Monitoring depth of anaesthesia

Comparison of cerebral metabolic rate of oxygen, blood flow, and bispectral index under general anesthesia

SIGNIFICANCE

The optical measurement of cerebral oxygen metabolism was evaluated.

AIM

Compare optically derived cerebral signals to the electroencephalographic bispectral index (BIS) sensors to monitor propofol-induced anesthesia during surgery.

APPROACH

Relative cerebral metabolic rate of oxygen ( rCMRO 2 ) and blood flow (rCBF) were measured by time-resolved and diffuse correlation spectroscopies. Changes were tested against the relative BIS (rBIS) ones. The synchronism in the changes was also assessed by the R-Pearson correlation.

RESULTS

In 23 measurements, optically derived signals showed significant changes in agreement with rBIS: during propofol induction, rBIS decreased by 67% [interquartile ranges (IQR) 62% to 71%], rCMRO 2 by 33% (IQR 18% to 46%), and rCBF by 28% (IQR 10% to 37%). During recovery, a significant increase was observed for rBIS (48%, IQR 38% to 55%), rCMRO 2 (29%, IQR 17% to 39%), and rCBF (30%, IQR 10% to 44%). The significance and direction of the changes subject-by-subject were tested: the coupling between the rBIS, rCMRO 2 , and rCBF was witnessed in the majority of the cases (14/18 and 12/18 for rCBF and 19/21 and 13/18 for rCMRO 2 in the initial and final part, respectively). These changes were also correlated in time ( R > 0.69 to R = 1 , p - values < 0.05 ).

CONCLUSIONS

Optics can reliably monitor rCMRO 2 in such conditions.

Verification of the performance of the Bispectral Index as a hypnotic depth indicator during dexmedetomidine sedation

Background

Differences in the effects of propofol and dexmedetomidine sedation on electroencephalogram patterns have been reported previously. However, the reliability of the Bispectral Index (BIS) value for assessing the sedation caused by dexmedetomidine remains debatable. The purpose of this study is to evaluate the correlation between the BIS value and the Modified Observer’s Assessment of Alertness/Sedation (MOAA/S) scale in patients sedated with dexmedetomidine.

Methods

Forty-two patients aged 20–80 years, who were scheduled for surgery under spinal anesthesia were enrolled. Spinal anesthesia was performed using 0.5% bupivacaine, which was followed by dexmedetomidine infusion (loading dose, 0.5–1 μg/kg for 10 min; maintenance dose, 0.3–0.6 μg/kg/h). The MOAA/S score was used to evaluate the level of sedation.

Results

A total of 215082 MOAA/S scores and BIS data pairs were analyzed. The baseline variability of the BIS value was 7.024%, and BIS value decreased, as the MOAA/S scored decreased. The correlation coefficient and prediction probability between the two measurements were 0.566 (P < 0.0001) and 0.636, respectively. The mean ± standard deviation values of the BIS were 87.22 ± 7.06, 75.85 ± 9.81, and 68.29 ± 12.65 when the MOAA/S scores were 5, 3, and 1, respectively. Furthermore, the cut-off BIS values in the receiver operating characteristic analysis at MOAA/S scores of 5, 3, and 1 were 82, 79, and 73, respectively.

Conclusions

The BIS values were significantly correlated with the MOAA/S scores. Thus, the BIS along with the clinical sedation scale might prove useful in assessing the hypnotic depth of a patient during sedation with dexmedetomidine.

Perioperative Management of Elderly patients (PriME): recommendations from an Italian intersociety consensus

BACKGROUND

Surgical outcomes in geriatric patients may be complicated by factors such as multiple comorbidities, low functional performance, frailty, reduced homeostatic capacity, and cognitive impairment. An integrated multidisciplinary approach to management is, therefore, essential in this population, but at present, the use of such an approach is uncommon. The Perioperative Management of Elderly patients (PriME) project has been established to address this issue.

AIMS

To develop evidence-based recommendations for the integrated care of geriatric surgical patients.

METHODS

A 14-member Expert Task Force of surgeons, anesthetists, and geriatricians was established to develop evidence-based recommendations for the pre-, intra-, and postoperative care of hospitalized older patients (≥ 65 years) undergoing elective surgery. A modified Delphi approach was used to achieve consensus, and the strength of recommendations and quality of evidence was rated using the U.S. Preventative Services Task Force criteria.

RESULTS

A total of 81 recommendations were proposed, covering preoperative evaluation and care (30 items), intraoperative management (19 items), and postoperative care and discharge (32 items).

CONCLUSIONS

These recommendations should facilitate the multidisciplinary management of older surgical patients, integrating the expertise of the surgeon, the anesthetist, the geriatrician, and other specialists and health care professionals (where available) as needed. These roles may vary according to the phase and setting of care and the patient's conditions.

Non-instrumental clinical monitoring does not guarantee an adequate course of general anesthesia. A prospective clinical study

BACKGROUND

Clinical monitoring is the most common method of adjusting the appropriate level of general anesthesia. However, episodes of intraoperative awareness (AWR) are still reported, suggesting that clinical observations may not be sufficient in some cases. The objective of this study was to compare the efficacy of clinical and instrumental neuromonitoring with auditory evoked potentials (AEP) in an intraoperative analysis of the proper level of general anesthesia.

METHODS

Patients scheduled for elective surgery were randomly divided into two groups. Subjects in the first group underwent intravenous, in the second group volatile anesthesia. The adequacy of anesthesia was analyzed using clinical parameters. All the participants were instrumentally monitored with the autoregressive AEP index (AAI). After the anesthesia, patients filled out a questionnaire on possible AWR.

