Comparison of two depth of anaesthesia monitors during general anaesthesia: electrophysiological and clinical assessment.

UNLABELLED: Cerebral state monitor (CSM) is a recently developed anaesthesia depth monitor based on EEG measurement. Medline search confirmed that the accuracy of this monitor has already been compared with BIS monitoring; however, we did not find any studies comparing CSM monitor with AEP monitoring. Therefore, the aim of our study was to investigate the correlation between AAI using AEP monitor and CSI (cerebral state index) using CSM monitor. METHODS: Prospective, observational study involving 39 ASA I-III patients undergoing lumbar discuss hernia operation. Simultaneous registration of CSI and AAI was performed during general anaesthesia. The identical values were off-line analysed. Additionally in 20 patients parallel registration of CSI and AAI was undertaken while anaesthesia was guided based on routine clinical signs. RESULTS: While analysing the data in the superficial, ideal and deep anaesthesia zones, we found that a relationship between CSI and AAI is weak. Our patients spent roughly the half of the clinical anaesthesia in the ideal zone based on the AAI index and less than 50% based on CSI. Almost one fifth of clinical anaesthesia based on AAI and nearly 40% based on CSI was spent in the deep anaesthesia zones. A superficial anaesthesia has been detected in 27% of time based on AAI and 17% based on CSI. CONCLUSIONS: CSI and AAI weakly correlated to each other. Depth of anaesthesia monitors may be useful in detecting patients who spend valuable time within the deep anaesthetic zone.

Auditory evoked potential index does not correlate with observer assessment of alertness and sedation score during 0.5% bupivacaine spinal anesthesia with nitrous oxide sedation alone.

PURPOSE: The aim of this study was to evaluate the auditory evoked potential (AEP) index as a hypnosis monitor during nitrous oxide (N(2)O) sedation added to spinal analgesia. METHODS: Forty-five patients scheduled to undergo surgery under spinal anesthesia were recruited after giving informed consent. Adequate anesthesia levels were confirmed, and a disposable AEP index sensor (aepEX, Medical Device Management) was placed. A tight facemask was fitted, and a fresh gas flow of 100% oxygen 10 L/min was provided. AEP index monitoring was then initiated, and measurements and observer assessment of alertness/sedation (OAA/S) scores were recorded manually. N(2)O was administered in stepwise increases in the end-tidal concentration of 33%, 50%, and 67%. Paired AEP index and OAA/S scores were obtained immediately before each change in N(2)O concentration. RESULTS: Sixteen patients were excluded from final analysis because of nausea, vomiting, or abnormal excitatory behaviors. The increases in N(2)O concentration induced significant decreases in OAA/S scores and no substantial AEP index changes. Although OAA/S scores of 1 and 2 were observed in only two and five patients, respectively, a reduction in the OAA/S score from 5 to 1 was associated with a significant decrease in AEP index to the level indicative of moderate sedation. CONCLUSION: The AEP index might not be a suitable indicator of light hypnosis as defined by an OAA/S score of ≥3 during sedation with N(2)O alone.

Neurophysiological assessment of the sedative and analgesic effects of a constant rate infusion of dexmedetomidine in the dog.

The sedative and analgesic effects of continuous rate infusion (CRI) of dexmedetomidine (DEX) were investigated in Beagle dogs (n=8) using auditory and somatosensory evoked potentials (AEPs and SEPs) recorded before, during and after a CRI of saline or DEX (1.0, 3.0, 5.0 µg/kg bolus, followed by 1.0, 3.0, 5.0 µg/kg/h CRI, respectively). The results showed a significant reduction in AEP at doses of 1.0 µg/kg/h and above and a significant reduction of the SEP at doses of 3.0 and 5.0 µg/kg/h. Neither the AEP nor the SEP was further reduced at 5.0 µg/kg/h when compared to 3.0 µg/kg/h, although a slower return towards baseline values was observed at 5.0 µg/kg/h. The mean plasma levels (±SEM) of DEX during infusion were 0.533±0.053 ng/mL for the 1.0 µg/kg/h dose, 1.869±0.063 ng/mL for the 3.0 µg/kg/h dose and 4.017±0.385 for the 5.0 µg/kg/dose. It was concluded that in adult dogs, a CRI of DEX had a sedative and analgesic effect that could be described quantitatively using neurophysiological parameters. Sedation was achieved at lower plasma levels than required for analgesia, and DEX had a longer (but not larger) effect with infusion rates above 3.0 µg/kg/h.

