Midlatency auditory evoked potentials in children: effect of age and general anaesthesia.

BACKGROUND: Midlatency auditory evoked potentials (MLAEP) are a promising tool for monitoring suppression of sensory processing during anaesthesia and might help to avoid awareness. MLAEP in children are different to those in adults and the exact changes during general anaesthesia are unknown. METHODS: In 49 children of age between 2 and 12 yr, MLAEP were recorded before anaesthesia, during tracheal intubation, at steady-state balanced anaesthesia, and after extubation. RESULTS: MLAEP were recordable in all children in the awake (premedicated) state with latencies but not amplitudes dependent on children's age. MLAEP latencies significantly increased during tracheal intubation and steady-state anaesthesia. Changes in amplitudes were inconsistent. All MLAEP variables returned to near baseline values after extubation. CONCLUSIONS: The results of this study imply that MLAEP can successfully be recorded during anaesthesia in children above the age of 2 yr. Further studies are necessary before MLAEP might be applicable for monitoring purposes in paediatric anaesthesia.

Concurrent recording of AEP, SSEP and EEG parameters during anaesthesia: a factor analysis.

BACKGROUND: Spontaneous EEG, mid-latency auditory evoked potentials (AEP) and somatosensory evoked potentials (SSEP) have been used to monitor anaesthesia. This poses the question as to whether or not EEG, AEP and SSEP vary in parallel with varying conditions during surgical anaesthesia. METHODS: A total of 81 variables (31 EEG, 22 SSEP, 28 AEP) were simultaneously recorded in 48 surgical patients during anaesthesia. A total of 307 cases of the 81 variables in stable anaesthetic states were recorded. A factor analysis was performed for this data set. RESULTS: Sixteen variables were excluded because of multicollinearity. We extracted 13 factors with eigenvalues >1, representing 78.3% of the total variance, from the remaining 65 x 307 matrix. The first three factors represented 12%, 11% and 10% of the total variance. Factor 1 had only significant loadings from EEG variables, factor 2 only significant loadings from AEP variables and factor 3 only significant loadings from SSEP variables. CONCLUSION: EEG, AEP and SSEP measure different aspects of neural processing during anaesthesia. This gives rise to the hypothesis that simultaneous monitoring of these quantities may give additional information compared with the monitoring of each quantity alone.

[Unwanted wakefulness during general anesthesia]. / Unerwünschte Wachheit während Allgemeinanästhesie.

Intraoperative wakefulness ("awareness") is still a relevant problem. Different stages of wakefulness exist: conscious awareness with explicit recall of pain in 0.03% and with nonpainful explicit recall in 0.1-0.2% of all anesthesias; amnesic awareness or implicit recall may occur with unknown, even higher incidences. Sufficient analgesia minimizes possible painful perceptions. Opioids, benzodiazepines, and N(2)O alone or combined lead to the highest incidences of nonpainful intraoperative wakefulness. Volatile anesthetics, etomidate, barbiturates, and propofol in sufficient doses effectively block any sensory processing and therefore abolish intraoperative wakefulness. Intraoperative awareness with recall may lead to sustained impairment of the patients, in severe cases even to a post-traumatic stress disorder (PTSD). The observation of clinical signs does not reliably detect intraoperative wakefulness in all cases; monitoring of end-tidal gas concentrations, EEG, or evoked potentials may help in prevention. Active information is recommended only for patients at higher risk. Complaints about recall of intraoperative events should be taken seriously; in cases of sustained symptoms psychological help may be necessary.

Ropivacaine 7.5 mg/ml versus bupivacaine 5 mg/ml for interscalene brachial plexus block--a comparative study.

We investigated ropivacaine 75 mg/ml in comparison with bupivacaine 5 mg/ml in patients receiving interscalene brachial plexus block (ISB) and general anaesthesia. In this randomized, double-blind, prospective clinical trial, each patient received an ISB block according to the technique originally described by Winnie and a catheter technique as per Meier. The rapidity of onset and the quality of sensory and motor block were determined. After general anaesthesia had been induced further parameters evaluated were consumption of local anaesthetic, opioid and neuromuscular blocking drug. After arrival in the recovery room, the patients were assessed for intensity of pain using a visual analog scale (VAS). One hundred and twenty patients were included in the study. The onset and development of sensory block was similar in both groups. Development and quality of motor block was also nearly identical for both local anaesthetics. Consumption of neuromuscular blocking drug and opioid did not differ between ropivacaine and bupivacaine. In the recovery room the mean pain score was less than 25 in both groups. There were no significant differences in terms of onset and quality of sensory or motor block during the intraoperative and early postoperative period. In addition we did not identify any side-effects related to the administration of the local anaesthetics. Ropivacaine 7.5 mg/ml and bupivacaine 5mg/ml proved to be nearly indistinguishable when administered for interscalene brachial plexus block.

