Unwarranted association between epidural analgesia and emergency delivery: critical review of methodological shortcomings

Linked articles: This Correspondence comments on Damhuis et al. and Tabernée Heijtmeijer et al.

Adherence and discontinuation of optimal heart failure therapies according to age

Background

Guideline-recommended disease-modifying pharmacological therapies for heart failure (HF) with reduced ejection fraction are underutilized, particularly among elderly patients.

Purpose

We examined adherence with and discontinuation of evidence-based HF pharmacotherapy, comprising of angiotensin-converting enzyme inhibitors (ACEi)/angiotensin-II receptor blockers (ARB), beta-blockers (BB) and mineralocorticoid receptor antagonists (MRA), according to age.

Methods

Using Danish nationwide registries, we included patients with a first HF diagnosis between 2011 and 2018. Patients were stratified into three age groups, <65 years (reference group), 65–79 years, and ≥80 years. The average daily drug dose was calculated as median proportions of target doses one year after inclusion. Adherence was estimated by the proportion of days covered (PDC), i.e., the total number of days with the drug available for a patient alive for the whole first year of the follow-up period. Discontinuation was defined as a break of >90 days, and the 5-year risk of discontinuation according to age groups was estimated with the Aalen-Johansen estimator. Multivariable Cox regression models were used to evaluate the treatment discontinuation rate according to age groups.

Results

We included a total of 29,482 patients (<65 9,449 (25.4% female), 65–79 13,746 (33.1%), ≥80 6,287 (46.3%)). Advancing age was associated with lower median proportions of daily target doses (ACEi 100%, 88%, 63%; ARB 75%, 67%, 50%; BB 75%, 56%, 44%), and lower adherence (ACEi/ARB 79.1%, 77.5%, 69.4%; BB 79.1%, 78.6%, 73.8%), in the <65, 65–79 and ≥80 age groups respectively, one year after inclusion. Age ≥80 was associated with a higher 5-year risk of discontinuation; cumulative incidence, ACEi/ARB 41%, 44%, 51%; BB 38%, 35%, 39%, in the same age group order as above (adjusted hazard ratio: ACEi/ARB 1.60 [95% CI, 1.51–1.69]; BB 1.33 [95% CI, 1.25–1.41]). Conversely, the risk of discontinuation of MRAs differed little with age (<65 50%, 65–79 54%, ≥80 56%), although MRA initiation in the most elderly was less frequent (<65 33%, 65–79 33%, ≥80 22%).

Conclusion

Among a nationwide cohort of HF patients, advanced age was associated with lower proportions of daily target doses, lower adherence, and a higher rate of discontinuation of ACEi/ARB and BBs. Focus on treatment adherence and optimal dosages among elderly HF patients could improve outcomes.

Funding Acknowledgement

Type of funding sources: None.

From Powders to Single Crystals: A Crystallographer's Toolbox for Small-Molecule Structure Determination

Although the crystal structures of small-molecule compounds are often determined from single-crystal X-ray diffraction (scXRD), recent advances in three-dimensional electron diffraction (3DED) and crystal structure prediction (CSP) methods promise to expand the structure elucidation toolbox available to the crystallographer. Herein, a comparative assessment of scXRD, 3DED, and CSP in combination with powder X-ray diffraction is carried out on two former drug candidate compounds and a multicomponent crystal of a key building block in the synthesis of gefapixant citrate.

Correlation of bupivacaine 0.5% dose and conversion from spinal anesthesia to general anesthesia in cesarean sections

BACKGROUND

Failed spinal anesthesia for cesarean sections may require conversion to general anesthesia. The aim of this study was to determine whether the administered spinal bupivacaine dose for performing a cesarean section under spinal anesthesia was related to the conversion rate to general anesthesia.

METHODS

Retrospective analysis was performed on 1252 electronic data and file of patients who underwent a cesarean section under spinal anesthesia between 2004 and 2011.

RESULTS

In 15 patients, spinal anesthesia was converted into general anesthesia due to block failure. Patients in whom a bupivacaine dose of 8 mg or smaller was administered had significantly higher conversion rate (3/61 (4.9%) patients and 12/1191 (1.0%) patients, respectively; p < 0.05.). The relative risk of conversion with a 8 mg dose or lower is 4.88 (95% CI 1.41 - 16.85).

CONCLUSION

This retrospective study shows that a low dose administration a bupivacaine 0.5% for spinal anesthesia in cesarean section patients elicits significantly more frequent conversion to general anesthesia.

Long-term results of trismus release in noma patients

Noma, also known as cancrum oris, is an infectious disease that results in a loss of orofacial tissue, due to gangrene of soft and bony tissue. It is especially seen in young children in the sub-Saharan region. Among the sequelae of patients who survive noma, trismus is one of the most disabling. This retrospective research studied the long-term results of trismus release in noma patients. Thirty-six patients could be traced in the villages and were included in the study. The mean mouth opening in this group was 10.3mm (95% CI: 7.0; 13.6mm) and the mean period after discharge from hospital was 43 months. Better mouth opening was observed in patients who continued physiotherapy after discharge, were older, and those with a 'soft' (vs. 'hard') inner and outer cheek on palpation. The result of trismus release in noma patients in the long term was extremely poor in this study.

The Entropy Module® and Bispectral Index® as Guidance for Propofol-Remifentanil Anaesthesia in Combination with Regional Anaesthesia Compared with a Standard Clinical Practice Group

This study was designed to investigate the impact of the Entropy Module® and Bispectral Index® (BIS) monitoring on drug consumption and recovery times compared with standard anaesthetic practice in patients undergoing orthopaedic surgery using a combination of regional and general anaesthesia as performed by an experienced anaesthesiologist. We hypothesised that electroencephalogram monitoring would lead to a lower drug consumption as well as shorter recovery times.

