Linear and non-linear heart rate metrics for the assessment of anaesthetists' workload during general anaesthesia

BACKGROUND

Excessive workload may impact the anaesthetists' ability to adequately process information during clinical practice in the operation room and may result in inaccurate situational awareness and performance. This exploratory study investigated heart rate (HR), linear and non-linear heart rate variability (HRV) metrics and subjective ratings scales for the assessment of workload associated with the anaesthesia stages induction, maintenance and emergence.

METHODS

HR and HRV metrics were calculated based on five min segments from each of the three anaesthesia stages. The area under the receiver operating characteristics curve (AUC) of the investigated metrics was calculated to assess their ability to discriminate between the stages of anaesthesia. Additionally, a multiparametric approach based on logistic regression models was performed to further evaluate whether linear or non-linear heart rate metrics are suitable for the assessment of workload.

RESULTS

Mean HR and several linear and non-linear HRV metrics including subjective workload ratings differed significantly between stages of anaesthesia. Permutation Entropy (PeEn, AUC=0.828) and mean HR (AUC=0.826) discriminated best between the anaesthesia stages induction and maintenance. In the multiparametric approach using logistic regression models, the model based on non-linear heart rate metrics provided a higher AUC compared with the models based on linear metrics.

CONCLUSIONS

In this exploratory study based on short ECG segment analysis, PeEn and HR seem to be promising to separate workload levels between different stages of anaesthesia. The multiparametric analysis of the regression models favours non-linear heart rate metrics over linear metrics.

Informatics and Medicine

Objectives: To clarify challenges and research topics for informatics in health and to describe new approaches for interdisciplinary collaboration and education. Methods: Research challenges and possible solutions were elaborated by scientists of two universities using an interdisciplinary approach, in a series of meetings over several months. Results and Conclusion: In order to translate scientific results from bench to bedside and further into an evidence-based and efficient health system, intensive collaboration is needed between experts from medicine, biology, informatics, engineering, public health, as well as social and economic sciences. Research challenges can be attributed to four areas: bioinformatics and systems biology, biomedical engineering and informatics, health informatics and individual healthcare, and public health informatics. In order to bridge existing gaps between different disciplines and cultures, we suggest focusing on interdisciplinary education, taking an integrative approach and starting interdisciplinary practice at early stages of education.

* See more detailed authors´ affiliations at the end of the article.

Plasma oxytocin and vasopressin do not predict neuropeptide concentrations in human cerebrospinal fluid

The involvement of the neuropeptides oxytocin (OXT) and vasopressin (AVP) in human socio-emotional behaviours is attracting increasing attention. There is ample evidence for elevated plasma levels upon a wide variety of social and emotional stimuli and scenarios, ranging from romantic love via marital distress up to psychopathology, with cause versus consequence being largely unclear. The present study examined whether plasma levels of both OXT and AVP are reflective of central neuropeptide levels, as assumed to impact upon socio-emotional behaviours. Concomitant plasma and cerebrospinal fluid (CSF) samples were taken from 41 non-neurological and nonpsychiatric patients under basal conditions. Although OXT and AVP levels in the CSF exceeded those in plasma, there was no correlation between both compartments, clearly suggesting that plasma OXT and AVP do not predict central neuropeptide concentrations. Thus, the validity of plasma OXT and AVP as potential biomarkers of human behaviour needs further clarification.

Cardiopulmonary resuscitation performance during simulator-based trainings: a comparative retrospective analysis of adherence to 2005 and 2010 guidelines

BACKGROUND

New cardiopulmonary resuscitation (CPR) guidelines have been published in 2010 emphasizing the importance of minimizing interruptions during chest compression. The aim of our study was to compare the simulator-based CPR training performance of physicians not specialized in anaesthesia and intensive care nurses before and after implementation of new resuscitation guidelines.

METHODS

In autumn 2010, a total of 74 scenarios during six 1.5 day simulation-based CPR trainings were performed. Four of them were conducted after the implementation of the 2010 guidelines. During each simulated scenario a programmed script standardized the conditions of the simulator and its reactions on the trainees' actions. CPR relevant parameters were extracted on the basis of the simulator's log files and no-flow-time fraction and median cardiac output of the simulator were calculated. Results before and after the guideline implementation were compared using the Wilcoxon Two Sample Test.

