Intensive care medicine has its origins in the successful use of positive pressure ventilation to treat acute respiratory failure associated with the poliomyelitis epidemic in Copenhagen in 1952, and mechanical ventilation remains a cornerstone in the provision of modern life support. This chapter will focus on assessing the need for ventilatory support in seriously ill patients in acute wards, emergency departments and critical care units; it will not consider ventilatory support during anaesthesia and surgery.

The need for ventilatory support is probably the commonest reason for patients requiring admission to critical care units, and the provision of mechanical ventilation has major resource implications. It also carries significant complications in the form of ventilator-associated pneumonia, ventilator-induced lung injury, barotrauma and adverse circulatory effects, all of which can contribute to both morbidity and mortality. Any associated requirement for sedative drugs has additional undesirable effects. Although a patient may appear to ‘need’ ventilatory support, it must also be considered whether, for that individual, it would be appropriate.

Besides those who work in intensive care, there are many others who encounter patients who appear to ‘need’ mechanical ventilation, such as ambulance crews or staff working in emergency departments, respiratory wards, or acute medical or surgical wards.