RESULTS

Data of 208 patients (87 in the first, and 121 in the second group) were analyzed. Before surgery there were no changes in AAI values between groups (80 vs. 78, P=0.5192). The mean values of clinical parameters changed, but five minutes after the nociceptive stimuli. The mean values of AAI at analyzed time points were specific for general anesthesia. In patients under intravenous anesthesia, we found more episodes of too low (46/608 vs.15/847, P<0.000) anesthesia. One case of AWR was found in the TIVA group.

CONCLUSIONS

AAI index is good indicator of patients' level of consciousness during general anesthesia. Standard clinical monitoring provides appropriate level of the procedure. However, it is insufficient during TIVA and does not prevent episodes of AWR.

Cortical functional activity in patients with generalized anxiety disorder

BACKGROUND

The neurological correlates of Generalised Anxiety Disorder (GAD) are not well known, however there is evidence of cortical dysregulation in patients with GAD. The aim of the study was to examine cortical functional activity in different cerebral regions in patients with GAD using electroencephalogram (EEG) nonlinear analysis to evaluate its contribution of anxiety severity.

METHODS

The cohorts consisted of 64 patients diagnosed with GAD as classified by the Structured Clinical Interview for the Diagnostic and Statistical Manual of the American Psychiatric Association-IV-TR. Anxiety severity was assessed using the Hamilton Rating Scale for Anxiety (HAMA) severity score, with 7 ≤ scores ≤ 17 indicating mild anxiety as A group (n = 31) and 18 and above indicating moderate-severe anxiety as B group (n = 33). Participants with clinical levels of depression symptoms were excluded. A healthy control group comprising 30 participants was matched for age and gender. Closed eyes EEGs were conducted, and between-group differences on non-linear parameter Correlation Dimension (D2) were analyzed. The association of D2 value with HAMA scores was analyzed using multiple linear stepwise regression.

RESULTS

Compared with the control group, D2 values were increased in anxiety groups (P < .05). For those with mild anxiety, this difference occurred in the left prefrontal regions (P < .05). For those with moderate-severe anxiety, significantly greater D2 values were observed in all of the cerebral regions, especially in the left cerebral regions and right temporal lobe (P < .01). When compared with those with mild anxiety, D2 values were significantly greater for those with moderate-severe anxiety in the right temporal lobe and all left cerebral regions except for left occipital lobe (P < .05). A positive correlation was observed between D2 values and moderate-severe anxiety HAMA scores.

CONCLUSIONS

The increased D2 values were found in the majority of cerebral regions in GAD patients, especially in the left cerebral regions and the right temporal lobe. The increased GAD severity positively correlates to the D2 values in a larger number of cerebral regions. This analysis method can potentially be used as a complementary tool to examine dysfunctional cortical activity in GAD.

Indicators used in livestock to assess unconsciousness after stunning: a review

Assessing unconsciousness is important to safeguard animal welfare shortly after stunning at the slaughter plant. Indicators that can be visually evaluated are most often used when assessing unconsciousness, as they can be easily applied in slaughter plants. These indicators include reflexes originating from the brain stem (e.g. eye reflexes) or from the spinal cord (e.g. pedal reflex) and behavioural indicators such as loss of posture, vocalisations and rhythmic breathing. When physically stunning an animal, for example, captive bolt, most important indicators looked at are posture, righting reflex, rhythmic breathing and the corneal or palpebral reflex that should all be absent if the animal is unconscious. Spinal reflexes are difficult as a measure of unconsciousness with this type of stunning, as they may occur more vigorous. For stunning methods that do not physically destroy the brain, for example, electrical and gas stunning, most important indicators looked at are posture, righting reflex, natural blinking response, rhythmic breathing, vocalisations and focused eye movement that should all be absent if the animal is unconscious. Brain stem reflexes such as the cornea reflex are difficult as measures of unconsciousness in electrically stunned animals, as they may reflect residual brain stem activity and not necessarily consciousness. Under commercial conditions, none of the indicators mentioned above should be used as a single indicator to determine unconsciousness after stunning. Multiple indicators should be used to determine unconsciousness and sufficient time should be left for the animal to die following exsanguination before starting invasive dressing procedures such as scalding or skinning. The recording and subsequent assessment of brain activity, as presented in an electroencephalogram (EEG), is considered the most objective way to assess unconsciousness compared with reflexes and behavioural indicators, but is only applied in experimental set-ups. Studies performed in an experimental set-up have often looked at either the EEG or reflexes and behavioural indicators and there is a scarcity of studies that correlate these different readout parameters. It is recommended to study these correlations in more detail to investigate the validity of reflexes and behavioural indicators and to accurately determine the point in time at which the animal loses consciousness.

[Evaluation of heart rate variability for monitoring the depth of anaesthesia in dogs. Investigations based on total intravenous anaesthesia using propofol alone or in combination with dexmedetomidine or remifentanil]

OBJECTIVE

Evaluation of heart-rate variability (HRV) as an indicator for autonomous activity to monitor anaesthesia in dogs during three different total intravenous anaesthetic protocols and three anaesthetic depth levels as well as before and after electrical nociceptive stimulation.

MATERIAL AND METHODS

Seven beagle dogs (14.3±1.7 kg) were used in a randomised experimental trial with a complete cross-over design. Each dog went through all three anaesthetic protocols, which were propofol alone (group P) and propofol combined with dexmedetomidine (3 µg/kg/h, group PD) or remifentanil (18 µg/kg/h, group PR). Propofol was given using target-controlled infusion. Three anaesthetic depth levels (light, medium, deep) were defined by target concentrations for propofol in the blood and were adapted to the individual animal and treatment (mean of 7, 9 and 11 µg/ml, and in combination with dexmedetomidine or remifentanil, a mean of 3, 5 and 7 µg/ml). During each anaesthetic level, a standardised supramaximal nociceptive electric stimulus (50 Hz, 50 V, 10 ms) was applied medially to the right forearm. The bipolar-derived electrocardiogram (ECG) was recorded continuously. For each anaesthetic depth, the RR-intervals recorded 2 minutes before and after each stimulation were included in the statistical analysis. Using an HRV analytical program (Kubios HRV), the frequency domain HRV-parameters low (LF) and high (HF) frequency and the time-domain HRV-parameters RR-intervals, standard deviation of all RR-intervals (SDNN) and the square root of the mean of the sum of the squares of the differences between consecutive RR-intervals (RMSSD) were determined.

