Depth of anesthesia. Midlatency auditory evoked potentials and cognitive function during general anesthesia.
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Anesthesia, General↗
Biomedical subjects
C Madler
Publications and source records attributed to C Madler.
[Premedication before endoscopic interventions: who is responsible?].
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Anti-Anxiety Agents↗
[Monitoring intraoperative processing of acoustic stimuli with auditory evoked potentials].
130 Patients undergoing elective intra-abdominal, gynaecological, urological or cardiac surgery were studied after institutional approval and informed consent. In all patients auditory-evoked potentials (AEP) were recorded in the awake state and during general anaesthesia. Latencies of the peaks V, Na, Pa, Nb and P1 were measured. V belongs to the brainstem-generated potentials, which demonstrates that auditory stimuli were correctly transduced. Na, Pa, Nb, P1 are generated in the primary auditory cortex of the temporal lobe. During anaesthesia with isoflurane, enflurane, thiopentone, etomidate and propofol the peak V remains unchanged, whereas the mid-latency auditory-evoked potentials (MLAEP) show marked increases in latencies and decreases in amplitudes or are even completely suppressed. This indicates a successful stimulus transmission up to the level of the brainstem and midbrain. However, stimulus processing in the primary auditory cortex is blocked. Under increasing end-expiratory concentrations of isoflurane MLAEP show a dose-dependent increase of latencies and decrease of amplitudes. Under surgical anaesthesia with 1.2 vol%, MLAEP are nearly completely suppressed. A different picture can be seen when MLAEP were recorded during anaesthesia with the receptor-specific anaesthetics midazolam, flunitrazepam, diazepam, fentanyl and ketamine. During anaesthesia with receptor-specific anaesthetics, the brainstem peak V as well as the mid-latency components remain nearly unchanged compared with AEP from awake patients. This indicates that auditory stimuli reach the primary auditory cortex and are processed at a primary cortical level. With increasing doses of fentanyl one can observe only a significant decrease of amplitudes for the late component P1.(ABSTRACT TRUNCATED AT 250 WORDS)
Acoustic Stimulation↗
Propofol/fentanyl versus etomidate/fentanyl for the induction of anesthesia in patients with aortic insufficiency and coronary artery disease.
The purpose of this study was to gain information about the hemodynamic effects following the induction of anesthesia with fentanyl and either 1 mg/kg of propofol (P) or 0.25 mg/kg of etomidate (E) in ASA III-IV patients with aortic insufficiency (AI) or coronary artery disease (CAD). Four patient groups resulted: (1) AI and P, n = 10; (2) AI and E, n = 10; (3) CAD and P, n = 6; and (4) CAD and E, n = 8. Hemodynamics were recorded in the awake state, following induction, intubation, and 10 minutes after intubation. No complications occurred in groups 1, 2, and 4. In 2 patients of group 3, who suffered from three-vessel CAD, induction resulted in severe hypotension associated with an increase in pulmonary capillary wedge pressure. Because of this, the investigation of group 3 was prematurely terminated after the sixth patient. The following changes were observed under general anesthesia: in all four groups, arterial pressure (AP), cardiac index (CI), and left ventricular stroke work index decreased. Significantly different values between group 1 (AI and P) and 2 (AI and E) were observed for heart rate (HR) (P less than E), stroke volume (SV) (P greater than E), arterial elastance (Ea), and systemic vascular resistance (SVR) (P less than E); differences between group 3 (CAD and P) and 4 (CAD and E) were seen for AP, Ea, and SVR (P less than E each). After tracheal intubation, baseline values of AP and HR were not surpassed in any group. Signs of systolic myocardial dysfunction were present in all groups (P greater than E).(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
[Sensory information processing during general anesthesia-- acoustic-evoked 30-40 Hz oscillations and intraoperative wakefulness during cesarean section].
