Ventilatory supportBMJ 2006; 333 doi: https://doi.org/10.1136/bmj.333.7559.138 (Published 13 July 2006) Cite this as: BMJ 2006;333:138
- Gordon Christie, consultant,
- Graeme P Currie, specialist registrar,
- Paul Plant, consultant
- Respiratory Unit, Aberdeen Royal Infirmary, Aberdeen.
- department of respiratory medicine, St James University Hospital, Leeds.
The introduction and widespread use of non-invasive ventilation (NIV) has revolutionised the management and survival of patients with an acidotic exacerbation of chronic obstructive pulmonary disease (COPD). Indeed, it is difficult to justify admitting patients with an exacerbation of COPD to hospitals where NIV is not readily available. A close fitting facemask or nose mask connected to a portable ventilator facilitates a non-invasive method of providing respiratory support to a spontaneously breathing patient. The mask can be removed easily, allowing patients to communicate, eat, drink, and take nebulised and oral drugs.
How non-invasive ventilation works
NIV provides a two level form of respiratory support, supplying inspiratory and expiratory positive airways pressure.
Inspiratory positive airways pressure, which is usually titrated up to 15-20 cm H2O, helps offload tiring respiratory muscles and reduce the work of breathing, improves alveolar ventilation and oxygenation, and increases elimination of CO2.
Expiratory positive airways pressure, usually at 4-6 cm H2O, helps “splint open” the airway and flushes CO2 from the mask. It also reduces the work of breathing by overcoming intrinsic positive end expiratory pressure, thereby reducing atelectasis and increasing the end tidal volume.
Oxygen is introduced either through a port in the facemask or through a more proximal channel in the ventilator system. It is not usually necessary to deliver humidified oxygen, but humidifiers can be added to the circuit.
When to use non-invasive ventilation in COPD
NIV is particularly successful in patients with hypercapnic respiratory failure (especially in those with an arterial blood pH of 7.25-7.35). It can also be used as a therapeutic trial before proceeding to mechanical ventilation …