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Biomedical subjects

A M Zbinden

Publications and source records attributed to A M Zbinden.

At least 55 records · Page 3Linked to original sources
PubMed1994

Ondansetron does not inhibit the analgesic effect of alfentanil.

5-Hydroxytryptamine (5-HT) causes antinociception via presynaptic 5-HT3 (5-HT subtype 3) receptors on primary afferent nociceptive neurones in the spinal cord dorsal horn. Therefore, ondansetron (a 5-HT3 receptor antagonist) may increase the perception of a noxious stimulus or decrease the effects of concurrently administered antinociceptive drugs. Using a randomized, double-blind, crossover study design, we have tested this hypothesis in eight healthy volunteers who, on three different days, received either ondansetron and placebo, ondansetron and alfentanil or placebo and alfentanil. Experimental pain was induced with heat, cold, mechanical pressure and electrical stimulation. Ondansetron alone did not change the response to any of the experimental tests, but alfentanil and the combination ondansetron-alfentanil significantly changed the response compared with ondansetron alone. There was no difference between alfentanil alone and the combination ondansetron-alfentanil. We conclude that ondansetron does not change the response to pressure, heat, cold or electrical nociceptive stimuli or antagonize the analgesic effect of alfentanil.

Adult↗
PubMed1994

Anesthetic depth defined using multiple noxious stimuli during isoflurane/oxygen anesthesia. I. Motor reactions.

BACKGROUND: Potency of inhaled anesthetics usually is defined by determining the minimal alveolar concentration (MAC) that prevents movement in 50% of patients in response to skin incision. Skin incision, however, is usually only a single event and, thus, determination of potency cannot be repeated in one patient. Traditional MACskin incision cannot be used to predict response to other noxious stimuli. The aim of this study was to investigate the effects of other noxious stimulation patterns and then compare these to MACskin incision measuring the end-tidal isoflurane concentrations with the corresponding arterial concentrations. METHODS: In 26 patients, the end-tidal and corresponding arterial isoflurane concentrations needed to suppress eye opening to verbal command and motor response after trapezius squeeze, 50 Hz electric tetanic stimulation, laryngoscopy, skin incision, and tracheal intubation in 50% of all patients were determined. RESULTS: The end-tidal (equivalent arterial) isoflurane concentrations (mean +/- SE, adjusted to sea level) expressed in vol% (to allow comparison) increased in the following order (mean +/- SE): vocal command 0.37 +/- 0.09 (0.36 +/- 0.09); trapezius squeeze 0.84 +/- 0.07 (0.65 +/- 0.07); laryngoscopy 1.00 +/- 0.12 (0.78 +/- 0.09); tetanic stimulation 1.03 +/- 0.09 (0.80 +/- 0.06); skin incision 1.16 +/- 0.10 (0.97 +/- 0.17); and intubation 1.76 +/- 0.13 (1.32 +/- 0.11). CONCLUSIONS: Different stimuli require different isoflurane concentrations to suppress motor responses. Tetanic stimulation and, to some extent, trapezius squeeze are reproducible and noninvasive stimulation patterns that can be used as an alternative to skin incision when evaluating potency of an anesthetic agent. In contrast to skin incision, they can be repeated.

Adult↗
PubMed1994

Anesthetic depth defined using multiple noxious stimuli during isoflurane/oxygen anesthesia. II. Hemodynamic responses.

