P118 The use of cumulative frequency curves to analyse sedated patients

INTRODUCTION: Excessive or inadequate sedation in intubated patients are both associated with increased morbidity and mortality. However, it is difficult to quantify the level of sedation accurately. Conventional sleep analysis does not quantify sedation effectively. Specific sedation analysis techniques have been developed but are labour-intensive and difficult to apply. We explored the potential of cumulative frequency curves of electroencephalograms (EEG) to quantify the level of sedation. METHODS: Left frontal EEG was obtained over 12-24 hours in 20 sedated and 2 non-sedated patients. Six hours of time correlated data (00:00-06:00) were analysed. Cumulative frequency curves were created for each patient. Measurements obtained were: peak (frequency in Hz occurring most often, x axis), areas under the curve at five frequencies (percentage time at the selected frequency) and average signal amplitude, at peak using a power calculation on y axis. RESULTS: For the 20 sedated patients 72±13,% (mean±SD) of study time was recorded at <1Hz and 91% ±5.7 at <4Hz (compared to 57.8 and 84.3% respectively for non-sedated patients). The peak amplitude of the signal took place at 0.45±0.32 Hz in sedated patients. The comparative amplitude determined by a comparative power determinant was 50.8±3.8 in sedated patients (c.f. 46 in non-sedated patients). CONCLUSION: This proof of concept study shows that signal amplitude and frequency can be measured using the cumulative frequency methodology and appears to differ between sedated and non-sedated patients. This methodology has the potential to provide a useful, simple and reproducible mechanism to analyse depth of sedation in intubated patients.