RESULTS

Neither the RR-intervals nor the currently available HRV-parameters which were derived from the RR-intervals were able to discriminate between the different anaesthetic depths levels. Nociception could only be represented by the RR-intervals.

CONCLUSION

Overall, the investigated standard HRV parameters offered no additional information for the monitoring of anaesthetic depths at the investigated, clinically used dose rates.

A wavelet transform based method to determine depth of anesthesia to prevent awareness during general anesthesia

Awareness during general anesthesia for its serious psychological effects on patients and some juristically problems for anesthetists has been an important challenge during past decades. Monitoring depth of anesthesia is a fundamental solution to this problem. The induction of anesthesia alters frequency and mean of amplitudes of the electroencephalogram (EEG), and its phase couplings. We analyzed EEG changes for phase coupling between delta and alpha subbands using a new algorithm for depth of general anesthesia measurement based on complex wavelet transform (CWT) in patients anesthetized by Propofol. Entropy and histogram of modulated signals were calculated by taking bispectral index (BIS) values as reference. Entropies corresponding to different BIS intervals using Mann-Whitney U test showed that they had different continuous distributions. The results demonstrated that there is a phase coupling between 3 and 4 Hz in delta and 8-9 Hz in alpha subbands and these changes are shown better at the channel T₇ of EEG. Moreover, when BIS values increase, the entropy value of modulated signal also increases and vice versa. In addition, measuring phase coupling between delta and alpha subbands of EEG signals through continuous CWT analysis reveals the depth of anesthesia level. As a result, awareness during anesthesia can be prevented.

Acceptably aware during general anaesthesia: 'dysanaesthesia'--the uncoupling of perception from sensory inputs

This review makes the case for 'dysanaesthesia', a term encompassing states of mind that can arise in the course of anaesthesia during surgery, characterised by an uncoupling of sensation and perceptual experience. This is reflected in a macroscopic, functional model of anaesthetically-relevant consciousness. Patients in this state can be aware of events but in a neutral way, not in pain, sometimes personally dissociated from the experiences. This makes events associated with surgery peripheral to their whole experience, such that recall is less likely and if it exists, makes any spontaneous report of awareness unlikely. This state of perception-sensation uncoupling is therefore broadly acceptable (a minimum requirement for acceptable anaesthesia) but since it is likely a dose-related phenomenon, may also represent a precursor for awareness with adverse recall. This hypothesis uniquely explains the often inconsistent responses seen during the experimental paradigm of the 'isolated forearm technique', wherein apparently anaesthetised patients exhibit a positive motor response to verbal command, but no spontaneous movement to surgery. The hypothesis can also explain the relatively high incidence of positive response to relatively direct questions for recall (e.g., using the Brice questionnaire; ∼1:500; the vast majority of these being neutral reports) versus the very low incidence of spontaneous reports of awareness (∼1:15,000; a higher proportion of these being adverse recollections). The hypothesis is consistent with relevant notions from philosophical discussions of consciousness, and neuroscientific evidence. Dysanaesthesia has important implications for research and also for the development of appropriate monitoring.

Analysis of neuron-specific enolase and S100B as biomarkers of cognitive decline following surgery in older people

BACKGROUND/AIMS

Post-operative cognitive decline is frequent in older individuals following major surgery; however, biomarkers of this decline are less clearly defined.

METHODS

Sixty-eight participants over the age of 60 provided blood samples at baseline and 24 h post-surgery. Cognitive decline was measured at baseline and 52 weeks post-surgery using the Cambridge Assessment for Mental Disorder in the Elderly, section B (CAMCOG) score. Plasma levels of neuron-specific enolase (NSE) and S100B were measured by ELISA.

RESULTS

Baseline NSE and the change in NSE levels between baseline and 24 h were correlated with the change in CAMCOG score between baseline and 52 weeks.

CONCLUSION

NSE concentrations may be a useful predictor of individuals at risk of more severe long-term cognitive decline.

Optimised anaesthesia to reduce post operative cognitive decline (POCD) in older patients undergoing elective surgery, a randomised controlled trial

Background

The study determined the one year incidence of post operative cognitive decline (POCD) and evaluated the effectiveness of an intra-operative anaesthetic intervention in reducing post-operative cognitive impairment in older adults (over 60 years of age) undergoing elective orthopaedic or abdominal surgery.

Methods and Trial Design

The design was a prospective cohort study with a nested randomised, controlled intervention trial, using intra-operative BiSpectral index and cerebral oxygen saturation monitoring to enable optimisation of anaesthesia depth and cerebral oxygen saturation in older adults undergoing surgery.

Results

In the 52 week prospective cohort study (192 surgical patients and 138 controls), mild (χ² = 17.9 p<0.0001), moderate (χ² = 7.8 p = 0.005) and severe (χ² = 5.1 p = 0.02) POCD were all significantly higher after 52 weeks in the surgical patients than among the age matched controls. In the nested RCT, 81 patients were randomized, 73 contributing to the data analysis (34 intervention, 39 control). In the intervention group mild POCD was significantly reduced at 1, 12 and 52 weeks (Fisher’s Exact Test p = 0.018, χ² = 5.1 p = 0.02 and χ² = 5.9 p = 0.015), and moderate POCD was reduced at 1 and 52 weeks (χ² = 4.4 p = 0·037 and χ² = 5.4 p = 0.02). In addition there was significant improvement in reaction time at all time-points (Vigilance Reaction Time MWU Z =  −2.1 p = 0.03, MWU Z = −2.7 p = 0.004, MWU Z = −3.0 p = 0.005), in MMSE at one and 52 weeks (MWU Z = −2.9 p = 0.003, MWU Z = −3.3 p = 0.001), and in executive function at 12 and 52 weeks (Trail Making MWU Z = −2.4 p = .0.018, MWU Z = −2.4 p = 0.019).

