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D Schwender

Publications and source records attributed to D Schwender.

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

Effects of surgical stimulation on midlatency auditory evoked potentials during general anaesthesia with propofol/fentanyl, isoflurane/fentanyl and flunitrazepam/fentanyl.

During general anaesthesia, midlatency auditory evoked potentials are suppressed in a dose dependent manner by a number of general anaesthetics. The activating effects of surgical stimuli on midlatency auditory evoked potentials have been demonstrated during light inhalational anaesthesia, and indicate that midlatency auditory evoked potentials reflect the activity of the central nervous system and not only anaesthetic concentrations. We investigated the effect of surgical stimulation (skin incision, sternotomy) on midlatency auditory evoked potentials under high dose opioid analgesia in 30 patients undergoing elective cardiac surgery. High dose opioid analgesia was maintained using fentanyl (1.2 mg.h-1) and combined with either propofol (4-8 mg.kg-1.h-1) (group I, n = 10), isoflurane (0.6-1.2 vol%) (group II, n = 10) or flunitrazepam (1.2 mg.h-1) (group III, n = 10). Midlatency auditory evoked potentials were recorded in the awake state, during general anaesthesia before skin incision, after skin incision and after sternotomy. During general anaesthesia there were marked statistically significant increases in latencies and decreases in amplitudes of midlatency auditory evoked potentials in the propofol/fentanyl and isoflurane/fentanyl groups. In contrast, in the flunitrazepam/fentanyl group there were only small changes of midlatency auditory evoked potentials. The latencies of the early cortical potentials were similar to those in the awake state. After skin incision as well as after sternotomy no significant changes of midlatency auditory evoked potentials could be observed in any of the experimental groups. These results indicate that activation of the auditory pathway by surgical stimuli may be blocked when analgesia is provided by high dose fentanyl.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia, General↗
PubMed1994

Mid-latency auditory evoked potentials in humans during anesthesia with S (+) ketamine--a double-blind, randomized comparison with racemic ketamine.

Mid-latency auditory evoked potentials (MLAEP) reflect the primary cortical processing of auditory stimuli. They are suppressed widely during general anesthesia. Under ketamine, in contrast, MLAEP seem to be preserved. Ketamine exists in two optical isomers, S (+) ketamine and R (-) ketamine, which differ in their pharmacodynamic properties. S (+) ketamine has a higher anesthetic-hypnotic and analgesic potency than R (-) ketamine or the racemic mixture of S (+) ketamine and R (-) ketamine. In a blinded, randomized evaluation we compared the effect of induction of general anesthesia with the more potent ketamine compound--S (+) ketamine--to induction with the racemic ketamine on MLAEP in 60 patients scheduled for minor gynecologic procedures. Anesthesia was induced with S (+) ketamine (1 mg/kg Group I, n = 30) or an equi-anesthetic dose of racemic ketamine (2 mg/kg, Group II, n = 30). Auditory evoked potentials (AEP) were recorded before, during, and after induction of general anesthesia. Latencies of the peaks V, Na, Pa, Nb, and P1 and amplitudes Na/Pa, Pa/Nb, and Nb/P1 were measured. A fast-Fourier transform was used to calculate the power spectra of the AEP. The baseline MLAEP peaks of the awake patients were of normal amplitude and demonstrated a characteristic periodic wave form morphology. Power spectra indicated high energy in the 30-40 Hz frequency range. After induction of general anesthesia with S (+) ketamine or racemic ketamine, there was no increase in latencies of peaks V, Na, Pa, Nb, or P1. No decrease in amplitudes Na/Pa, Pa/Nb, or Nb/P1 could be observed. There was no significant change in the power spectra.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Effects of benzodiazepines on mid-latency auditory evoked potentials.

Midlatency auditory evoked potentials (MLAEP) reflect primary cortical processing of auditory stimuli. The effects of benzodiazepines on MLAEP have not yet been studied. We examined the effects of intravenous induction of general anaesthesia using the benzodiazepines midazolam, diazepam and flunitrazepam on MLAEP in 30 patients scheduled for minor gynaecological procedures. Anaesthesia was induced with midazolam (0.2-0.3 mg.kg-1, Group I, n = 10), diazepam (0.3-0.4 mg.kg-1, Group II, n = 10) or flunitrazepam (0.03-0.04 mg.kg-1, Group III, n = 10). Auditory-evoked potentials were recorded before and five to ten minutes after induction of general anaesthesia. Latencies of the peak V, Na, Pa, Nb and Pl (ms) and amplitudes Na/Pa, Pa/Nb and Nb/P1 (microV) were measured. In the awake state, MLAEP had high peak to peak amplitudes and a periodic waveform. After induction of anaesthesia there was no or only a small increase in latencies of the peaks Na, Pa, Nb and P1, which was significant only for P1 in the midazolam group. Amplitudes Na/Pa, Pa/Nb and Nb/P1 decreased only slightly and which reached statistical significance only for Na/Pa in the flunitrazepam group. The MLAEPs do not change markedly in amplitude or latency during induction of general anaesthesia with benzodiazepines. Primary cortical processing of auditory stimuli seems to be preserved under benzodiazepines. This may be seen in connection with cases of intraoperative awareness and especially the perception of auditory stimuli during anaesthetic regimens where benzodiazepines are used to suppress consciousness.

