Non-clinical sciences/Lab medicine · Acid–base

Respiratory acidosis

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What it means

↓pH with ↑PaCO₂ from alveolar hypoventilation — CO₂ retention. Causes: COPD/asthma exacerbation, opioid or sedative overdose, neuromuscular weakness (GBS, myasthenia), chest-wall/OSA. Acute: little renal compensation (HCO₃ near normal); chronic: kidneys retain HCO₃ over days.

Worked example

COPD exacerbation: pH 7.28, PaCO₂ 9.0, HCO₃ 30 = chronic respiratory acidosis with renal (metabolic) compensation.

In the exam

A drowsy patient with an opioid overdose has pH 7.22, PaCO₂ 9.5 kPa and a near-normal bicarbonate.

What settles it

Respiratory acidosis = high CO₂ (a ventilation problem); a raised-anion-gap metabolic acidosis has low HCO₃ with a low/normal CO₂ (respiratory compensation).

Classically confused with

Metabolic acidosis (raised anion gap)

Source: StatPearls — Acid-base