Conclusion

POCD is common and persistent in older adults following surgery. The results of the nested RCT indicate the potential benefits of intra-operative monitoring of anaesthetic depth and cerebral oxygenation as a pragmatic intervention to reduce post-operative cognitive impairment.

Trial Registration

Controlled-Trials.com ISRCTN39503939

Accidental subcutaneous remifentanil infusion as a cause of delayed awakening after craniotomy

We report a case of accidental subcutaneous infusion of remifentanil as a cause of delayed awakening after a craniotomy.

Monitoring the depth of anaesthesia

One of the current challenges in medicine is monitoring the patients’ depth of general anaesthesia (DGA). Accurate assessment of the depth of anaesthesia contributes to tailoring drug administration to the individual patient, thus preventing awareness or excessive anaesthetic depth and improving patients’ outcomes. In the past decade, there has been a significant increase in the number of studies on the development, comparison and validation of commercial devices that estimate the DGA by analyzing electrical activity of the brain (i.e., evoked potentials or brain waves). In this paper we review the most frequently used sensors and mathematical methods for monitoring the DGA, their validation in clinical practice and discuss the central question of whether these approaches can, compared to other conventional methods, reduce the risk of patient awareness during surgical procedures.

Effective electroconvulsive therapy in a 92-year-old dementia patient with psychotic feature

A 92-year-old woman who suffered from dementia with psychotic feature was admitted to a psychiatric ward. She refused to eat or take any medications. After 0.5 mg i.v. injection haloperidol, prolongation of QTc interval occurred in the electrocardiogram. Therefore two sessions of electroconvulsive therapy (ECT) were performed carefully after informed consent was obtained by her family. Almost no psychotic symptoms were observed after the first ECT. No cognitive side-effects were observed during and after the two ECT sessions. This demonstrates that ECT can be used as an alternative treatment when elderly dementia patients with psychotic feature cannot tolerate medication.

Awareness in retrieval medicine

Awareness is the spontaneous recall of an event(s) that occurred during general anaesthesia and surgery. The incidence of awareness is approximately 0.2% of cases where neuromuscular blockers are used and half that where they are omitted. The majority of data relating to awareness is from anaesthetic practice. We report a case of awareness associated with an out-of-hospital transportation of a critically ill patient requiring a medical escort (retrieval). We discuss the risk factors associated with awareness during retrieval, in particular the trend toward excessive administration of neuromuscular blockers, and the unique challenges for the prevention of awareness within the retrieval environment.

Using EEG to monitor anesthesia drug effects during surgery

The use of processed electroencephalography (EEG) using a simple frontal lead system has been made available for assessing the impact of anesthetic medications during surgery. This review discusses the basic principles behind these devices. The foundations of anesthesia monitoring rest on the observations of Guedel with ether that the depth of anesthesia relates to the cortical, brainstem and spinal effects of the anesthetic agents. Anesthesiologists strive to have a patient who is immobile, is unconscious, is hemodynamically stable and who has no intraoperative awareness or recall. These anesthetic management principles apply today, despite the absence of ether from the available anesthetic medications. The use of the EEG as a supplement to the usual monitoring techniques rests on the observation that anesthetic medications all alter the synaptic function which produces the EEG. Frontal EEG can be viewed as a surrogate for the drug effects on the entire central nervous system (CNS). Using mathematical processing techniques, commercial EEG devices create an index usually between 0 and 100 to characterize this drug effect. Critical aspects of memory formation occur in the frontal lobes making EEG monitoring in this area a possible method to assess risk of recall. Integration of processed EEG monitoring into anesthetic management is evolving and its ability to characterize all of the anesthetic effects on the CNS (in particular awareness and recall) and improve decision making is under study.

Measuring anesthesia in children using the EEG

Advances in electroencephalogram (EEG) processing have produced new interest in measuring anesthesia using the EEG. There are a number of EEG-based anesthesia 'depth' monitors now available and their use in pediatric anesthesia is increasing. Although these monitors have been extensively studied in adults, there are relatively few studies examining their validity or use in children. To some extent we must rely on adult data. However, extrapolation of data from adults to children requires an in depth understanding of the physiology behind the data. The first question is what is being measured. What is anesthesia? A model of anesthesia has several components with arousal as a core component. Arousal can be linked to clinical observations, and correlates with anatomical and physiological studies. The EEG has characteristics that fairly consistently change with arousal during anesthesia, but the relationship between arousal and the EEG is imprecise and drug dependent. This relationship is the basis for using the EEG to measure anesthesia and provides only an indirect measure of consciousness and memory formation. A good understanding of how the EEG is related to anesthesia is essential when interpreting the EEG during anesthesia, and especially when extending the use of the EEG to measure anesthesia in children. Physiological studies in adults and children indicate that EEG-derived anesthesia depth monitors can provide an imprecise and drug-dependent measure of arousal. Although the outputs from these monitors do not closely represent any true physiological entity, they can be used as guides for anesthesia and in so doing have improved outcomes in adults. In older children the physiology, anatomy and clinical observations indicate the performance of the monitors may be similar to that in adults, although the clinical relevance of outcomes may be different. In infants their use cannot yet be supported in theory or in practice.

