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# Respiratory alkalosis

Over-breathing removes too much CO₂ and the blood turns alkaline; anxiety, pain, hypoxaemia, sepsis and pulmonary embolism cause it.

Updated 2026-11-01

## Structures involved

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- [Medulla oblongata](https://durgical.com/en/anatomy/medulla-oblongata/)
- [Pons](https://durgical.com/en/anatomy/pons/)
- [Pulmonary arteries](https://durgical.com/en/anatomy/right-pulmonary-artery/)
- [Right lower lobe](https://durgical.com/en/anatomy/inferior-lobe-of-right-lung/)
- [Left lower lobe](https://durgical.com/en/anatomy/inferior-lobe-of-left-lung/)

## In biochemistry

- [Acid–base interpretation (step by step)](https://durgical.com/en/biochemistry/topics/acid-base-interpretation/)
- [Acid–base compensation rules](https://durgical.com/en/biochemistry/topics/acid-base-compensation-rules/)

## In physiology

- [High altitude and acclimatization](https://durgical.com/en/physiology/high-altitude-and-acclimatization/)
- [Reading an arterial blood gas step by step](https://durgical.com/en/physiology/reading-an-arterial-blood-gas-step-by-step/)
- [Respiratory acidosis and alkalosis](https://durgical.com/en/physiology/respiratory-acidosis-and-alkalosis/)
- [Mixed acid–base disorders](https://durgical.com/en/physiology/mixed-acid-base-disorders/)
- [CO₂ transport and the Haldane effect](https://durgical.com/en/physiology/co-transport-and-the-haldane-effect/)
- [Control of breathing, chemoreceptors and lung reflexes](https://durgical.com/en/physiology/control-of-breathing-chemoreceptors-and-lung-reflexes/)

## What it is

A primary fall in pCO₂ (hypocapnia) from hyperventilation, with a rise in pH; acute or chronic and [kidney](https://durgical.com/en/anatomy/kidney/) -compensated.

## Who gets it

It is very common in emergency and hospital patients; it is also normal in pregnancy and in people living at high altitude, as in Bogotá and other Andean cities.

## Causes

- Hypoxaemia: pneumonia, pulmonary embolism, asthma, altitude, heart failure
- Central drive: anxiety and panic attacks, pain, fever, early sepsis, stroke, salicylates
- Hormonal: pregnancy (progesterone), hyperthyroidism
- Cirrhosis (ammonia and other substances stimulate the respiratory centre)
- Excessive mechanical ventilation

## Risk factors

- Rapid ascent to high altitude
- Anxiety disorders
- Acute lung disease
- Sepsis

## Pathophysiology

Alveolar ventilation exceeds CO₂ production, pCO₂ falls and pH rises. Within hours cell buffers release H⁺ (HCO₃⁻ falls about 2 mmol/L per 10 mmHg); over days the kidney excretes bicarbonate (a fall of 4–5 per 10 mmHg). Hypocapnia causes cerebral vasoconstriction (dizziness, blurred vision) and alkalaemia increases calcium binding to albumin, lowering ionised calcium: perioral and hand paraesthesia, carpopedal spasm. High pH shifts potassium and phosphate into cells.

## Classification

- Acute: high pH with near-normal HCO₃⁻
- Chronic: near-normal pH with low HCO₃⁻ (pregnancy, altitude, cirrhosis)

## Symptoms and signs

- Fast breathing or frequent sighing
- Dizziness, feeling faint
- Tingling around the mouth and in hands and feet
- Cramps or carpopedal spasm
- Palpitations, atypical chest pain

## Red flags

- Hyperventilation with hypoxaemia (embolism, pneumonia): never assume anxiety without ruling it out
- Fever and hypotension (early sepsis)
- Salicylate poisoning (tinnitus, vomiting, mixed acidosis)

## Diagnosis

**Clinical**
Look first for organic causes (hypoxaemia, sepsis, embolism, salicylates) before attributing it to anxiety.

**Tests**
Arterial gases (low pCO₂, high pH), alveolar–arterial oxygen gradient, electrolytes and ionised calcium, salicylate levels, pregnancy test, D-dimer by probability.

**Imaging**
[Chest](https://durgical.com/en/anatomy/region/chest/) X-ray; CT pulmonary angiography if embolism is suspected.

## Treatment

**Medical**
Treat the cause: oxygen in hypoxaemia, antibiotics in sepsis, anticoagulation in pulmonary embolism

**Conservative**
In an anxiety attack: reassurance, slow-breathing coaching, after ruling out other causes (paper-bag rebreathing is not advised because of hypoxaemia risk)

**Procedure**
On mechanical ventilation: adjust rate and volume

**Follow-up**
Monitoring of gases and electrolytes in severe cases

## Complications

- Tetany and seizures
- Arrhythmias
- Cerebral or coronary ischaemia from vasoconstriction in extreme cases

## Prognosis

Depends on the cause: benign in a panic attack, serious if it reflects sepsis or pulmonary embolism.

## Test yourself

Think of the answer, then tap the question to see it.

## Why does respiratory alkalosis cause tingling and carpopedal spasm?

High pH increases calcium binding to albumin and lowers ionised calcium, which excites nerves.

## Which serious cause of hyperventilation must not be mistaken for anxiety?

Pulmonary embolism (also early sepsis, pneumonia or salicylate poisoning).

## How much does HCO₃⁻ fall in chronic respiratory alkalosis?

About 4–5 mmol/L per 10 mmHg fall in pCO₂, through renal bicarbonate excretion.

## In which normal state is there chronic respiratory alkalosis?

Pregnancy, driven by progesterone, and living at high altitude.

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## Related conditions

- [Respiratory acidosis](https://durgical.com/en/conditions/respiratory-acidosis/)
- [Pulmonary embolism](https://durgical.com/en/conditions/pulmonary-embolism/)
- [Sepsis and septic shock](https://durgical.com/en/conditions/sepsis-and-septic-shock/)
- [Asthma](https://durgical.com/en/conditions/asthma/)
- [Cirrhosis](https://durgical.com/en/conditions/cirrhosis/)
- [Community-acquired pneumonia](https://durgical.com/en/conditions/community-acquired-pneumonia/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Respiratory alkalosis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000111.htm) (MedlinePlus, US National Library of Medicine, 2026); [Arterial Blood Gas (ABG) Test: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/arterial-blood-gas-abg-test/) (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).

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Source: https://durgical.com/en/conditions/respiratory-alkalosis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/respiratory-alkalosis/