Hemodynamic monitoring gives early warning of changes in a critically ill patient's condition. Accuracy is essential; for example, a blood pressure cuff is inaccurate at low pressures. Hospitalized adults will usually have a higher central venous pressure, so a CVP less than 4 cm H(2)O may indicate hypovolemia. Correlation between CVP level and blood volume is very poor in critically ill patients, so measurement of pulmonary capillary wedge pressure becomes essential. Measurement of cardiac output eliminates the need for arterial and mixed venous blood samples, and can be valuable in decision-making. Calculation of vascular resistance can also be very important in management of the critically ill. With today's facilities, routine clinical assessment is no longer adequate care for these patients.