Acoustic Stimulation↗
PubMed1993

[Mid-latency auditory evoked potentials during increasing doses of fentanyl].

OBJECTIVE: Intraoperative awareness, and especially the perception of auditory stimuli occur occasionally under general anaesthesia with high-dose opioids. Mid-latency auditory evoked potentials (MLAEP) reflect the primary cortical processing of auditory stimuli. Hence, we studied the effects of fentanyl on MLAEP. METHODS: Institutional approval and informed consent was obtained in 20 patients scheduled for cardiac surgery. Anaesthesia was induced with fentanyl (10 micrograms/kg every 7[ up to a total dosage of 50 micrograms/kg). Auditory evoked potentials were recorded before and 5[ after every fentanyl dose on vertex (positive) and mastoids on both sides (negative). Auditory clicks were presented binaurally at 70 dBnHL at a rate of 9.3 Hz. Using the electrodiagnostic system Pathfinder I (Nicolet), 1000 successive stimulus responses were averaged over a 100 ms post-stimulus interval and analysed off-line. Latencies of the peak V, Na, Pa, Nb P1 and amplitudes Na/Pa, Pa/Nb, Nb/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 and are the electrophysiological correlate of the primary cortical processing of the auditory stimuli. By means of a Fast-Fourier transformation power spectra of the AEP were calculated. RESULTS: In the awake state AEP peak latencies were in the normal range. Power spectra indicated high energy in the 30-40 Hz frequency range. During increasing dosages of fentanyl the brainstem response V was stable. P1 increased in latency and Nb/P1 decreased in amplitude after 10 micrograms/kg of fentanyl significantly. The primary cortical potentials Na, Pa, Nb changed only very slightly in latencies or amplitudes even under highest doses of fentanyl (50 micrograms/kg) and could be identified like in the awake patients. In the power spectra high energy persisted in the 30 Hz frequency range. CONCLUSION: MLAEP and especially the primary cortical potentials Na, Pa, Nb did not change markedly in amplitude or latency during high-dose fentanyl analgesia. There is no dose-dependent effect of fentanyl on MLAEP as it can be observed under volatile anaesthetics (isoflurane, enflurane). The primary cortical processing of auditory stimuli can be completely blocked by volatile anaesthetics, but is still preserved under highest doses of fentanyl. This may be seen in connection with cases of awareness and perception of auditory stimuli during high-dose fentanyl analgesia.

Aged↗
PubMed1993

Effects of increasing doses of alfentanil, fentanyl and morphine on mid-latency auditory evoked potentials.

We have studied dose-dependent effects of alfentanil, fentanyl and morphine on mid-latency auditory evoked potentials (MLAEP). Anaesthesia was induced with alfentanil 100 micrograms kg-1 every 5 min to a total dose of 500 micrograms kg-1 (group I, n = 10), fentanyl 10 micrograms kg-1 every 7 min to a total dose of 50 micrograms kg-1 (group II, n = 10) or morphine 1 mg kg-1 for induction and 0.5 mg kg-1 every 15 min to a total dose of 3 mg kg-1 (group III, n = 10). MLAEP were recorded before and 3-15 min after every opioid dose on vertex (positive) and mastoids on both sides (negative). Latencies of the peaks V, Na, Pa, Nb, P1 (ms) and amplitudes Na/Pa, Pa/Nb and Nb/P1 (microV) were measured. Fast-Fourier transformation was used to calculate power spectra of the AEP. In the awake state, MLAEP had high peak-to-peak amplitudes and a periodic waveform. Power spectra indicated high energy in the 30-40 Hz frequency range. During general anaesthesia with increasing doses of alfentanil, fentanyl and morphine, the brainstem response V was stable. There was a marked increase only in latency and decrease in amplitude of P1. In contrast, for the early cortical potentials Na and Pa, only small increases in latencies and decreases in amplitudes were observed. After the largest doses of alfentanil (500 micrograms kg-1), fentanyl (50 micrograms kg-1) and morphine (3 mg kg-1), Na, Pa and Nb showed a similar pattern as in awake patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Mid-latency auditory evoked potentials during ketamine anaesthesia in humans.

