A critical evaluation of monitoring in critical illness must recognize first that there are many different types of monitoring that may take place, and that each type of monitor may be evaluated appropriately by different standards.1 Monitoring may occur with imaging devices, analyzers that require the permanent removal of tissue or fluid for analysis, or monitors that observe physiology with either invasive or noninvasive methods without requiring an ex vivo sample.
Barie PS. Advances in Critical Care Monitoring. Arch Surg. 1997;132(7):734-739. doi:10.1001/archsurg.1997.01430310048008