With institutional review board approval and written informed consent, 90 adult patients undergoing surgery to the upper or lower extremity received regional anaesthesia for post- and intraoperative pain control and were randomised to receive general anaesthesia by propofol/remifentanil infusion controlled either solely by clinical parameters or by targeting Entropy or BIS values of 50. Recovery times and drug consumption were recorded.

Data from 79 patients were analysed. Compared with standard practice, patients with Entropy or BIS monitoring showed a similar propofol consumption (standard practice 101±22 μg/kg/minute, Entropy 106±24 μg/kg/minute, BIS 104±20 μg/kg/minute) and showed similar Aldrete scores (10/10) one minute after extubation: 9.1∓0.3, 9.2±0.6 and 9.3±0.5, respectively. Time points of extubation were 7.3±2.9 minutes, 9.2∓3.9 minutes and 6.8±2.9 minutes, respectively, demonstrating a significant difference between Entropy and BIS (P=0.023).

Compared with standard practice, targeting an Entropy or BIS value of 50 did not result in a reduction of propofol consumption during general anaesthesia combined with regional anaesthesia as performed by an experienced anaesthesiologist in orthopaedic patients.

Soft tissue landmark for ultrasound identification of the sciatic nerve in the infragluteal region: the tendon of the long head of the biceps femoris muscle

BACKGROUND AND OBJECTIVES

The sciatic nerve block represents one of the more difficult ultrasound-guided nerve blocks. Easy and reliable internal ultrasound landmarks would be helpful for localization of the sciatic nerve. Earlier, during ultrasound-guided posterior approaches to the infragluteal sciatic nerve, the authors recognized a hyperechoic structure at the medial border of the long head of biceps femoris muscle (BFL). The present study was performed to determine whether this is a potential internal landmark to identify the infragluteal sciatic nerve.

METHODS

The depth and the thickness of this hyperechoic structure, its relationship with the sciatic nerve and the ultrasound visibility of both were recorded in the proximal upper leg of 21 adult volunteers using a linear ultrasound probe in the range of 7-13 MHz. The findings were verified by an anatomical study in two cadavers.

RESULTS

The hyperechoic structure at the medial border of the BFL extended in a dorsoventral direction between 1.4+/-0.6 cm (mean+/-SD) and 2.8+/-0.8 cm deep from the surface, with a width of 2.2+/-0.9 mm. Between 2.6+/-0.9 and 10.0+/-1.5 cm distal to the subgluteal fold, the sciatic nerve was consistently identified directly at the ventral end of the hyperechoic structure in all volunteers. The anatomical study revealed that this hyperechoic structure corresponds to tendinous fibres inside and at the medial border of the BFL.

CONCLUSION

The hyperechoic BFL tendon might be a reliable soft tissue landmark for ultrasound localization of the infragluteal sciatic nerve.

[Target-controlled infusion. Clinical relevance and special features when using pharmacokinetic models]

Since its commercial introduction in 1996, target-controlled infusion (TCI) has become an established technique for administration of intravenous anaesthetics. Modern TCI systems, however, are characterized by an increasing number of additional options and features, such as the choice between different pharmacokinetic models and modes of application, which may confuse the less experienced user. This review describes the differences between pharmacokinetic models, modes of application and the effect of covariates as well as the consequences for dosing. The aim is to explicate for the user of modern TCI systems the underlying scientific concepts and the relevance for clinical practice.

Visualization of the course of the sciatic nerve in adult volunteers by ultrasonography

BACKGROUND

The sciatic nerve block by the posterior approaches represents one of the more difficult ultrasound-guided nerve blocks. Our clinical experiences with these blocks indicated a point slightly distal to the subgluteal fold as an advantageous position to allow good ultrasonic visibility. In this study, we systematically scanned the sciatic nerve from the subgluteal fold to the popliteal crease, to determine an optimal point for ultrasonographic visualization.

METHODS

After institutional approval and written informed consent, we recruited 15 volunteers to visualize the sciatic nerve from the subgluteal fold to the popliteal crease using a linear ultrasound probe in the range of 7-13 MHz. The ultrasonographic visibility of the sciatic nerve, nerve diameter (width and thickness), and skin-to-nerve distance at 20 equidistant points between the subgluteal fold and the popliteal crease were recorded.

RESULTS

The sciatic nerve could be successfully visualized in cross-section as a hyperechoic structure on ultrasound in all volunteers. In the course from subgluteal to the popliteal area, the shape of the sciatic nerve changed from flat to round, while the skin-nerve distance varied with the smallest skin-nerve distances at the popliteal crease and at 5.4 cm (on average) distal to the subgluteal fold. The best ultrasonographic visibility scores were found between 7.2 and 10.8 cm (on average) distal to the gluteal fold.

CONCLUSION

Between 5.4 and 10.8 cm from the subgluteal fold seems to be the best area to scan the sciatic nerve in terms of superficial nerve position and good ultrasonic visibility.

A needle guidance device compared to free hand technique in an ultrasound-guided interventional task using a phantom

In this in vitro study, a needle guidance device and a 'free hand' technique for ultrasound guided needle insertion were compared in a simulated ultrasound-guided interventional task using a porcine phantom. Residents inexperienced in using ultrasonography were asked to insert a needle, using an in-plane techniques, and to make contact with metal rods at a depth of 2 and 4 cm in the phantom. The transducer made angles of 90 degrees, 60 degrees and 45 degrees with the surface of the phantom. The times to perform the procedures were significantly shorter and the needle visualisation was significantly better when using the needle guidance device. The residents ranked their satisfaction with the needle-guidance device significantly better than the 'free-hand' technique. This device may be beneficial when performing ultrasound guided peripheral nerve blocks, especially by inexperienced operators.