We studied mid-latency auditory evoked potentials (MLAEP) during induction of general anaesthesia with ketamine 2 mg kg-1. MLAEP were recorded before, during and after induction of general anaesthesia on the vertex (positive) and mastoid (negative) positions. Latencies of the peak V, Na, Pa, Nb, P1 and amplitudes Na/Pa, Pa/Nb and Nb/P1 were measured. Fast-Fourier transformation was used to calculate power spectra of the MLAEP. In the awake state, MLAEP had large peak-to-peak amplitudes and a periodic waveform. Peak latencies remained within the normal range. Power spectra indicated high energy in the 30-40 Hz frequency range. After induction of general anaesthesia with ketamine, there was no change in latency of peaks V, Na, Pa, Nb, P1 and no apparent reduction in amplitudes Na/Pa, Pa/Nb and Nb/P1. In the power spectra, frequencies in the range of 30-40 Hz retained high energy. Amplitudes and latencies of MLAEP did not change during induction of general anaesthesia with ketamine. Primary processing of auditory stimuli in the primary auditory cortex seemed to be preserved under ketamine. Suppression of sensory (auditory) information processing must take place at a higher cortical level in a dissociative manner.

Adult↗
PubMed1993

Anaesthesia for coronary artery bypass grafting: opioid-analgesia combined with either flunitrazepam, propofol or isoflurane.

This is a prospective, open, randomized study comparing three different anaesthetic regimens with respect to haemodynamic stability (cardiac index and pressure measurements), ischaemia (ECG), and loss of awareness (midlatency auditory evoked potentials in 58 patients undergoing coronary artery surgery. Anaesthesia was based on fentanyl 0.01 mg kg-1 bw for induction and 0.8-2.0 mg h-1 in combination with nitrous oxide for maintenance before cardiopulmonary bypass and 0.2-0.6 mg h-1 without nitrous oxide during and after cardiopulmonary bypass. Eighteen patients were anaesthetised with flunitrazepam 0.01 mg kg-1 bw for induction and received thereafter 1-2 mg h-1 for maintenance (group F). In 40 patients anaesthesia was induced with etomidate and maintained with either isoflurane 0.4-1.2 vol% (group I) or propofol 4-10 mg kg-1 bw h-1 (group P). Vasodilators and inotropes were used for haemodynamic control when needed. Haemodynamic variables and ECG were studied at five timepoints (awake; after induction before surgery; after sternotomy; before cardiopulmonary bypass; and 20 min after separation from bypass). During surgical stimulation, vasodilators were needed significantly more frequently in group F, than in groups I and P. Surgery and sternotomy caused an increase in SVI and APs/SV in all groups. Differences between the groups were only found for systemic pressures, which after sternotomy were lowest in group I and before cardiopulmonary bypass were highest in group F. After termination of bypass all groups showed an increase in HR and a decrease in SVI, SVR, and LVSWI compared to the awake state, while CI remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

[Recovery of psychomotor and cognitive functions following anesthesia. Propofol/alfentanil and thiopental/isoflurane/ alfentanil].

Recent changes in the medical system have resulted in a significant increase of ambulatory surgical procedures. Therefore, a safe and short postoperative recovery period and, especially, the full recovery of complex psychological function after general anaesthesia have become increasingly important. In the present study we investigated the recovery of psychomotor and cognitive function after general anaesthesia with propofol/alfentanil and thiopentone/isoflurane/alfentanil. PATIENTS AND METHODS. Institutional approval and informed consent was obtained in 40 female ASA I or II patients undergoing diagnostic laparoscopy. As oral premedication the patients received chloracepat (10-20 mg) 45 min before the start of anaesthesia. Anaesthesia was induced in group I with propofol (2.5 mg/kg) and maintained with propofol (6-12 mg/kg/h)/alfentanil (0.05 mg/kg) and 50% N2O in O2. The patients of group II received thiopentone (5 mg/kg) for induction and isoflurane (0.5-1.5 vol%)/alfentanil (0.05 mg/kg) and 50% N2O in O2 for maintenance of general anaesthesia. In particular we measured the following parameters: (1) The recovery time, defined as the interval between the termination of the anesthetic and the patient's correct recall of her birth date. (2) The choice reaction times to optical stimuli (red or green light), which was used as a parameter for attention and psychomotor function. (3) The score in the "Zahlen-Verbindungs-Test" in which the patients had to connect numbers from 1 to 90 in correct order. This is also a parameter to quantify attention and psychomotor function. (4) The digit span which is a value derived from the number of correctly reproduced digits from a list presented to the patients. It is a measure of numerical memory. (5) The Munich Verbal Learning Test, which is the German version of the California Verbal Learning Test. It represents the number of correctly reproduced words from a previously presented list and is a measure of the verbal memory. (6) The Wisconsin Card Sorting Test, which serves to test the ability to plan and act and to form terms and concepts. (7) The State-Trait Anxiety Inventory, to quantify state anxiety. (8) Pain score, using a visual analogue scale. The tests were performed at four measurement points: the day before the operation and 30, 60, and 240 min after recovery. The "Zahlen-Verbindungs-Test", the digit span and the Munich Verbal Learning Test were presented in four parallel forms to minimize learning effects. For statistical analysis of the data the Wilcoxon test was employed within groups and the Mann-Whitney test between groups. RESULTS. The groups were comparable in age, weight, height and level of education. No significant difference was found between them in operation or anaesthesia time or in the total dosage of alfentanil. Recovery time in the propofol group was, at 10 min, significantly shorter than in the isoflurane group, with 16 min. Choice reaction times were significantly increased 30 min after recovery from anaesthesia in both groups. In the propofol group they returned to normal after 60 min, whereas in the isoflurane group significant increases could be observed even 240 min after recovery from the anaesthetic. Choice reaction times were significantly longer in the isoflurane group than in the propofol group 60 min and 240 min after anaesthesia. In the "Zahlen-Verbindungs-Test" the patients showed significantly worse results 30 min and 60 min after anaesthesia. The propofol group tended to be better than the isoflurane group, but the difference did not reach statistical significance. Also in the digit span, the scores were significantly lower 30 min after recovery from the anaesthetic. Here again the propofol group tended to be a little better than the isoflurane group 30 min, 60 min and 240 min after anaesthesia. In the Munich Verbal Learning Test both groups had lower scores 30 min and 60 min, the isoflurane group also 240 min, after recovery...

