Non-invasive ventilation (NIV) [advanced]

Types of NIV

CPAP = continuous positive airway pressure

  • Tight fitting mask which delivers fixed positive air pressure to keep the airways open
  • Indications: sleep apnoea; type 1 respiratory failure (e.g. acute pulmonary oedema)

BiPAP = bi-level positive airway pressure

  • Similar to CPAP, but the air pressure increases during the patient’s inspirations
    • ePAP = pressure during expiration
    • iPAP = pressure during inspiration
    • Pressure support = difference in pressure between ePAP and iPAP (i.e. the amount of ‘help’ given on inspiration)
  • Indication: type 2 respiratory failure (e.g. COPD exacerbation) with acidosis (pH<7.35) or exhaustion despite optimal medical therapy

NB. The oxygen concentration in the air can be adjusted because tubing from an oxygen supply can plug directly into the machine

Background physiology



  • Start at 4cmH2O and gradually increase to reduce hypoxia
  • Maximum of 12cmH2O
  • Start with high FiO2 and titrate down


  • Start at 15/3cmH2O (i.e. iPAP of 15cmH2O, ePAP of 3cmH2O) and gradually increase iPAP to 20-30cmH2O as tolerated to optimise respiratory rate, chest expansion and tidal volumes (6-8ml/kg ideal body weight)
  • Maximum of 30/8cmH2O
    • Increase iPAP to reduce hypercapnia and achieve normal pH
    • Titrate FiO2 to reach target oxygen saturations (88-92% or PaO2~8)


  • Too high CPAP or ePAP: reduced venous return which can cause hypotension
  • Too high iPAP: mask leak; stomach inflation leading which can cause aspiration (oesophageal opening pressure is 25cmH2O)
  • Both: patient discomfort; claustrophobia; pressure sores; dryness; pneumothorax



  • Severe facial deformity
  • Facial burns/trauma
  • Fixed upper airway obstruction
  • Inability to protect airway
  • Severe epistaxis
  • Vomiting
  • Apnoea

NB. NIV should not be used for asthma (just delays inevitable intubation) or pneumonia (unless patient is not for intubation).


  • pH<7.15
  • Undrained pneumothorax
  • Aspiration risk
  • GCS <8
  • Copious respiratory secretions
  • Poor respiratory drive
  • Need for continuous or near-continuous ventilatory assistance
  • Confusion/agitation
  • Facial/oesophageal/gastric surgery

Monitoring required

  • Oxygen saturation monitoring (aim 88-92% in COPD patients, 94-98% in non-COPD patients)
  • Regular arterial blood gasses (~30mins after each change to monitor pCO2 and subsequent pH)
    • In COPD, aim PaO2~8mmHg and improving pH
  • Blood pressure (check not becoming hypotensive)
  • Respiratory rate
  • Cardiac monitoring

Weaning off NIV         

  • Once the medications have had time to work and patients physiology has been corrected, NIV can be gradually weaned
  • Options:
    • Give patient time off NIV in day and gradually extend time off (leave overnight until last as respiratory drive naturally decreases)
    • Gradually reduce pressures

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