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U Grouven

Publications and source records attributed to U Grouven.

At least 19 recordsLinked to original sources
PubMed2006

[Aspects of sample size determination and power calculation illustrated on examples from rehabilitation research].

Often it is reported in medical studies that an expected effect could not be detected. This may be the case if the sample size had been too small to detect an effect which actually exists. This often is due to the fact that sound sample size estimation had been omitted prior to the study outset. As a result, it is not known how many persons should have been involved in the study to detect this effect if present. On the other hand, if sample size estimation has not been realized, more persons than needed might be included in the study. This is problematic for economic and in particular for ethical reasons. The aim of this paper is to point out the principles of sample size estimation as well as to emphasize its importance not only in general but also in medical rehabilitation research.

Clinical Trials as Topic↗
PubMed2004

Age-related effects in the EEG during propofol anaesthesia.

BACKGROUND: Age-related differences in the spectral composition of the EEG in induction and emergence times, and in drug consumption during propofol anaesthesia were investigated. METHODS: The EEGs of 60 female patients between 22 and 85 years of age were monitored continuously during standardized induction of anaesthesia with 2 mg of propofol kg(-1)60 s(-1). The EEGs were visually assessed in 20-s epochs according to a scale from A (awake) to F (very deep hypnosis). Visual EEG classifications, spectral parameters, and induction times were compared between different age groups. Additionally, data of 546 patients included in a multicentre study with 4630 patients (EEG monitor Narcotrend, MT MonitorTechnik, Bad Bramstedt, Germany) were analyzed with regard to age-dependent changes of propofol consumption using target-controlled infusion (TCI). RESULTS: During induction, patients older than 70 years reached significantly deeper EEG stages than younger patients, needed a longer time to reach the deepest EEG stage, and needed more time until a light EEG stage was regained. In patients aged 70 years and older, the total power, mainly in deep EEG stages, was significantly smaller due to a distinctly smaller absolute power of the delta frequency band. No single spectral parameter was able to reliably distinguish all EEG stages. During the steady state of anaesthesia, older patients needed less propofol for the maintenance of a defined stage of hypnosis than younger patients. CONCLUSION: Older patients differ from younger ones regarding the hypnotic effect of propofol and the spectral patterns in the EEG. For an efficient automatic assessment of the EEG during anaesthesia a multivariable approach accounting for age-effects is indispensable.

Adult↗
PubMed2004

The Narcotrend Index: classification algorithm, correlation with propofol effect-site concentrations, and comparison with spectral parameters.

A reliable assessment of the depth of hypnosis during sedation and general anaesthesia using the EEG is a subject of current interest. The Narcotrend Index implemented in the latest version 4.0 of the EEG monitor Narcotrend provides an automatic classification of the EEG on a scale ranging from 100 (awake) to 0 (very deep hypnosis, EEG suppression). The classification algorithms implemented in the EEG monitor Narcotrend are described. In a study the correlation of the propofol effect-site concentration with the Narcotrend Index and with the traditional spectral parameters total power, relative power in the standard frequency bands delta, theta, alpha, and beta, median frequency, 95% spectral edge frequency, burst-compensated spectral edge frequency, and spectral entropy was investigated. The Narcotrend Index had the highest average correlation with the propofol effect-site concentration and the smallest variability of the individual correlation values. Moreover, the Narcotrend Index was the only parameter which showed a monophasic trend over the whole investigated time period. The Narcotrend monitor can make a significant contribution to the improvement of the quality of anaesthesia by adjusting the dosage of hypnotics to individual patient needs.

Adolescent↗
PubMed2003

[The Narcotrend monitor. Development and interpretation algorithms].

The Narcotrend performs an automatic interpretation of the electroencephalogram (EEG) during anaesthesia. The classification algorithms have been developed on the basis of visually classified EEG epochs. The classification scheme which was used for these visual assessments has its origin in sleep analysis and was adapted for the EEG during anaesthesia. From the awake state to very deep anaesthesia, 15 stages (A, B(0-2), C(0-2), D(0-2), E(0-2), F(0-1)) are distinguished. The transformation of these stages into a numerical scale from 100 to 0 is a further refinement for a differentiated presentation of EEG effects. For the automatic classification multivariate discriminant functions are used. Age-related changes of the EEG were incorporated. The device contains functions for the identification of artifacts. The EEG can be recorded from a frontal channel using standard ECG electrodes, other electrode positions and types can be chosen. The device has been clinically and scientifically validated.