Ropivacaine 2 mg/mL vs. bupivacaine 1.25 mg/mL with sufentanil using patient-controlled epidural analgesia in labour.

BACKGROUND: In recent studies, minimum local analgesic concentrations have been defined as 0.93 mg/mL for bupivacaine and 1.56 mg/mL for ropivacaine for epidural analgesia for the first stage of labour, resulting in an analgesic potency ratio of 1 : 0.6. In the current study we compared ropivacaine and bupivacaine in a PCEA system (combined with sufentanil) taking this potency ratio into account but administering drug doses providing sufficient analgesia for all stages of labour. METHODS: In a prospective, double-blinded study 114 parturients were randomised to receive either ropivacaine 2 mg/mL with sufentanil 0.75 microg/mL or bupivacaine 1.25 mg/with sufentanil 0.75 microg/mL. After epidural catheter placement, PCEA was available with boluses of 4 mL, a lock-out time of 20 min and no basal infusion rate. We evaluated pain intensity during contractions, sensory and motor function, duration of labour, mode of delivery and neonatal outcome. Consumption of local anaesthetic and opioid drugs and PCEA system variables were recorded. RESULTS: Mean total consumption as well as mean hourly drug consumption was significantly increased in the ropivacaine-sufentanil group. No differences in analgesic quality, sensory or motor blocking potencies or neonatal outcome variables between groups were detected. Frequency of instrumental deliveries was significantly increased in the ropivacaine-sufentanil group. CONCLUSIONS: The results support the findings of previously published studies postulating ropivacaine to be 40-50% less potent for labour epidural analgesia compared to bupivacaine. However, we observed an increased frequency of instrumental deliveries with ropivacaine. To evaluate the clinical relevance of these findings, further investigations are warranted.

Discrimination of anesthetic states using mid-latency auditory evoked potential and artificial neural networks.

This study was undertaken to determine whether artificial neural network (ANN) processing of mid-latency auditory evoked potentials (MLAEPs) can identify different anesthetic states during propofol anesthesia, and to determine those parameters that are most useful in the identification process. Twenty-one patients undergoing elective abdominal surgery were studied. To maintain general anesthesia, the patients received propofol (3-5 mgkg(-1) h(-1) intravenously). Epidural analgesia at the level of T4-5 blocked painful stimuli. MLAEP was recorded continuously with patients awake, during induction, during maintenance of general anesthesia, and during emergence until the patients were recovered from anesthesia. Latencies of the 5 MLAEP peaks and three peak to peak amplitudes were measured, along with hemodynamic parameters (heart rate, systolic, and diastolic arterial blood pressure). Four-layer ANNs were used to model the relationship between the parameters of the MLAEP and the four different states (awake, adequate anesthesia, during/before intraoperative movement, and emergence from anesthesia). The best identification accuracy was obtained using only the five latencies. The combination of five latencies and three amplitudes did not improve the identification accuracy. Use of the only the three hemodynamic parameters produced a much poorer identification. This study suggests that the MLAEP has useful information for identifying different anesthetic states, especially in its latencies. A nonlinear discrimination approach, such as the ANN, can effectively capture the relation between the MLAEP patterns and the different states of anesthesia.

[Depth of anesthesia, awareness and EEG]. / Messung der Narkosetiefe, Awareness und EEG.

