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Why is the BIS Monitor needed when I already monitor other vital signs?Anesthesia providers have relied upon changes in vital signs, particularly blood pressure and heart rate, to infer anesthetic needs and effect. But, heart rate and blood pressure are not direct measures of depth of anesthesia or consciousness, and may be affected by a myriad of influences. For example, patients on beta-blockers may have altered heart rate response to anesthetics or surgical stimulation. While a patient who receive too little hypnotic agent can have a hypertensive response to laryngoscopy and intubation, hypertension is not necessarily a specific indication of inadequate hypnosis. Although the BIS monitor primary measures the hypnotic effect of anesthetic agents, it is also useful in assessing the total anesthetic state. Clinical experience and investigations have shown that the BIS index may rise transiently in response to surgical stimulation then resettle to a desirable level. This transient BIS “pop” likely reflects a period of cortical activation from spinal cord mechanisms. In controlled investigations, the administration of additional analgesic effect (e.g. narcotic administration) may blunt these BIS pops. In a similar fashion, levels of analgesic effect also influence the variability of the BIS trend during the course of surgery: with increasing narcotic doses the BIS trend is both smoother and less likely to demonstrate the transient activation. Thus the BIS trend display is a window into the analgesic state during the procedure. BIS monitoring provides additional information that completes the assessment of anesthetized patient. It provides a new perspective to view the changes in vital signs that patients develop during the course of anesthesia and surgery. Here are some recent abstracts/articles that may be of interest on this topic:
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