Biomedical subjects

S Schraag

Publications and source records attributed to S Schraag.

12 recordsLinked to original sources

PubMed2000

[Target controlled infusion (TCI)--status and clinical perspectives].

The technique of target controlled infusion (TCI) has influenced the development of intravenous anaesthesia substantially and opens the possibility of many new and exciting applications in peri-operative anaesthetic care. The launch of "Diprifusor" as the first commercially available TCI system for propofol was the cornerstone of a successful research period within the last decade, which evaluated the pharmacokinetic foundations of computer assisted intravenous drug delivery. We are now in a period where TCI technology is becoming a part of routine anaesthesia technique for the practitioner rather than a research tool for specialists and enthusiasts. This review gives an update on the rational pharmacokinetic basis of TCI development, the preliminary clinical experience with the new technique, the performance and accuracy of TCI devices and potential technical pitfalls in clinical routine. Besides clinical application in anaesthesia with "Diprifusor" TCI, target controlled systems are expected to play a significant role as research tools in the evaluation of drug interactions in anaesthesia and in the development of novel control techniques for the administration of sedative and analgesic drugs in the peri-operative period.

Anesthesia, Intravenous↗

PubMed1999

Interaction modeling of propofol and sufentanil on loss of consciousness.

STUDY OBJECTIVES: To examine the possible pharmacodynamic interaction of propofol and sufentanil with respect to the induction of loss of consciousness. DESIGN: Prospective, randomized, double-blinded study. SETTING: University hospital. PATIENTS: 30 female, ASA physical status I and II patients undergoing elective gynecologic surgery. INTERVENTIONS: Patients were allocated randomly to receive an individual combination of propofol (1, 2, 3, 4, 5, or 6 micrograms/ml) and sufentanil (0.1, 0.2, 0.3, 0.5, or 1.0 ng/ml) target blood concentrations using target-controlled infusions. MEASUREMENTS AND MAIN RESULTS: Study endpoint was loss of consciousness, which was tested by response to verbal commands and classified as responder or nonresponder, as assessed by the anesthetist, who was blinded to the drugs' target blood concentrations. Nonlinear association (interaction) of both drugs was accomplished with logistic regression analysis using the maximum likelihood method, based principally on the hypothesis of interaction: In [p/(1-p)] = beta 0 + beta 1 x Cprop + beta 2 x Csuf + beta 3 x Cprop x Csuf with a p-value < 0.05 for coefficient estimates considered significant. In the logistic regression model, sufentanil and propofol showed no supra-additive interaction regarding loss of consciousness (p = 0.5916). CONCLUSIONS: Our results give no evidence of additional hypnotic properties of sufentanil compared to the other fentanyl congeners, although logistic regression may be of limited value in modeling interaction of hypnotic-analgesic combinations.

Adult↗

PubMed1999

Lack of rapid development of opioid tolerance during alfentanil and remifentanil infusions for postoperative pain.

UNLABELLED: Studies in animals and volunteers have suggested the development of acute tolerance to opioid analgesics. In this article, we present data from patients who regulated their own target-controlled infusions of alfentanil and remifentanil to provide analgesia in the immediate postoperative period. Fifty-one patients received alfentanil for 24 h after cardiac surgery, and 30 patients received remifentanil for 6 h after orthopedic surgery. Satisfactory analgesia, defined as a rating of < or =3 on an 11-point visual analog scale, was obtained by patients after each type of surgery. The target concentrations of the opioids required to produce postoperative analgesia and the cumulative opioid doses administered over the course of the clinical observation suggest there was no tolerance to the analgesic effects of the opioids. The requirements for both analgesic drugs in individual patients had a large variation (>200%). We conclude that our results may indicate an absence of tolerance to opioids in postoperative analgesia. Nonetheless, our data show that the postoperative requirement for these rapidly acting drugs is qualitatively similar to that for other opioids in that dosage escalation does not occur. IMPLICATIONS: The development of acute tolerance to opioid analgesics has been suggested based on experimental studies in animals and volunteers. Our report from patients who self-controlled their analgesic requirements by using target-controlled infusions of alfentanil and remifentanil for postoperative analgesia provides no evidence of tolerance to opioids.

Aged↗

PubMed1999

The performance of electroencephalogram bispectral index and auditory evoked potential index to predict loss of consciousness during propofol infusion.