Comparison of A-line autoregressive index and observer assessment of alertness/sedation scale for monitored anesthesia care with target-controlled infusion of propofol in patients undergoing percutaneous vertebroplasty.

BACKGROUND: Percutaneous vertebroplasty (PV) with monitored anesthesia care (MAC) is a growing trend. Without adequate sedation, patient movement can affect and even interrupt the procedure during MAC. The aim of this study was to compare the performance of the auditory-evoked potential (AEP) index and the Observer Assessment of Alertness/Sedation (OAA/S) scale as indicators of depth of sedation in patients undergoing PV. METHODS: Two hundred and twenty patients in ASA II to III, aged 43 to 92 years, undergoing elective PV with MAC, were randomly allocated to the AEP or the OAA/S group (n = 110 each). Initially, all patients received 1 µg/kg of fentanyl and 0.02 mg/kg of midazolam intravenously and sedation with a target-controlled infusion (TCI) of propofol at a target concentration of 1.2 µg/mL. The concentration for the propofol TCI was adjusted in 0.2 µg/mL increments or decrements according to the A-Line autoregressive index (AAI) or the OAA/S scale. A blinded study nurse recorded the measured parameters. RESULTS: Some parameters were significantly different in the AEP group compared with the OAA/S group: lower AAI, lower OAA/S score, lower respiratory rates, and higher end-tidal carbon dioxide pressure were noted from local anesthetic infiltration to bone cement implantation, fewer patients whose movements affected the procedure (10 vs. 36, respectively, P < 0.001), and more adjustments of TCI (twice vs. once, respectively, P < 0.006). The surgeons' satisfaction was greater for the AEP group than for the OAA/S group. CONCLUSIONS: TCI propofol with AEP monitoring can provide less patient movement, better sedation, and higher surgeon satisfaction in patients during prone-position PV procedures than can TCI propofol with OAA/S monitoring.

[Neuromonitoring in anaesthesia]. / Narkosetiefenmessung in der Anästhesie - Neue Möglichkeiten und Ziele der Narkoseüberwachung.

Modern computer-based methods to monitor anesthesia are widespread. They are used in order to avoid awareness, to reduce consumption of anesthetics, to optimize recovery times and to detect prolonged times of deep anesthesia and associated immunsuppression, mortality and morbidity. This review illustrates the evidence with which these goals were achieved until now. Finally, a recommendation for each indication is given. The useage of EEG-monitoring may help to avoid awareness and allows a reduced of consumption of anesthetics. The question if a cumulated time of deep anesthesia is associated with elevated mortality might be of a certain importance in the future.

Assessment of gentamicin-induced vestibulotoxicity by click and galvanic vestibular-evoked myogenic potentials: a guinea pig investigation.

OBJECTIVE: The aim of this investigation carried out with guinea pigs was to study the possible effects of a gentamicin treatment on the saccular macula and on its afferent vestibular ganglion neurons. METHODS: The gentamicin-induced impairment was analyzed using vestibular-evoked myogenic potentials (VEMPs) elicited by both click and galvanic vestibular stimulations (GVS). Fifty microl of saline or gentamicin solution (40 mg/ml) was dropped over the round window membrane of the right (control) and left (lesion) cochleae, respectively. Four weeks after surgery, the VEMPs elicited with clicks and GVS were evaluated for each animal. Then, the animals were sacrificed in order to perform morphological and anti-Nav1.8 immunocytochemical analyses. RESULTS: Click- and GVS-VEMPs were obtained in all of the controls, whereas no potentials were obtained from gentamicin-treated animals. Lesions of sensory cells were observed in the saccular macula. In the injured vestibular ganglion, the percentage of voltage-gated sodium channel Nav1.8-like immunoreactive (Nav1.8-LI) neurons was significantly lower (38.9+/-0.7) than that (53.6+/-3.2) calculated in controls. CONCLUSIONS: Gentamicin-induced impairments of the saccular macula and afferents of guinea pigs can be evaluated by recording both click- and GVS-VEMPs. Both tests provide information on the sacculo-collic reflex pathway and could help a clinical diagnosis of gentamicin intoxication by conventional eardrops in the patient with a perforated eardrum.