Inferences on the phylogeography of the fungal pathogen Heterobasidion annosum, including evidence of interspecific horizontal genetic transfer and of human-mediated, long-range dispersal

Fungi in the basidiomycete species complex Heterobasidion annosum are significant root-rot pathogens of conifers throughout the northern hemisphere. We utilize a multilocus phylogenetic approach to examine hypotheses regarding the evolution and divergence of two Heterobasidion taxa associated with pines: the Eurasian H. annosum sensu stricto and the North American H. annosum P intersterility group (ISG). Using DNA sequence information from portions of two nuclear and two mitochondrial loci, we infer phylogenetic relationships via parsimony, Bayesian and median-joining network analysis. Analysis of isolates representative of the entire known geographic range of the two taxa results in monophyletic sister Eurasian and North American lineages, with North America further subdivided into eastern and western clades. Genetically anomalous isolates from the Italian presidential estate of Castelporziano are always part of a North American clade and group with eastern North America, upholding the hypothesis of recent, anthropogenically mediated dispersal. P ISG isolates from Mexico have phylogenetic affinity with both eastern and western North America. Results for an insertion in the mitochondrial rDNA suggest this molecule was obtained from the Heterobasidion S ISG, a taxon sympatric with the P ISG in western North America. These data are compatible with an eastern Eurasian origin of the species, followed by dispersal of two sister taxa into western Eurasia and into eastern North America over a Beringean land bridge, a pattern echoed in the phylogeography of other conifer-associated basidiomycetes.

Pharmakokinetische/pharmakodynamische Modelle für Inhalationsanästhetika

Pharmacokinetic models can be differentiated into two groups: physiological-based models and empirical models. Traditionally the pharmacokinetics of volatile anaesthetics are described using physiological-based models together with the respective tissue-blood distribution coefficients. The compartments of the empirical model have no anatomical equivalents and are merely the product of the mathematical procedure for parameter estimation. The end expiratory concentration of volatile anaesthetics is approximately equal to the arterial concentration and, therefore, the description of the transition between plasma and effect site for volatile anaesthetics plays a central role. The most important parameter here is the k(e0) value which is a time constant and describes the time delay for the transition from the central compartment to the calculated effect compartment. The k(e0) values for sevoflurane and isoflurane are the same but the concentration balance between the end-tidal concentration and the effect compartment occurs twice as quickly with desflurane. In clinical practice volatile anaesthetics are normally combined with N(2)O and/or opioids. This results in an additive interaction between volatile anaesthetics and N(2)O but a synergistic interaction of volatile anaesthetics with opioids. However, there are relatively few investigations on the interactions between the clinically widely used combination of volatile anaesthetics, N(2)O and opioids.

Reduction in anaesthetic drug consumption is correlated with mean titrated intra-operative Bispectral Index values

BACKGROUND

Several studies have shown a reduction in anaesthetic drug consumption with Bispectral Index (BIS) titration compared with standard clinical practice. However, the amount of reduction varied widely between 1% and 40%. We investigated the correlation between reduction in anaesthetic drug consumption and mean titrated BIS values.

METHODS

An analysis upon randomized controlled trials cited until January 2006 in MEDLINE and other databases investigating the potential reduction in anaesthetic (hypnotic) drug consumption with BIS titration was performed. Investigations with a marked difference (> 15%) in opioid drug consumption between the BIS group and the standard practice group were excluded. Correlations between amount of reduction in hypnotic drug use and the mean titrated BIS value were analysed with linear regression.

RESULTS

Fourteen manuscripts covering 2582 patients were included into the analysis. The mean BIS value in the standard clinical practice group averaged over all studies was 43.6 +/- 3.2 and the mean BIS value in the BIS-titrated group was 49.9 +/- 5.4. The amount of reduction in hypnotic drug use correlated significantly with the mean BIS values in the BIS-titrated groups (r =0.68) and with the differences between the mean BIS value in the BIS-titrated group and the mean BIS value in the standard clinical practice group (r = 0.70). Every point of BIS difference between the two groups resulted in a reduced hypnotic drug use of approximately 2%.

CONCLUSION

Despite differences in the study designs and in the drugs used, a linear correlation between the mean titrated BIS value and the hypnotic drug saving potential was found.

Depth of anaesthesia monitoring: what's available, what's validated and what's next?

Depth of anaesthesia monitors might help to individualize anaesthesia by permitting accurate drug administration against the measured state of arousal of the patient. In addition, the avoidance of awareness or excessive anaesthetic depth might result in improved patient outcomes. Various depth of anaesthesia monitors based on processed analysis of the EEG or mid-latency auditory-evoked potentials are commercially available as surrogate measures of anaesthetic drug effect. However, not all of them are validated to the same extent.

Wirkortäquilibration, Anschlagzeit, „time to peak effect“

Contrary to the situation in "classical" clinical pharmacology, non-steady state phenomena play a fundamental role for clinical pharmacology in anesthesia. Their understanding is of tantamount importance for the safe and efficient application of drugs relevant to anesthesia. Concepts like optimised target-controlled infusion (TCI), effect compartment targeting and the small margin of error tolerable during maintained spontaneous ventilation, force the anesthesiologist to acquire a firm understanding of the difference between the concentration time course at the effect side vs. time course of the plasma concentration. The underlying concepts, their application for the rational use of muscle relaxants, propofol with TCI systems, volatile anaesthetics and opioids will be discussed.

