What is the difference between CPAP and bilevel non-invasive ventilation?

CPAP delivers a single continuous pressure that holds airways open, whereas bilevel ventilation adds a higher pressure during inspiration to support each breath, which can help clear carbon dioxide in hypercapnic failure.

When is non-invasive ventilation not appropriate?

It generally requires a patient who is conscious enough to protect the airway and tolerate the mask; it is less suitable when the airway is unprotected or when respiratory failure is not responding, in which case intubation may be needed.

Non-Invasive Ventilation

Non-invasive ventilation is the delivery of positive-pressure ventilatory support through a mask or similar interface rather than an endotracheal tube or tracheostomy. In emergency care it is used to support breathing in selected forms of acute respiratory failure while avoiding the risks of intubation, when the patient can protect the airway and tolerate the interface.

Definition

Non-invasive ventilation is a form of mechanical ventilatory support that applies positive airway pressure through a non-invasive interface such as a face or nasal mask, including continuous positive airway pressure and bilevel positive-pressure modes, to improve oxygenation and reduce the work of breathing without an artificial airway placed in the trachea.

Scope

The topic covers what non-invasive ventilation is, the principal modes of continuous and bilevel positive airway pressure, the acute conditions in which it is best supported by evidence, and the importance of patient selection and monitoring for failure. It is presented as reference knowledge about the modality, not as instruction in pressure settings or candidacy for an individual patient.

Core questions

What distinguishes non-invasive from invasive ventilation?
How do continuous and bilevel positive airway pressure differ?
In which acute conditions is non-invasive ventilation best supported?
How is failure recognised so that intubation is not unduly delayed?

Key concepts

Continuous positive airway pressure (CPAP)
Bilevel positive airway pressure
Work of breathing and respiratory muscle unloading
Patient selection and contraindications
Monitoring for non-invasive ventilation failure
Interface tolerance and leak

Mechanisms

Positive airway pressure splints the upper airway and alveoli open, improving oxygenation, while inspiratory pressure support augments tidal volume and unloads the respiratory muscles, reducing the work of breathing. In hypercapnic respiratory failure this can improve carbon dioxide clearance and reverse respiratory acidosis; in cardiogenic pulmonary oedema, positive pressure reduces venous return and improves gas exchange. Because the airway is not secured, the approach depends on adequate consciousness, airway protection, and tolerance of the interface, and a key concept is timely recognition of failure so that intubation is not delayed. Even non-invasively, excessive pressures and volumes can contribute to lung injury, linking the modality to the broader concern of ventilator-induced lung injury.

Clinical relevance

Non-invasive ventilation is a major option for supporting breathing in selected acute respiratory failure, with the strongest evidence in chronic obstructive pulmonary disease exacerbations and cardiogenic pulmonary oedema. This entry describes its principles, indications, and limits as reference knowledge and does not provide settings, candidacy criteria, or treatment decisions for individual patients.

Epidemiology

Randomised evidence established benefit for non-invasive ventilation in acute exacerbations of chronic obstructive pulmonary disease, where it reduces the need for intubation, and clinical practice guidelines synthesise the indications across forms of acute respiratory failure. Outcomes depend heavily on appropriate patient selection and on recognising non-response.

History

Non-invasive positive-pressure ventilation moved into mainstream acute care after randomised trials in the 1990s, notably Brochard and colleagues' demonstration of benefit in chronic obstructive pulmonary disease exacerbations. Subsequent international guidelines consolidated the indications and cautions, distinguishing settings with strong evidence from those where the modality is less certain.

Debates

How broadly should non-invasive ventilation be applied in acute hypoxaemic respiratory failure?: While benefit is well established in chronic obstructive pulmonary disease exacerbations and cardiogenic pulmonary oedema, its role in de novo hypoxaemic respiratory failure is less certain because failure may delay needed intubation, and guidelines treat such use more cautiously.

Key figures

Laurent Brochard
Bram Rochwerg
Arthur Slutsky

Seminal works

brochard-1995
rochwerg-2017

Frequently asked questions

What is the difference between CPAP and bilevel non-invasive ventilation?: CPAP delivers a single continuous pressure that holds airways open, whereas bilevel ventilation adds a higher pressure during inspiration to support each breath, which can help clear carbon dioxide in hypercapnic failure.
When is non-invasive ventilation not appropriate?: It generally requires a patient who is conscious enough to protect the airway and tolerate the mask; it is less suitable when the airway is unprotected or when respiratory failure is not responding, in which case intubation may be needed.