Preliminary assessment of the AAI Index during isoflurane anaesthesia in dogs undergoing clinical procedures.

The auditory evoked potential (AEP) is correlated to anaesthetic depth. The AEP has been used in rats, pigs, dogs and humans to assess anaesthetic depth. This study was undertaken to determine whether the AAI Index derived from the AEP correlated with changes in end tidal isoflurane concentration in dogs. The average AAI Index was 21.8 +/- 10.5 and isoflurane concentration was 1.7 +/- 0.4%. Data were divided into 0.5% intervals of end tidal anaesthetic agent concentration (ETAA). When ETAA values were higher than 2.5% the AAI values were 2.1-2.5%, 1.6-2.0% and 1.1-1.5% higher than AAI values although not statistically different. The 2.1-2.5 % interval was statistically different from the 1.1-1.5% and <1.1% interval. The 1.6-2.0% interval was statistically different from the 1.1-1.5% and the <1.1% intervals. The 1.1-1.5% interval was statistically different from the <1.1% interval. The correlation between the AAI Index and isoflurane was -0.176 and was statistically significant (P = 0.0009). A linear regression between the AAI Index and isoflurane revealed the following relationship: AAI = 29.074 - (4.2755 x isoflurane) with a power of 0.913. The polynomial regression relationship was AAI = 53.334 - (35.715 x isoflurane) + (10.322 x isoflurane2) - (0.43646 x isoflurane3) with a power of 0.999. The AAI Index was found to correlate with changes in isoflurane concentration.

[Sedation and analgesia assessment tools in ICU patients]. / Quels sont les outils d'évaluation de la sédation et de l'analgésie?

Sedative and analgesic treatment administered to critically ill patients need to be regularly assessed to ensure that predefinite goals are well achieved as the risk of complications of oversedation is minimized. In most of the cases, which are lightly sedation patients, the goal to reach is a calm, cooperative and painless patient, adapted to the ventilator. Recently, eight new bedside scoring systems to monitor sedation have been developed and mainly tested for reliability and validity. The choice of a sedation scale measuring level of consciousness, could be made between the Ramsay sedation scale, the Richmond Agitation Sedation scale (RASS) and the Adaptation to The Intensive Care Environment scale-ATICE. The Behavioral Pain Scale (BPS) is a behavioral pain scale. Two of them have been tested with strong evidence of their clinimetric properties: ATICE, RASS. The nurses'preference for a convenient tool could be defined by the level of reliability, the level of clarity, the variety of sedation and agitation states represented user friendliness and speed. In fine, the choice between a simple scale easy to use and a well-defined and complex scale has to be discussed and determined in each unit. Actually, randomized controlled studies are needed to assess the potential superiority of one scale compared with others scales, including evaluation of the reliability and the compliance to the scale. The usefulness of the BIS in ICU for patients lightly sedated is limited, mainly because of EMG artefact, when subjective scales are more appropriated in this situation. On the other hand, subjective scales are insensitive to detect oversedation in patients requiring deep sedation. The contribution of the BIS in deeply sedation patients, patients under neuromuscular blockade or barbiturates has to be proved. Pharmacoeconomics studies are lacking.

Perspectives on sedation assessment in critical care.

Multiple studies have been undertaken to show that neurofunction monitors can correlate to objective sedation assessments. Showing a correlation between these 2 patient assessments tools may not be the correct approach for validation of neurofunction monitors. Two different methods of assessing 2 different modes of the patient's response to sedation should not be expected to precisely correlate unless the desire is to replace one method with the other. We provide a brief summary of several sedation scales, physiologic measures and neurofunction monitoring tools, and correlations literature for bispectral index monitoring, and the Ramsay Scale and the Sedation Agitation Scale. Neurofunction monitors provide near continuous information about a different domain of the sedation response than intermittent observational assessments. Further research should focus on contributions from this technology to the improvement of patient outcomes when neurofunction monitoring is used as a complement, not a replacement, for observational methods of sedation assessment.

