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U Grouven

Publications and source records attributed to U Grouven.

16 recordsLinked to original sources
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↗
PubMed1992

Application of adjusted survival curves to renal transplant data.

An important means in the analysis of survival time data is the estimation and graphical representation of survival probabilities. In this paper unifactorial parametric and non-parametric survival curve estimators and two types of adjusted survival curves based on a parametric multifactorial approach are applied to renal transplant data. It is shown that the resulting survival curves can differ substantially. The unifactorial survival curves yield biased results in case of serious disequilibrium in the data. This drawback of the unifactorial methods has been overcome by the use of adjusted survival curves which take possible distortions in the data set into account. The benefits of adjusted survival curves in assessing potentially prognostic factors are elucidated by the application to data from renal transplantation.

Humans↗
PubMedDate not supplied

Improved methods of estimating survival probabilities applied to renal transplant data.

In the evaluation of clinical studies of different kinds with survival time as the response variable to be analysed the estimation of survival probabilities plays an important role. The ordinary procedure in survival data analysis for estimating survival probabilities is the Kaplan-Meier product-limit estimator. However, in the case of heavy censoring or if the largest observed failure times are censored the product-limit method is known to be a biased estimator of the survival function. Recently, two improved methods of estimating survival functions, a semiparametric procedure and an approach using splines, were proposed (Klein JP, Lee SC and Moeschberger ML, Biometrics, 46 (1990) 795-811; Whittemore AS and Keller JB, Biometrics, 42 (1986) 495-506). These new methods are less biased than the product-limit estimator, especially for heavily censored data. A computer program based on the integrated statistical and graphical software package RS/1 was developed for the calculation and graphical representation of the new estimators. Their improved properties are illustrated by the application to renal transplant data.

Computer Graphics↗
PubMedDate not supplied

Automatic classification algorithms of the EEG monitor Narcotrend for routinely recorded EEG data from general anaesthesia: a validation study.

Impacts of hypnotic drugs on brain function are reflected in the EEG. The EEG monitor Narcotrend performs an automatic classification of the EEG using a scale which was proposed by Kugler for visual evaluation of the EEG. In this article the results of a validation study of the automatic classification algorithms implemented in the EEG monitor Narcotrend are presented. Visual and automatic classification of EEG data recorded in routine clinical practice were compared. The correlation between visual and automatic assessment was high (Spearman rank correlation r = 0.90, prediction probability Pk = 0.90) and a sufficient agreement between visual and automatic assessment was achieved for 92% of the analysed EEG epochs. The results of the study suggest that the automatic classification algorithms implemented in the EEG monitor Narcotrend yield a reliable assessment of the depth of hypnosis.

Algorithms↗
PubMedDate not supplied

Ordinal logistic regression in medical research.

Medical research workers are making increasing use of logistic regression analysis for binary and ordinal data. The purpose of this paper is to give a non-technical introduction to logistic regression models for ordinal response variables. We address issues such as the global concept and interpretation of logistic models, the model building procedure from a practical point of view, and the assessment of the model adequacy. For illustrative purposes we apply these methods to real data of a study investigating the association between glycosylated haemoglobin and retinopathy. We give some recommendations for the use and assessment of ordinal logistic regression models in medical research.

Analysis of Variance↗