BACKGROUND: The hemodynamic effects of isoflurane have been studied extensively. However, most data are obtained from volunteers or patients in the absence of surgical stimulation. The hemodynamic responses to various stimulation patterns of different intensity have not been evaluated. METHODS: In 26 patients, the ability of isoflurane to suppress motor and hemodynamic reactions in response to noxious stimulations of variable degree (trapezius squeeze, tetanic stimulation, laryngoscopy, skin incision, and laryngoscopy plus intubation) was evaluated by measuring arterial blood pressure and heart rate before and after stimulation. RESULTS: At concentrations that inhibited motor response to these stimuli in 50% of all patients, systolic blood pressure increased by 9 (trapezius squeeze), 15 (tetanic stimulation), 23 (laryngoscopy), 35 (skin incision) and 49 (intubation) mmHg, and heart rate by 5 (trapezius squeeze), 15 (tetanic stimulation), 17 (laryngoscopy), 36 (skin incision), and 36 (intubation) min-1 compared to the prestimulation values. An analysis using multiple regression showed that blood pressure response was influenced most by the type of stimulation followed by the concomitantly occurring motor reaction, the anesthesia time, and least by the isoflurane concentration per se. A high isoflurane concentration had no influence on the magnitude of blood pressure or heart rate increase to stimulation, but it decreased the prestimulation blood pressure and slightly increased the prestimulation heart rate. Heart rate responses were less consistent than those of blood pressure. CONCLUSIONS: Isoflurane used as a sole agent is unable to suppress hemodynamic reactions (blood pressure and heart rate) to painful stimuli. A "normal" blood pressure following stimulation can be achieved only if prestimulation blood pressure is depressed to levels that may be clinically unacceptable. The lack of motor response is not an accurate predictor of the ability of an agent to depress hemodynamic reaction.

Adult↗
PubMed1994

Accuracy, alarm limits and rise times of 12 oxygen analysers.

The Comité Européen de Normalisation recently proposed a new standard for 'the particular requirements of oxygen monitors for medical use'. The feasibility of this proposed standard was tested in respect of (1) accuracy of alarm activation (2) accuracy of oxygen display value during both continuous and cyclical gas flows (3) rise time during rapid changes in oxygen concentration in the following 12 analysers: Datex Capnomac II and Servomex 570A (paramagnetic); Brüel & Kjaer 1304 (magnetoacoustic); Criticare Poet II, Multinex, Dräger Oxydig, Dräger PM 8030, Megamed 046A (part of the Megamed 700 ventilator), Ohmeda 5120, Spacelabs Multigas, Teledyne TED 200 (galvanic); Kontron OM 810 (polarographic). All the analysers tested displayed an oxygen reading which was within +/- 3 vol% of the actual oxygen concentrations of the test gases (15, 21, 40, 60 and 100 vol%). A cyclical pressure of between -1.5 to +8 kPa did not affect the measured oxygen concentration as displayed by the Brüel & Kjaer 1304, Datex Capnomac II and Servomex 570A analysers. The remainder, however, showed, depending on their measuring principle, a display error of between -1 and +6 vol%. After exposure to high pressure all the oximeters functioned normally. Some of the tested devices showed more than 2% of deviation between their alarm activation and the preset alarm limits. Only the Kontron OM 810, the Megamed 046A and the Spacelabs Multigas monitors satisfied the requirements at all the tested oxygen concentrations. The time required by the oxygen analyser to display the rise from 29 to 92 vol % after a sudden change of concentration from 21 to 100 vol % O2 is defined as "rise time" and must not, according to the Comité Européen de Normalisation standard proposal, exceed the manufacturers' specification by more than a factor of 1.15.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗
PubMed1994

A multifactorial analysis of the spread of epidural analgesia.

The controversies about the factors determining the spread of epidural analgesia are partly due to inappropriate methodology or sample size of previous studies. We performed a multivariate regression analysis on 803 ASA class 1-2 non-atherosclerotic adults, undergoing lumbar epidural anaesthesia according to a predefined standardised procedure. The spread of epidural analgesia is more accurately studied by analysing dose/segment (R2 = 0.671) instead of spread (R2 = 0.271) as dependent variable. The impact of local anaesthetic (2% lidocaine CO2 or 0.5% bupivacaine) and addition of adrenaline is not significant. Spread significantly increases with increasing age, weight, body-mass index, dose of local anaesthetic, addition of fentanyl, higher site of injection, and decreasing body height. The impact of age and dose is higher under the age of 40 and at doses lower than 20 ml. Increasing the total dose increases the dose needed to block one spinal segment. Unknown idiosyncratic factors still determine a certain proportion of the sample variance. The addition of adrenaline to lidocaine and the use of bupivacaine improve the predictability of spread. In conclusion, we found clinically significant correlations between a group of factors and epidural spread. Alternative anaesthetic solutions lead to different degrees of predictability.

