Monotonicity of approximate entropy during transition from awareness to unresponsiveness due to propofol anesthetic induction

Miika Koskinen, Tapio Seppänen, Shanbao Tong, Seppo Mustola, Nitish V. Thakor

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


The ability to monitor the physiological effects of sedative medication accurately is of interest in clinical practice. During the anesthetic agent driven transition to unresponsiveness, nonstationary changes such as signal amplitude variations appear in electroencephalography. In this paper, it is studied whether the application of the approximate entropy (ApEn) method to electroencephalographic (EEG) signal produces a monotonic response curve during the transition from awareness to unresponsiveness. Data from fourteen patients, undergoing propofol anesthetic induction were studied. To optimize the ApEn performance, different parameter choices were carefully evaluated. It was assumed with our protocol, that the level of anesthesia changes monotonically with the elapsed induction time. The monotonicity of the ApEn change was assessed with the prediction probability statistic (P K). The monotonicity of the ApEn time-series depends on the parameters employed in the algorithm and the varying signal amplitude. Depending on the parameter values, the median P K value ranged from 0.886 to 0.527. Thus, a good directionality and concordance was observed, but the nonstationarity of the signal affected the results. In conclusion, EEG-based ApEn measure shows a nonlinear response during propofol induction. With a judicious choice of parameters, a monotonic response is confirmed using P K statistic.

Original languageEnglish (US)
Article number1608516
Pages (from-to)669-675
Number of pages7
JournalIEEE Transactions on Biomedical Engineering
Issue number4
StatePublished - Apr 2006


  • Approximate entropy
  • Depth of anesthesia
  • Independent component analysis (ICA)

ASJC Scopus subject areas

  • Biomedical Engineering


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