CPAP for oxygenation, BiPAP for ventilation
Expansion
CPAP delivers a single continuous pressure. It splints alveoli open, recruits collapsed lung and reduces preload and afterload. It improves oxygenation but does little for carbon dioxide.
- Type 1 respiratory failure: cardiogenic pulmonary oedema, pneumonia, atelectasis
- Obstructive sleep apnoea
BiPAP delivers a higher inspiratory and lower expiratory pressure. The difference between them augments tidal volume, so it clears carbon dioxide.
- Type 2 respiratory failure with respiratory acidosis: COPD exacerbation, neuromuscular disease, chest wall deformity, obesity hypoventilation
“CPAP for the oxygen, BiPAP for the carbon dioxide.”
The classic indication is a COPD exacerbation with pH 7.25 to 7.35 and a raised carbon dioxide despite maximal medical therapy.
Contraindications: reduced consciousness or inability to protect the airway, facial trauma or burns, vomiting, undrained pneumothorax, copious secretions, haemodynamic instability, and bowel obstruction.
Decide the ceiling of care before starting, since NIV may be either a bridge to intubation or the maximum treatment, and that distinction changes what happens when it fails.