RESULTS

Thirty-four out of 74 scenarios were included into the analysis. During training according to the 2010 guidelines, the no-flow-time fraction was lower (median: 21.8% [IQR: 16.1-27.1%] vs. 29.1 % [IQR: 25.0-30.9 %]; P=0.04). The median cardiac output increased from 1.60 L/min-1 [IQR: 1.50-1.65 L/min-1] to 1.90 L/min-1 [IQR: 1.80-2.10 L/min-1]; P<0.001) when the CPR training was conducted according to the 2010 resuscitation guidelines.

CONCLUSION

Non-anesthesiological physicians and intensive care nurses training demonstrated an improved CPR performance in a high-fidelity human patient simulator with respect to the median cardiac output and duration of no-flow-time when 2010 CPR guidelines were applied.

Monitors of the hypnotic component of anesthesia - correlation between bispectral index and cerebral state index

BACKGROUND

The current study examines whether analysis of identical EEG data results in a high correlation coefficient of BIS and CSI values during all anesthetic levels and assesses the concordance of both EEG monitors for displaying the level of anesthesia as defined by the manufacturers.

METHODS

EEG data of 40 patients undergoing elective surgery under general anesthesia with either sevoflurane/remifentanil or propofol/remifentanil were replayed to an EEG player and reanalysed by a BIS A-2000® monitor and a Cerebral State Monitor. Further, research into differences between CSI and BIS index values was performed, e.g., extraction of differences of ≥ 10 and ≥ 20 index points and of the EEG length with differing index values.

RESULTS

The overall correlation coefficient was 0.68 without significant difference between propofol or sevoflurane group. In 51.8% of all recordings, both EEG monitors agreed in their classification of the anesthetic level. The number and length of differing index pairs was influenced by varying time delays of index calculation and different algorithms of index computation.

CONCLUSION

In contrast to previous studies, our current approach combines the following conditions: analysis on basis of identical underlying EEG data from deep to light anesthesia, no guidance of anesthetic administration by one of the EEG-based monitors, avoidance of simultaneous EEG readings and the use of two different anesthetic regimens. Though the result of EEG analysis during anesthesia is similar with both monitors, CSI performance during propofol anesthesia was superior to sevoflurane anesthesia. Consequently, a lower agreement of classification of anesthetic levels between BIS and CSI was reached with the use of sevoflurane. Thus, CSI calculation seems not to be independent from anesthetic agent.

The mu-opioid receptor agonist remifentanil induces acute dysphoria irrespective of its analgesic properties

Mu-opioidergic agonists are believed to induce euphoria, whereas kappa-agonists are thought to lead to dysphoria. Our study investigated mood effects of remifentanil, a mu-receptor opioid agonist, in healthy male volunteers. Moreover, we examined interactions between mood and pain. Three conditions were investigated in 21 volunteers: saline, 0.05 and 0.15 microg kg(-1) min(- 1) remifentanil. Each condition was investigated during non-painful heat and during painful heat stimulation. Mood was measured with the von Zerssen's mood scale (Bf-S score) and pain intensity using a Visual Analogue Scale (VAS). High Bf-S scores are reflecting discontent and dysphoria. Changes were tested for significance using a linear mixed model approach. Remifentanil significantly increased Bf-S scores during painful heat (+91.4%), indicating a negative mood effect, although it reduced VAS scores of painful heat intensity (-49.0%). The type of sensory stimulation (non-painful versus painful) had no effect on mood. There was no interaction between remifentanil dose and type of stimulation. Our results provide evidence for negative mood effects of remifentanil. These effects occur with and without pain. Taken into account that remifentanil reduces pain, one could have expected analgesia-related amelioration of mood instead. In clinical practice, these remifentanil effects should be considered and a comedication might be advisable.

