ABG (15 L NRB)

pH

7.22

PaCO₂

85 mmHg

PaO₂

180 mmHg

HCO₃

34 mmol/L

Interpretation

• • Acidaemia + ↑CO₂ → respiratory acidosis
• • HCO₃ 34 → chronic compensation expected = 24 + 3.5 × (85-40)/10 = 39 — actual 34 lower than expected → acute-on-chronic
• • Over-oxygenation worsened hypercapnia

Next steps

• • Titrate O₂ to SpO₂ 88–92% via Venturi 24–28%
• • Bronchodilators, steroids, antibiotics if infective
• • NIV (BiPAP) if pH 7.25–7.35 after 1 h
• • Intubate if exhausted / pH <7.25 not improving