Biomedical subjects

A M Zbinden

Publications and source records attributed to A M Zbinden.

At least 19 recordsLinked to original sources

PubMed1998

Adding sodium bicarbonate to lidocaine enhances the depth of epidural blockade.

UNLABELLED: It is controversial whether adding CO2 or sodium bicarbonate to local anesthetics enhances the depth of epidural blockade. Repeated electrical stimulation is a reliable test for assessing epidural analgesia and evokes temporal summation. We used this test to investigate the analgesic effect of lidocaine, with or without CO2 or bicarbonate. Twenty-four patients undergoing epidural blockade with 20 mL lidocaine 2% at L2-3 were randomly divided into three groups: lidocaine hydrochloride, lidocaine CO2, and lidocaine plus 2 mL sodium bicarbonate 8.4%. Pain threshold after repeated electrical stimulation (five impulses at 2 Hz), pinprick, and cold test were performed at S1 and L4. Motor block was assessed. The addition of bicarbonate resulted in higher pain thresholds (P < 0.0001), faster onset of action (P = 0.009), and higher degree of motor block (P = 0.004) compared with lidocaine hydrochloride. We found no significant differences between lidocaine CO2 and hydrochloride. Most of these results were not confirmed by pinprick and cold tests. We conclude that the addition of sodium bicarbonate to lidocaine enhances the depth of epidural blockade, increases inhibition of temporal summation, and hastens the onset of block. Pinprick and cold are inadequate tests for comparing drugs for epidural anesthesia. IMPLICATIONS: We measured pain perception during epidural anesthesia by delivering electrical stimuli to the knee and foot. We found that the addition of sodium bicarbonate to the local anesthetic lidocaine enhances analgesia. We observed no effect of adding carbon dioxide to lidocaine.

Adult↗

PubMed1998

Tracheal intubation with rocuronium using the "timing principle".

UNLABELLED: We compared the endotracheal intubating conditions after rocuronium, using the "timing principle," with those after succinylcholine. The timing principle entails administration of a single bolus dose of nondepolarizing muscle relaxant, followed by an induction drug at the onset of clinical weakness. Forty-five patients were randomly assigned to three groups. Patients allocated to Groups 1 and 2 received rocuronium 0.6 mg/kg. At the onset of clinical weakness (onset of ptosis), anesthesia was induced with thiopental 4-6 mg/kg; intubation was accomplished after 45 s in Group 1 and after 60 s in Group 2. Patients in Group 3 received vecuronium (0.01 mg/kg) 3 min before the administration of thiopental and succinylcholine 1.5 mg/kg, and their tracheas were intubated 60 s later by a blind anesthesiologist. Intubating conditions were assessed according to a grading scale and were either good (5 patients in Groups 1 and 2, 4 patients in Group 3) or excellent (10 patients in Groups 1 + 2, 11 patients in Group 3) in all patients. Patients were interviewed postoperatively, and all were satisfied with the induction of anesthesia. We conclude that rocuronium 0.6 mg/kg provides good to excellent intubating conditions 45 and 60 s after the induction of anesthesia using the timing principle. IMPLICATIONS: We compared the ease with which a breathing tube could be placed in patients using three techniques. The standard technique (succinylcholine) was compared with two others in which a muscle-relaxing drug (rocuronium) was administered just before the anesthetic drug (so-called timing principle). No difference among the techniques was observed.

Adolescent↗

PubMed1998

Epidural fentanyl, adrenaline and clonidine as adjuvants to local anaesthetics for surgical analgesia: meta-analyses of analgesia and side-effects.