Algorithms↗
PubMed2003

Cortical activity assessed by Narcotrend in relation to haemodynamic responses to tracheal intubation at different stages of cortical suppression and reflex control.

BACKGROUND AND OBJECTIVE: Many anaesthesiologists still interpret haemodynamic responses as signs of insufficient cortical suppression. The aim was to illustrate how haemodynamics may only poorly reflect the level of cortical suppression and that electroencephalographic monitoring could indicate different relationships between cortical effects and haemodynamics. METHODS: Anaesthesia was induced with thiopental (7 mg kg(-1)), and fentanyl (2 microg kg(-1)) with succinylcholine (1.5 mg kg(-1)) for neuromuscular blockade in the 11 patients of Group 1. In Group 2 (n = 15), thiopental (7 mg kg(-1)) and succinylcholine (1.5 mg kg(-1)) were given. In Group 3, the patients (n = 13) received thiopental (7 mg kg(-1)), fentanyl (2 microg kg(-1)) and cisatracurium (0.1 mg kg(-1)), and they were intubated 3 min later than the patients in Groups 1 and 2. We determined conventional electroencephalographic (EEG) variables and classified 14 EEG stages in real-time ranging from A (= 1), indicating full wakefulness, to F1 (= 14), at profound cortical suppression. RESULTS: All groups had profound cortical suppression 45 s after thiopental administration, which rapidly decreased (EEG stage, 11 (6-13) versus 7 (2-13) at 4 min, P < 0.0001). Decreasing EEG stages were associated with increasing SEF 95, relative alpha and beta power and decreasing relative delta power. During tracheal intubation, profound cortical suppression remained unchanged in Groups 1 and 2. In Group 3, cortical suppression had decreased before laryngoscopy (P < 0.005). In Group 2, 11 patients had heart rate responses to tracheal intubation, whereas only two responded in Group 1 (P = 0.015) and three in Group 3 (P = 0.02). Thirteen patients in Group 2 had arterial pressure responses, and five in Group 1 (P = 0.038). Circulatory responses did not differ between Groups 1 and 3. CONCLUSIONS: Electroencephalographic monitoring was suitable to indicate in real-time that haemodynamics only poorly reflect rapidly changing levels of cortical suppression, and how haemodynamics and cortical activity depend on the applied combination of hypnotic and analgesic drugs during anaesthesia induction with thiopental.

Adolescent↗
PubMed2003

Influence of EEG monitoring on intraoperative stapedius reflex threshold values in cochlear implantation in children.

BACKGROUND: Cochlear implantation is a widely used means of treating deafness and severe hearing disorders. The surgical procedure includes inserting the cochlear implant electrode array into the cochlea and embedding the corresponding signal receiver in the mastoid bone behind the ear. Postoperative fitting of the externally worn speech processor is very important for successful use of the cochlear implant. For this purpose, electrically elicited stapedius reflex threshold values can be used. However, stapedius reflex threshold values measured intraoperatively are influenced by anaesthetics. The goal of this retrospective study was to find out whether electroencephalogram (EEG) control of anaesthesia produces more reliable reflex threshold values as a basis for the fitting of the speech processor. METHODS: Three groups of children, after surgery for cochlear implantation, were analysed with regard to the magnitude of intraoperative electrically elicited stapedius reflex threshold values and their deviations from postoperatively determined maximum comfortable levels (group 1: methohexital/remifentanil with EEG monitoring, n = 10; group 2: isoflurane/fentanyl with EEG monitoring, n = 9; group 3: isoflurane/fentanyl without EEG monitoring, n = 11). RESULTS: Children with EEG monitoring had significantly lower electrically elicited stapedius reflex threshold values and also significantly lower differences between intraoperative stapedius reflex threshold values and postoperatively determined maximum comfortable levels. CONCLUSIONS: Electroencephalogram monitoring in cochlear implantation is of considerable value in controlling anaesthesia and improving speech processor fitting based on more reliable intraoperative neurophysiological data.

Analysis of Variance↗
PubMed2001

[Epileptoform EEG activity: occurrence under sevoflurane and not during propofol application].