UNLABELLED: The bispectral index (BIS) of the electroencephalogram and middle latency auditory evoked potentials are likely candidates to measure the level of unconsciousness and, thus, may improve the early recovery profile. We prospectively investigated the predictive performance of both measures to distinguish between the conscious and unconscious state. Twelve patients undergoing lower limb orthopedic surgery during regional anesthesia additionally received propofol by target-controlled infusion for sedation. The electroencephalogram BIS and the auditory evoked potential index (AEPi), a mathematical derivative of the morphology of the auditory evoked potential waveform, were recorded simultaneously in all patients during repeated transitions from consciousness to unconsciousness. Logistic regression procedures, receiver operating characteristic analysis, and sensitivity and specificity were used to compare predictive ability of both indices. In the logistic regression models, both the BIS and AEPi were significant predictors of unconsciousness (P < 0.0001). The area under the receiver operating characteristic curve for discrete descending index threshold values was apparently, but not significantly (P > 0.05), larger for the AEPi (0.968) than for the BIS (0.922), indicating a trend of better discriminatory performance. We conclude that both the BIS and AEPi are reliable means for monitoring the level of unconsciousness during propofol infusion. However, AEPi proved to offer more discriminatory power in the individual patient. IMPLICATIONS: Both the bispectral index of the electroencephalogram and the auditory evoked potentials index are good predictors of the level of sedation and unconsciousness during propofol infusion. However, the auditory evoked potentials index offers better discriminatory power in describing the transition from the conscious to the unconscious state in the individual patient.

Aged↗

PubMed1998

Clinical utility of EEG parameters to predict loss of consciousness and response to skin incision during total intravenous anaesthesia.

We studied 30 female patients undergoing elective surgery, to assess the reliability of electroencephalogram spectral edge frequency and median frequency to predict loss of consciousness and movement in response to skin incision during total intravenous anaesthesia. Each patient received a different combination of propofol (1, 2, 3, 4, 5 or 6 micrograms.ml-1) and sufentanil (0.1, 0.2, 0.3, 0.5 or 1.0 ng.ml-1) target concentrations for induction of anaesthesia using target controlled infusions, assigned randomly. In a logistic regression model, spectral edge frequency was a significant determinant of both loss of consciousness (p = 0.0006) and movement to skin incision (p = 0.0044), whereas for median frequency no significant prediction model could be established. The probabilities of 50% and 95% no response for spectral edge frequency were 13.4 Hz and 6.8 Hz, respectively. The variability of the data limited the predictive value, so that spectral edge frequency was a poor predictor and median frequency was no predictor of response in the individual patient during total intravenous propofol/sufentanil anaesthesia.

Adult↗

PubMed1998

[The effect of total intravenous anesthesia with propofol, alfentanil and vecuronium (TIVA) on bronchial mucosal transport].

PURPOSE: The mucociliary escalator of the lung is an important protective transport system by means of which inhaled particles and microorganisms are removed from the tracheobronchial system. In the present prospective study the effect of total intravenous anaesthesia with propofol, alfentanil, vecuronium, and oxygen-air ventilation on bronchial mucus transport velocity (BTV) was investigated. METHOD: 10 patients undergoing major abdominal surgery were included in the study. In all patients anaesthesia was induced and maintained with propofol, alfentanil, and vecuronium. Ventilation was assisted with a mixture of air and oxygen (FiO2:0.35). The BTV was measured preoperatively in the conscious patients one day before surgery while they received local anaesthesia with 10 ml of 1 percent lidocaine and after the end of the operation during intubation anaesthesia. BTV was determined with a small volume of albumin microspheres labelled with technetium -99m, which was deposited on the dorsal surface at the lower ends of the right and left main bronches via a catheter placed in the inner channel of a fibre-optic bronchoscope [7]. The study was approved by the ethics committee of our hospital. RESULTS: The administered dose of propofol was 3.0 g (1.8-5.5), of alfentanil 26 mg (20-50), and of vecuronium 20 mg (16-34) (median with range). The duration of mechanical ventilation up to the time of measurement was 5 h (3.0-9.5). TIVA produced a decrease of BTV in the right (9.7 vs 4.9 mm/min) and left main bronchus (11.3 mm/min vs 5.3 mm/min). CONCLUSIONS: Total intravenous anaesthesia with propofol, alfentanil, and vecuronium depressed mucociliary flow in patients with healthy lungs. The period for recovery of mucociliary clearance and the possible disadvantage in patients with increased pulmonary risk (e.g. patients with chronic bronchitis and abdominal surgery) should be clarified in further studies.