Impact of patient age on propofol consumption during propofol-remifentanil anaesthesia

BACKGROUND

This study was designed to investigate the impact of patient age on propofol consumption and recovery time using a propofol-remifentanil anaesthetic standardized with Narcotrend EEG monitoring. The Narcotrend is a monitor for measuring the depth of anaesthesia based upon a six-letter classification from A (awake) to F (increasing burst suppression) including 14 substages.

METHODS

In 200 patients scheduled for minor orthopaedic surgery Narcotrend EEG electrodes were positioned on the patient's forehead as recommended by the manufacturer. Anaesthesia was induced with remifentanil 0.4 microg kg(-1) min(-1) and 2 mg kg(-1) propofol. Immediately after intubation remifentanil was reduced to a constant rate of 0.2 microg kg(-1) min(-1) whereas a propofol infusion was now started at 3 mg kg(-1) h(-1) and then adjusted accordingly to achieve a target Narcotrend stages of D(0-2) indicating general anaesthesia. At the end of surgery the propofol and remifentanil infusions were stopped without tapering, the time to unstimulated opening of eyes was determined, and the propofol consumption (given as mg kg(-1) h(-1)) was calculated from the total amount of infused propofol but without the induction bolus, from the actual body weight and the duration of propofol infusion. Furthermore, a linear regression analysis was applied for propofol consumption vs. age.

RESULTS

The ages of the patients studied ranged from 16 to 83 yr old and patients were classified as ASA I-III. Propofol consumption significantly decreased with the patients' age: 30 yr of age or below the propofol consumption was calculated as 5.9 +/- 1.7 mg kg(-1) h(-1), for 31-50 yr as 5.4 +/- 1.8 mg kg(-1) h(-1), for 51-70 yr as 4.5 +/- 1.7 mg kg(-1) h(-1) and above 70 yr as 3.5 +/- 1.4 mg kg(-1) h(-1). Linear regression analysis revealed propofol (mg kg(-1) h(-1)) = 9.136 - (0.0597 x age (yr)); R = 0.53. Concomitantly, the recovery time to opening of eyes increased with the patients' age: < or = 30 yr, 7.4 +/- 3.7 min; 31-50 yr, 9.5 +/- 4.0 min; 51-70 yr, 9.8 +/- 4.1 min; and > or = 71 yr, 14.9 +/- 12.1 min.

CONCLUSIONS

We conclude that with Narcotrend guidance, mean propofol consumption and recovery times are age dependent. However, as a result of large inter-individual variability, age per se does not allow a prediction of individual propofol need or recovery time.

Bispectral index and A-line AAI index as guidance for desflurane-remifentanil anaesthesia compared with a standard practice group: a multicentre study † ‡

BACKGROUND

This study was designed to investigate the impact of bispectral index (BIS) or A-line AAI index (based on middle-latency auditory evoked potential) monitoring on recovery times and drug consumption when compared with standard anaesthetic practice during desflurane-remifentanil anaesthesia.

METHODS

After having obtained approval from the institutional review board and written informed consent, 200 adult patients undergoing minor surgical procedures were randomized to receive a desflurane-remifentanil anaesthetic controlled either solely by clinical parameters or by BIS or AAI to the following target values: during maintenance of anaesthesia to a value of '50' (BIS) or '30' (AAI), 15 min before the end of surgery to '60' (BIS) or '45' (AAI). Recovery times and drug consumption were recorded by a blinded investigator.

RESULTS

Compared with standard practice, patients with BIS or AAI monitoring needed similar desflurane concentrations (standard practice 2.9 [0.5] vol%, BIS 3.3 [0.9] vol%, AAI 2.6 [0.5] vol%), and had similar recovery times (open eyes 5.6 [2.5] min, 5.9 [3.4] min, 5.0 [3.1] min; extubation 6.3 [2.4] min, 6.6 [3.5] min, 5.6 [3.0] min; stating name 7.3 [2.4] min, 7.6 [3.5] min, 7.3 [6.6] min).

CONCLUSIONS

Compared with standard anaesthetic practice BIS and AAI guided titration to the used target ranges did not result in a reduction of desflurane consumption or recovery times during minor surgery with use of remifentanil.

Comparison of BIS and AAI as measures of anaesthetic drug effect during desflurane-remifentanil anaesthesia

BACKGROUND

Autoregressive modelling with exogenous input of the middle-latency auditory evoked potential has been developed for monitoring of anaesthetic depth. This study was designed to investigate the dose-response relationship between endtidal desflurane concentrations and the Alaris Autoregressive Index (AAI, Alaris Medical, Hampshire, UK, version 1.4) or the bispectral index (Aspect Medical Systems, Newton, MA, USA, version XP).

METHODS

Twenty-one patients scheduled for radical prostatectomy were investigated. After premedication and induction of anaesthesia with propofol und remifentanil all patients received atracurium and a remifentanil background infusion at a constant rate of 0.1 micro g kg(-1) min(-1). During dissection of the prostate, desflurane endtidal concentrations were varied between 3 and 9 vol%. Both AAI and BIS were determined and compared with the respective endtidal desflurane concentration.

RESULTS

None of the patients showed a significant change of AAI values while changing the desflurane concentrations between 3 and 9 vol%. The dose-response of BIS values and desflurane concentrations was not uniform: two patients showed increasing BIS values with increasing desflurane concentrations, while in three patients BIS values remained unchanged. In 16 patients decreasing BIS values adequately reflected an increase in desflurane concentrations.