BACKGROUND: The risk/benefit ratio of adding fentanyl, adrenaline and clonidine to epidural local anaesthetics for improving intraoperative analgesia is unclear. This meta-analysis was performed to clarify this issue. METHODS: Trials retrieved by search were considered if they were prospective, controlled, epidural analgesia (without combining general anaesthesia) was planned and occurrence of pain during surgery or side-effects were reported. Papers entered meta-analysis if they reached a predefined minimum quality score. Pooled odds ratios (OR) and confidence intervals (CI) were computed. P < 0.05 was considered as significant. RESULTS: Eighteen trials were included in the analysis for fentanyl. Fentanyl decreased the likelihood of pain (OR = 0.21, 95% CI = 0.15-0.30, P < 0.001) and increased the incidence of pruritus (OR = 5.59, 95% CI = 3.12-10.05, P < 0.001) and sedation (OR = 1.88, 95% CI = 1.19-2.98, P = 0.003), compared to control (local anaesthetic without fentanyl). Fentanyl had no effect on respiratory depression, nausea, vomiting and Apgar score. One case of respiratory depression of a newborn was observed. Because of the very low number of trials selected, evaluation of adrenaline and clonidine was not feasible. CONCLUSION: The analysis of current literature shows that the addition of fentanyl to local anaesthetics for intraoperative epidural analgesia is safe and advantageous. The reduction in the incidence of pain during surgery is quantitatively high and therefore clinically significant. Side-effects are mild. Randomized, controlled trials have to be performed in order to clarify the role of adrenaline and clonidine as epidural adjuvants for surgical analgesia.

Adjuvants, Anesthesia↗

PubMed1997

[Data collection in anesthesia. Experiences with the inauguration of a new information system].

UNLABELLED: In many institutions information systems are used to process off-line anaesthesia data for invoices, statistical purposes, and quality assurance. Information systems are also increasingly being used to improve process control in order to reduce costs. Most of today's systems were created when information technology and working processes in anaesthesia were very different from those in use today. Thus, many institutions must now replace their computer systems but are probably not aware of how complex this change will be. Modern information systems mostly use client-server architecture and relational data bases. Substituting an old system with a new one is frequently a greater task than designing a system from scratch. This article gives the conclusions drawn from the experience obtained when a large departmental computer system is redesigned in an university hospital. METHODS: The new system was based on a client-server architecture and was developed by an external company without preceding conceptual analysis. Modules for patient, anaesthesia, surgical, and pain-service data were included. Data were analysed using a separate statistical package (RS/1 from Bolt Beranek), taking advantage of its powerful precompiled procedures. RESULTS: Development and introduction of the new system took much more time and effort than expected despite the use of modern software tools. Introduction of the new program required intensive user training despite the choice of modem graphic screen layouts. Automatic data-reading systems could not be used, as too many faults occurred and the effort for the user was too high. However, after the initial problems were solved the system turned out to be a powerful tool for quality control (both process and outcome quality), billing, and scheduling. The statistical analysis of the data resulted in meaningful and relevant conclusions. CONCLUSIONS: Before creating a new information system, the working processes have to be analysed and, if possible, made more efficient; a detailed programme specification must then be made. A servicing and maintenance contract should be drawn up before the order is given to a company. Time periods of equal duration have to be scheduled for defining, writing, testing and introducing the program. Modern client-server systems with relational data bases are by no means simpler to establish and maintain than previous mainframe systems with hierarchical data bases, and thus, experienced computer specialists need to be close at hand. We recommend collecting data only once for both statistics and quality control. To verify data quality, a system of random spot-sampling has to be established. Despite the large investments needed to build up such a system, we consider it a powerful tool for helping to solve the difficult daily problems of managing a surgical and anaesthesia unit.

Anesthesia↗

PubMed1997

Spinal anaesthesia inhibits central temporal summation.

In a previous investigation we found that extradural anaesthesia did not adequately inhibit temporal summation of repeated electrical stimuli: pain to repeated stimuli was blocked in only one of 10 patients, and pain thresholds to repeated stimuli were significantly lower than pain thresholds to a single stimulus. In this study we have investigated in 10 patients the effect of spinal anaesthesia on temporal summation, assessed by repeated electrical stimulation of the sural nerve. Plain 0.5% bupivacaine 18 mg was injected at L2-3. The pain threshold to a single electrical stimulus, summation threshold (increase in perception during repeated electrical stimuli with five impulses of the same intensity at 2 Hz), pinprick and cold sensation were assessed. After spinal anaesthesia, pain to both single and repeated stimulation, and pinprick and cold sensation, disappeared in all patients. We conclude that spinal anaesthesia inhibits temporal summation elicited by repeated electrical stimulation.

Adolescent↗

PubMed1997

Epidural epinephrine and clonidine: segmental analgesia and effects on different pain modalities.

