The association between intraoperative electroencephalogram-based measures and pain severity in the post-anaesthesia care unit.

This observational study aimed to identify simple electroencephalogram indices of inadequate intraoperative opioid-mediated nociceptive blockade and to compare these indices with routinely used clinical predictors of severe postoperative pain in adults. Intraoperative trend and waveform data (electrocardiogram, pulse oximetry and electroencephalogram) were collected, pain intensity in the post-anaesthesia care unit was quantified using an 11-point Verbal Rating Score, and opioid administration was recorded. Using the initial post-anaesthesia care unit Verbal Rating Score as the primary endpoint, the relationship between five possible explanatory variables--surgery type, depth of volatile anaesthesia (minimum alveolar concentration), electroencephalogram signs (state entropy, spindle-like activity and delta-band power) and estimated end-of-operation effect-site morphine concentrations--was examined. One hundred and thirteen patients were recruited, with 94 included in the final clinical and electroencephalogram data analysis. Fifty-two patients had moderate or severe pain (Verbal Rating Score > or = 5). State entropy was lower (46.5 +/- 2.9 vs 43.1 +/- 1.9, P = 0.04) and spindle-like activity higher (0.42 +/- 0.03 vs 0.50 +/- 0.02, P = 0.03) in the moderate/severe pain group. [corrected] These findings suggest that there is a modest association between electroencephalogram measures near the end of surgery and the severity of postoperative pain.

Episodic waveforms in the electroencephalogram during general anaesthesia: a study of patterns of response to noxious stimuli.

Previous studies of the electroencephalogram (EEG) during anaesthesia have identified two distinct patterns of change in response to a noxious stimulus, a classical arousal pattern and a paradoxical arousal pattern. We developed methods of EEG analysis to quantify episodic EEG patterns--namely sleep spindle-like ('10 Hz-score') and burst-suppression-like fluctuations in high frequencies ('high frequency variation index')--and used traditional power spectral quantification of non-episodic delta waves. We studied 30 healthy adult patients undergoing elective surgery under general anaesthesia with propofol, fentanyl (1.0, 2.5 or 4.0 microg/kg, n=10 for each group), muscle relaxant and sevoflurane. Prefrontal EEG data were recorded during the operation and analysed for changes in episodic patterns before and after noxious stimuli (intubation and incision). Before noxious stimuli, the EEG patterns varied markedly between patients and were not strongly correlated to calculated effect-site concentrations of fentanyl, propofol or sevoflurane. Noxious stimuli reduced the 10 Hz-score from 0.25 to 0.20 (P = 0.01) after intubation and from 0.33 to 0.27 (P = 0.01) after incision; and high frequency variation index from 2.8 to 2.0 (P=0.02) after incision--the classical arousal pattern. The nociception-induced reduction in spindles was greater in the low-dose fentanyl group (P = 0.01). There was less tachycardia in the high-dose fentanyl group (P = 0.002). It is possible to quantify such episodic EEG patterns during general anaesthesia and in this study noxious stimulation tended to reduce the prevalence of these patterns.

Can anaesthetists be taught to interpret the effects of general anaesthesia on the electroencephalogram? Comparison of performance with the BIS and spectral entropy.

BACKGROUND: Unlike the other physiological waveforms monitored in anaesthesia, the EEG lacks a regularly repeating pattern, implying that it would be very difficult for an anaesthetist to obtain any useful information from the raw EEG. There are, however, clear changes in the EEG caused by GABA-ergic anaesthetic agents. The anaesthetized EEG still looks like a random waveform, but clearly a different random waveform from that seen when conscious. METHODS: The aim of this study was to assess how 40 anaesthetists would perform at interpreting intra-operative EEGs compared with two processed EEG (pEEG) monitors, BIS and entropy, after a short educational presentation. Short segments of EEGs were used from the pre-induction phase, the intra-operative phase with adequate surgical anaesthesia, and the transition phase between these two states. RESULTS: While anaesthetists' performance varied widely, most could reliably differentiate an anaesthetized from a conscious EEG. Further, both humans (41% wrong) and machines (30% wrong) made mistakes. Unlike the anaesthetists, the pEEG monitors did not make a major error (i.e. producing a number in the conscious range (>85) when analysing an anaesthetized EEG or the converse error). CONCLUSION: A brief PowerPoint presentation enables anaesthetists to recognize the effects on the EEG of GABA-ergic anaesthetic agents. In the clinical context, it remains likely that the combination of a pEEG monitor that clearly presents the EEG and a clinician who has a good, basic understanding of, and a willingness to look at, the raw EEG will result in more accurate interpretation of the intra-operative EEG.