In a 62-year-old female patient without a history of epileptic seizures EEG monitoring (EEG monitor: Narcotrend) was routinely performed during propofol/remifentanil and during sevoflurane/remifentanil/nitrous oxide anaesthesia. In the first course of anaesthesia after a bolus of propofol 1% a continuous EEG slowing was followed by a burst suppression pattern without occurrence of epileptiform activity throughout this sequence. During the second course of anaesthesia the sevoflurane concentration was increased from 2 to 8 % by volume. After 5 min epileptiform activity appeared in the EEG at an endtidal concentration of 5.9% by volume.

Anesthesia, Inhalation↗
PubMed2001

Sharp transients in the EEGs of non-epileptic adult patients receiving sevoflurane.

OBJECTIVE: In this article unexpected EEG findings are described which were observed during EEG monitoring under sevoflurane anesthesia. METHOD: In seven non-epileptic adult patients sevoflurane was administered as inhalation anesthetic during routinely performed surgical operations. The EEG was recorded continuously as part of the standard monitoring process and served mainly as a dosage guide for anesthetics/narcotics. MAIN OUTCOME MEASURE: Occurrence of sharp transients in the EEG resembling distinctive waves which can be seen in epileptic disorders. RESULTS: In six of the seven patients under 8.0% sevoflurane, sharp transients were observed which appeared in very deep EEG stages, mostly with endtidal sevoflurane concentrations of 4.8-5.9%. The findings are in accordance with observations in non-epileptic children from our clinic. CONCLUSIONS: The clinical significance of the observed EEG pattern under sevoflurane anesthesia is still unclear. Taking into consideration that convulsive and nonconvulsive status epilepticus can be followed by signs of brain damage, it would appear to be important to further investigate the phenomenon.

Adult↗
PubMed2001

[Value of EEG monitoring in intensive care patients in plastic surgery--indications and experiences].

EEG monitoring can be performed at the patients' bedside and it is a valuable support in therapeutic decision making providing unique information about the functional state of the brain. Due to newer technical developments, EEG monitoring can be conducted rather easily. In this article, indications for EEG monitoring in plastic surgical patients are presented: controlling the level of sedation, use in states of increased intracranial pressure, screening the cerebral state in comatose patients, diagnosis and therapy of epileptic seizures, and the search for circumscribed cerebral abnormalities. Furthermore, practical experience with the use of the new EEG monitor Narcotrend, which is provided with an automatic EEG classification, is described.

Cerebral Cortex↗
PubMed2000

Epileptiform activity in the EEGs of two nonepileptic children under sevoflurane anaesthesia.

Two case reports of nonepileptic children are presented, who developed paroxysmal EEG potentials in routinely performed EEG recordings during inhalation of sevoflurane, 7 and 8% by volume respectively. Taking into account several reports from the literature about epileptiform potentials or convulsive movements under similar conditions, it seems to be important to investigate carefully the circumstances under which these phenomena appear as well as possible clinical consequences.

Anesthetics, Inhalation↗
PubMed1998

Using binary logistic regression models for ordinal data with non-proportional odds.

The proportional odds model (POM) is the most popular logistic regression model for analyzing ordinal response variables. However, violation of the main model assumption can lead to invalid results. This is demonstrated by application of this method to data of a study investigating the effect of smoking on diabetic retinopathy. Since the proportional odds assumption is not fulfilled, separate binary logistic regression models are used for dichotomized response variables based upon cumulative probabilities. This approach is compared with polytomous logistic regression and the partial proportional odds model. The separate binary logistic regression approach is slightly less efficient than a joint model for the ordinal response. However, model building, investigating goodness-of-fit, and interpretation of the results is much easier for binary responses. The careful application of separate binary logistic regressions represents a simple and adequate tool to analyze ordinal data with non-proportional odds.

Bias↗
PubMed1996

Implementation of linear and quadratic discriminant analysis incorporating costs of misclassification.