Bispectral index-controlled anaesthesia for electroconvulsive therapy*

BACKGROUND

The suggested induction dose of methohexital for electroconvulsive therapy (ECT) varies widely influencing efficacy of ECT and safety of anaesthesia. Bispectral index (BIS), a monitor of consciousness, may be useful to assure adequate hypnosis with optimized methohexital dose.

METHODS

Patients with medically resistant major depression (ICD10), scheduled for multiple ECT's, were studied. Depth of anaesthesia was BIS controlled. ECT was not performed until BIS dropped below 50. Initially anaesthesia was induced with methohexital 1.0 mg kg(-1), and stepwise reduced by 0.1 mg kg(-1) during consecutive treatments. If BIS did not drop below 50, the methohexital was supplemented by further boluses of 0.5 mg kg(-1), until the desired level of hypnosis was reached. The adequacy of the anaesthetic recommendation for methohexital (1.0-1.5 mg kg(-1)) as well as the psychiatric recommendation (0.75-1 mg kg(-1)) was investigated.

RESULTS

One-hundred and nine ECT's in 14 patients were studied. The recommended anaesthetic dose (1.0-1.5 mg kg(-1)) was inadequate in 40% of the treatments, with 12% exceeding 1.5 mg kg(-1), and 28% below 1.0 mg kg(-1). Psychiatric recommendation (0.75-1.0 mg kg(-1)) was inadequate in 49%, with 39% exceeding 1.0 mg kg(-1) and 10% undershooting at 0.75 mg kg(-1).

CONCLUSIONS

Methohexital for ECT showed a great variability, exceeding as well as undershooting the dosage recommendations widely. BIS monitoring may be useful to secure adequate hypnosis during muscle relaxation and treatment and may optimize ECT efficacy.

The effect of adding nitrous oxide on MAC of sevoflurane combined with two target-controlled concentrations of remifentanil in women

BACKGROUND AND OBJECTIVE

The aim of this prospective, randomized, double-blind study was to determine the effects of adding nitrous oxide on sevoflurane requirement for blunting sympathetic responses after surgical incision combined with two different target-controlled concentrations of remifentanil (1 and 3 ng mL(-1)) in female.

METHODS

102 female patients, aged 20-50 yr, ASA I, undergoing general anaesthesia for elective abdominal surgery were enrolled and randomly allocated to receive sevoflurane anaesthesia alone (Group A, n=53), or with the addition of 60% nitrous oxide (Group N, n=49). Patients of both groups were further assigned to receive a target-controlled remifentanil infusion with an effect-site concentration of either 1 ng mL(-1) (Group N1, n=27; Group A1, n=30), or 3 ng mL(-1) (Group N3, n=22; Group A3, n=23). Sympathetic responses to surgical incision were determined after a 20-min period of stable end-tidal sevoflurane and target-controlled remifentanil concentrations. Predetermined end-tidal sevoflurane concentrations and minimum alveolar concentration (MAC) for each group were determined using an up-and-down sequential allocation technique.

RESULTS

The MAC of sevoflurane was 3.96% (95% confidence interval, CI95: 3.69-4.23%) in Group A1 and 1.2% (CI95: 0.9-1.3%) in Group N1 (P < 0.01), while in Groups A3 and N3 the MAC of sevoflurane was 0.36% (CI95: 0.24-0.47%) and 0.18% (CI95: 0.1-0.3%), respectively (P < 0.05).

CONCLUSION

Adding 60% nitrous oxide reduces the MAC of sevoflurane by 70% when using a remifentanil concentration of 1 ng mL(-1) and 50% when using a remifentanil concentration of 3 ng mL(-1).

Desflurane accelerates patient response during the wake-up test for scoliosis surgery

PURPOSE

To evaluate if desflurane possesses a shorter wake-up onset time and less incidence of recall than fentanyl-based anesthesia.

METHODS

Forty ASA class I-II adolescents, were enrolled into either a desflurane (DES) group, or a fentanyl (FEN) group for scoliosis surgery. Bispectral index (BIS) was monitored continuously in all patients throughout the procedure; the relationship between the wake-up time and BIS value was evaluated.

RESULTS

Patients in the DES group had a significantly shorter wake-up onset than patients in the FEN group (4.1 +/- 0.6 vs 8.9 +/- 2.1 min, P < 0.01). No recall occurred during the wake-up test in the DES group, while five patients had recall in the FEN group, including two patients who recalled a given colour. Extubation time was significantly shorter in the DES group than in the FEN group (7.2 +/- 0.6 vs 16 +/- 11.9 min, P < 0.01). BIS values were significantly higher in the FEN group than in the DES group during anesthesia. (62 +/- 4.5 vs 42 +/- 5.3, P < 0.05) BIS after the wake-up test was similar in both groups (90 +/- 2.9 vs 93.8 +/- 2.5). There was a latency period (3.3 +/- 1.2 min) between the maximal BIS value and wake-up time in the FEN group but not in the DES group.

CONCLUSIONS

DES provides a significantly shorter onset time during the wake-up test and a rapid emergence after scoliosis surgery. BIS monitoring during the wake-up test was more informative when anesthesia was maintained with DES compared to FEN infusion.

Bispectral index monitoring quantifies depth of sedation during emergency department procedural sedation and analgesia in children

STUDY OBJECTIVE

The bispectral index monitor uses processed electroencephalogram signals to measure sedation depth on a unitless scale from 0 to 100 (0, coma; 40 to 60, general anesthesia; 60 to 90, sedated; 100, awake). It has been validated in the operating room as an objective measure of sedation depth with nondissociative general anesthesia; however, its usefulness in the pediatric emergency department (ED) for procedural sedation and analgesia has not been established. We determine the ability of the bispectral index to monitor depth of nondissociative procedural sedation and analgesia in children.