Rapid measurement of blood propofol levels: a proof of concept study.

OBJECTIVE: Despite many advantages over traditional volatile anaesthetic techniques, propofol total intravenous anaesthesia (TIVA) makes up a small percentage of general anaesthetics administered. One of the reasons for this is the absence of a clinically useful method for measuring blood propofol concentrations. We have designed and tested a prototype system for rapidly measuring blood plasma levels of propofol using solid phase extraction (SPE) methodology, coupled with colorimetric and spectrometric techniques. METHODS: Multiple venous blood samples were taken from 17 subjects during induction of anaesthesia with propofol. Samples were analysed in duplicate on both the prototype system and using High Performance Liquid Chromatography (HPLC). The prototype monitor response was calibrated against known methanol-based propofol standards and an estimate of the plasma concentration of propofol derived from regression analysis of the standard responses. RESULTS: Bland Altman analysis from a total of 87 samples gave 95% limits of agreement between the two methods of -0.34 to 0.42 microg mL(-1) (with no significant bias). The mean absolute prediction error was 8.9(7.5)%. The run time per sample on the prototype system was 4.5 min, including sample preparation. CONCLUSION: The results show that this methodology may be suitable for rapid and accurate clinical monitoring of propofol levels during general anaesthesia.

Cerebral cortical effects of desflurane in sheep: comparison with isoflurane, sevoflurane and enflurane.

BACKGROUND: Different volatile anesthetic agents have differing propensities for inducing seizures. A measure of the predilection to develop seizures is the presence of interictal spike discharges (spikes) on the electrocorticogram (ECoG). In this study, we investigated the propensity of desflurane to induce cortical spikes and made a direct objective comparison with enflurane, isoflurane, and sevoflurane. The ECoG effects of desflurane have not been previously reported. METHODS: After establishment of invasive monitoring and a parasagittal array of eight electrodes to record the ECoG; eight adult merino sheep were given a series of short inhalational anesthetics (using desflurane, enflurane, sevoflurane and isoflurane); each titrated to ECoG burst suppression. Anesthetic effect was estimated by the effects on the approximate entropy of the ECoG. The effect of anesthetic on the spike-rate in the ECoG was analyzed using a non-linear mixed-effect method with a sigmoid Emax model. RESULTS: A similar 'depth of anesthesia' was achieved for each agent, as estimated by the approximate entropy. The mean (SD) values of Emax for the spike-rate vs. approximate entropy relationship were desflurane 0.5 (0.9), enflurane 17.2 (4.0), isoflurane 0.7 (1.2), and sevoflurane 5.3 (1.2) spikes/min. The spike rate caused by desflurane was similar to isoflurane and significantly lower than that of enflurane (P < 0.001), and sevoflurane (P = 0.009). CONCLUSION: Desflurane induces minimal cerebral cortical spike activity when administered to burst suppression, consistent with its low propensity for inducing seizures in non-epileptic brains. The agents can be ranked by their relative ability to cause spike activity: enflurane >> sevoflurane > isoflurane = desflurane.

Embedding of multidimensional time-dependent observations.

A method is proposed to reconstruct dynamic attractors by embedding of multivariate observations of dynamic nonlinear processes. The Takens embedding theory is combined with independent component analysis to transform the embedding into a vector space of linearly independent vectors (phase variables). The method is successfully tested against prediction of the unembedded state vector in two case studies of simulated chaotic processes.

Influence of environmental conditions on hydrogen peroxide formation by Streptococcus gordonii.