Adolescent↗
PubMed1994

Simulation of inhalational anaesthetic uptake using a lung model with charcoal.

A physical lung model for simulation of volatile anaesthetic uptake is described. Two communicating water-filled chambers simulate pulmonary mechanics allowing adjustment of functional residual capacity, resistance and compliance. The uptake of the volatile anaesthetics is reproduced by pumping gas from the lung chamber through a charcoal absorber at different rates; using a second pump for a bypass an arterial to end-tidal gradient can be generated. Changes of cardiac output are simulated by adjusting pump speed and of alveolar ventilation by adapting the ventilator setting. The results are reproducible and correspond with patient studies and computer stimulation, not necessitating empirical correction factors as in a previously described oil-based lung model. The model can serve as a teaching instrument, for the comparison and testing of anaesthetic equipment and the development of feedback systems.

Anesthetics, Inhalation↗
PubMed1993

Accuracy and cross-sensitivity of 10 different anesthetic gas monitors.

OBJECTIVE: The objective of this study was to test the accuracy and cross-sensitivity of commercially available anesthetic gas monitors. METHODS: Using gas chromatography (GC) as a reference method, the accuracy, cross-sensitivity, and ability to recognize an erroneously selected agent were determined in the following 10 monitors for volatile anesthetics: Datex Capnomac Ultima-S, Datex Capnomac, Ohmeda 5330 agent monitor, Iris Dräger, Andros Dräger PM 8020 (all monochromatic, infrared analyzers), Nellcor N-2500E, Criticare POET II, Irina Dräger (all polychromatic, infrared analyzers), Siemens Servo Gas Monitor 120 (a piezoelectric analyzer), and Brüel & Kajer Type 1304 (a photoacoustic analyzer). Accuracy was determined at 0.5, 1, 2, and 4 times the minimal alveolar concentration (MAC) of either halothane or isoflurane in oxygen (O2). The cross-sensitivity tests were performed with 70 vol% nitrous oxide in O2, 5 vol% carbon dioxide in O2, 0.032 vol% alcohol in O2, and 70% water vapor in O2. The photoacoustic analyzer showed a higher accuracy for isoflurane than the polychromatic infrared monitors. The greatest inaccuracy with isoflurane was found in the Iris Dräger monitor, which had a maximal bias percentage by volume (vol%) of 0.09 at 0.5 MAC. (This bias was within the manufacturer's specified tolerance of +/- 0.1 vol% or 10% relative difference of reading, whichever is greater.) Irina Dräger was the most accurate analyzer with halothane (mean % bias [relative %] +/- SD, 0.9 +/- 2.0%). The greatest bias with halothane was found in the monochromatic infrared analyzers, with a maximal % bias at 0.5 MAC of 50.3% of the GC reading (12.4% with a new inner Nafion tube) found in the Datex Ultima monitor. The Siemens gas monitor showed a cross-sensitivity for water vapor (-0.248 vol%). The monochromatic infrared analyzers showed a small sensitivity to alcohol (additional deviation of 0.011 to 0.147 vol% at 2 MAC isoflurane) but no sensitivity to nitrous oxide. No cross-sensitivity was found in the polychromatic infrared and photoacoustic analyzers. An incorrect selection of anesthetic agent when using a monochromatic infrared analyzer can be fatal; for example, when using halothane and selecting isoflurane the values measured by the Datex Capnomac monitor were nearly 6 times: below the actual value (i.e., 1 vol% "isoflurane" on the display = 6 vol% halothane in reality). CONCLUSIONS: The photoacoustic measurement principle is more accurate than the other methods, although the polychromatic infrared analyzers are safer because they detect erroneously selected agents.

Anesthesia, Inhalation↗
PubMed1993

Isoflurane minimum alveolar concentration decreases during anesthesia and surgery.

