Induction of anaesthesia with propofol according to the adjusted ideal body mass in obese and non-obese patients: an observational study

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

Blood pressure measurement in obese patients: non-invasive proximal forearm versus direct intra-arterial measurements

Background: In obesity, accurate perioperative blood pressure measurement using upper arm, non-invasive blood pressure (NIBP) is technically challenging. Proximal forearm NIBP may be an acceptable substitute. Mean arterial blood pressures (MAP) estimated by proximal forearm NIBP were compared with direct intra-arterial measurements. It was hypothesised that the measurement techniques would be interchangeable if between-technique MAP differed ≤ 20% and MAP ratios were < 1.2 and > 0.8. Method: A total of 30 adults with body mass index ≥ 30 kg/m2 in whom perioperative intra-arterial blood pressure measurement was considered mandatory were enrolled. MAP measurements using the two techniques were obtained at three random intervals in each patient. Bland­Altman analyses were employed. Results: Forearm mean NIBP MAP overestimated mean intra-arterial MAP by 2.2 (SD 8.1; range from 23.8 to ­19.4 mmHg; p = 0.011, 95% CI 3.9 to 0.5). However, Bland­Altman analyses revealed a wide dispersion with several MAP differences and MAP ratios exceeding the pre-specified bounds for interchangeability. Conclusion: Forearm NIBP could not be considered interchangeable with direct intra-arterial MAP measurements in obese patients

A comparison of induction of anaesthesia using two different propofol preparations

ABSTRACT. Background: Investigators have reported inter-patient variability with regard to propofol dosage for induction of anesthesia,since early dose finding studies. With the arrival of generic formulations of propofol, questions have arisen regarding furthervariability in dose requirements. Various studies have confirmed that generic propofol preparations are pharmacokineticallyand pharmacodynamically equivalent to Diprivan®. Nevertheless a number of practitioners are under the impression thatcertain generic propofol preparations require greater doses for induction of anaesthesia than does Diprivan®.Methods: 20 female patients of ASA status I-II, between the ages of 18-55 years, scheduled for routine surgery were randomlyallocated to two groups to undergo induction of anaesthesia using two different propofol formulations; Diprivan® andPropofol 1% Fresenius®. Either preparation was administered using a target-controlled infusion of propofol (STEL-TCI)targeting the plasma (central) compartment at a concentration of 6 µg.ml-1, employing the pharmacokinetic parameters ofMarsh et al. A processed EEG (bispectral index) was continuously recorded. Loss of consciousness (LOC) was regarded asthe moment at which the patient could not keep her eyes open and was confirmed by the absence of an eyelash reflex.At this point propofol administration was discontinued and data were recorded for a further two minutes, before administeringan appropriate opioid and/or nitrous oxide/volatile agent and/or muscle relaxant to maintain anaesthesia. Time to LOCafter start of propofol administration, and the dose of propofol administered during induction were annotated.Results: There were no demographic differences between the groups. There were no differences between the groups withregard to the mean dose for LOC, time to LOC and to the mean BIS values obtained at the following stages: awake, at LOC,at 1 and 2 minutes after LOC as well as the lowest recorded value.Conclusions: Our results confirm that the two propofol formulations that we studied, are pharmacologically equivalent withregard to induction of anaesthesia. Other mechanisms can explain the variability in clinical response to bolus administrationof propofol. The most important is the recirculatory or "front-end" kinetics of propofol in which cardiac output plays a majorrole, as well as the rate of drug administration. Emulsion degradation can also influence dose-response and in this regardit should be noted that the addition of foreign substances such as lignocaine, can result in rapid deterioration of the soya-bean emulsion