Hydrogen peroxide generated by viridans group streptococci has an antagonistic effect on many bacterial species, including a number of pathogens, in the oral environment. This study examines the influence of a variety of environmental conditions on rates of hydrogen peroxide synthesis by Streptococcus gordonii. Hydrogen peroxide was synthesized at every concentration of glucose and sucrose tested from 10 microM to 1 M, with the highest rates occurring at 0.1 mM sucrose and 1 mM glucose. S. gordonii appeared to have an intracellular store of polysaccharide which supported hydrogen peroxide formation even when the assay buffer contained no carbohydrate. Most heavy metal ions inhibited peroxidogenesis, and anaerobic conditions induced adaptive down-regulation of hydrogen peroxide synthesis; however, peroxidogenesis was generally insensitive to moderate increases in salt concentration, alteration of the mineral content of the assay solution, and changes in pH between 5.0 and 7.5. In contrast, stimulation of peroxidogenesis occurred in 1 mM Mg(2+) and 10 to 50 mM potassium L-lactate. Maximum peroxidogenesis occurred during the mid-logarithmic and late-logarithmic phases of bacterial growth. These bacterial responses may have significant implications for oral ecology and oral health.

Vaccination against anthrax with attenuated recombinant strains of Bacillus anthracis that produce protective antigen.

The protective efficacy of several live, recombinant anthrax vaccines given in a single-dose regimen was assessed with Hartley guinea pigs. These live vaccines were created by transforming DeltaANR and DeltaSterne, two nonencapsulated, nontoxinogenic strains of Bacillus anthracis, with four different recombinant plasmids that express the anthrax protective antigen (PA) protein to various degrees. This enabled us to assess the effect of the chromosomal background of the strain, as well as the amount of PA produced, on protective efficacy. There were no significant strain-related effects on PA production in vitro, plasmid stability in vivo, survival of the immunizing strain in the host, or protective efficacy of the immunizing infection. The protective efficacy of the live, recombinant anthrax vaccine strains correlated with the anti-PA antibody titers they elicited in vivo and the level of PA they produced in vitro.

The alpha-hemolysin of Streptococcus gordonii is hydrogen peroxide.

The alpha-hemolysin of viridans group streptococci, which causes greening of intact erythrocytes, is a potential virulence factor as well as an important criterion for the laboratory identification of these bacteria; however, it has never been purified and characterized. The alpha-hemolysin of Streptococcus gordonii CH1 caused characteristic shifts in the A403, A430, A578, and A630 of sheep hemoglobin. A spectrophotometric assay was developed and used to monitor purification of alpha-hemolysin during extraction in organic solvents and separation by reverse-phase high-performance liquid chromatography (HPLC). The alpha-hemolysin was identical to hydrogen peroxide with respect to its effects on erythrocyte hemoglobin, oxygen-dependent synthesis by streptococci, insensitivity to proteases, inactivation by catalase, differential solubility, failure to adsorb to ion-exchange chromatography resins, and retention time on a reverse-phase HPLC column. The amount of hydrogen peroxide present in HPLC-fractionated spent culture medium was sufficient to account for all alpha-hemolytic activity observed.

Breath-by-breath analysis of oxygen uptake using the Datex Ultima.

The Datex Capnomac Ultima monitor combines a sidestream rapid gas analyser with a spirometer. In theory the integral of simultaneous flow and oxygen concentration during inspiration is the inspired and expired volume of oxygen. From the difference between these two amounts, oxygen consumption (VO2) can be estimated. VO2 was measured in patients under general anaesthesia and compared with that obtained simultaneously using a Datex Deltatrac metabolic monitor. Two techniques to compensate for the delay in rise time of the oxygen sensor were evaluated. The first method steepened the oxygen curve exponentially, and the second used a linear statistical correction. The linear correlation coefficients for VO2 between the Ultima and the Deltatrac were 0.87 and 0.78 for the two methods. The 10th to 90th centile range for error was -67.4-59.8 ml min-1 for the exponential method and -53.2-56.1 ml min-1 for the statistical method. The Ultima may be used with moderate accuracy to measure oxygen uptake during anaesthesia.

Alteration of pyruvate metabolism in African trypanosomes during differentiation from bloodstream into insect forms.