BACKGROUND: It is not known whether epidural epinephrine has an analgesic effect per se. The segmental distribution of clonidine epidural analgesia and its effects on temporal summation and different types of noxious stimuli are unknown. The aim of this study was to clarify these issues. METHODS: Fifteen healthy volunteers received epidurally (L2-L3 or L3-L4) 20 ml of either epinephrine, 100 microg, in saline; clonidine, 8 microg/kg, in saline; or saline, 0.9%, alone, on three different days in a randomized, double-blind, cross-over fashion. Pain rating after electrical stimulation, pinprick, and cold perception were recorded on the dermatomes S1, L4, L1, T9, T6, T1, and forehead. Pressure pain tolerance threshold was recorded at S1, T6, and ear. Pain thresholds to single and repeated (temporal summation) electrical stimulation of the sural nerve were determined. RESULTS: Epinephrine significantly reduced sensitivity to pinprick at L1-L4-S1. Clonidine significantly decreased pain rating after electrical stimulation at L1-L4 and sensitivity to pinprick and cold at L1-L4-S1, increased pressure pain tolerance threshold at S1, and increased thresholds after single and repeated stimulation of the sural nerve. CONCLUSIONS: Epidural epinephrine and clonidine produce segmental hypoalgesia. Clonidine bolus should be administered at a spinal level corresponding to the painful area. Clonidine inhibits temporal summation elicited by repeated electrical stimulation and may therefore attenuate spinal cord hyperexcitability.

Adrenergic alpha-Agonists↗

PubMed1996

Analgesic effect in humans of subanaesthetic isoflurane concentrations evaluated by evoked potentials.

The aim of this study was to see if an analgesic effect of subanaesthetic concentrations of isoflurane could be detected with evoked potentials elicited by nociceptive stimuli. We studied 10 healthy volunteers breathing three steady-state subanaesthetic concentrations of isoflurane (0.08, 0.16 and 0.24 vol% end-tidal). Reaction time, subjective pain intensities and evoked vertex potentials to laser (LEP) and electrical (SEP) stimuli were recorded and compared with auditory evoked potentials (AEP). Compared with baseline, the subanaesthetic concentrations of isoflurane did not change the latencies of the evoked potentials, but caused a significant reduction in the amplitudes of the LEP and SEP at 0.16 and 0.24 vol% and of the AEP at all three concentrations. There were no changes in perceived pain intensity, and isoflurane produced similar reductions in evoked potentials elicited by both nociceptive and non-nociceptive stimuli. The reaction time was increased significantly at 0.24 vol% isoflurane. The results demonstrated that subanaesthetic isoflurane concentrations caused similar changes in evoked potentials with both painful and non-painful stimuli, with no effect on perceived pain intensity.

Acoustic Stimulation↗

PubMed1996

Fuzzy logic control of inspired isoflurane and oxygen concentrations using minimal flow anaesthesia.

In order to evaluate the performance of feedback fuzzy logic control of inspired oxygen and isoflurane concentrations, we studied 30 patients undergoing discectomy for lumbar (n = 26) or cervical (n = 4) disc herniation. Patients were allocated random to one of two groups: a standard group (n = 15) with low flow anaesthesia (1.2-1.3 litre min-1) and manual control of gas concentrations; and a fuzzy group (n = 15) with minimal flow (0.5 litre min-1) and fuzzy logic feedback control of gas concentrations. Fuzzy logic control achieved and maintained very accurately the desired isoflurane concentration. Oxygen concentration was controlled more precisely than in the standard group. Delivery and costs of oxygen and nitrous oxide were significantly lower in the fuzzy group (P < 0.01). Accumulation of foreign gases was observed in one patient during low flow and in 11 patients during minimal flow anaesthesia. In conclusion, fuzzy logic control of inspired oxygen and isoflurane concentration during minimal flow anaesthesia was reliable and reduced anaesthetic gas delivery and costs.

Adult↗

PubMed1996

Psychophysical and electrophysiological responses to experimental pain may be influenced by sedation: comparison of the effects of a hypnotic (propofol) and an analgesic (alfentanil).