BACKGROUND: It generally is assumed that the potency of inhalational anesthetics remains unchanged during the course of the administration of an anesthetic. Only one study has indicated a decrease of minimum alveolar concentration with time. In this study, an effect of the duration of anesthesia administration and surgery on the potency of isoflurane was investigated by determining MACtetanus (the minimum alveolar concentration that prevents movement in response to electrical tetanic stimulation in 50% of patients) before and after surgery. METHODS: Ten patients who underwent removal of a herniated intervertebral disc were anesthetized with isoflurane only. Reaction to a standardized electrical stimulation applied to the forearm was observed and was graded as movement or no-movement. The isoflurane concentration was increased in steps of 0.10 vol% if the patient moved and decreased in steps of 0.10 vol% if no reaction was seen, until a "movement/no-movement/movement" or "no-movement/movement/no-movement" pattern, respectively, was achieved. RESULTS: MACtetanus decreased in all patients from 1.28 +/- 0.22 vol% (mean +/- SD) before surgery to 1.04 +/- 0.22 vol% after surgery (P < 0.01). When the prestimulation arterial blood pressure or the maximal increase in blood pressure caused by stimulation at the individual MACtetanus before surgery were compared to the corresponding values at the individual MACtetanus after surgery, no significant difference could be found. The prestimulation heart rate and the maximal increase in heart rate were significantly lower after surgery, even though the end-tidal isoflurane concentration was 0.24 vol% lower at the individual MACtetanus after surgery. CONCLUSION: The authors conclude that MACtetanus decreases during the administration of anesthesia and the performance of surgery.

Adult↗
PubMed1993

Nitrous oxide decreases solubility of isoflurane and halothane in blood.

This study investigated the effects of carrier gases on the solubility of isoflurane or halothane in blood. The blood/gas partition coefficients (lambda blood/gas) of 1 minimum alveolar anesthetic concentration of isoflurane or halothane in 100% oxygen, 30% oxygen with 70% nitrous oxide, 100% nitrous oxide or air were measured at 37 degrees C, with blood from four donors. The values of isoflurane or halothane in 100% nitrous oxide (1.42 +/- 0.03; 2.59 +/- 0.05) were lower (P < 0.05) than those obtained when using 100% oxygen (1.53 +/- 0.02; 2.71 +/- 0.05) or air (1.54 +/- 0.03; 2.74 +/- 0.05). To determine the effect of absence of oxygen in the blood containing nitrous oxide on solubility, lambda blood/gas of 1 minimum alveolar anesthetic concentration of isoflurane or halothane in 100% oxygen, a gas mixture (30% oxygen and 70% nitrous oxide) or 100% nitrous oxide were measured under the same conditions. The values of isoflurane or halothane in 100% nitrous oxide (1.29 +/- 0.03; 2.25 +/- 0.08) and in a gas mixture of 30% oxygen and 70% nitrous oxide (1.33 +/- 0.04; 2.29 +/- 0.05) were lower (P < 0.05) than those obtained with 100% oxygen (1.40 +/- 0.03; 2.37 +/- 0.04). We conclude that nitrous oxide decreases the lambda blood/gas of isoflurane or halothane, and that this change of solubility, although small, increases the uptake rate of halothane or isoflurane.

Adult↗
PubMed1992

How can a standard software package for data management in anesthesia be achieved?

Collecting data for administrative, statistical, medical, and organizational purposes is becoming increasingly important in anesthesia. In 1986 the Swiss Society for Anesthesiology decided to create a program that would be compatible for different computers and would expedite data collection. The system developed was called Information System for Operations (ISOP), which was written in the database and programming system Massachusetts General Hospital Utility Multi Programming System (MUMPS). It was installed in eight hospitals and met the initial requirements, but the individual requirements of the hospitals were greatly underestimated. MUMPS has an impressive data storage capability and handling when used in a personal computer (PC) network. The user-interface, however, is inferior to other PC packages, partly because windowing and mouse support were not implemented when the ANSI standard was set. Improved statistical programs, a module for on-line data acquisition, and intensive care unit (ICU) use will be additional modules to the program.

