Monitoring depth of anesthesia utilizing a combination of electroencephalographic and standard measures.

BACKGROUND: For decades, monitoring depth of anesthesia was mainly based on unspecific effects of anesthetics, for example, blood pressure, heart rate, or drug concentrations. Today, electroencephalogram-based monitors promise a more specific assessment of the brain function. To date, most approaches were focused on a "head-to-head" comparison of either electroencephalogram- or standard parameter-based monitoring. In the current study, a multimodal indicator based on a combination of both electro encephalographic and standard anesthesia monitoring parameters is defined for quantification of "anesthesia depth." METHODS: Two hundred sixty-three adult patients from six European centers undergoing surgery with general anesthesia were assigned to 1 of 10 anesthetic combinations according to standards of the enrolling hospital. The anesthesia multimodal index of consciousness was developed using a data-driven approach, which maps standard monitoring and electroencephalographic parameters into an output indicator that separates different levels of anesthesia from awake to electroencephalographic burst suppression. Obtained results were compared with either a combination of standard monitoring parameters or the electroencephalogram-based bispectral index. RESULTS: The anesthesia multimodal index of consciousness showed prediction probability (P(K)) of 0.96 (95% CI, 0.95 to 0.97) to separate different levels of anesthesia (wakefulness to burst suppression), whereas the bispectral index had significantly lower PK of 0.80 (0.76 to 0.81) at corrected threshold P value of less than 0.05. At the transition between consciousness and unconsciousness, anesthesia multimodal index of consciousness yielded a PK of 0.88 (0.85 to 0.91). CONCLUSION: A multimodal integration of both standard monitoring and electroencephalographic parameters may more precisely reflect the level of anesthesia compared with monitoring based on one of these aspects alone.

Postoperative cognitive dysfunction.

BACKGROUND: Older patients in particular are vulnerable to memory disturbances and other types of cognitive impairment after surgical operations. In one study, roughly 12% of patients over age 60 had postoperative cognitive dysfunction (POCD) three months after surgery. This is an important issue in perioperative care as extensive surgery on older patients becomes more common. METHOD: Selective review of the literature. RESULTS: POCD is usually transient. It is diagnosed by comparing pre- and postoperative findings on psychometric tests. Its pathogenesis is multifactorial, with the immune response to surgery probably acting as a trigger. Factors that elevate the risk of POCD include old age, pre-existing cerebral, cardiac, and vascular disease, alcohol abuse, low educational level, and intra- and postoperative complications. The findings of multiple randomized controlled trials indicate that the method of anesthesia does not play a causal role for prolonged cognitive impairment. POCD is associated with poorer recovery and increased utilization of social financial assistance. It is also associated with higher mortality (hazard ratio 1.63, 95% confidence interval 1.11-2.38). Persistent POCD enters into the differential diagnosis of dementia. CONCLUSION: POCD can markedly impair postoperative recovery. The findings of pertinent studies performed to date are difficult to generalize because of heterogeneous patient groups and different measuring techniques and study designs. Further investigation is needed to determine which test instruments are best for clinical use and which preventive strategies might lessen the incidence of POCD.

Awareness under general anesthesia.

BACKGROUND: Awareness while under general anesthesia, and the later recall of what happened during surgery, can be experienced by patients as horrific events that leave lasting mental trauma behind. Patients may have both auditory and tactile perception, potentially accompanied by feelings of helplessness, inability to move, pain, and panic ranging to an acute fear of death. For some patients, the experience of awareness under anesthesia has no sequelae; for others, however, it can lead to the development of post-traumatic stress disorder, consisting of complex psychopathological phenomena such as anxiety, insomnia, nightmares, irritability, and depression possibly leading to suicidality. METHODS: The literature on the subject was selectively reviewed. RESULTS: In the absence of risk factors awareness phenomena occur in one to two per 1000 operations under general anesthesia (0.1% to 0.2%) and are thus classed as an occasionally occurring critical event. In children, the risk of such phenomena occurring is 8 to 10 times higher. These phenomena are due to an inadequate depth of anesthesia with incomplete unconsciousness. They can be promoted by a number of risk factors that are either patient-related (ASA class III or above, medication abuse), surgery-related (Caesarean section, emergency procedures, surgery at night), or anesthesia-related (anesthesia without benzodiazepines, use of muscle relaxants). CONCLUSION: Strategies for avoiding awareness phenomena under anesthesia include the training of staff to know about the problem and, specifically, the use of benzodiazepines, the avoidance of muscle relaxants if possible, and shielding the patient from excessive noise. EEG monitoring is effective but provides no guarantee against awareness. If awareness under anesthesia occurs despite these measures, the patient must be given expert, interdisciplinary treatment as soon after the event as possible in order to minimize its potential sequelae.

