Non-invasive ventilation (NIV) is a way of providing ventilatory support to patients in respiratory failure without using an invasive airway device (e.g. endotracheal, naso-tracheal or tracheostomy tube). Careful use of these, have been shown to not only reduce the need for invasive ventilation, in acutely unwell patients, but also improve mortality rates.

The devices are becoming increasingly commonplace in medical practice and can be set up by trained professionals in the Emergency Department, ICU, respiratory wards and even at home for some patients.

As an F1 you may commonly come across NIV for patients with severe exacerbations of Chronic Obstructive Pulmonary Disease (COPD) or Heart Failure (HF) and patients with obstructive sleep apnoea who use a particular version of it overnight.

Generally though, if you are considering a patient might need NIV, a senior clinician must be involved!

Types
As a F1, the two main types of NIV that you should know of:

• Continuous positive airway pressure (CPAP).
• Bi-level positive airway pressure (BiPAP).

CPAP provides a single level of pressure throughout inspiration and expiration. During inspiration, the additional pressure recruits more alveoli and so surface area across which gas exchange can occur increases. On expiration, the patient has to breathe against the same pressure so those alveoli remain open at the end expiration. This again prolongs gas exchange time (i.e. by increasing functional residual capacity* and recruiting more alveoli surface area when previously they were collapsed).

*Functional residual capacity being the air remaining after a normal or tidal expiration.

BiPAP uses two levels of pressure instead of one. One pressure for inspiration (inspiratory positive airway pressure or IPAP) and one for expiration (expiratory positive airway pressure or EPAP). The IPAP level is higher than the EPAP level and works in the same way that CPAP does on inspiration. It also gives additional respiratory support to reduce the patients work required to breathe; thus preventing fatigue of the respiratory muscles. Where BiPAP differs, is that the EPAP pressure normally lower than the fixed pressure delivered by CPAP during expiration. The patient therefore finds it easier to breathe out but still gets the benefit of more recruited alveoli being open at the end of expiration. The difference between the IPAP and EPAP pressure is known as the pressure support.

Indications
This is not a decision to be made by an FY1.

There’s no hard and fast rule about when to use NIV but generally, it is used in patients who are not ventilating in spite of full medical management, with some examples being:

• Acute pulmonary oedema where diuresis has failed.
  • With CPAP by increasing ventilation and reducing work of breathing.
• Type 2 respiratory failure (for example in COPD exacerbations), where nebulisers and IV treatments have failed to ensure good oxygenation.
  • With BiPAP to increase ventilation, reduce work of breathing and improve hypercarbia.

Most hospitals will have a guideline detailing at what degree of acidosis or hypercapnia NIV should be considered

How to start it?
Lots of hospitals now have specialist nurses or physiotherapists that set patients up on NIV but the principles are helpful as an F1, especially if out of hours you need to make changes to the set up!

Changes should be driven by seniors.

CPAP:

• Ensure well-fitting mask and counsel the patient that it may be claustrophobic and an unpleasant sensation (some people describe it as having your head stuck out of the window of a speeding car).
• Choose an appropriate level of supplemental oxygen. 
• Start low – usual settings are 5, 7.5 or 10 cmH2O, so start at 5 cmH2O and titrate to response.
• Titration should be by 2-3 cmH2O every 5 minutes until a satisfactory response achieved .
• Avoid going above pressures of 15-17 cmH2O!

BiPAP:

• Again, ensure a well-fitting mask and counsel the patient.
• Supplemental oxygen.
• Again start low:
  • EPAP usually starts at 4-5 cmH2O.
  • IPAP is the pressure you change. Start at 10 cmH2O then titrate by 2-5 cmH2O increments every 10 minutes until therapeutic response or patient tolerability reached. 
  • IPAP can reach a setting of 20 cmH2O – definitely have a senior or an experienced NIV nurse if your patient is requiring any higher. Consider ITU involvement!
• Monitoring should occur with serial ABGs (or arterial line samples). The BTS guidelines state that if NIV has failed by 4 hours, invasive mechanical ventilation should be considered.
• The weaning process takes about 4 days, gradually increasing the amount of time that the patient spends off the ventilator. 
  • Often by providing cycles of 1 hour on NIV, 2 hours off. And then overnight, continued NIV to allow rest.

Contraindications
There are few absolute contraindications to NIV:

• Respiratory or cardiac arrest.
• Lack of consent or uncooperative patients (they will pull it off).
• Facial trauma/burns.
• Reduced GCS <8, i.e. inability to protect their own airway.
• Untreated pneumothorax.
• Skull base fracture (can cause iatrogenic pneumocephalus).
• Persistent vomiting 

Lack of experienced staff is also a contraindication to consider.

Relative contraindications include:

• Extreme anxiety.
• Morbid obesity.
• Copious respiratory secretions.
• Poor respiratory drive.

If one of the relative contraindications are present, your senior should be making the decision about NIV.

Counselling points and potential complications
Be sure to go through the following when explaining NIV to your patient so they can make informed consent. The most common complications are:

• Anxiety/claustrophobia (it is helpful to start by placing it on their face intermittently, then ask them to hold it & increasing pressures slowly).
• Stomach distension, vomiting and/or aspiration.
• Irritation to the eyes and raised intraocular pressure.
• Pressure sores around the fit of the mask (work with nurses to ensure a better fit is used with gauze to support the seal of the masks).
• Congestion of nasal sinuses.
• Raised intracranial pressure.
• Can cause hypotension if the patient is hypovolaemic.
  • By reducing venous return from the lungs, often due to creating too high pressures of air/ hyper inflation.

Final Point
NIV can be a very useful tool to support patients with respiratory distress even all other resuscitative methods have failed.

However, always involve a senior (even if over the phone) to determine if this is most appropriate. And find an appropriately trained clinician (including senior respiratory nurses) who are comfortable setting up the NIV.

Please remember that extensive explanation and reassurance can dramatically help patient tolerance!

Written by Dr Emily Cramond-Wong, Trust grade ST1

Updated by Dr Gurvinder Sidhu (CTF PGDip MedEd) on 30th May 2025.