Indications
CPAP
- Acute cardiogenic pulmonary oedema with respiratory distress not resolving with initial medical therapy — the principal ED indication for CPAP.
- Type 1 (hypoxaemic) respiratory failure from other causes, on specialist advice.
BiPAP (NIV)
- Acute hypercapnic respiratory failure, classically an exacerbation of COPD with persisting respiratory acidosis (pH <7.35, raised PaCO2) despite initial medical management and controlled oxygen therapy.
- Other causes of acute-on-chronic ventilatory failure (chest wall disease, neuromuscular disease, obesity hypoventilation) per BTS/ICS guidance.
Per the BTS/ICS guideline, NIV should be started promptly once an acidotic exacerbation of COPD is confirmed (pH <7.35) if it has not resolved with an hour of standard medical treatment and controlled oxygen — do not wait for further deterioration.
Contraindications & cautions
Contraindications
- Undrained pneumothorax (drain first, or treat concurrently).
- Facial trauma/burns or fixed upper airway obstruction preventing mask fit.
- Vomiting, high aspiration risk, inability to protect the airway, reduced consciousness (relative — depends on cause and reversibility).
- Life-threatening hypoxaemia or haemodynamic instability requiring immediate invasive ventilation.
Cautions
- Agree ceiling of care and escalation plan (including whether intubation is appropriate) before starting, wherever possible.
- Confusion/agitation reduces mask tolerance and effectiveness.
- Copious secretions — NIV does not substitute for airway clearance.
Preparation
- Explain the procedure, the sensation of the mask and pressure, and agree a plan if it is not tolerated or does not work — reduces anxiety and improves compliance.
- Baseline observations and arterial blood gas before starting.
- Sit the patient up (30–45° or higher) to optimise diaphragmatic mechanics.
- Continuous SpO2 monitoring, ECG, and frequent blood pressure; ensure IV access.
- Agree ceiling of care/escalation status with the patient (or via best interests) and document clearly before initiation, particularly for COPD patients with recurrent presentations.
Equipment
NIV/CPAP ventilator with pressure-targeted mode
Full face mask (first-line interface) — correctly sized
Head straps/harness
Supplemental oxygen entrainment/blender
Arterial blood gas kit
SpO2, ECG, non-invasive blood pressure monitoring
Skin protection for the nasal bridge
Suction, ready at the bedside
Starting settings
CPAP (pulmonary oedema)
- Typical starting pressure around 5–10 cmH2O, titrated to respiratory rate, work of breathing and oxygenation.
- High-flow oxygen entrainment to maintain target saturations.
BiPAP (AECOPD, per BTS/ICS)
- IPAP — starting conventions vary between the national guideline and local protocols (commonly 10–15 cmH2O); titrate upward fairly quickly according to response (respiratory rate, SpO2, PaCO2, PaO2, comfort) toward a usual target of ~20 cmH2O. Follow your department's NIV protocol.
- EPAP started at 3–4 cmH2O; routine titration usually goes no higher than 4–6 cmH2O. EPAP above 8 cmH2O is a high setting reserved for specific physiology (e.g. obesity hypoventilation) with senior/specialist input — it is IPAP, not EPAP, that climbs toward 20 cmH2O.
- Target oxygen saturation 88–92% in COPD to avoid worsening hypercapnia.
- Permissive hypercapnia (pH target ~7.2–7.25) may be accepted to avoid excessive pressures in severe airflow obstruction, per specialist guidance.
Mask fitting & initiation
Select interface
Full face mask is the usual first-choice interface in the acute setting; nasal masks are less effective acutely due to mouth leak.
Fit before strapping
Hold the mask in place by hand first to let the patient acclimatise, before securing with headgear — reduces claustrophobia and early rejection of NIV.
Minimise leak, protect skin
Adjust straps for the least leak with the least tension; apply protective dressing to the nasal bridge to prevent pressure injury.
Titrate pressures
Increase IPAP/EPAP or CPAP pressure stepwise according to response, reassessing work of breathing, comfort and gas exchange rather than fixed increments alone.
Monitoring & blood gas timing
- Continuous SpO2 and clinical observation from initiation; repeat arterial blood gas at around 1 hour after starting or after any significant setting change, to confirm the expected trend in pH/PaCO2.
- Escalate promptly if the gas fails to improve or deteriorates — do not simply continue unchanged NIV in a failing patient.
- Watch for gastric distension, mask intolerance, pressure injury, and worsening conscious level.
- Have a clear pre-agreed trigger for stepping up to invasive ventilation or stepping down to palliation, depending on the patient's ceiling of care.
Escalation planning & ceilings of care
- Establish before starting NIV whether invasive ventilation would be appropriate if NIV fails — this conversation should not be deferred until the patient has deteriorated further.
- Involve respiratory/critical care teams early, especially for recurrent COPD presentations or where NIV failure is likely.
- For patients for whom NIV is the ceiling of treatment, ensure this is documented clearly along with a symptom-management plan if NIV does not achieve its goals.
Pitfalls & pearls
- Confusing CPAP and BiPAP indications is a common error — CPAP for pulmonary oedema, BiPAP for hypercapnic ventilatory failure.
- Do not start NIV in an undrained pneumothorax.
- A patient who is not improving on NIV after an appropriately titrated trial needs urgent senior review, not simply "more time."
- Explain and reassure early — a panicking patient fighting the mask will fail even well-set NIV.
- Repeat the blood gas — do not rely on saturations alone to judge hypercapnic response.
DOPS pointers
RCEM curriculum: Intermediate/Higher Procedural Skill. What assessors look for at each entrustment level:
| 1 | Observed only — can distinguish CPAP vs BiPAP indications and describe typical starting settings. |
| 2a | Performs with supervisor present: correct mode/pressure selection, mask fitting, initial titration. |
| 2b | Manages the whole initiation and early monitoring sequence including gas timing and documentation. |
| 3 | Indirect supervision: recognises NIV failure early, escalates appropriately, manages ceiling-of-care discussions. |
| 4 | Independent; supervises others and leads departmental NIV pathway/escalation decisions. |
References
- Davidson AC, Banham S, Elliott M, et al. British Thoracic Society/Intensive Care Society Guideline for the ventilatory management of acute hypercapnic respiratory failure in adults. Thorax 2016;71(Suppl 2):ii1–ii35.
- British Thoracic Society. Non-invasive ventilation in acute exacerbations of COPD — clinical resources, brit-thoracic.org.uk.
- RCEM Curriculum 2021 — Emergency Medicine Specialty Learning Outcomes: intermediate/higher procedural skills (DOPS).