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Novel responsiveness index measures the level of sedation in cardiac ICU patients


Sedation is an integral part of the management of patients requiring mechanical ventilation in the ICU. At present, sedation is usually managed by clinical assessments, often in conjunction with a protocol for adjusting drug doses. This approach has been shown to decrease ventilation times and is considered the best practice in recent guidelines [1]. Such scales, however, provide only intermittent and, to some extent, subjective information about the patient's state. Also, not every scale used in clinical practice is validated for ICU use and interobserver variation may occur.


We have developed a novel method that analyzes the patterns in the electromyographic (EMG) component of the frontal biopotential signal that are associated with activation and arousal processes. By quantifying the amount and magnitude of the response patterns in the past 60 minutes, a responsiveness index (RI) ranging between 0 and 100 (0 corresponds to a nonresponsive patient and 100 to a high amount of responses) is derived. Previously, we have compared the RI with EEG spectral entropy [2] in general ICU patients. Now we have studied the performance of the RI with 17 cardiac ICU patients and compared these with the development dataset analyzed by Viertiö-Oja and colleagues [2]. A subgroup of 17 patients (of total 30 patients) with a clinically assessed low probability of encephalopathy was used as the primary development data. The patients in both datasets were consenting adult ICU patients with non-neurologic primary ICU diagnosis. A modified Ramsay score was used as a reference of the sedation level.


The performance of the RI in reference to the Ramsay scores was analyzed by computing the prediction probability (PK). The development and test data contained 213 and 96 eligible Ramsay assessments, respectively. The for separating deep PK sedation levels 4 to 6 from levels 1 to 3 was 0.91 (0.03) in the development data and 0.96 (0.02) in the test data. For separating all Ramsay levels, the PK values in the development data and test data were 0.82 (0.02) and 0.89 (0.02), respectively.


These results showed good RI performance in the cardiac ICU data. The RI continues to show promise as an indicator of the level of sedation in ICU patients.


  1. Nasraway SA, et al.: Crit Care Med. 2002, 30: 117-118. 10.1097/00003246-200201000-00019

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  2. Viertiö-Oja H, et al.: Crit Care. 2006,10(Suppl 1):P442. 10.1186/cc4789

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Lapinlampi, P., Viertiö-Oja, H., Särkelä, M. et al. Novel responsiveness index measures the level of sedation in cardiac ICU patients. Crit Care 13 (Suppl 1), P398 (2009).

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  • Responsiveness Index
  • Development Data
  • Spectral Entropy
  • Development Dataset
  • Ramsay Score