ABSTRACT
Background: Obesity changes body composition including fat free mass (FFM), regarded as the "pharmacologically active mass". Scaling drug doses to obese patients by total body mass (TBM) results in overdose. We aimed to determine the success rate of inducing anaesthesia in normal, overweight and obese patients with propofol, using an adjusted body mass scalar (ABM), which embodies the increased FFM of obese patients. Methods: Ninety-six patients were divided into three groups according to body mass index (BMI): normal, overweight and obese. Propofol 2 mg/kg ABM was administered according to the equation: ABM = IBM + 0.4(TBM IBM), where IBM = ideal body mass. Induction success was assessed clinically and by electroencephalographic spectral entropy. Results: The groups were similar regarding gender, age, height and IBM. One patient was morbidly obese (BMI = 44). State entropy (SE) decreased to < 60 in 33/33, 28/29 and 33/34 patients in the normal-weight, overweight and obese groups respectively, an overall success rate of 97.5% (95% confidence interval 92.7% to 99.4%). Median lowest achieved SE values and median times that SE remained < 60 did not differ between groups, however the individual values ranged widely in allthree groups. Induction failed in the two patients whose SE did not decrease to < 60 (one overweight and one obese). Conclusions: The ABM-based propofol induction dose has a high success rate in normal, overweight and obese patients. Further studies are required to determine the feasibility among morbidly obese patients
Subject(s)
Body Composition , Body Mass Index , Obesity , PropofolABSTRACT
Background and Aim: Recently an electroencephalographic (EEG) spectral entropy module (M-ENTROPY) for an anaesthetic monitor has become commercially available. We compared its performance as an indicator of the state of anaesthesia with that of an older conventional quantitative EEG (QEEG) module (M-EEG) by the same manufacturer (Datex-Ohmeda Division; Instrumentarium Corp.; Helsinki; Finland). Methods: There were 40 ASA class I or II subjects; aged between 16-60 years; who underwent elective abdominal surgery. EEG data were collected from the printouts of the respective modules. The data presented here were related to four levels of anaesthesia: Pre-anaesthetic wakefulness (state A); 2 sevoflurane endtidal (ET) concentration after completion of surgery (state B); low ET sevoflurane concentrations (~ 0.5) just prior to regaining responsiveness (state C); and post-anaesthetic responsiveness (state D). Results: In terms of the prediction probability (Pk statistic); response entropy (RE) and state entropy (SE) produced higher values (0.95-1.0) than the best performing QEEG variable; frontal amplitude (0.86-0.95). Only RE scores did not overlap between states A and B or between B and D. The misclassification of subjects between states C and D was far lower for RE (28) than for any of the conventional QEEG measures (90). Conclusion: In on-line monitoring spectral entropy is superior in distinguishing states of anaesthesia and is also easier to use than conventional QEEG. It is speculated that the artefact rejection strategies accorded spectral entropy might significantly benefit conventional QEEG analysis