Inapparent adverse intraoperative wakefulness is still a relevant problem in modern anaesthetic routine. It can be associated with serious negative effects on the postoperative recovery of the patients. Several different procedures have been developed to monitor and therefore avoid intraoperative situations of wakefulness during general anaesthesia. The most promising methods are the PRST-score, calculated from changes in the blood pressure, heart rate, sweating and tear production, the so-called isolated forearm technique, spontaneous EEG and its derived parameters such as spectral edge frequencies or BIS and finally mid-latency auditory evoked potentials. The observation of clinical autonomic signs, even including the calculation of the PRST-score does not seem to be valid enough to indicate or predict intraoperative wakefulness. The isolated forearm technique can be regarded as the most reliable tool to detect intraoperative wakefulness, but it can only be applied for a very limited period of time. The processed EEG with the median frequency, spectral edge frequency or bispectral index are important scientific tools to quantify central anaesthetic effects especially to develop pharmacodynamic-pharmacokinetic models of anaesthetic action. But they seem to be less suitable to indicate situations of intraoperative wakefulness or awareness. The mid-latency auditory evoked potentials are depressed dose-dependently by a series of anaesthetic agents, which correlate with the occurrence of situations of intraoperative wakefulness and awareness. There is a hierarchical correlation between certain values of the MLAEP and intraoperative wakefulness defined by purposeful movements, amnesic awareness with only implicit recall and conscious awareness with explicit recall. For some of the most commonly used anaesthetics reasonable threshold values of the MLAEP for the different states of consciousness have already been determined. Future studies in broad patient populations with all of the different routinely used anesthetics and procedures will have to finally identify the importance of the recording of mid-latency auditory evoked potentials as a routine method to assess the depth of anaesthesia.

Activation of mu- and delta-opioid receptors causes presynaptic inhibition of glutamatergic excitation in neocortical neurons.

BACKGROUND: The mechanism underlying the depressant effect of opioids on neuronal activity within the neocortex is still not clear. Three modes of action have been suggested: (1) inhibition by activation of postsynaptic potassium channels, (2) interaction with postsynaptic glutamate receptors, and (3) presynaptic inhibition of glutamate release. To address this issue, the authors investigated the effects of mu- and delta-receptor agonists on excitatory postsynaptic currents (EPSCs) and on membrane properties of neocortical neurons. METHODS: Intracellular recordings were performed in rat brain slices. Stimulus-evoked EPSCs mediated by different glutamate receptor subtypes were pharmacologically isolated, and opioids were applied by addition to the bathing medium. Possible postsynaptic interactions between glutamate and opioid receptors were investigated using microiontophoretic application of glutamate on neurons functionally isolated from presynaptic input. RESULTS: delta-Receptor activation by d-Ala2-d-Leu5-enkephalin (DADLE) reduced the amplitudes of EPSCs by maximum 60% in a naltrindole-reversible manner (EC50: 6-15 nm). In 30-40% of the neurons investigated, higher concentrations (0.1-1 micrometer) of DADLE activated small outward currents. The mu-receptor selective agonist d-Ala2-N-MePhe5-Gly5-ol-enkephalin (0.1-1 micrometer) depressed the amplitudes of EPSCs by maximum 30% without changes in postsynaptic membrane properties. In the absence of synaptic transmission, inward currents induced by microiontophoretic application of glutamate were not affected by DADLE. CONCLUSIONS: Activation of mu- and delta-opioid receptors depresses glutamatergic excitatory transmission evoked in neocortical neurons by presynaptic inhibition. A weak activation of a postsynaptic potassium conductance becomes evident only at high agonist concentrations. There is no evidence for a postsynaptic interaction between glutamate and opioid receptors.

[Induction of anesthesia for a patient with sleep apnea syndrome]. / Narkoseeinleitung bei einem Patienten mit Schlaf-Apnoe-Syndrom.

