Effect of an intubation dose of rocuronium on Spectral Entropy and Bispectral Index (TM) responses to laryngoscopy during propofol anaesthesia

Background. The spectral entropy of the electroencephalogram has been proposed to monitor the depth of anaesthesia. State Entropy (SE) reflects the level of hypnosis. Response Entropy (RE), computed from electroencephalogram and facial muscle activity, reflects the response to nociceptive stimulation. We evaluated the effect of rocuronium on Bispectral Index (TM) (BIS) and entropy responses to laryngoscopy. Methods. A total of 25 patients were anaesthetized with propofol using a target-controlled infusion. At steady state, they randomly received 0.6 mg kg(-1) rocuronium (R) or saline (S). After 3 min, a 20 s laryngoscopy was applied. BIS, RE and SE were recorded continuously and averaged over 1 min during baseline, at steady state, 2 min after R or S administration (R/S+2) and 0, 1, 2 and 3 min after laryngoscopy (L0, L1, L2, L3). Results. At R/S+2, the RE-SE gradient was higher in Group S than in Group R. Laryngoscopy provoked an increase in BIS, RE and SE. Comparing R/S+2 and L0 values in Groups R and S, BIS increased from 43 (6) to 49 (8) and 42 (9) to 51 (15), SE increased from 43 (7) to 50 (8) and 41 (10) to 55 (12), and RE increased from 46 (8) to 54 (9) and 47 (12) to 66 (15), respectively. BIS and SE did not differ between groups. At L0, RE and RE-SE were higher in Group S [66 (15) and 11 (4), respectively] than in Group R [54 (9) and 4 (2), respectively]. Conclusions. Rocuronium alters the RE-SE gradient and the RE and RE-SE responses to laryngoscopy. Muscle relaxation may confound interpretation of entropy monitoring.