Anesthesia Department, Hospital↗
PubMed1992

Gas leakage in eight anaesthesia circle systems.

Eight currently used factory-new anaesthesia circle systems (Dräger Cicero, Dräger Sulla, Dräger AV1, Gambro Engström Elsa, Megamed 700A, Ohmeda Modulus II Plus, Siemens Ventilator 710 and Siemens Servo Ventilator 900 D with circle system) and a Megamed 077 which had been clinically used for 11 years were tested for gas leaks according to the Draft European Standard Anaesthetic Workstations and Their Modules. All measurements were performed using the Cicero ventilator developed by Dräger with its integrated test program for the detection of system leakage. All the factory-new systems showed leakage rates of less than 50 ml min-1 at a test pressure of 3 kPa (30 cmH2O). In the 'manual' position and with the soda-lime canister and the volumeter (or flow-sensor) included, the following leak rates were determined: Dräger Cicero, 5.0 ml min-1; Dräger Sulla, 22.8 ml min-1; Dräger AV1, 7.7 ml min-1; Gambro Engström Elsa, 33.4 ml min-1; Megamed 700A, 11.5 ml min-1; Ohmeda Modulus II Plus, less than 0.1 ml min-1; Siemens Ventilator 710, 0.3 ml min-1; Siemens Servo Ventilator 900D with circle system 985, 9.6 ml min-1; Megamed 077, 47.5 ml min-1. All anaesthesia breathing circle systems tested performed below the leakage limit of 100 ml min-1 proposed by the draft standard.

Anesthesia, Closed-Circuit↗
PubMed1991

Is the end-tidal partial pressure of isoflurane a good predictor of its arterial partial pressure?

End-tidal partial pressure of isoflurane (PE'iso) may be used as a measure of anaesthetic depth. During uptake, an arterial partial pressure (Paiso) which is considerably less than PE'iso (Paiso/PE'iso much less than 1) leads to underestimation of depth of anaesthesia and, during elimination, PE'iso/Paiso much less than 1 will lead to an overestimation of anaesthetic depth. We measured Paiso/PE'iso during a 60-min uptake period of 1% isoflurane and PE'iso/Paiso during the subsequent 60-min elimination period in 26 patients (age 13-88 yr, ASA I-III) undergoing various surgical procedures. After 15 min of isoflurane uptake, Paiso/PE'iso of 26 patients was mean 0.78 (SD 0.10) and this increased only marginally at 60 min (0.79 (0.09)), whereas during elimination, PE'iso/Paiso was in the range 0.79 (0.14)-0.83 (0.11). Predictability of Paiso in a given patient is hindered by the high SD of Paiso/PE'iso and PE'iso/Paiso, but it may be improved by taking into account age, ASA physical status category, vital capacity, inspired minus end-tidal isoflurane partial pressure and arterial minus end-tidal carbon dioxide partial pressure during uptake; and obesity, end-tidal isoflurane partial pressure and arterial minus end-tidal carbon dioxide partial pressure during elimination. However, even with multiple regression analysis (to account for the various possible variables), clinically useful prediction of Paiso/PE'iso and PE'iso/Paiso in a particular patient is not possible (residual SD 0.084 and 0.113, respectively).

Adolescent↗
PubMed1991

Fresh gas utilization of eight circle systems.

The fresh gas utilization (FGU) of a semi-closed breathing system is defined as the ratio of the amount of gas reaching the patient's lungs to the total amount of fresh gas flowing into the breathing system. It indicates to what extent a breathing system conserves anaesthetic gases and provides inspired gas concentrations as close as possible to those in the fresh gas, even at low fresh gas flows (FGF). We have measured FGU in eight circle systems used conventionally in Europe: Dräger Cicero, Dräger Sulla 808V with circle system 8 ISO and ventilator Ventilog, Dräger AV1, Ohmeda Modulus II Plus, Gambro Engström Elsa, Siemens Servo Ventilator 900 D with circle system 985, Siemens Ventilator 710 and Megamed 700A with circle system 219. The Tests were performed according to the Draft European Standard "Anaesthetic Workstations and Their Modules". None of the systems tested showed the characteristics of an ideal system which would reach 100% FGU with an FGF less than minute volume. At FGF 3 litre min-1, FGU was: Gambro Engström Elsa 97.8%, Siemens Servo Ventilator 900 D with circle system 96.1%, Dräger Cicero 93.4%, Ohmeda Modulus II Plus 93.1%, Dräger 8 ISO 92.3%, Dräger AV1 87.6%, Megamed 700A 77.0% and Siemens Ventilator 710 74.1%.

