Rocuronium dose-dependently suppresses the spectral entropy response to tracheal intubation during propofol anaesthesia.

BACKGROUND The Entropy Module anaesthesia monitor displays two spectral entropy-based indices, response entropy (RE) and state entropy (SE). The difference between RE and SE (RE-SE), which mainly reflects electromyography activation, is thought to indicate the adequacy of antinociception. Little is known, however, about the effects of neuromuscular blocking agents on the RE-SE. We investigated the effects of rocuronium on the RE-SE response to tracheal intubation. METHODS Forty-four patients were randomly assigned to receive one of four rocuronium doses (0.3, 0.6, 0.9, and 1.2 mg kg(-1)). Anaesthesia was induced by propofol target-controlled infusion. Rocuronium was administered 2 min after anaesthesia induction. Tracheal intubation was performed 7 min after anaesthesia induction. Arterial pressure, heart rate (HR), bispectral index (BIS), RE, SE, and patient movement were recorded. RESULTS All EEG-derived indices (BIS, RE, SE, and RE-SE) increased after tracheal intubation. The maximum increase in the indices after tracheal intubation was significantly suppressed by an increase in the rocuronium dose. Patient movement after tracheal intubation was suppressed by an increase in the rocuronium dose. All indices were higher in patients who moved during or after tracheal intubation than in those who did not move. Rocuronium dose did not affect the mean arterial pressure or HR in response to tracheal intubation. CONCLUSIONS The RE-SE response to tracheal intubation was suppressed by increasing the rocuronium dose. Estimates of nociception using RE-SE should be interpreted carefully in different states of muscle paralysis during general anaesthesia.