Although monitoring of critically ill patients has made giant steps forward in the past 15 years, such monitoring techniques must be viewed as a calculated risk, since a small but finite proportion of patients who are monitored by invasive techniques will suffer untoward and, occasionally, catastrophic consequences. Minimizing the risk involves careful general evaluation of the patient, adherence to strict indications for use of invasive techniques, and care coupled with experience in the actual manipulation. The specific procedure or procedures to be undertaken must be felt to be essential to the successful outcome of the care of the patient. The treatment of all critically ill patients must be individualized, and the monitoring techniques employed should be similarly individualized. With such a judicious approach, a great deal of valuable information can be obtained, and an effective and intelligent therapeutic regimen outlines so as to assure a successful outcome in as many patients as possible.