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Respiratory Acidosis
Related Subjects: Asthma |Acute Severe Asthma |Exacerbation of COPD |Pulmonary Embolism |Cardiogenic Pulmonary Oedema |Pneumothorax |Tension Pneumothorax |Respiratory (Chest) infections Pneumonia |Fat embolism |Hyperventilation Syndrome |ARDS |Respiratory Failure |Diabetic Ketoacidosis
🩸 Analysis of Respiratory Acidosis (ABG)
- 📉 pH: < 7.35 (acidaemia)
- 🫁 PaCO₂: > 5.3 kPa (retained CO₂)
- 🧪 HCO₃⁻: > 24 mmol/L (renal compensation if chronic)
- 🌬️ PaO₂: often low/normal depending on hypoxia
⚡ Aetiology
- CO₂ retention → increased carbonic acid → acidosis
- Kidneys compensate by retaining HCO₃⁻ (in chronic cases)
🦠 Causes
- Chronic or acute respiratory failure with CO₂ retention
- COPD (most common chronic cause)
- 💉 Sedative overdose (↓ respiratory drive)
- 🧠 Stroke, severe head injury
- 🌊 Severe pulmonary oedema
- 💪 Neuromuscular weakness (e.g. MND, Guillain-Barré, myasthenia)
👀 Clinical Features
- 🌀 Confusion, agitation, headache
- ✋ Asterixis (“flapping tremor”)
- 😴 Drowsiness → coma if severe
💊 Management
- 🎯 Treat underlying cause (e.g., bronchodilators + steroids in COPD)
- 🫁 Ventilatory support if needed:
- 💨 Non-invasive ventilation (NIV) in hypercapnic COPD exacerbation
- 🛏️ Intubation & mechanical ventilation if severe / unresponsive
- ❌ Avoid excessive oxygen in chronic CO₂ retainers (risk of worsening hypercapnia)
Acid–Base Disorders — Expected Patterns & Common Causes ⚖️
| Disorder | pH | PaCO₂ | HCO₃⁻ | Key Causes |
|---|---|---|---|---|
| Metabolic Acidosis | ↓ (<7.35) | ↓ (respiratory compensation) | ↓ |
|
| Metabolic Alkalosis | ↑ (>7.45) | ↑ (respiratory compensation) | ↑ |
|
| Respiratory Acidosis (Acute) | ↓ (<7.35) | ↑ | Normal (no time for renal comp.) |
|
| Respiratory Acidosis (Chronic) | Slightly ↓ / near-normal | ↑ | ↑ (renal compensation) |
|
| Respiratory Alkalosis (Acute) | ↑ (>7.45) | ↓ | Normal |
|
| Respiratory Alkalosis (Chronic) | Slightly ↑ / near-normal | ↓ | ↓ (renal compensation) |
|
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