Respiratory Acid–Base Disorders

Kidneys, Electrolytes & Acid–Base · ICU Decoded chapter 54 · Locked — free with a referral

By Dr Javed Akhtar · Last reviewed 3 October 2026

Cited to ATS acid–base reference · BTS/ICS 2016.

Key points

With acute respiratory acidosis, pH falls 0.08 for every 10 mmHg rise in PaCO₂ (chronic: 0.03).
Hypercapnia plus hypoxemia signals alveolar hypoventilation ± V/Q mismatch; address the driver (obstruction, NM weakness, CNS depression).
ICU respiratory alkalosis comes from early sepsis, PE, pain, over-ventilation, or pregnancy; never just sedate the sepsis hyperventilator.
Permissive hypercapnia is a lung-protective strategy, not a therapeutic target.
Winter's formula for metabolic acidosis: expected PaCO₂ = (1.5 × HCO₃⁻) + 8 ±2.

Investigations

First tests: Arterial blood gas, Sodium, potassium, bicarbonate, urea and creatinine, Respiratory and ventilator assessment.

Only if indicated: Chest X-ray, Targeted toxicology tests.

Repeat monitoring: Arterial blood gas.

Management pathways in this chapter

Evaluating Respiratory Acid–Base Disturbances

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The pathway step by step, with its decision points
Treatment orders with doses
Why and when to send each test

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