Discriminant analysis plays an important role in biological and medical research. In practice, standard linear and quadratic methods are often applied which assume equal costs of misclassification. However, there can be situations where misclassifications between certain groups may be more serious than between other groups. Such considerations can be taken into account by using classification methods which incorporate misclassification costs. The widely applied statistical packages BMDP, SAS, and SPSS do not offer the possibility of using unequal misclassification costs for discriminant analysis with more than two groups. In this paper a menu-driven, user-friendly PC program written in Borland Pascal is introduced which performs linear and quadratic discriminant analysis for g > or = 2 groups allowing for the incorporation of misclassification costs.

Bias↗
PubMed1995

[Changes with age in EEG during anesthesia].

The number of older persons who have to undergo surgical procedures is steadily growing. For these patients the risks of anaesthesia are often increased because of their past medical history and their restricted physiological resources. Apart from parameters of the cardiovascular system, the electroencephalogram (EEG) represents a supplementary method for intraoperative monitoring, because cerebral alterations caused by anaesthetics or narcotics are directly reflected in the EEG. In routinely conducted registrations of the EEG in the operating theatre it appeared that the EEG of older persons differed from the EEG of younger patients. The aim of the present study was to further investigate the effect of patients' age on the EEG during anaesthesia. METHODS. Three data sets from different EEG registrations were analysed. The first data set consisted of inductions of anaesthesia with 7 mg/kg body weight thiopental in 43 patients from 17 to 80 years of age (mean 53.6 +/- 16.7 years) using derivations C3-P3 and Cz-A1. The second data set included 69 EEG registrations of general anaesthesia induced with barbiturates and maintained with enflurane in patients from 16 to 83 years (mean 51.4 +/- 17.7 years). The third data set comprised inductions of anaesthesia with 2 mg/kg body weight propofol. EEGs of the second and third data set were recorded with the EEG monitor 'Narkograph' using derivation C3-P3 and derivations C3-P3/C4-P4, respectively. Classification of the EEGs was performed according to the proposals of Kugler [12]. The basis for the statistical analysis of all data sets was formed by parameters from the power spectra of the EEG recordings. RESULTS. The data from inductions of anaesthesia with thiopental and propofol showed EEG patterns from alpha-EEG to burst suppression activity, whereby periods with burst suppressions could more often be observed in the EEG of older people. Under thiopental burst suppression activity occurred in 20% of patients up to 50 years, in 47% of those between 50 and 70 years and in 89% over 70 years. The corresponding figures for propofol were 0%, 5% and 54%, respectively. Figure 2 depicts the correlation between age and power for the thiopental data. The power decreases with increasing age of the patients. This result led to further investigations of the effect of patients' age on the power in different EEG stages. Of special interest were deep stages of anaesthesia, because especially in these stages visual inspections revealed smaller amplitudes of the EEG signal for older patients than for younger persons. Figure 3 shows the power in the delta frequency band in deep stages of barbiturate-induced enflurane anaesthesia for patients of different age groups. The power in the delta frequency band distinctly decreases for geriatric patients. The same effect could be observed for the propofol data (Fig. 4). CONCLUSIONS. The EEG represents an important method for effective intraoperative monitoring and contributes to an individually adjusted course of anaesthesia, especially for geriatric patients. In these patients, clinical signs such as parameters of the cardiovascular system, which are usually used to judge the depth of anaesthesia, are often altered by the patient's past medical history or by drugs. Furthermore, geriatric patients show a reduced need for narcotic agents. However, the variation of the required dosage is greater in older than in younger persons. The results of the present study show that with regard to an automatic classification of the EEG during anaesthesia, alterations of the EEG with age have to be taken into account.

Adolescent↗
PubMed1995

[Channel selection for EEG-monitoring in anesthesia].

