The chapter highlights two main features:

• Acute severe asthma should be considered the unstable angina of respiratory medicine.

• Asthma kills.

Incidence

In many countries, in the 30–40 years up to 2000, there was a steep rise in hospital admissions for asthma, accounting for ≈100,000 per year in England and Wales, half of which were <15 years of age. In children, males have a higher admission rate than females, the opposite being true for adults. In the UK there had been a similar but less marked increase in asthma deaths, which latterly seems to be falling slowly probably because of better long-term prophylactic treatment.

Over the period 1995–2001, acute severe asthma accounted for 1.7% of admissions to adult general critical care units across England, Wales and Northern Ireland. Of these, 57% were mechanically ventilated within the first 24 h. Unit mortality was 7.1% and hospital mortality 9.8%[1].

Causes

Asthma is an inflammatory disease of the lower airways that may be associated with specific identifiable allergy (atopic or extrinsic asthma) or not (non-atopic or intrinsic asthma). The latter starts more commonly in mid-and late adult life.

It is a disease of exacerbation with either full remission or persistence of symptoms (chronic severe asthma). Exacerbation may be due to:

• specific allergen exposure — environmental, food or occupational,

• air pollution — gaseous or particulate,

• treatment non-compliance,

• infection — viral or bacterial,

• thunderstorms.