Introduction

Noninvasive ventilation (NIV) is the delivery of ventilatory support without the need for an invasive artificial airway. It has a role in the management of acute or chronic respiratory failure and is increasingly being established in the treatment of patients with heart failure. Noninvasive ventilation is advocated in a range of acute and chronic conditions as well as home ventilation.

Modes

Continuous positive airway pressure

Continuous positive airway pressure (CPAP) provides a pneumatic splint that holds the upper airway open. It provides positive airway pressure throughout all phases of the ventilatory cycle, but does not provide any inspiratory support. End-expiratory pressure is usually limited to 5 to 10 cmH2O; higher pressures tend to result in gastric distension.

Bi-level positive airway pressure

Bi-level positive airway pressure ventilation provides two preset levels of positive pressure, the lower at the end ofexpiration and the higher during inspiration. Ventilatory support is delivered by the transition between these two pressure levels; initiation of inspiratory pressure rise may be patient triggered or mandatory.

Pressure-limited ventilation

Ventilators are set to deliver inspiratory support up until a preset airway pressure is reached. Inspiration and expiration are triggered by the patient.

Mechanism of action

Noninvasive ventilation decreases the work of breathing by assisting with the respiratory effort and decreasing the amount of negative pressure needed to generate a breath. It improves pulmonary mechanics and oxygenation by increasing functional residual capacity, decreasing transdiaphragmatic pressure and decreasing diaphragmatic electromyographic activity. This leads to an increase in tidal volume, a decrease in respiratory rate and an increase in minute ventilation.