3 - Oxygen therapy, continuous positive airway pressure and non-invasive ventilation

Summary

It is not surprising, to anyone trained in anaesthesia or critical care, that ventilation can be successfully maintained by non-invasive methods. Following induction of anaesthesia, patients are routinely ventilated non-invasively, using an anaesthetic face-mask and ‘bag’ system before intubation. It is also well known that modern critical care units originated during the paralytic polio epidemics of the 1950s and 1960s (see Chapter 20). Prior to these pandemics, patients with respiratory muscle paralysis were successfully ventilated for prolonged periods using negative pressure non-invasive tank and cuirass ventilators. However, during these particular pandemics the incidence of bulbar paresis was unusually high, and it was the introduction of tracheal intubation and positive pressure ventilation that resulted in a dramatic reduction in mortality. These events, together with the smaller size and lower cost of ‘iron lungs’, heralded a marked decline in the practice of non-invasive respiratory support during the 1970s.

Interest in non-invasive methods of support was rekindled in the 1980s by the discovery that the beneficial effect of positive end-expiratory pressure (PEEP) could be reproduced using non-invasive delivery systems. The development of more comfortable masks as a result of improvements in plastics technology should also be acknowledged as significantly contributing to this change. It was then a logical, but nevertheless very innovative, step to use the same interface to attempt to deliver ventilatory support.