Neuropsychological and neurophysiological investigations indicate that the underlying framework of adequate sensory information processing is a 30-40 Hz oscillatory brain mechanism, which also can be observed in mid-latency auditory evoked potentials (MLA-EP). Since high incidence of stimuli perception and wakefulness is a phenomenon during Caesarean section under general anaesthesia it was studied if auditory evoked 30-40 Hz oscillation correlate with intraoperative wakefulness during this surgical procedure. Following informed consent, 21 patients were selected for elective Caesarean section. Anaesthesia was induced with thiopentone (5 mg/kg b.w. i.v.) and maintained with thiopentone bolus injection (1-2 mg/kg b.w.i.v). and O2/N2O 1:1 according to clinical signs of adequate anaesthesia. After delivery, a balanced anaesthetic technique using fentanyl, enflurane and N2O in O2 1:1 was employed. Clinical signs of intraoperative wakefulness were spontaneous movements of the limbs, mimics, eye-opening, wakefulness after auditory stimulation (tape A: crying baby, tape B: classical music), one hour and 24 hours postoperatively reported dreams, hallucinations and detailed reports about intraoperative events. Auditory evoked potentials were recorded on-line before and during general anaesthesia, during the entire surgical procedure. Latencies of the peaks V, Na, Pa were measured. Employing Fast-Fourier transformation analysis, corresponding power spectra were calculated to analyse energy portions of AEP's frequency components. Spontaneous motoric movements occurred in 60% of the patients and did not correlate with heart rate, blood pressure or other clinical signs of inadequate anaesthesia. Provoked motoric reactions were 4 times as often after presentation of tape A as after tape B.(ABSTRACT TRUNCATED AT 250 WORDS)
Acoustic Stimulation↗
[The effect of thiopental on mid-latency auditory evoked potentials and their frequency analysis].
The effect of Thiopentone on mid-latency auditory evoked potentials has not yet been examined sufficiently. Therefore, mid-latency auditory evoked potentials during induction of general anaesthesia with thiopentone were studied. Following informed consent in 10 patients scheduled for elective surgery, anaesthesia was induced with thiopentone (5 mg/kg b.w. i.v.). Assisted ventilation via face mask with 100% O2 was performed until the first purposeful movement of the limbs appeared. Then a second bolus of thiopentone (2 mg/kg b.w. i.v.) was given and general anaesthesia was maintained according to anaesthesiological and operative necessities. Auditory evoked potentials were recorded in the awake and on-line when thiopentone was injected up to 9 min after the onset of general anaesthesia. Latencies of the peaks V, Na, Pa were measured. Using Fast-Fourier-Transform-Analysis, corresponding power spectra were calculated to analyse energy portions of the AEP frequency components. In the awake state peak latencies were in the normal range. Corresponding power spectra indicated energy maxima in the 30-40 Hz frequency range. After induction of general anaesthesia an increase in latencies of the peaks Na, Pa could be observed. The energy in the 30-40 Hz range became suppressed, the AEP energy maxima shifted to the low frequency range. These effects were observable until 3 min after injection. When the first purposeful movement of a limb occurred, Na, Pa latencies returned to normal values and most part of the AEP-energy was in the 30-40 Hz range as in the awake.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Sensory information processing during general anaesthesia: effect of isoflurane on auditory evoked neuronal oscillations.
There is evidence from neuropsychological and psychophysical measurements that sensory information is processed in discrete time segments. The segmentation process may be described as neuronal oscillation at a frequency of 30-40 Hz. Stimulus-induced neuronal oscillations of this frequency are found in the middle latency range of the auditory evoked potential (AEP). We have studied the effect of different end-tidal concentrations of isoflurane on auditory evoked 30-40 Hz neuronal oscillations. We studied 13 patients undergoing intra-abdominal urological and gynaecological procedures. AEP were recorded in the awake state and during end-expiratory steady state isoflurane concentrations of 0.3, 0.6 and 1.2 vol%. These incremental doses of isoflurane caused a stepwise decrease in frequency of oscillations. The decrease in oscillation frequency and sometimes the disappearance of oscillatory components may be interpreted as suppression of sensory information processing. The measurement of auditory evoked neuronal oscillations in the AEP appears to be a promising tool to monitor both sensory information processing capacity and depth of anaesthesia.