Based on a case report, we offer brief guidelines on the perioperative management of patients with Sleep-Apnea-Syndrome (SAS) who present with a high incidence of a difficult airway and a high risk of respiratory depression during the perioperative period. A 39 year old male patient with a body mass index of 34.22 kg/m2 and receiving continuous-positive-airway-pressure-(CPAP) therapy for known SAS was scheduled for elective plastic surgery. After induction of anaesthesia and direct laryngoscopy no adequate airway could be established and the patient became hypoxic, hypercapnic and developed hypotension and bradycardia. With the use of a laryngeal mask airway the patient was stabilized and did not show neurologic sequale after immediate awakening. The following fiberoptic intubation of the awake patient, still showing tendency of upper airway obstruction, confirmed the difficult anatomical structures. The subsequent general anesthesia was uneventful. The patient received CPAP therapy and was monitored during the first postoperative night in the Intensive Care Unit. He made an uneventful recovery. He was advised to have regional anaesthesia or planned fiberoptic intubation, where possible, in the case of further anesthetic intervention. SAS has major implications for the anaesthesiologist and whenever patients exhibiting the high risk factors (obesity, male sex, history of intense snoring, impaired daytime performance, nonrefreshing daytime naps) are presented for surgery this condition should be considered. Elective surgery should be postponed until after adequate examination and treatment when necessary. Patients with SAS should always be suspected of having cardiopulmonary dysfunctions such as hypertension, cardiac dysrhythmia or cor pulmonale. It is most important to avoid sedative premedication, to initiate CPAP therapy preoperatively, to encourage regional anaesthesia if possible and to ensure close monitoring over the complete perioperative period. Planned fiberoptic intubation, preferably with surgical personnel available for an emergency airway, is a safe method for the induction of anaesthesia. Postoperatively, patients are at high risk from respiratory depression, even in the awake state. Postoperative opioid analgesia, no matter what route, should only be given under close monitoring. Independently of regional or general anaesthesia there is an increased risk of respiratory depression in the middle of the first postoperative week, suspected to be caused by the catching up on lost REM-sleep, due to shifts in the normal sleep pattern during the first postoperative days.

Comparison of five sedation scoring systems by means of auditory evoked potentials.

OBJECTIVE: To review five sedation scoring systems and to determine their correlation with an objective method for assessing the level of sedation by means of auditory evoked potentials (AEP) in critically ill patients. DESIGN: Prospective clinical study. SETTING: Multidisciplinary intensive care unit in a university hospital. PATIENTS: Ninety-five consecutive patients requiring sedation during intensive care therapy. MEASUREMENTS AND RESULTS: Previous studies have shown that auditory evoked potentials, especially latencies of the midlatency component N(b), could serve as an indicator of depth of anaesthesia. In the present study we used this electrophysiological method to evaluate sedation during intensive care therapy. Changes in latency of peak N(b) were compared with various levels of sedation assessed by five established sedation scoring systems. As in anaesthesia, latencies of N(b) increased with increasing depth of sedation. Among the scoring systems, the one developed by Ramsay correlated best with changes in N(b) latency (r2=0.68). The coefficient of determination, r2, of the other scores ranged from 0.56 to 0.61. CONCLUSION: For the assessment of sedation, several scoring systems have been introduced into clinical practice, but the differentiation of deeper sedation levels, especially, remains poor. In this study we compared auditory evoked potentials, as an objective method with which to assess the level of sedation, with five different sedation scoring systems. In comparison with changes in latency of the midlatency component N(b), Ramsay's sedation score showed the closest correlation. Objective electrophysiological monitoring is desirable during long-term sedation.

[Ambulatory anesthesia: which preoperative screening tests are required]. / Ambulante Anästhesie: Welche Voruntersuchungen sind notwendig?

The volume of preoperative screening investigations for outpatient anaesthesia ranges from few, selectively ordered investigations to extensive routine diagnostic procedures. It seem appropriate to reevaluate benefit and efficacy of routine preoperative assessment programs. The purpose of preoperative diagnostic is to assess the risk of anaesthesia and surgery for the patient. As shown by a number of studies, preoperative screening investigations seldom disclose new pathological findings of clinical relevance. Abnormal laboratory results in otherwise healthy patients rarely alter the anaesthetic management of the patient and are not related to perioperative complications. Extensive use of costly diagnostic procedures considerably increases health care budgets. A more selective approach to order preoperative investigations promises considerable savings. To achieve costeffective evaluation an efficient organisation of properative assessment must be established to avoid costly delay and on day-of-surgery-cancellations. There is no medicolegal obligation to perform routine diagnostic testing. The anaesthetist must be sufficiently informed in time to assess the perioperative risk of the patient and to alter anaesthetic management as necessary. According to the presented studies a clinical history and a through physical examination represent an effective method of screening for the presence of disease. Careful medical history evaluation and physical examination can avoid extensive investigations in apparently healthy individuals and the latter should only be ordered if indicated.

Power spectral analysis of the electroencephalogram during increasing end-expiratory concentrations of isoflurane, desflurane and sevoflurane.