The conventional multichannel electroencephalogram is quite inconvenient for long-term monitoring in the operating theatre or intensive care unit. Recording of the EEG would be easier if a small number of channels was sufficient. Aiming at reduction of channels, leads from different regions of the scalp were analysed visually and with regard to their spectral content. METHODS. Electrode placements corresponded to the International 10/20 System (Fig. 1). EEG recordings were made with a conventional device (ES 12,000), a personal computer, and a spectral analyser. TWO-CHANNEL RECORDINGS. Retrospective analysis was performed on data from 392 patients (age 14-90 years) whose anaesthesia was induced with various anaesthetics/narcotics, for instance thiopental, ketamine, etomidate, halothane, and enflurane. The EEG was recorded using C3-P3 and Cz-A1. For each patient the changes of spectral parameters during the course of the induction were plotted and visually analysed. For statistical analyses a 30-s epoch of each patient was randomly selected from the first few minutes after the beginning of induction. TEN-CHANNEL RECORDINGS. In ten gynaecological patients (age 26-55 years) EEG recordings were performed during induction of anaesthesia with thiopental in combination with fentanyl, N2O and O2. The set of channels consisted of Fz'-Cb1, F3'-Cb1, Cz-Cb1, C3-Cb1, P3-Cb1, Oz-Cb1, Fz'-F3', F3'-C3, C3-P3, and P3-Oz. The electrodes Fz' and F3' were positioned on the forehead near to Fz and F3, respectively. These sites were chosen because they allow easy application of electrodes. The relationship between channels was calculated with Bravais-Person's coefficient of correlation for the power and the absolute power in the frequency bands delta (0.5-3.5 Hz), theta (3.5-7.5 Hz), alpha (7.5-12.5 Hz), and beta (> 12.5 Hz). RESULTS. In visual and statistical analyses of the two- and ten-channel recordings under the influence of anaesthetics/narcotics, similar changes of EEG activity could be observed in all channels. Although differences in the absolute power of the frequency bands were present, there was high conformity in the composition of the spectral content of the different channels. Classification of the EEG into stages of anaesthesia by means of a single channel led to consistent results for all channels. Alpha activity as leading feature of the awake state predominated occipitally. In channels including the region around the ears, contamination with EKG artifacts was observed. CONCLUSIONS. EEG patterns under the influence of different anaesthetics/narcotics are adequately represented by a reduced number of channels. For the choice of an appropriate set of channels the following aspects should be considered. Contamination with artifacts should be as low as possible, electrode sites should easily be accessible, and special features of the awake state should be identifiable. Experience with routinely conducted EEG recordings in the operating theatre and the intensive care unit showed that the channels C3-P3 or C4-P4 provide a sufficient basis for automatic staging of the depth of anaesthesia, which is implemented in the EEG monitor Narkograph.

Adolescent↗
PubMed1995

A PC program for unbiased and predictive linear and quadratic discriminant analysis.

Discriminant analysis plays an important role in biological and medical research. The most popular methods of discrimination in practical applications are parametric methods like linear and quadratic discriminant analysis. However, there exist modifications of these approaches, namely unbiased and predictive discriminant analysis, which lead to reduced error rates in certain situations. In this paper a menu-driven, user-friendly PC program written in Borland Pascal 7.0 is introduced which performs unbiased and predictive linear and quadratic discriminant analysis.

Bias↗
PubMed1995

Pre-transplant hypertension: a major risk factor for chronic progressive renal allograft dysfunction?

Despite of advances in 1-year survival rates of renal allografts, no comparable achievements have been made in long-term graft survival. To identify risk factors for chronic progressive renal allograft dysfunction we conducted a retrospective study in 639 patients transplanted between 1983 and 1990. Graft function was assessed by the slope of individual 1/creatinine regression lines and chronic progressive graft dysfunction was defined as a slope of the 1/creatinine line of > 0.1 dl/mg/year, indicating a loss of glomerular filtration rate of > 10 ml/min/year regardless of the initial serum creatinine value. A number of possible risk factors were determined and analysed by linear regression analysis. One hundred and six patients (16.6%) showed chronic progressive graft dysfunction. No correlation was found between the rate of functional deterioration and the age and gender of the donor or the recipient, the blood group, the prevalence of hepatitis B or C, the number of blood transfusions, the total ischaemia time, or the number of kidneys from female donors grafted into male recipients. Chronic progressive graft dysfunction was associated with the number of HLA-B/DR mismatches (P = 0.04) and with a first acute rejection episode later than 60 days after transplantation (P < 0.001). Chronic progressive graft dysfunction also occurred in the absence of an acute rejection episode. Significantly (P < 0.001) more patients with chronic progressive graft dysfunction were hypertensive not only 12 months after transplantation, but also at the time of transplantation, indicating that hypertension may not only be secondary to deteriorating graft function, but that hypertension per se leads to graft damage and initiates chronic progressive graft dysfunction. All efforts should be made to control blood pressure adequately to improve long-term survival of renal allografts.

Adult↗