Adult↗

PubMed1998

Patient-maintained remifentanil target-controlled infusion for the transition to early postoperative analgesia.

We studied 30 male patients in the early postoperative period to assess the efficacy, safety and feasibility of a patient-demand, target-controlled infusion (TCI) of remifentanil. All patients received the same TCI-based propofol-remifentanil anaesthetic for elective orthopaedic surgery. At the end of surgery, infusion of remifentanil was reduced progressively until patients were breathing spontaneously. After extubation and transfer to the post-anaesthesia care unit, patients were given control of a hand-set and were able to increase the target remifentanil blood concentration by increments of 0.2 ng ml-1. If there were no demands, the TCI controller automatically reduced the target concentration. Pain scores, sedation level, ventilatory frequency, oxygen saturation and nausea were assessed. Mean time to onset of satisfactory analgesia (VAS < or = 3, out of 10) was 18.9 (95% confidence interval (Cl) 15.8-21.9) min at a mean target remifentanil concentration of 2.02 (Cl 1.87-2.16) ng ml-1. There were no episodes of hypoxaemia and the lowest ventilatory frequency was 9 bpm. Nausea occurred in 26.6% of patients and 10% vomited. The majority of patients were only slightly sedated. These results imply an effective tool without respiratory side effects in the early postoperative period after anaesthesia using remifentanil as the analgesic component.

Adult↗

PubMed1998

Recovery from opioid anesthesia: the clinical implication of context-sensitive half-times.

UNLABELLED: The context-sensitive half-time, the time required for a 50% decrease in drug concentration, has been proposed to predict the speed of recovery after infusions of i.v. anesthetics. We studied 40 patients to compare the clinical recovery characteristics of alfentanil and sufentanil. Patients were randomly allocated to receive either sufentanil/propofol (Group 1) or alfentanil/propofol (Group 2) total i.v. anesthesia by target-controlled infusions (TCI), assuming an equipotency ratio of 500:1. After discontinuation, times to tracheal extubation and to discharge from the postanesthesia care unit were measured, as were drug concentrations up to 24 h. The TCI bias was -17.1% for sufentanil and -16.9% for alfentanil. We found no difference in mean extubation times between the groups (48.7 min in Group 1 versus 46.4 min in Group 2), whereas discharge criteria were fulfilled significantly (P = 0.039) earlier after alfentanil (99.5 min) compared with sufentanil (131.3 min). The relative decrement values to tracheal extubation were 62.1% for sufentanil and 48.0% for alfentanil, compared with 75.7% and 65.0% for discharge, respectively. Based on a difference in propofol requirements, we suggest an actual sufentanil to alfentanil equipotency ratio of 1:300. We conclude that the decay in pharmacodynamic effect is not only the result of pharmacokinetics. IMPLICATIONS: Computer simulations may help to anticipate the clinical behavior of anesthetic drugs. In a clinical setting, we tested whether the recovery characteristics after i.v. anesthesia could be explained by a pharmaco-kinetic value, which describes the decline of drug concentrations in the body. This was not fully achieved.

Adult↗

PubMed1997

Perioperative respiratory events in smokers and nonsmokers undergoing general anaesthesia.

BACKGROUND: The prevalence of respiratory diseases in smokers and nonsmokers and the incidence of perioperative respiratory events (PREs) were investigated for patients undergoing general anaesthesia. The aim was to quantify well-known problems and to identify possible new associations between smoking and PREs. METHODS: From July 1992 to December 1994, risk factors, demographic data, and PREs were documented by an automatically readable anaesthetic record (ARAR). PREs were used as defined by the German Society of Anaesthesiology and Intensive Care. RESULTS: Of 26961 subsequent anaesthesias in adults, 7122 (26.4%) were performed in smokers with a prevalence of chronic bronchitis of 23.3% (4.8% in nonsmokers). 1573 PREs occurred in 1397 (5.2%) of all anaesthetics. 459 events concerned intubation problems and problems in technical airway management. 1114 specific respiratory events (SPREs) like re-intubation, laryngospasm, bronchospasm, aspiration, hypoventilation/hypoxaemia and others had a total incidence of 5.5% in smokers and 3.1% in nonsmokers. The relative risk (RR) of SPREs was 1.8 in all smokers, 2.3 in young (16-39 years) smokers, and 6.3 in obese young smokers. The RR of perioperative bronchospasm was 25.7 in young smokers with chronic bronchitis. CONCLUSION: The impact of smoking on perioperative respiratory problems should make anaesthetists take this widespread preoperative condition seriously, particularly in young adults. The presented method of incident reporting (based on a national classification) could contribute to future research in anaesthetic epidemiology.