CONCLUSION

Changes of desflurane concentrations during deep anaesthesia were adequately displayed only in 16 of 21 cases by BIS but in none of the cases by AAI monitoring.

Comparability of Narcotrend index and bispectral index during propofol anaesthesia

BACKGROUND

The dimensionless Narcotrend (NCT) index (MonitorTechnik, Germany, version 4.0), from 100 (awake) to 0, is a new index based on electroencephalogram pattern recognition. Transferring guidelines for titrating the Bispectral Index (BIS, Aspect Medical Systems, USA, version XP) to the NCT index depends on their comparability. We compared the relationship between BIS and NCT values during propofol anaesthesia.

METHODS

Eighteen adult patients about to have radical prostatectomy were investigated. An epidural catheter was placed in the lumbar space and electrodes for BIS and NCT were applied as recommended by the manufacturers. After i.v. fentanyl 0.1 mg, anaesthesia was induced with a propofol infusion. After intubation, patients received bupivacaine 0.5% 15 ml via the epidural catheter. Forty-five minutes after induction, the propofol concentration was increased to substantial burst suppression pattern and then decreased. This was done twice in each patient, and BIS and Narcotrend values were recorded at intervals of 5 s. The efficacy of NCT and BIS in predicting consciousness vs unconsciousness was evaluated using the prediction probability (P(K)).

RESULTS

We collected 38 629 artefact-free data pairs of BIS and NCT values from the respective 5-s epochs. Because of artefacts, another 5008 epochs had been excluded from data analysis (3855 epochs for the NCT index alone, 245 epochs for the BIS alone and 908 epochs for both indices). Mean (sd) values in awake patients were 94 (6) for Narcotrend and 91 (8) for BIS. With loss of the eyelash reflex, both values were significantly reduced, to 72 (9) for NCT (P<0.001) and to 77 (11) for the BIS index (P<0.001). The PK value for loss of eyelash reflex was similar for BIS (0.95) and NCT (0.93). Decreasing BIS values coincided with decreasing NCT values. A sigmoid model [NCT index=52.8+26.8/(1+exp(-(BIS-78.3)/4.8))(0.4); r=0.52] described the correlation between BIS and NCT index in a BIS range between 100 and 50. For BIS values lower than 50, a second sigmoid model with a correlation of r=0.83 was applied [NCT index=6.6+45.3/(1+exp(-(BIS-29.8)/2.4)) (0.6) r=0.83]. The relationship between burst suppression ratio (BSR) and NCT index was best described by the following sigmoid model: NCT index=265/(1+exp((-BSR+108)/-49); r=0.73.

CONCLUSIONS

We found a sufficient correlation between BIS and NCT index, but deviations from the line of identity in some ranges require attention. Therefore, a simple 1:1 transfer from BIS to NCT values is not adequate. Our results might serve as a blueprint for the rational translation of BIS into NCT values.

Comparison of Alaris AEP index and bispectral index during propofol-remifentanil anaesthesia

BACKGROUND

The Alaris AEP monitor(TM) (Alaris, UK, version 1.4) is the first commercially available auditory evoked potential (AEP) monitor designed to estimate the depth of anaesthesia. It generates an "Alaris AEP index" (AAI), which is a dimensionless number scaled from 100 (awake) to 0. This study was designed to compare AAI and BIS(TM) (Aspect, USA, version XP) values at different levels of anaesthesia.

METHODS

Adult female patients were premedicated with diazepam 0.15 mg kg(-1) orally on the morning of surgery. Electrodes for BIS and Alaris AEP monitoring and a headphone to give auditory stimuli were applied as recommended by the manufacturers. Anaesthesia was induced with remifentanil (0.4 microg kg(-1) min(-1)) and a propofol target-controlled infusion (Diprifusor(TM) TCI, AstraZeneca, Germany) to obtain a predicted concentration of initially 3.5 microg ml(-1). After loss of consciousness the patients were given 0.5 mg kg(-1) of atracurium. After tracheal intubation, remifentanil was given at 0.2 microg kg(-1) min(-1) and the propofol infusion was adjusted to obtain BIS target values of 30, 40, 50, and 60. AAI and BIS values were recorded and matched with the predicted propofol effect-site concentrations. Prediction probability was calculated for consciousness vs unconsciousness. Values are mean (SD).

RESULTS

Fifty female patients, 53 (15), range 18-78 yr, ASA I or II were studied. Mean values before induction of anaesthesia were 95 (4), range 99-82 for BIS and 85 (12), range 99-55 for AAI. With loss of eyelash reflex both values were significantly reduced to 64 (13), range 83-39 for BIS (P<0.05) and 61 (22), range 99-15 for AAI (P<0.05). The prediction probability P(K) for consciousness vs unconsciousness (i.e. loss of eyelash reflex) was better for BIS (P(K)=0.99) than for AAI (P(K)=0.79). At a BIS of 30, 40, 50, and 60 the corresponding AAI values were 15 (6), 20 (8), 28 (11), and 40 (16), and these were significantly different.

CONCLUSIONS

During propofol-remifentanil anaesthesia a decrease of the depth of anaesthesia as indicated by BIS monitoring is accompanied by corresponding effects shown by the AAI. However, wide variation in the awake values and considerable overlap of AAI values between consciousness and unconsciousness, suggests further improvement of the AAI system is required.

Bispectral index (BIS) and burst suppression: revealing a part of the BIS algorithm

OBJECTIVE

The bispectral index (BIS) is a complex EEG parameter which integrates several disparate descriptors of the EEG into a single variable. One of the subparameters incorporated in the BIS is the suppression ratio, quantifying the percentage of suppression during burst suppression pattern. The exact algorithm used to synthetize the information to the BIS value is unpublished and still unknown. This study provides insight into the integration of the suppression ratio into the BIS algorithm.