We studied the effects of increasing end-expiratory concentrations of isoflurane (0.3, 0.6, 0.9, 1.2 vol.%) (n = 12 patients), desflurane (1.5, 3.0, 4.5, 6.0 vol.%) (n = 12 patients) and sevoflurane (0.5, 1.0, 1.5, 2.0 vol.%) (n = 12 patients) on power spectral analysis of the electroencephalogram (EEG). Spectral edge frequency (SEF), total power (TP) and relative power in the delta, theta, alpha and beta band were calculated. EEG changes were very similar within the three groups. SEF decreased, TP and relative power in the delta and theta band increased, power in the beta band decreased in a dose-dependent fashion with comparable regression lines. This indicates that MAC equivalent administration of isoflurane, desflurane and sevoflurane in clinically applied dose ranges is associated with equipotent EEG suppression.

Conscious awareness during general anaesthesia: patients' perceptions, emotions, cognition and reactions.

We interviewed 45 patients, who answered advertisements (n = 21) or were referred by colleagues (n = 24), about their experience of intraoperative awareness using a standardized questionnaire. Auditory perceptions, hearing sounds or voices were mentioned by all patients (45 of 45): 33 of 45 patients understood and recalled conversations; 21 of 45 patients had visual perceptions; 12 of 21 recognized things or faces; 29 of 45 patients felt being touched; three patients had the sensation of moderate pain; and eight patients were in severe pain. Patients' feelings were mostly related to paralysis (27 of 45), helplessness (28 of 45), anxiety and fear (22 of 45); 18 were in severe panic. All patients (45 of 45) recognized the situation as a real event: 22 of 45 patients experienced unpleasant after effects; 11 suffered from anxiety and nightmares; and three developed post-traumatic stress disorder syndrome and required medical treatment. Twenty of 45 patients were especially attentive to emotionally relevant remarks on their own person, their disease and the course of their operation. The accuracy of sensory perception indicates a very high level of cognitive performance of patients during intraoperative awareness.

[Quality of pain management in preclinical care of acutely ill patients]. / Qualität schmerztherapeutischer Massnahmen bei der präklinischen Versorgung akut kranker Patienten.

UNLABELLED: The aim of this study was to evaluate the quality of pain management in prehospital emergency care and to get more information about the administration of analgesics in prehospital patients. METHODS: Patients with painful diseases or injuries who had been brought to Munich hospital's were included in the study. Immediately after having reached the hospitals' emergency department, they were evaluated using a 101-point visual analogue scale for the severity of pain at four predefined periods. Information about the patient, the diagnosis, and the analgesic treatment used by the emergency teams were drawn from the patient's chart. RESULTS: A total of 462 patients were included in the study. The mean pain score on arrival of the emergency team was 64 points; 36.5% of the patients were treated with analgesics. In 28.1% the emergency team tried to reduce pain through external measures (i.e., setting of fractures). In 35.3% there was no therapeutic intervention. In cases in which analgesic therapy was initiated, a definite reduction in pain was achieved during emergency care. Visual analogue scores decreased from 70 points at the beginning to 29 points at arrival to the hospital's emergency department. Analgesics were most frequently used for patients with cardiopulmonary diseases (47.2%), followed by patients with traumatic accidents (35.5%) and patients with acute abdominal pain (25.2%). Of the analgesics, opioids were given most frequently (87.0%). Nonopioid analgesic agents were used in 32.1%. The results of our investigation demonstrate that in many cases the administration of analgesics is not individualized to the patients needs. CONCLUSION: During the prehospital period of emergency care many patients suffer from severe pain. The development of patient-oriented concepts concerning pain management could contribute to improvement of pain therapy in prehospital emergency medicine.

Improvement in the therapy of multiply injured patients by introduction of clinical management guidelines.

A trauma algorithm representing the guidelines for the management of emergency treatment of severe blunt trauma was implemented at our institution in 1994. By comparison of two prospectively recorded cohorts of multiply injured patients, the clinical efficacy of these guidelines was analysed. The algorithm cohort comprised 74 patients over the period January 1994 to June 1996, and the Control cohort 126 patients over the period April 1988 to December 1993. To evaluate procedural quality of early clinical trauma management, nine criteria were applied. After implementation of the algorithm there was an improvement in all parameters reflected by a significant reduction of missed injuries and important time savings. Mortality rates in the cohorts were calculated after subdivision into three groups (I-III) with moderate (ISS: 18-24), high (ISS: 25-49) and very high (ISS: 50-75) injury severity. All cohort subgroups were comparable with respect to ISS values, age, initial loss of consciousness (GCS) and shock rate. In all subgroups of the algorithm cohort mortality rates were reduced: group I: 0 versus 20 per cent (p < 0.05); group II: 8 versus 24 per cent (p < 0.05); group III: 40 versus 71 per cent. Improvements in both therapeutic process and outcome were observed after implementation of the trauma algorithm.