[Postoperative acute mitral regurgitation. Unexpected finding after minor non-cardiac surgery]

This report describes the case of a 59-year-old man who was scheduled for general anesthesia with propofol, sufentanil and sevoflurane for removal of a metal implant. The patient was classified as American Society of Anesthesiologists (ASA) II status because of an asymptomatic mitral valve prolapse and medically treated arterial hypertension. During induction of narcosis a pulsoxymetrically measured inadequate increase in oxygen saturation after preoxygenation was noticed and a moderate respiratory obstruction occurred intraoperatively, but anesthesia was uneventfully completed and the patient was extubated. However, 3 h later the patient developed severe dyspnea, hypoxia, tachycardia and arterial hypotension. Physical examination revealed a new grade 4/6 systolic murmur radiating to the axilla and X-ray showed bilateral pulmonary edema. Neither electrocardiographic nor biochemical manifestations of acute myocardial infarction were identified but transthoracic echocardiography revealed fluttering of the posterior leaflet of the mitral valve with grade III regurgitation and dilation of the left atrium. Coronary angiography was normal and left ventriculography confirmed severe mitral regurgitation. Mitral valve repair was successfully performed 22 h after presentation of symptoms. Mitral regurgitation is a common finding on echocardiography, seen to some degree in over 75% of the population. The etiology of mitral valve insufficiency which can be caused by pathologic changes of one or more of the components of the mitral valve, including the leaflets, annulus, chordae tendineae, papillary muscles, or by abnormalities of the surrounding left ventricle and/or atrium are discussed. Rupture of mitral chordae tendineae is infrequent and causes acute hemodynamic deterioration and needs corrective surgery. Valve replacement should be performed only if mitral valve repair is not possible. Echocardiography is an invaluable tool in determining the severity of regurgitation, the integrity of the mitral valve apparatus, the extent of left ventricular enlargement, and the ejection fraction. Acute mitral valve regurgitation caused by a rupture of chordae tendineae should be considered in the differential diagnosis of perioperative acute pulmonary edema.

Informatics and medicine--from molecules to populations

OBJECTIVES

To clarify challenges and research topics for informatics in health and to describe new approaches for interdisciplinary collaboration and education.

METHODS

Research challenges and possible solutions were elaborated by scientists of two universities using an interdisciplinary approach, in a series of meetings over several months.

RESULTS AND CONCLUSION

In order to translate scientific results from bench to bedside and further into an evidence-based and efficient health system, intensive collaboration is needed between experts from medicine, biology, informatics, engineering, public health, as well as social and economic sciences. Research challenges can be attributed to four areas: bioinformatics and systems biology, biomedical engineering and informatics, health informatics and individual healthcare, and public health informatics. In order to bridge existing gaps between different disciplines and cultures, we suggest focusing on interdisciplinary education, taking an integrative approach and starting interdisciplinary practice at early stages of education.

[Current level of patients' knowledge of anaesthesiology]

The anaesthesiologist's competence in anaesthesia, intensive care medicine, pain therapy and emergency medicine is accepted throughout the medical society. Nevertheless, during the last decades patient surveys demonstrated a considerable lack of information of the responsibility of our work. By continuous education and information anaesthesiologists have aimed to improve the information and decision-making process for the patient. This multicentre trial was designed to investigate the current public view on our profession in seven German hospitals. In-hospital patients were asked to fill out a standardised questionnaire prior to the anaesthesia premedication visit and a total of 692 questionnaires (77%) were analysed. Results demonstrated an increased level of knowledge for anaesthesia (>95%), intensive care medicine (74%), and pain therapy (50% acute pain; 32% severe pain). In the case of emergency medicine (10%) the in-hospital and out-of-hospital responsibilities were not clear among patients. We conclude that the continuous distribution of information in recent years has contributed to improving patients' knowledge on interdisciplinary responsibilities. Future efforts should focus on the gaps in patient's knowledge to allow the patient to ask the right questions necessary for decision-making.