In the presence of glucose and ample oxygen, insect form African trypanosomes release pyruvate more than 100-fold more slowly than do bloodstream forms. This rate decrease could not be accounted for simply by an increased mitochondrial pyruvate oxidation rate as inhibiting mitochondrial respiration increases pyruvate efflux to rates only 2-3% of that observed for bloodstream form trypanosomes. Alternatively, decreased pyruvate efflux from insect form trypanosomes could not be accounted for by decreased pyruvate transporter activity, which, surprisingly, was nearly as high in insect form trypanosomes as reported by us earlier for bloodstream forms (J.P. Barnard, B. Reynafarje, and P.L. Pedersen (1993) J. Biol. Chem. 268, 3654-3661). Rather, the low pyruvate efflux rate appears to be due primarily to reduced levels of the enzyme pyruvate kinase, which, in contrast to conclusions of an earlier study, is readily detected in insect form trypanosomes in the absence of added activators at an activity level about 4% of that found in bloodstream forms. Insect form pyruvate kinase seems to be located in the cytosol and exhibits kinetic profiles and constants nearly identical to those reported by us earlier for the bloodstream form enzyme (J.P. Barnard, and P.L. Pedersen (1988) Mol. Biochem. Parasitol. 31, 141-148). It is suggested that the reduced levels of pyruvate kinase, and hence the reduced pyruvate efflux rates, in insect form trypanosomes result from down regulation of the gene encoding the cytosolic enzyme.

Glucose catabolism in African trypanosomes. Evidence that the terminal step is catalyzed by a pyruvate transporter capable of facilitating uptake of toxic analogs.

The protozoan parasite Trypanosoma brucei derives its metabolic energy exclusively from a unique type of glycolysis in which pyruvate derived from glucose catabolism is released into the host bloodstream. In this study, this terminal metabolic step has been examined in detail. Pyruvate release from trypanosomal cells supplied with glucose is very rapid, proceeding with an apparent Vmax of 214 nmol x min-1 x mg-1. Counterflow experiments with [14C]pyruvate demonstrate that this metabolic end product can be taken up by actively metabolizing cells consistent with the presence of a plasma membrane transporter. The findings that [14C] acetate exhibits a much lower capacity for cell entry and that the structural analog alpha-cyano-3-hydroxycinnamic acid inhibits pyruvate release provide additional support for the presence of a pyruvate transporter. The substrate analog and alkylating agent 3-bromopyruvate inhibits completely both cell motility and pyruvate release. Surprisingly, however, it is a poor inhibitor of pyruvate transport per se. Rather, its preferential site of action and that of iodoacetic acid were identified by radiolabeling studies and microsequence analysis as glyceraldehyde-3-phosphate dehydrogenase. In extending these studies, 3-bromopyruvate was found to be over 20 times less effective in inhibiting glyceraldehyde-3-phosphate dehydrogenase in intact erythrocytes than in trypanosomal cells. However, in sonicated preparations from both cell types, the enzyme exhibits nearly identical sensitivities to inhibition by 3-bromopyruvate. Experiments reported here provide the first direct evidence that pyruvate release in African trypanosomes is catalyzed by a specific transport system and implicate this transporter as a vehicle for delivering toxic alkylating agents into trypanosomal cells.

Purification in a single step and kinetic characterization of the pyruvate kinase of Trypanosoma brucei.

The pyruvate kinase of Trypanosoma brucei can be purified to homogeneity in one step by affinity elution from a phosphocellulose column with the substrate phosphoenolpyruvate (PEP) and the allosteric activator fructose-2,6-diphosphate (FDP). The purified enzyme has a specific activity of 175 mumol min-1 (mg protein)-1 and a subunit molecular mass of 59 kDa as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Kinetic studies of the pure enzyme show that an increase in the PEP concentration decreases the apparent Km for adenosine diphosphate (ADP) and that an increase in the ADP concentration decreases the half saturation point (S0.5) for PEP. Likewise, the allosteric activator FDP decreases both the apparent Km for ADP and the S0.5 for PEP. ADP concentrations above 0.2 mM inhibit trypanosomal pyruvate kinase.