METHODS

EEG data of 10 healthy volunteers during propofol infusion were analyzed. Propofol concentrations were ramped up to 4 predetermined concentrations (1, 2, 3, 4, 6, 8, 9, or 12 microg/ml) using a computer controlled infusion pump (STANPUMP). EEG recordings were performed with an Aspect A-1000 EEG monitor (Version 3.22). The relationship of the processed EEG variables bispectral index and suppression ratio, calculated by the Aspect A-1000 monitor, was analyzed.

RESULTS

Up to 40% suppression ratio the average BIS values remained constant regardless of suppression ratios (r = 0.13). Beyond a suppression ratio of 40%, BIS and suppression ratio were invariably linearly correlated (r = -1). At a suppression ratio > or = 40% the BIS value could be calculated as BIS = 50 - suppression ratio/2.

CONCLUSIONS

Suppression ratio values > 40% are linearly correlated with BIS values from 30 to 0. An increasing anesthetic drug effect resulting in an increase of the duration of suppression to a suppression ratio up to 40% is not adequately reflected by the BIS value.

Opioid-induced respiratory depression is associated with increased tidal volume variability

BACKGROUND AND OBJECTIVE

mu-agonistic opioids cause concentration-dependent hypoventilation and increased irregularity of breathing. The aim was to quantify opioid-induced irregularity of breathing and to investigate its time-course during and after an opioid infusion, and its ability to predict the severity of respiratory depression.

METHODS

Twenty-three patients breathing spontaneously via a continuous positive airway pressure (CPAP) mask received an intravenous (i.v.) infusion of alfentanil (2.3 microg kg(-1) min(-1), 14 patients) or pirinitramide (piritramide) (17.9 microg kg(-1) min(-1), nine patients) until either a cumulative dose of 70 microg kg(-1) for alfentanil or 500 microg kg(-1) for pirinitramide had been achieved or the infusion had to be stopped for safety reasons. Tidal volumes (VT) and minute ventilation were measured with an anaesthesia workstation. For every 20 breaths, the quartile coefficient was calculated (Qeff20V(T)).

RESULTS

Both the decrease of minute volume and the increase of Qeff20V(T) during and after opioid infusion were highly significant (P < 0.001, ANOVA). Patients in which the alfentanil infusion had to be terminated prematurely had lower minute volumes (P = 0.002, t-test) and higher Qeff20V(T) (P = 0.034, t-test) than those who received the complete dose. Changes in the regularity of breathing measured as Qeff20V(T) parallel those of minute ventilation during and after opioid infusion.

CONCLUSIONS

Opioids cause a more complicated disturbance of the control of respiration than a mere resetting to higher PCO2. Furthermore, Qeff20V(T) appears to predict the severity of opioid-induced respiratory depression.

Application of semilinear canonical correlation to the measurement of the electroencephalographic effects of volatile anaesthetics

BACKGROUND AND OBJECTIVE

The common parameters of the electroencephalogram quantify a shift of its power spectrum towards lower frequencies with increasing anaesthetic drug concentrations (e.g. spectral-edge frequency 95). These ad hoc parameters are not optimized for the content of information with regard to drug effect. Using semilinear canonical correlation, different frequency ranges (bins) of the power spectrum can be weighted for sensitivity to changes of drug concentration by multiplying their power with iteratively determined coefficients, yielding a new (canonical univariate) electroencephalographic parameter.

METHODS

Electroencephalographic data obtained during application of volatile anaesthetics were used: isoflurane (n = 6), desflurane (7), sevoflurane (7), desflurane during surgical stimulation (12). Volatile anaesthetic end-tidal concentrations varied between 0.5 and 1.6 minimum alveolar concentration (MAC). The canonical univariate parameter and spectral-edge frequency 95 were determined and their correlation with the volatile anaesthetic effect compartment concentration, obtained by simultaneous pharmacokinetic-pharmacodynamic modelling, were compared.

RESULTS

The canonical univariate parameter with individually optimized coefficients, but not with mean coefficients, was superior to the spectral-edge frequency 95 as a measure of anaesthetic drug effect. No significant differences of the coefficients were found between the three volatile anaesthetics or between the data with or without surgical stimulus. The coefficients for volatile anaesthetics were similar to the coefficients for opioids, but different from coefficients for propofol and midazolam.

CONCLUSIONS

The canonical univariate parameter calculated with individually optimized coefficients, but not with mean coefficients, correlates more accurately and consistently with the effect site concentrations of volatile anaesthetics than with spectral-edge frequency 95.

Onset of propofol-induced burst suppression may be correctly detected as deepening of anaesthesia by approximate entropy but not by bispectral index

The bispectral index (BIS) is a complex EEG variable that combines several disparate descriptors of the EEG into a single value. Approximate entropy is a novel EEG measure that quantifies the regularity of a data time series such as EEG. We report two patients in which the EEG effect of propofol was quantified very similarly by BIS and approximate entropy. However, at the beginning of burst suppression of the EEG, BIS did not indicate an increased anaesthetic drug effect, while approximate entropy did.

Pharmacodynamic interaction of nitrous oxide with sevoflurane, desflurane, isoflurane and enflurane in surgical patients: measurements by effects on EEG median power frequency

BACKGROUND AND OBJECTIVE

This study investigates the interaction of sevoflurane and nitrous oxide on EEG median power frequency of 2.5 Hz during surgery.

