Monitoring the critically ill patient.

It has long been recognised that the physiological response of the patient to a stress or disease process will very largely determine the outcome. It is important, therefore, to monitor the physiological responses of patients since this not only allows the assessment of physiological reserve but will also give a baseline against which the effectiveness of any applied treatment can be judged. Basic knowledge of the principles of monitoring and correct interpretation of data is important since a failure to do so can result in misdirected therapy. Much of what will be discussed in this review revolves around the maintenance of normal aerobic metabolism and thus maintenance of viable cell function and measurement of the degree of tissue oxygenation. Reduced supply of oxygen over demand for oxygen results in cell injury and organ dysfunction. Only by assessing this dysfunction can appropriate modifications of therapy be undertaken.