METHODS

This was an observational study conducted in a children's hospital ED. Procedural sedation and analgesia was performed in the standard manner, with the addition of bispectral index monitoring and simultaneous clinical sedation scoring (modified Ramsay Sedation Scale [range 1 to 8; 1=alert, 8=unresponsive]). Paired bispectral index and Ramsay Sedation Scale scores were assigned every 5 minutes during the sedation. Ramsay Sedation Scale scores were assigned by a single study investigator blinded to the bispectral index score. An emergency physician independently administered all medications for procedural sedation and analgesia. The correlation between the paired bispectral index/Ramsay Sedation Scale scores was determined by using a repeated-measures regression analysis. Receiver operator characteristic (ROC) curves were constructed to determine the ability of the bispectral index to discriminate various thresholds of sedation depth.

RESULTS

A convenience sample of 20 patients was enrolled, providing 217 paired bispectral index/Ramsay Sedation Scale measurements. Median age was 4.6 years (range 0.4 to 16.7 years). Fourteen patients received midazolam with fentanyl; the remainder received pentobarbital. Bispectral index scores ranged from 40 to 98 (mean 81.6+/-16.1). Ramsay Sedation Scale scores ranged from 1 to 8 (median 3; interquartile range 2 to 4). The simple Pearson correlation between paired bispectral index and Ramsay Sedation Scale scores was -0.78 (95% confidence interval [CI] -0.83 to -0.72; P<.001). After adjustment for the nonindependence of intrapatient data with bivariate repeated-measures analysis, the correlation was -0.67 (95% CI -0.90 to -0.43; P<.001). The linear regression coefficient between bispectral index and Ramsay Sedation Scale scores was estimated to be between -5.7 and -12.7. ROC curve analysis demonstrated moderate to high discriminatory power of bispectral index scores in predicting level of sedation throughout the sedation continuum, with areas under the curve at least 0.87 for all Ramsay Sedation Scale score thresholds. Bispectral index scores between 60 and 90 predicted with moderate accuracy traditional clinical levels of sedation typically encountered during procedural sedation and analgesia in the pediatric ED.

CONCLUSION

Bispectral index monitoring correlated with clinical sedation scores and may serve as a useful, objective adjunct in quantifying depth of nondissociative procedural sedation and analgesia in children.

Bispectral index-guided administration of anaesthesia: comparison between remifentanil/propofol and remifentanil/isoflurane

BACKGROUND AND OBJECTIVE

The bispectral index of the electroencephalogram is a measure of the hypnotic component of anaesthesia and can be used to guide the administration of anaesthesia. This study compares bispectral index-guided anaesthesia with remifentanil and either propofol or isoflurane.

METHODS

Eighty consenting patients were randomly assigned to two groups. Following induction with propofol and remifentanil, anaesthesia was maintained with remifentanil/propofol or remifentanil/isoflurane. Remifentanil infusion rates were guided by haemodynamic responses--maintaining mean arterial pressure and heart rate within 20% of baseline. Propofol and isoflurane administration was guided using the bispectral index (45-60). Thirty minutes before the end of surgery, morphine was administered (0.15 mg kg(-1) intravenously). Fifteen minutes before end of surgery, propofol and isoflurane were reduced (bispectral index 60-75). At the end of surgery, the anaesthetic agents were discontinued. Groups were compared for recovery, remifentanil doses and signs of inadequate anaesthesia using the chi2-test and ANOVA (P < 0.05).

RESULTS

The duration of surgery was longer in the propofol/remifentanil group (121 +/- 53 versus 94 +/- 40 min). Recovery data were not different between groups. The remifentanil infusion rate was significantly lower with additional isoflurane (0.18 +/- 0.06 microg kg(-1) min(-1)) than with additional propofol (0.31 +/- 0.20 microg kg(-1) min(-1)). The propofol infusion rate was 123 +/- 48 microg kg(-1) min(-1); isoflurane concentration was 0.66 +/- 0.13%.

CONCLUSIONS

Bispectral index-guided anaesthesia with remifentanil plus propofol or isoflurane results in the absence of postoperative recall and a fast recovery with both drug combinations. In our patients, at comparable bispectral index-levels, haemodynamic control requires higher doses of remifentanil with propofol than with isoflurane.

Continuous nervous system monitoring, EEG, the bispectral index, and neuromuscular transmission

In critically ill patients, the central nervous system remains vulnerable to multiple insults including ischemia, hemorrhagic events, and encephalopathy. The peripheral nervous system is vulnerable in the setting of neuro-muscular blockade (NMB), related drug-drug interactions, and drug-clinical state interactions. Optimal assessment of the nervous system is done by means of the clinical neurological examination. In this manner, orientation, arousal, and responsiveness to stimulation provide feedback on focal and global stability of the central nervous system. Where clinical evaluation is compromised, such as with deep sedation and NMB, risk of undetected seizure activity, and/or progression of neurological injury increases dramatically. A patient receiving NMB risks breakthrough awareness and pain. Long-term complications of NMB including prolonged weakness or paralysis as well as post-traumatic stress dramatically increase morbidity and length of stay. Technologies such as electroencephalogram (EEG) and bispectral index (BIS trade mark ) monitoring are effective for assessing cerebral function as well as level of sedation or arousal, respectively, in patients with a compromised neurological assessment. Neuromuscular transmission (NMT) monitoring by means of peripheral nerve stimulation and assessment of the evoked response may be utilized, within the context of clinical assessment, to determine level of chemical paralysis and minimize dosing of NMB agents. This article explores utilization and differentiates technologies such as EEG, BIS, and NMT monitoring. Monitoring parameters are illustrated using a case study approach.