Sedation may influence the responses of some experimental pain models used to test analgesic efficacy. In this study we compared the effects of a sedative (propofol) and analgesic (alfentanil) on: nociceptive reflex to single and repeated electrical stimulations; mechanical pressure pain; and evoked potentials elicited by nociceptive (electrical and laser) and non-nociceptive (acoustical) stimulation. We studied 12 healthy volunteers with two subanaesthetic concentrations of propofol and two analgesic concentrations of alfentanil. Both propofol and alfentanil increased the threshold for nociceptive reflex to single electrical stimulations, but only alfentanil increased the threshold for nociceptive reflex to repeated electrical stimulations. The pressure pain tolerance thresholds were increased significantly by alfentanil, whereas propofol significantly decreased the thresholds (hyperalgesia). Propofol and alfentanil induced similar reductions in the amplitudes of the evoked potentials elicited by nociceptive (electrical and laser) and non-nociceptive (acoustical) stimulation, whereas only alfentanil reduced the perceived pain to nociceptive stimulations. We have shown that sedation can influence both the psychophysical and electrophysiological responses of some experimental pain tests used to measure analgesic efficacy, and that propofol in subhypnotic doses, has no analgesic effect on painful electrical and heat stimulations, but has a hyperalgesic effect on mechanical pressure pain.

Adult↗

PubMed1996

Effect of racemic mixture and the (S+)-isomer of ketamine on temporal and spatial summation of pain.

We have compared the analgesic efficacy of the racemic mixture and the stereoisomer (S+) of the NMDA antagonist ketamine. In a double-blind, three-way crossover, placebo-controlled study, we assessed the following: pain evoked by small/large area pressure stimuli, pain detection threshold and pain ratings to small/large area of heat stimuli, pain detection threshold and pain rating to heat stimuli of brief/long duration, summation pain threshold and pain ratings to repeated heat/electrical stimuli, side effects and reaction time. Plasma concentrations of 350 ng ml-1 for ketamine (racemic) and 180 ng ml-1 for ketamine (S+) were tried. We found that ketamine (racemic) prolonged the reaction time more than ketamine (S+). Both drugs affected pain caused by repeated stimuli or stimuli of long duration equally or more than a single stimulus of short duration. They also affected pain evoked from large areas equally or more than pain evoked from small areas. The (S+)-isomer was approximately twice as potent as the racemic mixture of ketamine in inhibiting central summation.

Adult↗

PubMed1996

Fuzzy logic control of mechanical ventilation during anaesthesia.

We have examined a new approach, using fuzzy logic, to the closed-loop feedback control of mechanical ventilation during general anaesthesia. This control system automatically adjusts ventilatory frequency (f) and tidal volume (VT) in order to achieve and maintain the end-tidal carbon dioxide fraction (FE'CO2) at a desired level (set-point). The controller attempts to minimize the deviation of both f and VT per kg body weight from 10 bpm and 10 ml kg-1, respectively, and to maintain the plateau airway pressure within suitable limits. In 30 patients, undergoing various surgical procedures, the fuzzy control mode was compared with human ventilation control. For a set-point of FE'CO2 = 4.5 vol% and during measurement periods of 20 min, accuracy, stability and breathing pattern did not differ significantly between fuzzy logic and manual ventilation control. After step-changes in the set-point of FE'CO2 from 4.5 to 5.5 vol% and vice versa, overshoot and rise time did not differ significantly between the two control modes. We conclude that to achieve and maintain a desired FE'CO2 during routine anaesthesia, fuzzy logic feedback control of mechanical ventilation is a reliable and safe mode of control.

Adolescent↗

PubMed1996

Factors associated with hypotension and bradycardia after epidural blockade.

In order to identify patient-, anesthesia-, and surgery-related factors influencing the probability of hypotension and bradycardia after epidural blockade, an observational study was conducted on 1050 nonpregnant patients. Backward stepwise logistic regression was performed on the variables hypotension (systolic blood pressure < 90 mm Hg) and bradycardia (heart rate < or = 45 bpm). Hypotension and bradycardia occurred in 158 and 24 patients, respectively. The probability of hypotension increased when epidural fentanyl was administered (odds ratio [OR] = 2.18; 95% confidence interval [CI] = 1.16-4.11), with body weight and spread of epidural analgesia, and decreased when a tourniquet was used (OR = 0.01, CI = 0.01-0.02) and bupivacaine instead of carbonated lidocaine was administered (OR = 0.28, CI = 0.14-0.60). Sensitivity and specificity of the model were 89% and 88%, respectively. The probability of bradycardia was less in women (OR = 0.05, CI = 0.01-0.41) and when a tourniquet was used (OR = 0.04, CI = 0.02-0.09). Sensitivity and specificity were 50% and 97%, respectively. In conclusion, our analysis can contribute to identification of patients at high risk to develop hypotension and bradycardia after epidural blockade. If bupivacaine instead of carbonated lidocaine is used and epidural fentanyl is not administered a decrease in the incidence of hypotension may be anticipated.