Schwerwiegende Risiken und Komplikationen der epiduralen Neurolyse nach Racz

Racz's minimal invasive epidural catheter procedure, also known as "epidural neuroplasty" is not only utilized in patients suffering from failed spine surgery ("failed back surgery syndrome") but also increasingly applied to non-surgical back pain patients to prevent chronification or deterioration. Its hypothesized principle of action is local epidural lysis of adhesions, neurolysis of vertebral nerve roots and local lavage of proinflammatory mediators by repeated injection of local anesthetics, corticosteroids, hyaluronidase and hypertonic saline solution. However adverse events are well known to occur in epidural neuroplasty. Complications of epidural neuroplasty are due to the procedure itself or due to specific drugs-related side effects. Unintended dural puncture, administration of the drugs to the subarachnoid or subdural space, catheter shearing, infection and severe hemodynamic instability during application are most commonly observed adverse events. Complications related to the procedure itself occur immediately, while complications relating to drug administration show later onset. Within this context, we report a case of severe meningitis with neurologic sequelae in a patient who received Racz catheter-treatment for unspecific low-back pain and provide an overview of the literature on other potential severe complications. As a consequence, we recommend that the Racz catheter procedure as yet should be restricted to controlled clinical trials with rigorous inclusion- and exclusion criteria.

Perioperative Schmerztherapie in der Kniegelenkendoprothetik

Total knee arthroplasty (TKA) is associated with significant postoperative pain. Adequate analgesics and techniques are required for early mobilization, continuous passive motion and intensified physical therapy as well as for high-quality postoperative analgesia.However, in the immediate postoperative setting the excessive nociceptive input can be blocked by using doses which are most frequently associated with adverse effects like dizziness, nausea and vomiting, sedation and risk of respiratory depression. The use of peripheral nerve blocks is recommended after orthopaedic surgery. After TKA, the continuous "3 in 1 nerve block" has been proven to be more effective than conventional patient controlled intravenous opioid therapy as well as than epidural analgesia accompanied by side effects. Postoperative analgesic techniques influence surgical outcome, duration of hospitalization and re-convalescence. The use of regional analgesia after TKA may initially lead to higher costs but it is counterbalanced by a reduction in morbidity and mortality, decrease in hospitalization, improved re-convalescence and a better functional outcome.

Awareness and the EEG power spectrum: analysis of frequencies

BACKGROUND

Power spectral analysis is a well-established method for the analysis of EEG signals. Spectral parameters can be used to quantify pharmacological effects of anaesthetics on the brain and the level of sedation. This method, in numerous variations, has been applied to depth of anaesthesia monitoring and has been incorporated into several commercially available EEG monitors. Because of the importance of EEG spectral analysis, we evaluated the performance of each frequency in the power spectrum regarding detection of awareness.

METHODS

Ninety artefact-free EEG segments of length 8 s were obtained from a database that contains perioperatively recorded EEG data. For the present analysis, EEG data were selected from 39 patients with propofol-remifentanil or sevoflurane-remifentanil anaesthesia with a period of awareness. Half of the EEG segments were recorded during periods of awareness as defined by an adequate response to the command 'squeeze my hand'. The other half were from unresponsive patients. The power spectral density was calculated for each segment. The performance of each frequency bin of the power spectrum as a detector of awareness was assessed with a remapped prediction probability rPK, i.e. the prediction probability PK mapped to a range of 0.5-1.

RESULTS

The remapped prediction probability was high (rPK>0.8) for low frequencies (<15 Hz) and for high frequencies (>26 Hz), with a minimum (rPK<0.55) at 21 Hz. Indentations in the 'performance spectrum' occur at the power-line frequency (50 Hz) and its harmonics and at 78 Hz, probably caused by the continuous impedance measurement of another device used in parallel. With the exception of the indentations, the remapped prediction probability of the high frequencies (>35 Hz) was >0.95.

CONCLUSIONS

The best performance for the detection of awareness was achieved by EEG power spectral frequencies from >35 Hz up to 127 Hz. This frequency band may be dominated by muscle activity. The frequency band between 15 and 26 Hz may be of limited value, as reflected by lower rPK values.

[Treatment of anaphylactic reactions: a review of guidelines and recommendations]

In the present review, guidelines and recommendations for the treatment of anaphylactic reactions are presented and evaluated. Herefore, publications of German and non-German societies and expert groups have been selected and, in addition to that, we have chosen a number of articles that were cited frequently and, as far as we are concerned, have a relevant meaning for this theme. None of the traditionally applied remedies - epinephrine and intravascular volume, histamine receptor blockade, inhaled betamimetics and steroids - have been proven efficacious by means of evidence-based medicine. Due to the variability of the symptoms of anaphylaxis, it is widely accepted that such a clinical proof is unlikely to come. In contrast to this, there is lack of a consense as to substantial elements of the therapy, above all with regard to dosage and application mode for epinephrine and likewise concerning amount and kind of intravenous fluids. Hence, the physician in charge has to face the necessity either to follow the guidelines of his institution (if there are any) or to blend his own therapeutic regime according to his own convictions.