METHODS

Sevoflurane concentrations required for electroencephalographic median power frequency between 2 and 3 Hz were measured in 25 patients during gynaecological laparotomies. Nitrous oxide was randomly administered at 0, 20, 40, 60 and 75 vol%, subsequently two different concentrations in each patient. The data were analysed using isobolographic analysis together with previously published data on nitrous oxide-isoflurane, -enflurane, or -desflurane interaction.

RESULTS

The interaction is described by the equation: C volatile anaesthetic/C0 volatile anaesthetic + C N2O/C0 N2O=1 (C is the concentrations for a drug combination to achieve the desired effect; C0 is the concentration for single drug use). The parameters are C0 isoflurane=1.11 vol% (95% CI 1.03-1.19), C0 enflurane=1.64 (1.52-1.77), C0 desflurane=5.31 (4.92-5.73), C0 sevoflurane=2.12 (1.96-2.29), C0 N2O=174 (153-202). These parameters decrease by 6% (2.5-10) for every 10 years of patients' age > 40 years.

CONCLUSIONS

The interaction is compatible with additivity. The potency of nitrous oxide to substitute the volatile anaesthetics is less than anticipated from previously reported MAC values.

Shannon entropy applied to the measurement of the electroencephalographic effects of desflurane

BACKGROUND

The Shannon entropy is a standard measure for the order state of sequences. It quantifies the degree of skew of the distribution of values. Increasing hypnotic drug concentrations increase electroencephalographic amplitude. The probability density function of the amplitude values broadens and flattens, thereby changing from a skew distribution towards equal distribution. We investigated the dose-response relation of the Shannon entropy of the electroencephalographic amplitude values during desflurane monoanesthesia in comparison with previously used electroencephalographic parameters.

METHODS

Electroencephalographic records previously obtained in 12 female patients during gynecologic laparotomies were reanalyzed. Between opening and closure of the peritoneum, desflurane vapor settings were varied between 0.5 and 1.6 minimum alveolar concentration. Electroencephalographic Shannon entropy, approximate entropy, median electroencephalographic frequency, SEF 95, total power, log total power, and Bispectral Index were determined, and their correlations with the desflurane effect compartment concentration, obtained by simultaneous pharmacokinetic-pharmacodynamic modeling, were compared.

RESULTS

The electroencephalographic Shannon entropy increased continuously over the observed concentration range of desflurane. The correlation of the Shannon entropy (R2 = 0.84+/-0.08, mean +/- SD) with the desflurane effect compartment concentrations is similar to approximate entropy (R2 = 0.85+/-0.12), SEF 95 (R2 = 0.85+/-0.10), and Bispectral Index (R2 = 0.82+/-0.13) and is more statistically significant than median frequency (R2 = 0.72+/-0.17), total power (R2 = 0.67+/-0.18), and log total power (R2 = 0.80+/-0.09).

CONCLUSIONS

The Shannon entropy seems to be a useful electroencephalographic measure of anesthetic drug effect.

Surgical Stimulation Shifts EEG Concentration–Response Relationship of Desflurane

Background

Anesthesiologists routinely increase the delivered anesthetic concentration before surgical stimulation in anticipation of increased anesthetic requirement to achieve certain goals (e.g., amnesia, unconsciousness, and immobility). Electroencephalographic monitoring is one method of determining indirectly anesthetic effect on the brain. The present study investigated the effect of surgical stimuli on the concentration-response relation of desflurane-induced electroencephalographic changes.

Methods

The electroencephalographic activity was recorded from 24 female patients who received only desflurane after a single induction dose of propofol. Twelve patients served as a control group before surgical stimulation. The other 12 patients, all undergoing lower abdominal surgery, were investigated between opening and closure of the peritoneum. Desflurane vaporizer settings were randomly increased and decreased between 0.5 and 1.6 minimum alveolar concentration as long as anesthesia was considered adequate. Spectral edge frequency 95, median power frequency, and Bispectral Index were calculated. Desflurane effect-site concentrations and the concentration-effect curves for spectral edge frequency 95, median power frequency, and Bispectral Index were determined by simultaneous pharmacokinetic and pharmacodynamic modeling.

Results

Surgical stimulation shifted the desflurane concentration-electroencephalographic effect curves for spectral edge frequency 95, median power frequency, and Bispectral Index toward higher desflurane concentrations. In the unstimulated group, 2.2 +/- 0.74 vol% desflurane were necessary to achieve a Bispectral Index of 50, whereas during surgery, 6.8 +/- 0.98 vol% (mean +/- SE) were required.

Conclusions

During surgery, higher concentrations of the volatile anesthetic are required to achieve a desired level of cortical electrical activity and, presumably, anesthesia.

Electroencephalogram approximate entropy correctly classifies the occurrence of burst suppression pattern as increasing anesthetic drug effect

BACKGROUND

Approximate entropy, a measure of signal complexity and regularity, quantifies electroencephalogram changes during anesthesia. With increasing doses of anesthetics, burst-suppression patterns occur. Because of the high-frequency bursts, spectrally based parameters such as median electroencephalogram frequency and spectral edge frequency 95 do not decrease, incorrectly suggesting lightening of anesthesia. The authors investigated whether the approximate entropy algorithm correctly classifies the occurrence of burst suppression as deepening of anesthesia.

METHODS

Eleven female patients scheduled for elective major surgery were studied. After propofol induction, anesthesia was maintained with isoflurane only. Before surgery, the end-tidal isoflurane concentration was varied between 0.6 and 1.3 minimum alveolar concentration. The raw electroencephalogram was continuously recorded and sampled at 128 Hz. Approximate entropy, electroencephalogram median frequency, spectral edge frequency 95, burst-suppression ratio, and burst-compensated spectral edge frequency 95 were calculated offline from 8-s epochs. The relation between burst-suppression ratio and approximate entropy, electroencephalogram median frequency, spectral edge frequency 95, and burst-compensated spectral edge frequency 95 was analyzed using Pearson correlation coefficient.