Cost analysis of three anesthetic regimens under auditory evoked potentials monitoring in gynecologic laparoscopic surgery.

BACKGROUND: Cost analyses of different anesthetic techniques have not been investigated in Taiwan. We compared propofol-based total intravenous anesthesia (TIVA), sevoflurane (SEVO) and desflurane (DES) anesthesias for cost and outcome under A-line auditory evoked potentials (AEP) monitoring. METHODS: We studied 90 consecutive female patients (ASAI-II) scheduled to undergo elective gynecologic laparoscopic surgery. The study was prospective, randomized, and single-blind in design. All patients were randomly divided into 3 groups: i.e. groups TIVA, SEVO and DES. The A-line auditory evoked potential index (AAI) was maintained between 15-25. At the start of skin closure, the applied anesthetic was discontinued, and time of recovery from anesthesia was thenceforth reckoned until spontaneous opening of eyes and extubation. The costs of drugs were counted in New Taiwan (NT) dollars. RESULTS: The total cost was significantly higher in the SEVO and DES groups than in the TIVA group (NT 1,243, 1028, and 889, respectively) (P < 0.001). In addition, the cost of the principal anesthetic drug was significantly higher in the SEVO than in the DES and TIVA groups (NT 756, 530, and 468, respectively) (P < 0.01). Faster recovery was seen in the TIVA group than in the DES group and SEVO group (8.2, 13.7, 16.2 min, respectively) (P < 0.001). Incidences of postoperative nausea, vomiting, and pain were not significantly different among 3 groups. CONCLUSIONS: The cost of TIVA with propofol was less than SEVO or DES anesthesia and moreover, propofol TIVA offered benefit of faster recovery in our study.

Use of cerebral monitoring during anaesthesia: effect on recovery profile.

This review article examines the effect of cerebral monitoring using an EEG-based device [i.e. bispectral index (BIS), patient state analyzer (PSA), auditory evoked potential (AEP), cerebral state index (CSI), or entropy] on titration of anaesthetic, analgesic and cardiovascular drugs during surgery. In addition, articles discussing the effects of these cerebral monitoring devices on recovery profiles following general anaesthesia, postoperative side effects, and anaesthetic costs are reviewed.

Midlatency auditory-evoked potentials in the assessment of sedation in cardiac surgery patients.

OBJECTIVES: Midlatency auditory-evoked potentials (MLAEPs) may provide an objective measure of depth of sedation. The aim of this study was to evaluate MLAEPs for measuring sedation in cardiac surgery patients. DESIGN: Prospective study. SETTING: Intensive care unit of a university hospital. PARTICIPANTS: Twenty-two patients scheduled for elective coronary artery bypass grafting. INTERVENTIONS: MLAEPs were obtained at 5 time points: the day before surgery (baseline), 1 hour before surgery, after premedication, postoperatively during deep (Ramsay 6) and moderate (Ramsay 4) sedation, and the day after surgery. MEASUREMENTS AND MAIN RESULTS: The latency of the Nb MLAEP component increased from 44 ms (38-60 ms; median, range) at baseline to 49 ms (41-64 ms) after premedication (p = 0.03) and further to 63 ms (48-80 ms) during deep sedation after surgery (P < 0.01). Although a decreasing clinical level of sedation after rewarming was not associated with a significant change in Nb latency (61 ms [42-78 ms]), the MLAEP NaPa amplitude increased from 0.9 muV (0.4-1.6 microV) to 1.3 muV (0.8-3.9 microV; p = 0.01). Nb latency remained increased the day after surgery (49 ms [37-71 ms]) as compared with baseline (p < 0.01). CONCLUSIONS: MLAEP latencies can reflect subtle changes in auditory perception, while amplitudes seem to change with transition between deep levels of sedation.

Does the A-line ARX-lndex provide a reasonable assessment of anaesthetic depth in dogs undergoing routine surgery?

