Continuous Positive Airways Pressure (CPAP)
CPAP (Continuous Positive Airway Pressure) provides constant positive pressure via a nasal or full-face mask. Consider in acute respiratory distress not responding to medical therapy — always discuss with a senior. ⚠️ Requires close monitoring by experienced staff to avoid complications.
📌 Indications
- Acute pulmonary oedema (confirmed on CXR).
- Obstructive sleep apnoea (OSA).
- Sometimes used as a bridge in Type I respiratory failure (e.g. pneumonia, post-op atelectasis).
🚨 Escalation: ITU Referral
- Falling GCS (risk of airway compromise).
- SpO₂ <90% on high-flow O₂ via non-rebreather mask.
- PaO₂ <8 kPa on ABG despite oxygen therapy.
- Refractory pulmonary oedema despite diuretics and vasodilators.
- Systolic BP >90 mmHg is generally required for safe CPAP initiation.
⚠️ Be Ready for Intubation
- Absolute indication: apnoea or profound respiratory depression (RR <10/min).
- Persistent hypoxaemia or hypercapnia despite optimal CPAP + medical management.
- Deteriorating mental status or inability to protect airway → urgent ITU referral.
⚡ Physiological Effects of CPAP
- 💉 Reduces preload: increased intrathoracic pressure ↓ venous return.
- 🫀 Lowers afterload: augments LV ejection, improving stroke volume in LV failure.
- 🫁 Respiratory effects: alveolar recruitment, airway splinting, ↑ functional residual capacity, ↓ work of breathing.
- Typical starting pressure: 5 cm H₂O, titrate up to 10 cm H₂O if needed.
⛔ Contraindications
- Reduced consciousness (AVPU ≤ P) → cannot protect airway.
- Dementia or agitation → intolerance to mask.
- Systolic BP <90 mmHg → risk of cardiovascular collapse.
- Pneumothorax.
- Facial trauma or base of skull fracture.
- Type II respiratory failure (CO₂ retention) — consider BiPAP instead.
⚠️ Complications
- Hypotension (due to ↓ venous return and cardiac output).
- Aspiration (air insufflation can overcome oesophageal sphincter).
- Gastric distension (risk of vomiting, discomfort).
- Anxiety/panic due to tight-fitting mask and hypoxia.
🛑 When to Stop CPAP
- Continue until lungs clear of crackles and patient haemodynamically stable.
- Wean airway pressure first, then reduce FiO₂ and step down to a facemask.
- If no improvement within 30 minutes → discontinue and escalate care.
🌟 Teaching pearl: In acute pulmonary oedema, CPAP rapidly improves oxygenation and reduces preload/afterload, often buying time for diuretics and vasodilators to work. Always have an intubation backup plan before starting CPAP.
Case examples
- 💨 Case 1 – Age 72: Presented to A&E with acute shortness of breath, frothy pink sputum, and hypoxia (SpO₂ 84% on air). CXR showed pulmonary oedema due to acute left ventricular failure.
Management: CPAP started at 10 cm H₂O alongside IV furosemide and nitrates. Oxygenation improved rapidly, avoiding intubation.
Teaching point: In cardiogenic pulmonary oedema, CPAP reduces preload and afterload, improving gas exchange and cardiac performance.
- 😴 Case 2 – Age 55: Overweight man reported loud snoring, witnessed apnoeas, and daytime sleepiness. Overnight oximetry showed repetitive desaturations; sleep study confirmed moderate OSA.
Management: CPAP during sleep eliminated apnoeas and improved daytime alertness and blood pressure.
Teaching point: In obstructive sleep apnoea, CPAP splints the upper airway open, preventing collapse during inspiration.
- 🌬️ Case 3 – Age 68: Known COPD with type 2 respiratory failure (pH 7.31, pCO₂ 8.4 kPa, HCO₃⁻ 31 mmol/L) presented with acute dyspnoea and fatigue. Initially treated with controlled oxygen but remained hypercapnic.
Management: Trial of non-invasive ventilation (BiPAP), but early CPAP used to improve alveolar recruitment and reduce work of breathing.
Teaching point: CPAP or BiPAP may prevent intubation in COPD exacerbations by supporting ventilation and reducing CO₂ retention.
