The effect of neuromuscular block and noxious stimulation on hypnosis monitoring during sevoflurane anesthesia.
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.


CONCLUSIONS
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.
Ekman
Andreas
A
Department of Physiology and Pharmacology, Section for Anesthesiology and Intensive Care Medicine, Karolinska Institute, Stockholm, Sweden. andrease@ltkalmar.se
Stålberg
Erik
E
Sundman
Eva
E
Eriksson
Lars I
LI
Brudin
Lars
L
Sandin
Rolf
R
D000328:Adult; D000732:Androstanols / Q000008:administration & dosage / Q000494:pharmacology*; D018685:Anesthetics, Inhalation; D001921:Brain / Q000187:drug effects*; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D003243:Consciousness / Q000187:drug effects*; D004558:Electric Stimulation / Q000379:methods; D004569:Electroencephalography; D004576:Electromyography; D005072:Evoked Potentials, Auditory / Q000187:drug effects*; D005260:Female; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D011939:Mental Recall / Q000187:drug effects; D008738:Methyl Ethers; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods; D009388:Neostigmine / Q000494:pharmacology; D003473:Neuromuscular Nondepolarizing Agents / Q000008:administration & dosage / Q000494:pharmacology*; D017288:Pain Threshold / Q000187:drug effects*; D011446:Prospective Studies; D012107:Research Design; D000077123:Rocuronium; D000077149:Sevoflurane; D013997:Time Factors; D014459:Ulnar Nerve
D000732:Androstanols; D018685:Anesthetics, Inhalation; D002800:Cholinesterase Inhibitors; D008738:Methyl Ethers; D003473:Neuromuscular Nondepolarizing Agents; D000077149:Sevoflurane; D009388:Neostigmine; D000077123:Rocuronium