The monitoring of anaesthetic depth is usually based on the subjective assessment of the patient. An objective assessment of anaesthesia has only recently become possible. The auditory-evoked response has predictable changes in response to increasing doses of anaesthetic agents. Recent advances have brought about a regression model with exogenous input of the auditory-evoked response, the A-line ARX-Index (AAI Index). The AAI Index is a dimensionless number between 0 and 100. This technology has been incorporated into the AEP (auditory-evoked potential) monitor that is utilised to assess anaesthetic depth in humans. This study was undertaken to determine if the AEP monitor was useful in dogs. Ten dogs were enrolled in the study. After a full clinical and otoscopic examination, dogs were premedicated with acetylpromazine and morphine. Anaesthesia was induced with thiopentone and maintained with halothane. End-tidal carbon dioxide, temperature, pulse oximetry, blood pressure and the electrocardiogram were monitored and recorded every 5 minutes. Anaesthetic depth was assessed as either being adequate or inadequate by the anaesthetist during surgery. An AEP monitor was attached to the patient and automatically collected AAI Index data. The anaesthetist was blinded to the AEP monitor. Following the completion of the surgical procedure, the patient was allowed to wake up with the AEP monitor attached. The AAI Index was analysed to compare adequate with inadequate anaesthesia during the period of surgery and awake with sleep data during recovery. All AAI Index values associated with inadequate anaesthesia were greater than 31 while adequate values were less than 35. The difference between the groups was statistically significant and the power was 0.97. Statistically, the awake and sleep values were significantly different with a power of 0.99. From this study it can be concluded that the AAI Index shows good prospect for the evaluation of anaesthetic depth in dogs undergoing surgery. A larger study is needed to confirm these results.

Propofol and sevoflurane in subanesthetic concentrations act preferentially on the spinal cord: evidence from multimodal electrophysiological assessment.

BACKGROUND: Animal experiments in recent years have shown that attenuation of motor responses by general anesthetics is mediated at least partly by spinal mechanisms. Less is known about the relative potency of anesthetic drugs in suppressing cortical and spinal electrophysiological responses in vivo in humans, particularly those, but not only those, connected with motor responses. Therefore, we studied the effects of sevoflurane and propofol in humans using multimodal electrophysiological assessment. METHODS: We studied nine healthy volunteers in two sessions during steady state sedation with 0.5, 1.0, and 1.5 microg/l (targeted plasma concentration) propofol or 0.2 and 0.4 vol% (end-tidal) sevoflurane. Following a 15-min equilibration period, motor responses to transcranial magnetic stimulation and peripheral (H-reflex, F-wave) stimulation were recorded, while electroencephalography and auditory evoked responses were recorded in parallel. RESULTS: At concentrations corresponding to two thirds of C(50 awake), motor responses to transcranial magnetic stimulation were reduced by approximately 50%, H-reflex amplitude was reduced by 22%, F-wave amplitude was reduced by 40%, and F-wave persistence was reduced by 25%. No significant differences between sevoflurane and propofol were found. At this concentration, the Bispectral Index was reduced by 7%, and the middle-latency auditory evoked responses were attenuated only mildly (N(b) latency increased by 11%, amplitude P(a)N(b) did not change). In contrast, the postauricular reflex was suppressed by 77%. CONCLUSIONS: The large effect of both anesthetics on all spinal motor responses, compared with the small effect on electroencephalography and middle-latency auditory evoked responses, assuming that they represent cortical modulation, may suggest that the suppression of motor responses to transcranial magnetic stimulation is largely due to submesencephalic effects.

Assessment of vestibular ototoxicity of ear drops by recording of vestibular evoked potentials to acceleration impulses.

INTRODUCTION: The cochlear ototoxicity of several ear drops is well documented in the literature, but very few studies exist on the vestibular ototoxicity of these topical drugs. GOAL OF STUDY: To develop an animal model for the assessment of the vestibular ototoxicity of ear drops. MATERIALS AND METHODS: Two animal groups, consisting of five fat sand rats (FSRs) each, underwent unilateral labyrinthectomy. Normal saline was topically applied into the middle ear cavity of rats in the first group for 7 days (control group). Rats in the second group were treated in the same way by topical gentamicin solution. Cochlear function was assessed by the recording of auditory evoked potential (ABPs) thresholds, and vestibular function was assessed by the recording of vestibular evoked potentials (VsEPs) to angular accelerations. RESULTS: In the control group, except for the amplitude of the first wave, there was no significant difference in the VsEPs recorded before and after topical application. In the gentamicin group, VsEPs could not be recorded after 7 days, and ABPs were recorded in one case only, with a threshold of 100 dB sound pressure level (SPL). CONCLUSION: VsEPs seem to be a reliable measure for evaluating the vestibular ototoxicity of topical ear drops.