Anesthesia, Closed-Circuit↗
PubMed1991

[Inspiratory and expiratory resistance of 8 semi-closed circle systems].

The resistance of a circle system is an important factor that determines the respiratory effort of the patient. The inspiratory and expiratory resistances were measured in eight semi-closed circle systems used in Europe: Dräger Cicero, Dräger 8 ISO, Dräger AV1, Ohmeda Modulus II Plus, Gambro Engström Elsa, Siemens Servo Ventilator 900 D with circle system 985, Siemens Ventilator 710, and Megamed 700A with circle system 219. The measurements were all performed in the position "spontaneous breathing" according to a new proposal of the CEN (Comité Européen de Normalisation). The following circle systems exceeded the proposed limit of 0.6 kPa at a gas flow of 60 l/min (with CO2-Absorber): Dräger AV1 in expiration and Siemens Servo Ventilator in both expiration and inspiration. The expiratory resistance was also determined by using intermittent flows. The results differed, as the expiratory gas flow can be influenced by the falling or rising ventilator bellows. The authors conclude that considerable differences exist between various breathing systems and that not all systems can be recommended for use in patients with limited breathing force, such as small children.

Airway Resistance↗
PubMed1989

Parameters influencing the response time of volatile anesthetics monitors.

In a given inhalational anesthetic analyzer, response (RT) is usually thought to be a constant value, however, several factors may influence RT. RT's measured under ideal conditions for the Beckman LB 2, the Normac (Datex), the Servo S 120 (Siemens) and the Irina (Dräger) were 107 +/- 5, 589 +/- 14, 538 +/- 30, and 166 +/- 15 msec, respectively. In addition, we investigated the RT of a Beckman LB 2 analyzer under conditions which may occur in clinical practice (non ideal conditions). Increasing aspirating flow (AF) resulted in shorter RT's, the effect being most pronounced when AF was below 200 ml/min. Interposing a filter prolonged RT by 80%. The type of the inhalational anesthetic (halothane or isoflurane), humidity and temperature of the carrier gas as well as size and direction of the concentration step change did not influence RT. Increasing length or internal diameter (ID) of the sample tube resulted in longer RT's. Changing the sample tube material from glass to Teflon or polyethylene resulted in a slight increase of RT, but the increase was dramatic when rubber or silicone tubes were used. The partition coefficient of halothane in the material of a particular sample tube was directly correlated to the corresponding RT in this sample tube. The influence of different sampling places was studied by interposing copper or corrugated rubber tubing between the place where the concentration step change occurred and the place where the gas was sampled, the measured time was called total response time (TRT). Using corrugated rubber tubes instead of copper tubes increased TRT two to four times. More distal gas sampling and/or lower flow rates caused longer TRT's. Compared with sampling in its center, gas sampling near the walls of the tube resulted in an increase in TRT of 13-45%. It is concluded that the response time of an infrared inhalational anesthetic analyzer is not a constant parameter, but varies between 100 and 4000 msec depending on the characteristics of the analyzer, the sample line, and the place of gas sampling.

Anesthesia, Inhalation↗
PubMed1989

Pulse oximetry in methaemoglobinaemia. Failure to detect low oxygen saturation.

The results of pulse oximetry saturation in a patient with a high level of methaemoglobinaemia, who subsequently underwent intravenous methylene blue treatment, are presented. The reasons for the erroneously low values after treatment are explained. Pulse oximeters currently available are not helpful in patients treated with methylene blue and should be used with caution in patients who present with cyanosis of unknown origin.

Adult↗