Recognizing hypovolaemia.

Clinical shock is a common problem of the critically ill patient. Assessment of the circulating volume is important to assure adequate oxygen supply to the tissues, and hypovolaemia must be treated promptly to avoid organ dysfunction. The author reviews the diagnostic approach, focusing on clinical and "surrogate" markers of volume status. Clinical signs are often late indicators and the monitoring of hemodynamic variables through cardiac catheterism can be misleading. The fluid challenge approach provides a useful diagnostic test of hypovolaemia, and a method for titrating the dose of fluid tailored to the individual's requirement.