Cerebral haemodynamic physiology during steep Trendelenburg position and CO2 pneumoperitoneum

The steep (40) Trendelenburg position optimizes surgical exposure during robotic prostatectomy. The goal of the current study was to elucidate the influence of this patient positioning on cerebral blood flow and zero flow pressure (ZFP), and to assess the validity of different methods of evaluating ZFP. In 21 consecutive patients who underwent robotic endoscopic radical prostatectomy under general anaesthesia, transcranial Doppler flow velocity waveforms and invasive arterial and central venous pressure (CVP) waveforms suitable for analysis were recorded throughout the whole operative procedure in 14. The ZFP was determined by regression analysis of the pressure-flow plot and by different simplified formulas. The effective cerebral perfusion pressure (eCPP), pulsatility index (PI), and resistance index (RI) were determined. While patients were in the Trendelenburg position, the ZFP increased in parallel with the CVP. The PI, RI, gradient between the ZFP and CVP, and the gradient between the CPP and the eCPP did not increase significantly (P0.05) after 3 h of the steep Trendelenburg position. Using the formula described by Czosnyka and colleagues, the ZFP correlated closely with that calculated by linear regression throughout the course of the operation. Prolonged steep Trendelenburg positioning and CO2 pneumoperitoneum does not compromise cerebral perfusion. ZFP and eCPP are reliable variables for assessing brain perfusion during prolonged steep Trendelenburg positioning

Population pharmacokinetics and pharmacodynamics in anesthesia, intensive care and pain medicine

Purpose of review Population modeling is a relatively new pharmacological discipline, the development of which has largely been stimulated by the need for accurate models for the pharmacokinetics and dynamics of anesthetic agents. Recent findings Population-based modeling is now considered superior to older, more traditional modeling methods. Nonlinear mixed-effect modeling - a commonly used population-based modeling approach - estimates intraindividual and interindividual variability, limits the influence of outlying samples and individuals through the use of Bayesian statistical analysis, and provides a potential means of optimizing drug delivery regimens, especially when used to define pharmacokinetic-dynamic models for target-controlled infusion systems. In addition to being used for pharmacokinetic modeling, in which the influence of factors such as age, weight and illness can be studied, it is a powerful tool for the study of the influence of multiple factors on drug pharmacodynamics. Summary Nonlinear mixed-effect population-based modeling has become the gold standard method of pharmacokinetic and pharmacodynamic analysis during new drug development and during subsequent pharmacological studies. Population-based modeling techniques have been applied to numerous aspects of drug delivery in anesthesia, intensive care and pain medicine

Bispectral index values and propofol concentrations at loss and return of consciousness in patients with frontal brain tumours and control patients

The influence of frontal brain tumours on bispectral index (BIS) measurements and propofol requirements is unknown. The primary aim of our study was to determine whether BIS values recorded at loss and return of consciousness (LOC and ROC, respectively) differ between patients with unilateral frontal brain tumours and control patients. Secondary goals were to compare propofol requirements for LOC and to determine whether there were significant inter-hemispheric differences between BIS values in tumour and control patients. We enrolled 20 patients with a frontal brain tumour and 20 control patients. Bilateral BIS measurements were done during induction of propofol anaesthesia, during recovery of consciousness, and during a second induction of anaesthesia. The isolated-forearm test was used to determine the moments of LOC1, ROC, and LOC2. Arterial blood samples were obtained every 4 min for determination of measured propofol concentrations. The median BIS values recorded at LOC1, ROC, and LOC2 did not differ between the groups. There were no significant inter-hemispheric differences in BIS in tumour and control patients. The median [inter-quartile range (IQR)] total propofol doses at LOC1 were 82 (7592) and 78 (6891) mg in tumour and control patients, respectively. The median (IQR) measured plasma propofol concentrations at LOC1 were 12 (914) and 13 (1115) g ml(1) in the tumour and control groups, respectively. The presence of a frontal brain tumour did not affect ipsilateral BIS values, and so need not influence the placement of unilateral BIS electrodes if BIS monitoring is used to titrate propofol anaesthesia