Adult↗
[Mass accidents from the anesthesiologic viewpoint].
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Analgesics↗
[Acoustic evoked potentials of medium latency and intraoperative wakefulness during anesthesia maintenance using propofol, isoflurane and flunitrazepam/fentanyl].
Auditory evoked potentials have been used as an indicator of awareness. During combined local and general anesthesia clinical signs of adequate anesthesia are difficult to evaluate. In the present study we combined peridural analgesia with three techniques of general anesthesia. Intraoperative wakefulness was documented and correlated with cardiocirculatory parameters as well as with mid-latency auditory evoked potentials (MLAEP). METHODS. After institutional approval and informed consent 30 patients undergoing elective laparotomy were studied as follows: first, continuous peridural analgesia was instituted in all patients to block painful sensation of surgical stimuli and the anesthetic level was maintained at T5. Then general anesthesia was induced with propofol 2.5 mg/kg i.v. (group I, n = 10), thiopental 5 mg/kg i.v. (group II, n = 10), or etomidate 0.2 mg/kg i.v. (group III, n = 10) and maintained with propofol 3-5 mg/kg per hour i.v. (group I), isoflurane 0.4-0.8 vol.-% (group II), or flunitrazepam 0.005-0.01 mg/kg i.v. and fentanyl 0.0025-0.005 mg/kg i.v. bolus injections every 20-30 min (group III). Heart rate and arterial pressure were registered continuously. Purposeful movements of the limbs, eye-opening, or other movements as well as coughing were documented as signs of intraoperative wakefulness. AEP were recorded in the awake state, after induction, and during maintenance of general anesthesia. Latencies of the peaks V, Na, and Pa were measured. By fast-Fourier transformation corresponding power-spectra were calculated to analyze the energy content of the AEP frequency components. RESULTS. Intraoperative wakefulness occurred statistically significantly more often in the patients of group III than in those of groups I and II. There was no correlation between wakefulness and cardiocirculatory parameters. Latencies of peaks V, Na, and Pa in the awake patients were in the normal range; the corresponding power-spectra had their major energy content in the 30-40-Hz range. After induction of general anesthesia with propofol, thiopentone, and etomidate as well as during maintenance of general anesthesia with propofol and isoflurane peak latencies of Na and Pa increased, frequencies in the 30-40 Hz range became suppressed, and MLAEP energy maxima shifted to the low-frequency range. In contrast, during maintenance of general anesthesia with flunitrazepam/fentanyl peak latencies of Na and Pa returned to awake values and frequencies in the range of 30 Hz regained energy dominance in the corresponding power-spectra. CONCLUSIONS. The maintenance of MLAEP and the primary cortical complex Na/Pa correlates with the incidence of motor signs of wakefulness. During the combination of regional and general anesthesia, isoflurane and propofol seem to provide better suppression of intraoperative wakefulness than bolus injections of flunitrazepam/fentanyl.
Adult↗
Analysis of oscillatory components in perioperative AEP-recordings: a nonparametric procedure for frequency measurement.
Auditory evoked potentials (AEPs) were recorded in 15 patients scheduled for minor gynecological procedures. The suppression of a middle latency oscillation about 40 Hz was observed during 2 minutes after injection of the anesthetic agent propofol. The decrease in oscillation frequency during anesthetic induction was evaluated with a fast Fourier transformation (FFT) and a rank-correlation procedure (RCP). With AEPs having a short epoch of 100 ms the frequency resolution of the RCP was better than the frequency resolution of the FFT. The rank-correlation function of the RCP indicates an initial drop of oscillation frequency from 44 Hz to 37 Hz during 1 minute after anesthetic induction. During the second minute after the infusion of propofol, the oscillation frequency decreases from 37 Hz to 19 Hz. It is suggested that the suppression of neuronal oscillations in the AEP represents a loss of sensory information processing. The measurement of middle latency oscillations in the AEP is proposed to be a promising indicator for the intraoperative stage of anesthesia.
