Patients admitted to intensive care units are either in a state of acute physiological instability or in danger of becoming unstable. On admission and throughout the stay in the intensive care unit, the patient is assessed by both medical and nursing personnel to develop medical and nursing diagnosis, upon which further assessment and treatment will be based. The value of physiological monitoring depends on the ability of the personnel to use the instrumentation when indicated, to properly perform the procedure incorporating the instrument, to accurately interpret the findings, and to disturb the patient as little as possible. It should be obvious that use of instruments. should impose minimal or hopefully no further insult on an already traumatized organism.