RESULTS

Higher isoflurane concentrations were associated with higher burst-suppression ratios. Electroencephalogram median frequency (r = 0.34) and spectral edge frequency 95 (r = 0.29) increased, approximate entropy (r = -0.94) and burst-compensated spectral edge frequency 95 (r = -0.88) decreased with increasing burst-suppression ratio.

CONCLUSION

Electroencephalogram approximate entropy, but not electroencephalogram median frequency or spectral edge frequency 95 without burst compensation, correctly classifies the occurrence of burst-suppression pattern as increasing anesthetic drug effect.

Free and bound leptin levels during human pregnancy

Leptin is a hormone secreted from adipocytes and trophoblasts which might influence energy metabolism during gestation. In this study we evaluated the course of free and bound leptin levels in 22 healthy pregnant women and compared these values to those in non-pregnant women matched for body mass index (BMI) and age. Serum concentrations of both leptin components and plasma levels of estradiol, progesterone, insulin, non-esterified fatty acids and glucose were measured at each trimester. The BMI increased from the first to the second trimester (22.8 +/- 3.1 and 24.7 +/- 2.9, respectively; p < 0.05) and remained stable thereafter (third trimester 25.3 +/- 2.9 kg/m2). Free leptin and bound leptin did not differ between patients and controls in the first trimester of pregnancy. Free leptin levels increased from the first (122 (60)) to the second trimester (181 (60) pmol/l; p < 0.05) and remained constant (third trimester 181 (76) pmol/l; difference between second and third trimesters, NS). Bound leptin increased from the second (0.43 (0.16)) to the third trimester (0.57 (0.21) nmol/l; p < 0.05). Only bound leptin was higher in the patient group in the third trimester compared to controls (p < 0.01). Our findings of a shift in free leptin to bound leptin in late pregnancy may indicate different physiological roles for both components. Free leptin may reflect maternal fat stores, whereas bound leptin may regulate maternal metabolism via central effects on food intake and energy expenditure.

Approximate entropy as an electroencephalographic measure of anesthetic drug effect during desflurane anesthesia

BACKGROUND

The authors hypothesized that the electroencephalogram (EEG) during higher anesthetic concentrations would show more "order" and less "randomness" than at lower anesthetic concentrations. "Approximate entropy" is a new statistical parameter derived from the Kolmogorov-Sinai entropy formula which quantifies the amount of regularity in data. The approximate entropy quantifies the predictability of subsequent amplitude values of the EEG based on the knowledge of the previous amplitude values. The authors investigated the dose-response relation of the EEG approximate entropy during desflurane anesthesia in comparison with spectral edge frequency 95, median frequency, and bispectral index.

METHODS

Twelve female patients were studied during gynecologic laparotomies. Between opening and closure of the peritoneum, end-tidal desflurane concentrations were varied between 0.5 and 1.6 minimum alveolar concentration (MAC). The EEG approximate entropy, median EEG frequency, spectral edge frequency 95, and bispectral index were determined and the performance of each to predict the desflurane effect compartment concentration, obtained by simultaneous pharmacokinetic-pharmacodynamic modeling, was compared.

RESULTS

Electroencephalogram approximate entropy decreased continuously over the observed concentration range of desflurane. The performance of the approximate entropy (prediction probability PK = 0.86 +/- 0.06) as an indicator for desflurane concentrations is similar to spectral edge frequency 95 (PK = 0.86 +/- 0.06) and bispectral index (PK = 0.82 +/- 0.06) and is statistically significantly better than median frequency (PK = 0.78 +/- 0.06).

CONCLUSIONS

The amount of regularity in the EEG increases with increasing desflurane concentrations. The approximate entropy could be a useful EEG measure of anesthetic drug effect.

Effect of human corticotropin-releasing hormone on gonadotropin secretion in cycling and postmenopausal women

OBJECTIVE

To test the hypothesis that corticotropin-releasing hormone (CRH) is linked to stress-associated reproductive dysfunction in the human by determining if the administration of human corticotropin-releasing hormone (hCRH) results in an inhibition of gonadotropin secretion.

DESIGN

Twenty-four-hour prospective study with frequent (every 10 minutes) blood sampling.

SETTING

University Clinical Research Center.

INTERVENTIONS

Sequential 8-hour infusions of normal saline, hCRH (1 to 5 micrograms/kg per hour), and hCRH plus naloxone (2 mg/h).

SUBJECTS

Four normal cycling women and four postmenopausal women.

MAIN OUTCOME MEASURES

Plasma luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), and adrenal and ovarian steroids.

RESULTS

In response to hCRH, a prompt and sustained rise in cortisol (F) was noted in both normal cycling women and postmenopausal women. No inhibition of LH or FSH was noted during either the hCRH or hCRH plus naloxone infusion in either group of women. Unexpectedly, elevations in the mean LH peak amplitude and the transverse mean LH concentration were noted in the postmenopausal women during the infusion of hCRH as compared with saline. The infusion of hCRH had no apparent effect on concentrations of PRL, FSH, and gonadal and adrenal steroids (except for F).

CONCLUSIONS

Under these conditions, intravenously administered hCRH has no inhibitory effect on gonadotropin secretion in either premenopausal or postmenopausal women. The mechanism by which stress exerts its deleterious effect on reproductive function in the human remains unknown.