Adjuvants, Anesthesia↗

PubMed1996

Five oxygen-nitrous oxide proportioning systems compared.

The majority of contemporary gas delivery modules, on anaesthetic workstations, are equipped with oxygen-nitrous oxide proportioning systems which should prevent the delivery of hypoxic gas mixtures. We investigated five modules, of two different types, using fresh gas flows ranging from 50 mL min-1 to 20 L min-1 with minimally acceptable proportions of oxygen and maximally acceptable proportions of nitrous oxide set at the flow control valves. The oxygen concentrations of the resulting gas mixtures were measured at the fresh gas outlet of the gas delivery modules. All the modules prevented the delivery of hypoxic fresh gas flows both under normal and abnormal working conditions (unequal supply of gas pressures). All systems showed increased O2 concentrations at fresh gas flows below 1 L min-1. The systems can be used with low flow anaesthesia techniques with one exception (Dameca) also with minimal flow techniques.

Anesthesiology↗

PubMed1995

The accuracy of the flowrate in flush-devices of disposable pressure transducers.

BACKGROUND: Arterial and venous pressure is commonly measured using fluid filled catheters. To avoid obstruction they are continuously spilled by a flush-device. The accuracy of the flowrate has not been investigated previously. METHODS: The accuracy of 5 different flush-devices available in Switzerland was checked for flowrate when factory new, after a single sterilization with ethylen-oxide, in a long-term test over 96 hours, after repeated handling of the integrated bypass and under application of a pulsing counter-pressure. RESULTS: Flow is linearly related to differential-pressure and is constant over time. The flow of each flush-device at 200 mmHg differential-pressure was below the indicated 3 ml per hour (1.69 - 2.49 ml/h). Sterilization in two types produced a significant but not relevant difference in flowrate. Longtime-use, bypass actuation and pulsing pressure did not alter the flowrate significantly (p <0.05). In two factory-new flush-devices and 4 re-used ones a plugged capillary induced cessation of flow. CONCLUSIONS: Flowrate in flush-devices is accurate under sterilization, longtime use, bypass-actuation and pulsing counter pressure. A plugged capillary occurred in a few new and reused flush-devices, which can be the explanation for clotted catheters in clinical use.

Blood Pressure Determination↗

PubMed1995

Carbon dioxide analysers: accuracy, alarm limits and effects of interfering gases.

Six mainstream and twelve sidestream infrared carbon dioxide (CO2) analysers were tested for accuracy of the CO2 display value, alarm activation and the effects of nitrous oxide (N2O), oxygen (O2) and water vapour according to the ISO Draft International Standard (DIS)#9918. Mainstream analysers (M-type): Novametrix Capnogard 1265; Hewlett Packard HP M1166A (CO2-module HP M1016A); Datascope Passport; Marquette Tramscope 12; Nellcor Ultra Cap N-6000; Hellige Vicom-sm SMU 611/612 ETC. Sidestream analysers: Brüel & Kjaer Type 1304; Datex Capnomac II; Marquette MGA-AS; Datascope Multinex; Ohmeda 4700 OxiCap (all type S1: respiratory cycles not demanded); Biochem BCI 9000; Bruker BCI 9100; Dräger Capnodig and PM 8020; Criticare Poet II; Hellige Vicom-sm SMU 611/612 A-GAS (all type S2: respiratory cycles demanded). The investigations were performed with premixed test gases (2.5, 5, 10 vol%, error < or = 1% rel.). Humidification (37 degrees C) of gases were generated by a Dräger Aquapor. Respiratory cycles were simulated by manually activated valves. All monitors complied with the tolerated accuracy bias in CO2 reading (< or = 12% or 4 mmHg of actual test gas value) for wet and dry test gases at all concentrations, except that the Marquette MGA-AS exceeded this accuracy limit with wet gases at 5 and 10 vol% CO2. Water condensed in the metal airway adapter of the HP M1166A at 37 degrees C gas temperature but not at 30 degrees C. The Servomex 2500 (nonclinical reference monitor), Passport (M-type), Multinex (S1-type) and Poet II (S2-type) showed the least bias for dry and wet gases. Nitrous oxide and O2 had practically no effect on the Capnodig and the errors in the others were max. 3.4 mmHg, still within the tolerated bias in the DIS (same as above). The difference between the display reading at alarm activation and the set point was in all monitors (except in the Capnodig: bias 1.75 mmHg at 5 vol% CO2) below the tolerated limit of the DIS (difference < or = 0.2 vol%). The authors conclude that the tested monitors are safe for clinical used (except those failing the DIS limits). The accuracy of the CO2-reading (average of mean absolute bias) is better in the M-type than in the S1- or S2-type analysers although no statistical (nor clinical) significant differences could be detected. Most manufacturers work with stricter limits than those proposed by the DIS.

