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TECHNOLOGY, COMPUTING, AND SIMULATION

The Effect of Neuromuscular Block and Noxious Stimulation on Hypnosis Monitoring During Sevoflurane Anesthesia

Andreas Ekman, MD, DEAA^*, Erik Stålberg, MD, PhD, Eva Sundman, MD, PhD^*, Lars I. Eriksson, MD, PhD^*, Lars Brudin, MD, PhD, and Rolf Sandin, MD, PhD^*

From the *Department of Physiology and Pharmacology, Section for Anesthesiology and Intensive Care Medicine, Karolinska Institute, Stockholm; Department of Clinical Neurophysiology, Uppsala University Hospital, Uppsala; and Department of Medicine and Care, Linköping University, Linköping, Sweden.

Address correspondence and reprint requests to Andreas Ekman, MD, DEAA, Department of Anesthesiology and Intensive Care, Regional Hospital, S-391 85, Kalmar, Sweden. Address e-mail to andrease{at}ltkalmar.se.

BACKGROUND: There are conflicting results on the influence of neuromuscular block (NMB) on the bispectral index (BIS). We investigated the influence of two degrees of NMB on BIS, Alaris auditory-evoked potential index (AAI), and the electromyogram (EMG) obtained with needle electrodes from the frontal and temporal muscles, immediately adjacent to the BIS-sensor.

METHODS: Twenty patients were anesthetized with sevoflurane, titrated for 30 min to an end-tidal concentration of 1.2% (baseline). Rocuronium was infused to 50% (partial) and 95% (profound) depression of the first twitch in a train-of-four response, the order being randomly chosen. Noxious tetanic electrical stimulation was applied at four occasions: 1) at baseline (control measurement), 2 and 3) at each degree of NMB, and 4) after neostigmine reversal. BIS, AAI, and EMG were obtained 2 min before and 2 min after each noxious stimulation.

RESULTS: Median BIS and AAI at baseline were 44 (39–50) and 15 (14–16), respectively. The two degrees of NMB did not affect BIS, AAI, and EMG before noxious stimulation. In contrast, profound NMB altered the BIS and AAI responses to noxious stimulation when compared with partial NMB, (BIS P = 0.01, AAI P < 0.01), after neostigmine reversal (BIS P < 0.01, AAI P = 0.01) and compared with baseline (BIS P = 0.08, AAI P = 0.02). No significant increase in EMG was found.

CONCLUSION: BIS and AAI responses to noxious tetanic electrical stimulation are affected by the degree of NMB during sevoflurane anesthesia whereas NMB does not affect BIS or AAI in the absence of noxious stimulation.

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