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Patient State Index (PSI) measures depth of sedation in intensive care patients



To investigate whether the electroencephalogram (EEG)-based Patient State Index (PSI) indicates the level of sedation as measured by Ramsay score in intubated and mechanically ventilated patients in the ICU.


Prospective, single-blinded observer study.


Surgical intensive care unit.


Forty-one consecutive adult patients requiring intubation and ventilation during intensive care therapy.

Measurements and results

Following skin preparation with alcohol and placement of EEG electrodes, PSI was recorded while patients were ventilated and sedated with constant drug infusion rates. After 30 min, the level of sedation was measured by an assessor, who was blinded to PSI values, using the Ramsay sedation score. For analysis, the mean of PSI values measured during the last minute before clinical assessment of sedation was calculated. General Linear Model (GLM) analysis revealed significant differences between the PSI values at different levels of sedation as measured by the Ramsay score, except for the differentiation of level 5 from levels 4 and 6 (p>0.3) and level 2 from level 3, where only a trend was reached (p=0.077). The prediction probability of PSI was 0.920±0.037.


As the high prediction probability and the analysis of paired comparisons suggest, PSI may be used to quantify the level of propofol/sufentanil sedation in ICU patients. Further studies are required to test whether these promising results can be verified for other drug combinations.

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Fig. 1


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The authors thank Warren D. Smith, PhD (Professor, Biomedical Engineering Program, California State University, Sacramento, CA) for providing PKMACRO software and the helpful support in installation and use of the programme. The authors thank the nurses of the anaesthesiology intensive care unit for their support.

Author information

Correspondence to Gerhard Schneider.

Additional information

This work was financed from departmental sources and supported by a grant from B. Braun AG, Melsungen, Germany.

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Schneider, G., Heglmeier, S., Schneider, J. et al. Patient State Index (PSI) measures depth of sedation in intensive care patients. Intensive Care Med 30, 213–216 (2004).

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  • Sedation
  • Monitoring of sedation
  • Intravenous anaesthetics
  • Electroencephalogram
  • Patient State Index
  • Intensive care therapy
  • Artificial respiration