Consciousness monitoring in ventilated patients: bispectral EEG monitors arousal not delirium.
OBJECTIVE
Bispectral index (BIS) is being evaluated as a monitor of consciousness, yet it is unclear what components of consciousness (i.e., arousal vs. content of consciousness) the BIS measures. This study compared BIS levels to well-validated clinical measures of arousal and the presence or absence of delirium.


METHODS
A prospective, blinded, observational cohort study.


METHODS
124 mechanically ventilated, adult, medical ICU patients.


RESULTS
Using BIS 3.4 and BIS-XP 4.0 algorithms, BIS values were calculated immediately prior to clinical assessments. The clinical assessments included the Richmond Agitation-Sedation Scale (RASS) and presence or absence of delirium using the Confusion Assessment Method for the ICU. A total of 484 assessments were collected among 124 patients. BIS-XP values demonstrated greater correlation with RASS than BIS 3.4 ( R(2)=0.36 vs. 0.20), although considerable overlap of BIS-XP scores remained across RASS levels. Median BIS-XP values for delirious and nondelirious observations were 74 and 96, respectively, while BIS 3.4 values were 91 and 96, respectively. However, neither BIS 3.4 nor BIS-XP were significantly associated with delirium after controlling for RASS value.


CONCLUSIONS
In comparison with clinical measures of arousal in mechanically ventilated patients, BIS-XP algorithm demonstrated stronger correlation with RASS levels than did BIS 3.4, yet marked overlap across different levels of arousal persist using both algorithms. After controlling for level of arousal, neither BIS-XP nor BIS 3.4 algorithms distinguished between the presence and absence of delirium.
Ely
E Wesley
EW
Tennessee Valley Veteran's Affairs Healthcare System, Geriatric Research, Education and Clinical Center, Vanderbilt University School of Medicine, Nashville, TN, USA. wes.ely@vanderbilt.edu
Truman
Brenda
B
Manzi
Donna J
DJ
Sigl
Jeffrey C
JC
Shintani
Ayumi
A
Bernard
Gordon R
GR
D000465:Algorithms; D001143:Arousal; D016292:Procedural Sedation / Q000145:classification*; D003243:Consciousness; D003693:Delirium / Q000175:diagnosis; D016903:Drug Monitoring / Q000379:methods; D004569:Electroencephalography; D005260:Female; D006801:Humans; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods*; D011446:Prospective Studies; D012121:Respiration, Artificial; D012984:Software; D018709:Statistics, Nonparametric
D006993:Hypnotics and Sedatives