Bi-spectral index, entropy and predicted plasma propofol concentrations with target controlled infusions in Indian patients
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Many processed electroencephalographic signals are used now to help the anaesthesiologist titrate the depth of sedation. We investigated the relationship between target plasma propofol concentration and objective end-points of sedation— Bispectral Index (BIS), State Entropy (SE) and Response Entropy (RE)—at clinical end-points as assessed by Modified Observer Assessment of Alertness/sedation Scale (MOAAS) in Indian patients.
Eighteen ASA 1 and 2 Indian adult patients scheduled to undergo elective surgery were included. The target control infusion (TCI) of propofol was administered using ‘Diprifusor’. The level of sedation was assessed using MOAAS by the anaesthesiologist. BIS, SE, RE were recorded throughout. TCI was started at 0.5 μg/ml and increased by 0.5 μg/ml every 6 min till MOAAS scores reached 0 or there was sustained BIS value less than 30.
The EC50 and EC95 of predicted plasma propofol concentration for loss of consciousness (assessed by loss of response to verbal command), were 2.3 and 2.8 μg/ml respectively and for loss of response to painful stimuli (trapezius squeeze) were 4.0 and 5.0 μg/ml respectively. The BIS and entropy values (EC50 and EC95) for loss of consciousness and response to painful stimuli in Indian patients were estimated. The preliminary relation of target plasma propofol concentration with BIS was found to be BIS = 100.5–16.4 × (Target concentration).
The target plasma propofol concentrations required to produce unconsciousness and loss of response to painful stimuli in Indian patients have been estimated. Also, the relations between target plasma concentration and objective measures of different levels of anaesthesia have been established.
Keywordsanaesthesia depth anaesthetics i.v awareness entropy monitoring, bispectral index pharmacokinetics pharmacology
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