Adult↗
[Middle-latency auditory evoked potentials during high-dose opioid analgesia].
Neuropsychological and neurophysiological investigations indicate that a 30-40 Hz oscillatory brain mechanism is necessary for the adequate uptake and processing of elementary successive sensory events. An oscillatory component of that particular frequency range can be observed in the mid-latency auditory evoked potential (MLAEP). It is suppressed under non-specific anesthetic agents (agents not acting on specific structures of the brain or receptors). Opioids produce analgesia, sedation, and are also used for induction and maintenance of general anesthesia. The effect of opioids on MLAEP has not yet been examined sufficiently. Because intraoperative wakefulness and awareness is not rarely observed under high-dose opioid analgesia, the effect of general anesthesia with fentanyl on MLAEP and auditory evoked neuronal 30-40 Hz oscillation was studied. Following informed consent in 20 patients scheduled for elective surgery, anesthesia was induced with fentanyl 0.01-0.02 mg/kg i.v. Auditory evoked potentials (AEP) were recorded before and 5 min after the start of general anesthesia over the vertex (positive) and mastoids on both sides (negative). Auditory clicks were presented binaurally at 70 dBnHL with a frequency of 9.3 Hz. Using the electrodiagnostic system Pathfinder I (Nicolet Co.), 1000 successive stimuli were averaged over a 100-ms post-stimulus period and analyzed off-line. Latencies of the peaks V, Na, and Pa were measured. By Fast-Fourier Transform-analysis corresponding power spectra were calculated to analyze energy portions of the AEP frequency components. In the awake state AEP showed an oscillatory component between 20- and 100-ms post-stimulus latency. Corresponding power spectra indicated a dominant 30-40 Hz frequency.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
[Mid-latency auditory evoked potentials during induction of intravenous anesthesia using midazolam, diazepam and flunitrazepam].
Since intraoperative awareness is not infrequently observed under balanced anaesthetic regimens employing benzodiazepines for suppression of consciousness, we studied the effect of intravenous induction of general anaesthesia using the benzodiazepines midazolam, diazepam and flunitrazepam on mid-latency auditory evoked potentials and auditory evoked neuronal 30-40 Hz oscillation. Following informed consent in 30 patients scheduled for minor gynaecological procedures, anaesthesia was induced with midazolam (0.2-0.3 mg/kg b.w. i.v., group I n = 10), diazepam (0.3-0,4 mg/kg b.w., i.v., group II n = 10) or flunitrazepam (0.03-0.04 mg/kg b.w., i.v., group III n = 10). Auditory evoked potentials were recorded before, during and after induction of general anaesthesia on vertex (positive) and mastoides on both sides (negative). Auditory clicks were presented binaurally at 70 dBnHL with a frequency of 9.3 Hz. Using the electrodiagnostic system Pathfinder I (Nicolet), 1000 successive stimuli were averaged over a 100 ms poststimulus period and analysed off-line. Latencies of the peak V, Na, Pa were measured. By means of Fast-Fourier transformation-analysis corresponding power spectra were calculated to analyse energy portions of the AEP frequency components. In the awake state AEP showed an oscillatory component between 20 and 100 ms poststimulus latency. Corresponding power spectra indicated a predominant 30-40 Hz frequency. After induction of general anaesthesia using midazolam, diazepam and flunitrazepam, there was no increase in latencies of the peaks V, Na, Pa, but only a small decrease in amplitudes Na/Pa without statistical significance. The auditory evoked mid-latency neuronal oscillation persisted under induction of general anaesthesia with midazolam, diazepam, flunitrazepam.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Induction of anaesthesia in patients undergoing aortocoronary bypass surgery: propofol versus etomidate.
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Aged↗
[Sensory information processing during general anesthesia. The effect of propofol and ketamine on mid-latency auditory evoked potentials].