Toluene ototoxicity in rats: assessment of the frequency of hearing deficit by electrocochleography.

To identify the frequency range most sensitive to toluene-induced auditory damage, the auditory function of adult Long-Evans rats exposed to 1750 ppm of toluene (6 h/day, 5 days/week, 4 weeks), was tested by recording auditory-evoked potentials directly from the round window of the cochlea. The present electrocochleographic findings do not support a specific mid- to high-frequency loss of auditory sensitivity. On the contrary, the electrophysiologic data, obtained for audiometric frequencies ranging from 2 to 32 kHz, showed a hearing deficit not only in the mid-frequency region (12-16 kHz), but also in the mid-low-frequency region (3-4 kHz). Actually, the effect of toluene was independent of the frequency in our experimental conditions. Histological analysis was consistent with electrophysiologic data because a broad loss of outer hair cells occurred in both mid- and mid-apical coil of the organ of Corti.

Auditory evoked potentials in the assessment of central nervous system effects of antimigraine drugs.

Because the "intensity dependence" of cortical auditory evoked potentials (IDAP) is under serotonergic control, it can be used to assess central antimigraine effects of 5HT1B/1D agonists. We measured IDAP before and 2 h after naratriptan (5 mg, n = 19) and zolmitriptan (5 mg, n = 19) in healthy volunteers. IDAP was expressed as the amplitude-stimulus intensity function ("ASF slope"). Naratriptan tended to increase ASF slope (mean difference 0.23 +/- 0.62 microV/10 dB, p = 0.06) while zolmitriptan (0.08 +/- 0.95 microV/10 dB, p = 0.35) did not. We assessed the suitability of IDAP for measuring central antimigraine drug effects using repeatability data (see companion paper). We calculated the trade-off between the size of the expected drug effects (ASF slope difference) and the necessary sample size. Because of poor repeatability 36 to 80 subjects are required to detect ASF slope changes in the 0.25-0.5 microV/10 dB range. These data can be used to design trials using IDAP.

Ototoxicity assessment of a gentamicin sulfate otic preparation in dogs.

Vestibulotoxic and ototoxic effects often are seen after long-term, high-dose systemic treatment with gentamicin, but toxic effects after topical use have not been reported in animals, to the authors' knowledge. Vestibular and auditory effects of twice daily otic gentamicin treatment for 21 days were evaluated in 10 dogs with intact tympanic membranes and in the same 10 dogs after experimental bilateral myringotomy. Each dog served as its own control; 7 drops of gentamicin sulfate (3 mg/ml in a buffered aqueous vehicle) were placed in 1 ear, and 7 drops of vehicle were placed in the opposite ear. Treatment and control ears were reversed after myringotomy. Vestibular function was evaluated daily by neurologic examination and behavioral assessment. Auditory function was evaluated twice weekly by determination of brain stem auditory evoked potentials. Gentamicin sulfate placed in the ear of clinically normal dogs with intact or ruptured tympanic membranes, in the quantities used in this study, did not induce detectable alteration of cochlear or vestibular function. Serum gentamicin concentration after 21 days of treatment was detectable in only 2 dogs and was an order of magnitude below documented toxic concentrations.

Neuropsychological and neurophysiological assessment of the central effects of interleukin-2 administration.

Neuropsychiatric disturbances may occur following interleukin-2 (IL2) administration. We studied the effects of IL2 infusion on cerebral functions in 7 patients with neuropsychological tests and event-related evoked potentials (P300). We observed a failure in the cognitive performances, an increase in latency, and a decrease in amplitude of P300. These effects followed IL2 administration and were reversible.