Novel measure for EEG/EMG responsiveness may indicate the level of sedation in ICU patients

Introduction

The level of sedation in ICU patients is difficult to assess, and relies on clinical assessments such as the Ramsay score. These tests discriminate deep sedation poorly. We evaluated a novel measure, EEG/EMG responsiveness, and compared it with Ramsay scores. EEG/EMG responsiveness was calculated by applying an algorithm that detects abrupt changes in the measured EEG signal indicative of a patient's arousal or activation. The results were compared with those obtained using the EEG entropy.

Methods

Thirty consenting general ICU patients with non-neurologic primary ICU diagnosis were investigated for a maximum of 72 hours. The Response Entropy (RE) and State Entropy (SE) values as well as the EEG signals from which the EEG/EMG responsiveness was calculated were recorded from forehead electrodes using the Entropy™ Module (GE Healthcare). When possible, the Ramsay score was evaluated every 30 min by a single trained observer, amounting to a total of 370 assessments.

Results

Figure 1a,b shows the distributions of the EEG/EMG responsiveness and RE values for the six Ramsay levels. The box diagrams indicate the median and quartile values. The obtained prediction probability P_K = 0.86 for EEG/EMG responsiveness to distinguish deep Ramsay levels 4–6 from levels 1–3 was significantly higher than the corresponding P_K values 0.80 and 0.79 for RE and SE (P < 0.05). In the subgroup of 18 patients judged clinically to have no acute brain disorders, the P_K values for EEG/EMG responsiveness, RE, and SE (0.91, 0.85, and 0.84) were significantly higher (P < 0.001) than those in the remaining subgroup of 12 patients with encephalopathy (0.78, 0.73, and 0.75).

Figure 1

Conclusion

The novel measure of EEG/EMG responsiveness shows promise as an indicator for the level of sedation.