Experimental evidence from various neuropsychological and neurophysiological fields indicates that an oscillatory brain mechanism in a frequency range of 30-40 Hz is necessary for adequate sensory information processing. An oscillatory component of that particular frequency range can also be observed in the mid-latency auditory evoked potentials. Thus general anesthesia can be defined as a suppression of sensory information processing, and the effect of the i.v. anesthetics, Propofol and ketamine, on auditory perception and auditory-evoked potentials was therefore studied. In 22 patients anesthesia was induced with Propofol (2.5 mg/kg body weight, group I: n = 10) or ketamine (2 mg/kg body weight, group II: n = 12). Auditory-evoked potentials were recorded before, during, and after induction of general anesthesia. In the awake state, an oscillatory component with an energetically dominant 30-40 Hz frequency was present between 20 and 100 ms poststimulus latency. Propofol suppressed the mid-latency oscillatory component, whereas the component persisted under ketamine. Under Propofol, the 30-40 Hz leading frequency shifted to the lower frequency range, whereas under ketamine, the AEP were still dominated by a 30-40 Hz oscillation. Propofol suppresses the oscillatory brain mechanism necessary for adequate sensory information processing like various other general anesthetics. In contrast to Propofol, ketamine does not alter auditory perception. Suppression of sensory information processing must take place at a higher cortical level in a dissociative manner. The persistence of a 30-40 Hz oscillation must be seen in connection with dreams and hallucinations as reported for the drug and may be interpreted as insufficient suppression of sensory information processing under ketamine anesthesia.
Adult↗
Auditory evoked potentials indicate the loss of neuronal oscillations during general anaesthesia.
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Acoustic Stimulation↗
Effects of enflurane on myocardial ischaemia in the dog.
The effects of experimentally induced, severe coronary artery stenosis on regional changes in myocardial blood supply, cardiac function, and metabolism were studied in 14 dogs. The anterior interventricular branch of the left coronary artery (LAD) was constricted such that arterial inflow was reduced by 80%. Nine dogs were given enflurane in a concentration of 2.2 vol.% (1 MAC) in air, and five animals received no enflurane (controls). Regional myocardial blood supply was measured by the tracer microspheres technique, using 8-micron microspheres labelled with five different radioisotopes. Regional cardiac function (end-diastolic length of the muscle fibres = EDL; segmental shortening during systole = delta L) was estimated with the aid of two ultrasonic crystals which were placed in the subendocardial layer of the myocardium supplied by the LAD. Regional myocardial metabolism (oxygen consumption; lactate extraction) was evaluated from arterial and coronary venous blood samples. The latter were collected selectively from the region supplied by the LAD via the great cardiac vein. The results showed that, during severe coronary artery stenosis comparable to clinical conditions, apart from the known actions on systemic haemodynamics and contractility, enflurane had beneficial effects on regional myocardial variables. This was indicated by reduced regional contraction, measured as EDL and delta L; unchanged subendocardial blood flow without any redistribution; and improved lactate extraction in the ischaemic region.
Animals↗
[Characterization of the effect of analgesics on the assessment of experimental pain in man. Pethidine and tramadol in a double-blind comparison].
The effect of the opioid analgesics tramadol and pethidine on experimentally induced pain was investigated in a double blind study with healthy volunteers. Using a constant current shocker, compensating the changes of the skin resistance, a constantly increasing pain stimulus was produced. Detection-, pain-, and tolerance-thresholds were assessed before and three times after intravenous injection of either pethidine (1 mg/kg bodyweight), tramadol (2 mg/kg bodyweight) or placebo (NaCl). While the two analgesics caused an increase of all three thresholds the placebo did not cause any threshold changes. The rise of the detection threshold after application of tramadol and pethidine suggests a sedation effect. However, in relation to the analgesic effect this sedation effect is stronger with tramadol than with pethidine. With the dosage used in this experiment, there is no difference in the analgesic effect of tramadol and pethidine. Compensating for intra- and interindividual changes in skin resistance, the pain stimulation method used in this study provides a good quantification of the effects of analgesics.
Adult↗