It is useful to consider time in critical illness from two perspectives. The first of these begins logically with onset of the pathology. With the exception of conditions such as myocardial infarction or trauma where this moment is marked by a classic symptom or an external event, then defining time zero is difficult. For this reason, an organisational frame of reference, such as hospital admission or time of referral to specialist team, is more commonly used. Delay following this organisational time is important because it is often a modifiable factor with regard to the delivery of health care. However, pathophysiological timing remains relevant because if the disease process is dynamic (and this is part of the hypothesis of this study) then it determines the phenotype of disease at any particular moment.