause tetany? High pH increases calcium binding to albumin and lowers ionised calcium. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/conditions/metabolic-alkalosis/) ## Related conditions - [Hypokalaemia](https://durgical.com/en/conditions/hypokalaemia/) - [Infantile hypertrophic pyloric stenosis](https://durgical.com/en/conditions/infantile-hypertrophic-pyloric-stenosis/) - [Cushing syndrome](https://durgical.com/en/conditions/cushing-syndrome/) - [Heart failure](https://durgical.com/en/conditions/heart-failure/) - [Chronic obstructive pulmonary disease (COPD)](https://durgical.com/en/conditions/chronic-obstructive-pulmonary-disease/) Educational information, not medical advice. For any symptom, see a health professional. Sources: [Alkalosis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/001183.htm) (MedlinePlus, US National Library of Medicine, 2026); [Chloride - urine test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003601.htm) (MedlinePlus, US National Library of Medicine, 2026); [Low blood potassium: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000479.htm) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011). [← All conditions](https://durgical.com/en/conditions/) ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/conditions/metabolic-alkalosis/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/metabolic-alkalosis/