A study of the Bispectral Index Monitor during procedural sedation and analgesia in the emergency department

STUDY OBJECTIVE

The Bispectral Index Monitor has been validated as an objective measure of sedation depth in the operating room; however, its value for states other than general anesthesia remains unclear. We hypothesized that bispectral index monitoring would reliably correlate with traditional definitions of sedation depth in emergency department patients undergoing procedural sedation and analgesia.

METHODS

In this prospective observational study we measured the Bispectral Index score and a modified Ramsay Sedation Scale score every 5 minutes in a convenience sample of adult ED patients undergoing procedural sedation and analgesia. Investigators and treating physicians were blinded to Bispectral Index scores, which were later correlated with modified Ramsay Sedation Scale scores. We constructed receiver operating characteristic curves to determine the most discriminatory Bispectral Index score thresholds for sedation depth.

RESULTS

Two hundred seventy paired readings were obtained from 37 patients. Despite being statistically significant (P <.0005), the correlation between the Bispectral Index Monitor and modified Ramsay Sedation Scale scores was only moderate (Spearman rho=-0.690) and displayed wide variability. A modified Ramsay Sedation Scale score consistent with mild-to-moderate sedation corresponded to Bispectral Index scores of 34 (general anesthesia) to 98 (fully awake), whereas a modified Ramsay Sedation Scale score consistent with deep sedation corresponded to Bispectral Index scores of 40 to 98. Areas under receiver operating characteristic curves demonstrated moderate (0.83 to 0.86) discriminatory power at all modified Ramsay Sedation Scale thresholds, with the exception of a modified Ramsay Sedation Scale score of 7 or less, which demonstrated high discriminatory power (0.95). A Bispectral Index score of greater than 83 reliably excluded general anesthesia, and a Bispectral Index score of 70 or less reliably identified general anesthesia.

CONCLUSION

Bispectral index monitoring reliably predicted patients undergoing procedural sedation and analgesia who were sedated to the point of general anesthesia from those with lesser degrees of sedation but did not discriminate mild-to-moderate sedation or moderate-to-deep sedation, as measured by the Ramsay Sedation Scale score for the patients undergoing procedural sedation and analgesia in our ED.

Effect of volatile anesthetics on interhemispheric EEG cross-approximate entropy in the rat

Dissimilarity of the electroencephalogram (EEG) between the two hemispheres was characterized by cross-approximate entropy (C-ApEn), an information statistical parameter applicable to nonlinear, aperiodic signals. EEGs were recorded bipolarly with pairs of epidural electrodes in the left and right frontal cortices. The signals were filtered for 1-100 Hz and digitized at 200 Hz. Inhaled anesthetic concentration was varied between 0.3 and 2.1% with 45-min equilibration periods while the rats were breathing spontaneously. Anesthetics produced concentration-dependent changes in C-ApEn. A greater dynamic range of C-ApEn was obtained by reducing the epoch length from 2 s to 100 ms. At a 0.4% inspired agent concentration halothane caused an increase of C-ApEn, whereas isoflurane did not. When the inspired concentrations of both agents were greater than 0.4%, C-ApEn dose-dependently decreased as agent concentrations increased. Isoflurane depressed C-ApEn more than did halothane at all equivalent minimum alveolar concentration levels, but the two agents became equipotent at 1.5% inspired concentration. C-ApEn fell below the awake baseline at 0.8% anesthetic concentration that also abolished the righting reflex. C-ApEn increased after high-pass filtering (>20 Hz) and decreased after-low pass filtering (<20 Hz) of the digitized EEG; the anesthetic dependence of C-ApEn was diminished by both filters. The results suggest that C-ApEn of bihemispheric EEG is a sensitive, agent-specific correlate of anesthetics' central effect.

Quantitative electroencephalography of medetomidine, medetomidine-midazolam and medetomidine-midazolam-butorphanol in dogs

The purpose of this study was to evaluate the effects of the administration of an alpha2-adrenoceptor agonist alone and in combination with other derivatives on brain wave activity. In addition, the diagnostic values of the electroencephalogram (EEG) for judging the depth of the balanced anaesthesia with an alpha2-adrenoceptor agonist was evaluated. The treatments comprised 20 microg/kg medetomidine (Me-20), 80 microg/kg medetomidine (Me-80), 20 microg/kg medetomidine and 0.5 mg/kg midazolam (Me-Mi) administered intramuscularly, and 20 microg/kg medetomidine with 0.5 mg/kg midazolam and 0.1 mg/kg butorphanol (Me-Mi-Bu). The EEG was recorded continuously at pre-administration, and at 7, 10, 20, 30, 45 and 60 min after administration. The recorded data were analysed by separating the power spectrum into 1-3, 4-7, 8-13 and 14-30 Hz bands. Spectral-edge analysis was used to calculate the spectral edge frequency 90 (SEF90) and the median edge frequency (MEF). Time-related changes in power spectrum analysis showed a significant increase in the Me-80 group in the 1-3 Hz band. The power for 1-3 Hz in the Me-80 group was significantly higher than in all the other groups. In the 14-30 Hz band, there was a significant reduction of power in all groups following administration of the agents. The SEF90 frequencies were significantly reduced in all groups except for the Me-20 group after administration of the agents. The SEF90 frequencies in the Me-20, Me-Mi and Me-Mi-Bu were all significantly higher than those in the Me-80 group. However, there was no significant difference between the Me-20, Me-Mi and Me-Mi-Bu groups in any analyses. Our results demonstrated that the changes in quantitative EEG made by the Me-Mi-Bu and Me-Mi groups were similar to those made by Me-20 groups. Present results suggest that the EEG should be interpreted with caution in assessing the anaesthetic level in balanced anaesthesia in dogs.

