How useful does a monitor need to be before it is considered worthy of routine intraoperative use?

Take for example, body temperature monitoring.  It is rare to make intraoperative clinical decisions based on the body temperature monitor, yet it is used for virtually every case.  Do we really need neuromuscular blockade monitors whenever a muscle relaxant is given, but no one would suggest that they not be used?  The use of train of four monitoring took a number of years to become a standard even at the institution where the concept was developed (WA Kofke, personal communication).  There now exist monitors that provide significant information about the interaction of certain commonly used types of anesthetic drugs with neurons that appear to be important for aspects of the phenomena we call general anesthesia.  Studies have consistently shown that these monitors improve administration of many types of general anesthetics as indicated by shorter time to wake up, less time in the PACU and often less overall dose of anesthetic drug.  As a bonus these monitors may also provide a warning about an increased potential for some types of intraoperative awareness.  Are the current generations of brain activity monitors true “depth of anesthesia monitors?”  My answer to this is no.  Will the current generation of brain activity monitors warn against all situations in which awareness during anesthesia possible?  Again my answer is no.  However despite their limitations, the data provided by these devices, when interpreted appropriately, may provide useful information that, in my experience, frequently improves the precision of anesthesia delivery, improves patient through put by decreasing the incidence of delayed awakening, decreases the dose of anesthetic used and might also warn against the potential for awareness.  However, as with other monitors, I have been in clinical situations in which BIS monitoring was unhelpful, misleading and even distracting.

David S. Smith, M.D., Ph.D.