[Sevoflurane and the nervous system]. / Sevofluran und Nervensystem.

During sevoflurane anaesthesia cerebral blood flow is preserved or slightly decreased. Cerebral oxygen consumption is reduced to 50% under 1 MAC sevoflurane. Autoregulation of cerebral blood flow and responsiveness of cerebral blood flow to changes in Pa CO2 are widely preserved. Sevoflurane produces a dose dependent increase in intracranial pressure and a decrease in cerebrovascular resistance that can not be observed under hypocapnic conditions. Central stimulus processing, the electroencephalogram and sensory evoked potentials are suppressed under sevoflurane in a dose dependent fashion. The electrophysiological data indicate that intraoperative awareness phenomena should be suppressed with sevoflurane 1.5-2.0 vol.%. Recovery of cognitive and psychomotor functions seems to be faster and more complete after sevoflurane than after isoflurane anaesthesia. In inducing seizure like EEG or muscle activity, sevoflurane seems to be comparable with isoflurane. There is no limitation of sevoflurane use in patients with concomitant psychiatric or neurological diseases, and sevoflurane may be valuable addition in neurosurgery or carotid surgery.

Midlatency auditory evoked potentials predict movements during anesthesia with isoflurane or propofol.

To determine threshold values, sensitivity, and specificity of midlatency auditory evoked potentials (MLAEP) for prediction of spontaneous intraoperative movements, 40 patients undergoing elective laparotomy were studied. Continuous epidural analgesia was used in all patients. To maintain general anesthesia, the patients in Group 1 (n = 20) received isoflurane (0.4-1.2 vol%), and the patients in Group 2 (n = 20) received propofol (3-5 mg x kg(-1) x h(-1) intravenously). Spontaneous movements were documented intraoperatively. Auditory evoked potentials were recorded continuously until the end of anesthesia. Latencies of the peaks V, Na, Pa, Nb, and P1 (ms) and amplitudes Na/Pa, Pa/Nb, and Nb/P1 (microV) were measured. Changes of MLAEP latencies and amplitudes during anesthesia were similar in both groups. Anesthesia led to statistically significant increases in the latencies of Na, Pa, Nb, and P1 and decreases in the amplitudes of Na/Pa, Pa/Nb, and Nb/P1 compared with the awake state. Before and during spontaneous movement observed intraoperatively or during emergence from anesthesia, the latencies of the peaks Na, Pa, Nb, and P1 decreased, and the amplitudes Na/Pa, Pa/Nb, Nb/P1 increased significantly. A threshold value of 60 ms of Nb proved to be most predictive of movement during anesthesia. MLAEP recording seems to be a promising method to monitor the level of anesthesia as defined by spontaneous movement during anesthesia.

Midlatency auditory evoked potentials and motor signs of wakefulness during anaesthesia with midazolam.

We have studied midlatency auditory evoked potentials (MLAEP) and motor signs of wakefulness during anaesthesia with midazolam in 10 patients undergoing elective laparotomy under continuous extradural analgesia. Anaesthesia was induced with midazolam 0.3 mg kg-1 and maintained with midazolam 0.3-0.9 mg kg-1 h-1. Motor signs of wakefulness were documented as spontaneous movements and movements after simple commands (open eyes or move arms). MLAEP were recorded continuously awake, and during anaesthesia until the end of anaesthesia. Latencies of the peaks V, Na, Pa, Nb and P1 (ms) and amplitudes of the peaks Na/Pa, Pa/Nb and Nb/P1 (microV) were measured. Twenty-five movements were observed during anaesthesia; 15 movements in six patients were in response to commands. In two patients supplementary isoflurane was given. Latencies of the MLAEP peaks Pa, Nb and P1 increased slightly during anaesthesia. Amplitudes for Na/Pa, Pa/Nb and Nb/P1 did not change significantly. The high incidence of motor signs of wakefulness associated with preserved MLAEP indicated a high level of cortical neural activity and none of the MLAEP variables predicted movement during anaesthesia with midazolam.