Quality of perioperative AEP—variability of expert ratings

BACKGROUND

Previous studies suggest that auditory evoked potentials (AEP) may be used to monitor anaesthetic depth. However, during surgery and anaesthesia, the quality of AEP recordings may be reduced by artefacts. This can affect the interpretation of the data and complicate the use of the method. We assessed differences in expert ratings of the signal quality of perioperatively recorded AEPs.

METHODS

Signal quality of 180 randomly selected AEP, recorded perioperatively during a European multicentre study, was rated independently by five experts as 'invalid' (0), 'poor' (1), or 'good' (2). Average (n=5) quality rating was calculated for each signal. Differences between quality ratings of the five experts were calculated for each AEP: inter-rater variability (IRV) was calculated as the difference between the worst and best classification of a signal.

RESULTS

Average signal quality of 57% of the AEPs was rated as 'invalid', 39% as 'poor', and only 4% as 'good'. IRV was 0 in only 6%, 1 in 62%, and 2 in 32% of the AEP, that is in 32% one expert said signal quality was good, whereas a different expert thought the identical signal was invalid.

CONCLUSIONS

There is poor agreement between experts regarding the signal quality of perioperatively recorded AEPs and, as a consequence, results obtained by one expert may not easily be reproduced by a different expert. This limits the use of visual AEP analysis to indicate anaesthetic depth and may affect the comparability of AEP studies, where waveforms were analysed by different experts. An objective automated method for AEP analysis could solve this problem.

[Approximate entropy of anesthesia EEG: compromise between calculation time and clinical validity]

Approximate entropy, a measure of regularity, can be used to analyze the electroencephalogram of patients in general anesthesia to discriminate between different states of consciousness. EEG burst suppression patterns reflect a state of deep anesthesia. Due to the instationary character of this EEG pattern approximate entropy values do not correctly classify the patient state. Possible solutions to this problem may be limited by the demand of computing power for entropy calculation and the reaction time following changes in patient state. Different approaches for an online monitoring application are examined.

Dose-dependent regional cerebral blood flow changes during remifentanil infusion in humans: a positron emission tomography study

BACKGROUND

The current study investigated dose-dependent effects of the mu-selective agonist remifentanil on regional cerebral blood flow (rCBF) in volunteers using positron emission tomography (PET).

METHODS

Ten right-handed male volunteers were included in a 15O-water PET study. Seven underwent three conditions: control (saline), low remifentanil (0.05 microg x kg(-1) x min(-1)), and moderate remifentanil (0.15 microg x kg(-1) x min(-1)). The remaining three participated in the low and moderate conditions. A semirandomized study protocol was used with control and remifentanil conditions 3 or more months apart. The order of low and moderate conditions was randomized. Cardiovascular and respiratory parameters were monitored. Categoric comparisons between the control, low, and moderate conditions and a pixelwise correlation analysis across the three conditions were performed (P < 0.05, corrected for multiple comparisons) using statistical parametric mapping.

RESULTS

Cardiorespiratory parameters were maintained constant over time. At the low remifentanil dose, significant increases in relative rCBF were noted in the lateral prefrontal cortices, inferior parietal cortices, and supplementary motor area. Relative rCBF decreases were observed in the basal mediofrontal cortex, cerebellum, superior temporal lobe, and midbrain gray matter. Moderate doses further increased rCBF in mediofrontal and anterior cingulate cortices, occipital lobe transition, and caudal periventricular grey. Significant decreases were detected in the inferior parietal lobes. These dose-dependent effects of remifentanil on rCBF were confirmed by a correlation analysis.

CONCLUSION

Remifentanil induced dose-dependent changes in relative rCBF in areas involved in pain processing. At moderate doses, rCBF responses were additionally detected in structures known to participate in modulation of vigilance and alertness. Insight into the mechanisms of opioid analgesia within the pain-processing neural network may lead to a better understanding of antinociception and opioid treatment.