Adolescent↗

PubMed1996

The role of ascorbic acid and xylitol in etomidate-induced adrenocortical suppression in humans.

Etomidate-induced suppression of cortisol biosynthesis is a result of a blockade of 11-beta-hydroxylation in the adrenal gland, mediated by the imidazol radical of etomidate. Since the generation of steroids requires reductive and energy rich equivalents, the present study examined whether supplementation with ascorbic acid or xylitol, a major source of NADPH, could attenuate adrenal suppression by etomidate in human subjects by promoting the turnover rate of 11-beta-hydroxylase. During continuous etomidate/alfentanil anaesthesia for pelviscopic surgery 30 female patients received either Ringer's lactate, xylitol (0.25 g kg-1 h-1) or ascorbic acid (0.5 g h-1) intravenously (i.v.). The plasma concentrations of cortisol, aldosterone and dehydroepiandrosterone (DHEA) were recorded for 5 h after end of surgery and a stimulation with synthetic ACTH was performed. The results showed no evidence of a clinically relevant attenuating effect of ascorbic acid or xylitol on etomidate-induced adrenocortical suppression. However, the observed suppression of cortisol levels was not enough to allow an attenuating affect to be measured.

Adolescent↗

PubMed1995

[Intravenous anesthesia--current aspects].

Intravenous anaesthesia as a defined technique has become popular in recent years, since new developed drugs and more sophisticated application systems were introduced into clinical practice. However, only a minority of anaesthesiologists really practise this new technique. The scientific basis of continuous intravenous anaesthesia has not been spread widely in the anaesthetic community yet. The following review therefore focusses on recent findings and developments in the field of pharmacology, pharmacokinetics, pharmacodynamics and modern application systems of intravenous anaesthetic drugs. The new opioid remifentanil is described, new aspects in the interpretation of pharmacokinetic data are presented and the concept of context-sensitive halftimes as a parameter to estimate the decrease in clinical effect of intravenous anaesthetics is introduced. Drug effect in clinical anaesthesia is a result of equilibration of the drug with the effect site (Biophase). By means of defining the effect site equilibration time (t1/2ke0 and the drugs concentration at which this effect is achieved (Cp50) the pharmacodynamic properties of each intravenous anaesthetic can be characterised. Computerised pharmacokinetic data can be used to generate stable drug concentrations (target plasma concentration) when connected to an infusion pump. These target controlled systems are able to reach a predefined level rapidly and to maintain it. Thus pharmacodynamic interactions of intravenous drugs can be evaluated. The newly found properties of propofol, such as antiemetic, anticonvulsive and antioxidant, and its present clinical use are described. Finally, modern continuous intravenous anaesthetica techniques have been feasible only by the development of efficient application systems. The text gives an overview of the properties of modern syringe pumps and future developments of "smart" pumps.

Analgesics, Opioid↗

PubMed1994

Decision making in high dependency environments--can we learn from modern industrial management models?

Increasing complexity and increased restraints affect the task of patient management in High Dependency Environments, which has become intricate and difficult. Medical knowledge alone is not enough any longer for proper patient care. Management ability and facilities are required. Current medical knowledge should be expanded by management methods and techniques. By looking at management models in the industry, we found striking similarities between the industrial management situation and clinical patient management. Both systems share complexity in structure, complexity in interaction and evolutionary character. Clinical patient management can be compared with a navigation process. The patient is steered by a control system, and course information is given by control dimensions. Clinical patient management becomes a succession of steering activities influenced by the surrounding systems. This system can be structured in three interacting layers: an operational level, in which information is collected and actions executed; a strategic level in which strategies based on goal-oriented mental anticipation of a probabilistic system are formulated; and a normative level at which principles and norms are defined. It is possible then, to define the tools which have to be developed and implemented to improve clinical management capabilities. At the operational level these tools are addressed to improve clinical decision making by providing information in an ergonomical way. They include artifact elimination, data reduction, increase in meaningful information and unwanted data filtering. At the strategic level, tools to check the feasibility of the applied strategies have to be developed, such as: ideal patient course plots and increased training in strategic thinking.(ABSTRACT TRUNCATED AT 250 WORDS)

Decision Making↗