Midlatency auditory evoked potentials do not allow the prediction of recovery from general anesthesia with isoflurane

PURPOSE

To investigate midlatency auditory evoked potentials (MLAEP) waveforms during recovery from anesthesia. The hypothesis was that MLAEP are sensitive variables to discriminate between states of consciousness and unconsciousness during emergence from anesthesia.

METHODS

MLAEP were recorded in the awake state and during the wake-up phase from isoflurane anesthesia in 22 female patients undergoing ophthalmologic surgery. During emergence from anesthesia the changes in latency and amplitude of MLAEP components Na, Pa and Nb were compared with the awake level. The next day the patients were asked for explicit memory for the recovery period.

RESULTS

In 72% of the patients the MLAEP waveforms were completely suppressed during isoflurane anesthesia. When the patients responded and opened their eyes spontaneously 38 +/- 12 min after anesthesia, the latencies of Na (18.3 +/- 1.2 vs 17.6 +/- 1.3; P = 0.013) and Nb (47.4 vs 7.1 vs 44.7 +/- 7.8; P = 0.048) remained prolonged compared with awake values. In contrast, the amplitudes NaPa and PaNb had regained baseline level. Nine patients had explicit memory for the immediate recovery period. However, there was no difference for any MLAEP component between patients with and without memory at any time.

CONCLUSIONS

The persistent changes of MLAEP latency components Na and Nb indicated impaired auditory signal processing 38 min after isoflurane anesthesia. There was a marked intra- and inter-individual variability during reversal of the anesthetic induced MLAEP changes. This limits the prediction of recovery of consciousness in the individual patient during emergence from anesthesia.

Effect of medetomidine on electroencephalography and use of a quantitative electroencephalograph for evaluating sedation levels in dogs

This study was designed to characterize the effect of medetomidine (Med) on canine electroencephalography (EEG), to evaluate the use of quantitative EEG for assessing sedation levels and to explore the correlation between the serum concentration of Med and the quantitative EEG. Four groups of dogs were given Med at doses of 20, 40, 80 and 160 microg/kg (Med-20, Med-40, Med-80 and Med-160 groups). Following Med administration, there was synchrony between each unipolar EEG lead. On EEG power spectrum analysis of the bipolar leads, all groups showed a significant depression of the 14-30 Hz components. The power of the 1-3 Hz component in the Med-80 and Med-160 groups was significantly increased, although there were few changes in the other groups. Similar results were obtained from raw data analysis. As a result of quantitative EEG analysis, spectrum edge frequency 90 analysis (SEP90) showed that the frequency was significantly reduced in all groups after Med administration. A dose-response effect was observed in all groups except for the Med-160 group. Both of these EEG analyses were significantly correlated with the serum concentration of Med. However, the result of the SPF90 analysis sugested a stronger correlation than that for median edge frequency analysis. In conclusion, care must be taken in veterinary clinical diagnoses when Med is used during EEG recording, as Med may cause increased activity in the low frequency band and a decrease in high frequency band activity. In addition, quantitative EEG analysis may be useful in assessing the depth of sedation and in further studies on Med administration.

Routine intra-operative assessment of pain and/or depth of anaesthesia by nurse anaesthetists in clinical practice

Patient safety and comfort during general anaesthesia and surgery are to a considerable extent dependent on the capability of anaesthesia personnel to interpret directly monitored as well as indirect clinical signs of pain and/or depth of anaesthesia. The aim of the present study was to evaluate how nurse anaesthetists in their clinical routine work assess and interpret intra-operative responses evoked by pain stimuli and/or insufficient depth of anaesthesia. A questionnaire was designed to assess the perceived relevance and validity of cardiovascular, respiratory, mucocutaneous, eye-associated, and muscular responses for routine assessment of intra-operative pain and/or insufficient depth of anaesthesia in patients undergoing surgery under general anaesthesia. Data were obtained from 223 nurse anaesthetists working at nine different university anaesthesia departments in Sweden. A number of significant indicators for pain and depth of anaesthesia could be identified for spontaneously breathing as well as for mechanically ventilated patients. No variable was considered entirely specific for either intra-operative pain or depth of anaesthesia. Changes in breathing rate/volume, central haemodynamics (BP, HR), lacrimation, and presence of moist and sticky skin were given higher score values as indicators of pain than as indicators of depth of anaesthesia. Occurrence of grimaces, attempted movements, and presence of non-centred pupils were variables considered more indicative of insufficient depth of anaesthesia than intra-operative pain. In conclusion, it is obvious from the present data that indirect physiological signs of intra-operative pain and depth of anaesthesia are still considered of importance by Swedish anaesthesia nurses in the anaesthetic management of surgical patients.

Direct current auditory evoked potentials during wakefulness, anesthesia, and emergence from anesthesia

Direct current auditory evoked potentials (DC-AEPs) are a sensitive indicator of depth of anesthesia in animals. However, they have never been investigated in humans. To assess the potential usefulness of DC-AEPs as an indicator of anesthesia in humans, we performed an explorative study in which DC-AEPs were recorded during propofol and methohexital anesthesia in humans. DC-AEPs were recorded via 22 scalp electrodes in 19 volunteers randomly assigned to receive either propofol or methohexital. DC-AEPs were evoked by binaurally presented 2-s, 60-dB, 800-Hz tones; measurements were taken during awake baseline, anesthesia, and emergence. Statistical analysis included analysis of variance and discriminant analysis of data acquired during these three conditions. About 500 ms after stimulus presentation, DC-AEPs could be observed. These potentials were present only during baseline and emergence-not during anesthesia. Statistically significant differences were found between baseline and anesthesia and between anesthesia and emergence. In conclusion, similar effects, as reported in animal studies of anesthetics on the DC-AEPs, could be observed in anesthetized humans. These results demonstrate that DC-AEPs are potentially useful in the assessment of cortical function during anesthesia and might qualify the method for monitoring anesthesia in humans.