Blood Gas Analysis↗

PubMed1995

Arterial pressure control with isoflurane using fuzzy logic.

Arterial pressure is still one of the most important measures in estimating the required dose of inhaled anaesthetics. It is measured easily and reacts rapidly which makes it suitable as a variable for feedback control of depth of anaesthesia. Fuzzy logic, a novel approach to feedback control, was used to control arterial pressure in 10 patients during intraabdominal surgery by automatic adjustment of the concentration of isoflurane in fresh gas. During anaesthesia, fuzzy control periods of 45-min duration were alternated randomly with human control periods of equal duration. During the skin incision period (-3 to + 12 min) 48.2% of all fuzzy control pressure values were within +/- 10% of the desired mean arterial pressure compared with 40.4% of the human control values (P < 0.05). The corresponding values for the remainder of the operation were 78.3% and 83.2%, respectively. Thus fuzzy out-performed human control at skin incision, but was slightly inferior during the rest of the operation. We conclude that fuzzy logic is a promising new technique for control of isoflurane delivery during routine anaesthesia.

Adult↗

PubMed1995

Analgesic effect in humans of subanaesthetic isoflurane concentrations evaluated by experimentally induced pain.

The analgesic effect of subanaesthetic concentrations of ether, trichloroethylene, methoxyflurane and halothane has been investigated previously using either clinical assessment or pain threshold measurements, but with conflicting results. The purpose of the present study was to evaluate the analgesic effect of isoflurane using experimental pain models. We studied 12 healthy volunteers at three randomly chosen subanaesthetic isoflurane concentrations: low (0.10-0.14 vol%), middle (0.16-0.20 vol%) and high (0.22-0.26 vol%). We used thermal pain detection and pain tolerance thresholds to argon laser stimulation, pressure pain detection and pain tolerance thresholds, immersion of the hand in ice water, and the nociceptive reflex to single and repeated (temporal summation) electrical stimulations, as experimental models to assess analgesia. There were no significant changes in the response to heat, cold or mechanical pressure at any of the subanaesthetic concentrations of isoflurane used. The nociceptive reflex thresholds to single stimulations, but not the thresholds for repeated stimulations, were significantly increased in all three isoflurane groups compared with baseline values. The difference between the different isoflurane concentrations was not statistically significant. In experimental pain models, subanaesthetic isoflurane concentrations have little or no analgesic potency.

Adult↗

PubMed1995

A multifactorial analysis to explain inadequate surgical analgesia after extradural block.

A multivariate analysis of inadequate extradural analgesia was carried out prospectively on 1051 patients undergoing lumbar extradural anaesthesia for surgery performed on structures innervated by T10-S5. Ninety-six patients (9%) experienced pain during surgery. Age, extradural fentanyl, diazepam sedation and duration of surgery had no significant influence. We found some weak evidence that the type of surgery affects the risk of feeling pain. The probability of pain increased with increasing weight, except in overweight women, and was significantly greater for both shorter and taller patients, relative to patients of average height. The probability of pain decreased with increasing dose of local anaesthetic, increasing spread of extradural analgesia, addition of adrenaline, and fentanyl or thiopentone sedation. In conclusion, patient-, surgery- and anaesthesia-related factors influence the risk of inadequate extradural analgesia. If such factors are taken into account, an increase in the success rate may be anticipated.

Adolescent↗