[Drug addiction and anaesthesia: most popular recreational drugs in Germany and anaesthesiological management of drug addicts]. / Der Suchtkranke in der Anästhesie - Substanzabhängigkeiten und perioperative Behandlungsstrategien.

Drug addicts need special anesthesiological care due to their co-morbidities, their modified need for analgesics and anesthetics and/or their specific substitution therapies. In spite of the high incidence of addiction worldwide controlled studies and evidence based recommendations for the anaesthesiological management of the patients are missing. The perioperative care is not the treatment of addiction, on the contrary the specific aspects of a chronic disease have to be accepted. Equally important perioperative treatment strategies for the management of drug addicts include: 1. stabilisation of the physical dependence by substitution therapies. 2. avoidance of distress or craving. 3. perioperative stress relief. 4. strict avoidance of inadequate analgesic treatment. 5. postoperative optimization with regional or systemic analgesia with non-opioids, opiods and co-analgesics. 6. consideration of specific physical or psychological comorbidities. Inadequate analgesic treatment is known to be responsible for relapses into addiction and has strictly to be avoided. This holds true even for people with long term drug abstinence.

[Pharmacotherapy--physostigmine administered post-operatively]. / Pharmakotherapie--physostigmin post OP.

The central anticholinergic syndrome should be considered in patients with altered mental status following anaesthesia. Physostigmine, a reversible acetylcholinesterase inhibitor, is a first-line medicament for the therapy of the central anticholinergic syndrome. Physostigmine crosses the blood-brain barrier and elevates acetylcholine levels in the brain. For prevention of postanaesthetic shivering, for treatment of intoxications and postoperative pain, and for patients suspected of having antimuscarinic delirium physostigmine is also indicated.

Electroencephalographic mapping during routine clinical practice: cortical arousal during tracheal intubation?

We used quantitative analysis of the electroencephalogram (EEG) in 42 patients to assess the effect of tracheal intubation after induction of anesthesia with etomidate and sufentanil using standard clinical practice. The EEG was recorded from eight bipolar electrode derivations and Z-transformed relative to age expected normative data for relative power in the delta, theta, alpha, and beta frequency bands. Tracheal intubation resulted in classical cortical arousal, as indicated by acceleration of the EEG frequencies. Significant effects were seen in all frequency bands, most pronounced in the alpha frequency band, with the largest increase bilaterally in the fronto-temporal regions (F-values: Delta - 9.592, P < 0.001; theta - 1.691, P < 0.001; alpha - 18.439, P < 0.001; beta - 4.504, P < 0.001). Changes in alpha and delta power during induction of anesthesia were correlated with the dose of etomidate (P < 0.05). Changes in alpha after tracheal intubation were correlated at the parietooccipital brain regions to the dose of sufentanil (P < 0.05). Individual titration of the dose of etomidate and sufentanil, as during routine clinical practice, is not sufficient to block the strong noxious stimulation of tracheal intubation and results in cortical arousal. The clinical impact of this cortical wake-up phenomenon is undetermined.

Representation of somatosensory evoked potentials using discrete wavelet transform.

OBJECTIVE: Somatosensory evoked potentials (SEP) have been shown to be a useful tool in monitoring of the central nervous system (CNS) during anaesthesia. SEP analysis is usually performed by an experienced human operator. For automatic analysis, appropriate parameter extraction and signal representation methods are required. The aim of this work is to evaluate the discrete wavelet transform (DWT) as such a method for an SEP representation. METHODS: Median nerve SEP were derived in 52 female patients, scheduled for elective surgery with SEP monitoring, under clinically proven conditions in the awake state. The discrete wavelet transform implemented as the multiresolution analysis was adopted for evaluating SEP. The suitability of the wavelet coefficients was investigated by calculating the error between the averaged response and the corresponding wavelet reconstructions. RESULTS: SEP can be represented by a very small number of wavelet coefficients. Although the individual SEP waveform has an influence on the number and selection of wavelet coefficients, in all subjects more than 84% of the SEP waveform energy can be represented by a set 16 wavelet coefficients. CONCLUSIONS: The discrete wavelet transformation provides an efficient tool for SEP representation and parameterisation. Depending on the specific problem the DWT, can be adjusted to the desired accuracy, which is important for the subsequent development of automatic SEP analysers.

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.