Non-clinical sciences/Lab medicine · Acid–base

Respiratory alkalosis

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What it means

↑pH with ↓PaCO₂ from hyperventilation — blowing off CO₂. Causes: anxiety/pain, early PE, early sepsis, salicylate poisoning (early), high altitude, pregnancy (progesterone drive).

Worked example

A tachypnoeic anxious young woman: pH 7.50, PaCO₂ 3.2, HCO₃ normal.

In the exam

After a panic attack a young woman is tachypnoeic with peri-oral tingling; pH 7.50, PaCO₂ 3.1 kPa, bicarbonate normal.

What settles it

Respiratory alkalosis = low CO₂ from over-breathing; metabolic alkalosis = high HCO₃ (vomiting/diuretics) with a compensatory high-normal CO₂.

Classically confused with

Metabolic alkalosis

Source: StatPearls — Acid-base