[Fractal dimension--a new EEG-based method of assessing the depth of anaesthesia].
BACKGROUND
It has been suggested that analysis of the EEG signal using the fractal dimension method may be useful for assessment of depth of anaesthesia.


METHODS
Thirty ASA I and II patients, scheduled for elective surgery under general anaesthesia were induced with midazolam, fentanyl and propofol and paralyzed with rocuronium or cis-atracurium. Clinical signs of the depth of anaesthesia were classified to one of five OAA/S levels. Standard vital parameters were observed and brain electrical activity was measured using the bispectral index (BIS) and burst suppression ratio (BSR). The EEG signal was recorded and processed postoperatively to calculate Higuchi's fractal dimension (FD). The latter was presented as a derivative: (D(F)-1) x 100.


RESULTS
Mean correlation coefficients between OAA/S scale levels, and BIS and (D(F)-1) x 100 values, were respectively: 0.749+/-0.172 and 0.753+/-0.220. In 28 (93.3%) patients, BIS correlated well with FD (r=0.63+/-0.33). In twenty cases, burst suppression occurred and the correlation coefficient between BIS and DF was much lower (r=0.5860+/-3650), when compared to the group of 10 patients in which no burst suppression was detected (r=0.711+/-0.251). Appropriate correction was made using the following formula: D(FK)=D(F)-(D(F) x BSR). The mean correlation coefficient between BIS values and D(FK) in the BS group was r=0.629+/-0.331. In all cases, the mean correlation coefficient between (D(F)-1) x 100 and BIS was r=0.661+/-0.307 (p<0.001).


CONCLUSIONS
The fractal dimension method can be regarded as equal to BIS for assessment of depth of anaesthesia.
Willand
Monika
M
Oddział Kliniczny Anestezjologii i Intensywnej Terapii SUM w Katowicach. anestitsos@sum.edu.pl
Rudner
Robert
R
Olejarczyk
Elzbieta
E
Wartak
Magdalena
M
Marciniak
Radosław
R
Stasiowski
Michał
M
Byrczek
Tomasz
T
Jałowiecki
Przemysław
P
D000328:Adult; D000732:Androstanols; D000768:Anesthesia, General; D018686:Anesthetics, Intravenous; D001279:Atracurium; D017558:Elective Surgical Procedures; D004569:Electroencephalography; D005260:Female; D005283:Fentanyl; D017709:Fractals; D006801:Humans; D008297:Male; D008874:Midazolam; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D003473:Neuromuscular Nondepolarizing Agents; D011237:Predictive Value of Tests; D015742:Propofol; D011446:Prospective Studies; D015203:Reproducibility of Results; D000077123:Rocuronium; D012815:Signal Processing, Computer-Assisted
D000732:Androstanols; D018686:Anesthetics, Intravenous; D003473:Neuromuscular Nondepolarizing Agents; D001279:Atracurium; D008874:Midazolam; D005283:Fentanyl; D000077123:Rocuronium; D015742:Propofol