Purpose: Assessing nociception and sedation in mechanically ventilated patients in the ICU is challenging, with few reliable methods available for continuous monitoring. Measurable cardiovascular and neurophysiological variables, such as blood pressure, heart rate, frontal EEG, and frontal EMG, might provide a medium for sedation and nociception monitoring. The hypothesis of this explorative study is that the aforementioned variables correlate with the level of sedation, as described by the Richmond Agitation-Sedation score (RASS).

Methods: Thirty adult postoperative ICU patients on mechanical ventilation and receiving intravenous sedation, excluding patients with primary neurological disorders, head injury, or need for continuous neuromuscular blockage. Continuous measurements of bispectral index (BIS), EMG power (EMG), EMG-derived Responsiveness Index (RI), averaged blood pressure variability (ARV), and Surgical Pleth Index (SPI) were tested against repeated RASS measurements, and separately against responsiveness to painful stimuli at varying RASS levels.

Inclusion Criteria:

• Adult patients (over 18 years old)
• Postoperative ICU admission (planned and un-planned admissions), on mechanical ventilation via an endotracheal tube, with invasive hemodynamic monitoring via an arterial line
• receiving intravenous sedation by continuous infusion (propofol, midazolam).

Exclusion Criteria:

primary neurological disorders (including stroke, cardiac arrest with probable hypoxic brain injury, intracranial hemorrhage, and head injury with reduced level of consciousness prior to intubation), the continuous use of neuromuscular blocking agents during monitoring, confirmed meningitis or encephalitis, or a short data collection time (less than 12 hours).

Postoperative patients, requiring postoperative critical care.