An assessment of the validity of spectral entropy as a measure of sedation state in mechanically ventilated critically ill patients.
OBJECTIVE
To assess whether the Entropy Module (GE Healthcare, Helsinki, Finland), a device to measure hypnosis in anesthesia, is a valid measure of sedation state in critically ill patients by comparing clinically assessed sedation state with Spectral Entropy


METHODS
Prospective observational study.


METHODS
Teaching hospital general ICU.


METHODS
30 intubated, mechanically ventilated patients without primary neurological diagnoses or drug overdose receiving continuous sedation.


METHODS
Monitoring of EEG and fEMG activity via forehead electrodes for up to 72h and assessments of conscious level using a modified Ramsay Sedation Scale.


RESULTS
475 trained observer assessments were made and compared with concurrent Entropy numbers. Median State (SE) and Response (RE) Entropy values decreased as Ramsay score increased, but wide variation occurred, especially in Ramsay 4-6 categories. Discrimination between different sedation scores [mean (SEM) P(K) value: RE 0.713 (0.019); SE 0.710 (0.019)] and between lighter (Ramsay 1-3) vs.deeper (Ramsay 4-6) sedation ranges was inadequate [P(K): RE 0.750 (0.025); SE 0.748 (0.025)]. fEMG power decreased with increasing Ramsay score but was often significant even at Ramsay 4-6 states. Frequent "on-off" effects occurred for both RE and SE, which were associated with fEMG activity. Values switched from low to high values even in deeply sedated patients. High Entropy values during deeper sedation were strongly associated with simultaneous high relative fEMG powers.


CONCLUSIONS
Entropy of the frontal EEG does not discriminate sedation state adequately for clinical use in ICU patients. Facial EMG is a major confounder in clinical sedation ranges.
Walsh
Timothy S
TS
Edinburgh Royal Infirmary, 51 Little France Crescent, Old Dalkeith Road, EH16 4SA Edinburgh, Scotland. twalsh@staffmail.ed.ac.uk
Ramsay
Pamela
P
Lapinlampi
T Petteri
TP
Särkelä
Mika O K
MO
Viertiö-Oja
Hanna E
HE
Meriläinen
Pekka T
PT
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016292:Procedural Sedation; D016638:Critical Illness; D004569:Electroencephalography / Q000187:drug effects; D004576:Electromyography / Q000187:drug effects*; D019277:Entropy; D005260:Female; D006801:Humans; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012121:Respiration, Artificial; D018709:Statistics, Nonparametric; D013997:Time Factors
D006993:Hypnotics and Sedatives