Adult↗
PubMed1993

[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↗
PubMed1993

[Acoustic evoked potentials of medium latency. Anesthesia induction with S-(+)-ketamine versus ketamine racemate].

Mid-latency auditory evoked potentials (MLAEP) reflect the primary cortical processing of auditory stimuli. They are widely suppressed during general anaesthesia with volatile anaesthetics. Under ketamine, in contrast, they seem to be preserved, which has been interpreted as indicating insufficient suppression of consciousness during ketamine anaesthesia. Ketamine exists in two optical isomeres, S-(+)-ketamine und R-(-)-ketamine, which differ in their pharmacodynamic properties: S-(+)-ketamine has higher anaesthetic-hypnotic and analgesic potency than R-(-)-ketamine. It thus appears obvious to question whether S-(+)-ketamine has a different effect on the primary cortical processing of sensory, i.e., auditory stimuli. We therefore studied the effects of S-(+)-ketamine versus ketamine-racemate on MLAEP. PATIENTS AND METHODS. Institutional approval and informed consent were obtained for 40 patients scheduled for minor gynaecological procedures. The patients were assigned randomly to one of the two experimental groups. All experimental evaluations were conducted under double-blind conditions. Anaesthesia was induced with S-(+)-ketamine 1 mg/kg (group I, n = 20) or ketamine-racemat 2 mg/kg (group II, n = 20). MLAEP were recorded before, during, and after induction of general anaesthesia from the vertex (positive) and mastoids on both sides (negative). Auditory clicks were presented binaurally at 70 dBnHL at a rate of 9.3 Hz. Using the electrodiagnostic system Pathfinder I (Nicolet), 1000 successive stimulus responses were averaged over a 100-ms poststimulus interval and analysed off-line. Latencies of the peak V, Na, Pa, Nb, P1, N1, and amplitudes Na/Pa, Pa/Nb, and Nb/P1 were measured. V belongs to the brainstem-generated potentials, which demonstrates that auditory stimuli were correctly transduced. Na, Pa, Nb, P1, and N1 are generated in the primary auditory cortex of the temporal lobe and are the electrophysiological correlate of the primary cortical processing of the auditory stimuli. A Fast-Fourier transformation calculated powerspectra of the AEP. RESULTS. In the awake state, AEP peak latencies were in the normal range. MLAEP had high amplitudes and a periodic wave form. Powerspectra indicated high energy in the 30-40-Hz frequency range. After induction of general anaesthesia with (S+)-ketamine or ketamine-racemat, there was no increase in the latencies of the peaks V, Na, Pa, Nb, P1, and N1. No decrease in amplitudes Na/Pa, Pa/Nb, or Nb/P1 could be observed. In the power spectra, frequencies in the range of 30-40 Hz retained high energy. CONCLUSIONS. MLAEP do not change in amplitude or latency during induction of general anesthesia with S-(+)-ketamine or ketamine-racemat. Primary cortical processing of auditory stimuli seems to preserved under S-(+)-ketamine and ketamine-racemat. This must be viewed in connection with dreams and hallucinations and could be interpreted as inadequate suppression of auditory information processing during general anaesthesia with S-(+)-ketamine and ketamine-racemat.

Adult↗
PubMed1992

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↗
PubMed1991

[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↗
PubMed1991

[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↗
PubMed1991

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↗