Humidity and measurement of volatile propofol using MCC-IMS (EDMON)

The bedside Exhaled Drug MONitor - EDMON measures exhaled propofol in ppbv every minute based on multi-capillary column - ion mobility spectrometry (MCC-IMS). The MCC pre-separates gas samples, thereby reducing the influence of the high humidity in human breath. However, preliminary analyses identified substantial measurement deviations between dry and humid calibration standards. We therefore performed an analytical validation of the EDMON to evaluate the influence of humidity on measurement performance. A calibration gas generator was used to generate gaseous propofol standards measured by an EDMON device to assess linearity, precision, carry-over, resolution, and the influence of different levels of humidity at 100% and 1.7% (without additional) relative humidity (reference temperature: 37°C). EDMON measurements were roughly half the actual concentration without additional humidity and roughly halved again at 100% relative humidity. Standard concentrations and EDMON values correlated linearly at 100% relative humidity (R²=0.97). The measured values were stable over 100min with a variance ≤ 10% in over 96% of the measurements. Carry-over effects were low with 5% at 100% relative humidity after 5min of equilibration. EDMON measurement resolution at 100% relative humidity was 0.4 and 0.6 ppbv for standard concentrations of 3 ppbv and 41 ppbv. The influence of humidity on measurement performance was best described by a second-order polynomial function (R²≥0.99) with influence reaching a maximum at about 70% relative humidity. We conclude that EDMON measurements are strongly influenced by humidity and should therefore be corrected for sample humidity to obtain accurate estimates of exhaled propofol concentrations.

Treatment of intraoperative hypotension with cafedrine/theodrenaline versus ephedrine : A prospective, national, multicenter, non-interventional study-the HYPOTENS trial

BACKGROUND

Sympathomimetic drugs are a therapeutic cornerstone for the management of hypotensive states like intraoperative hypotension (IOH). While cafedrine/theodrenaline (C/T) is widely used in Germany to restore blood pressure in patients with IOH, more research is required to compare its effectiveness with alternatives such as ephedrine (E) that are more commonly available internationally.

METHODS

HYPOTENS (NCT02893241, DRKS00010740) was a prospective, national, multicenter, open-label, two-armed, non-interventional study that compared C/T with E for treatment of IOH. We describe a prospectively defined cohort of patients ≥50 years old with comorbidities undergoing general anesthesia induced with propofol and fentanyl. Primary objectives were to examine treatment precision, rapidity of onset and the ability to restore blood pressure without relevant increases in heart rate. Secondary endpoints were treatment satisfaction and the number of required additional boluses or other accompanying measures.

RESULTS

A total of 1496 patients were included in the per protocol analysis. Overall, effective stabilization of blood pressure was achieved with both C/T and E. Post-hoc analysis showed that blood pressure increase from baseline was more pronounced with C/T. Fewer additional boluses or other accompanying measures were required in the C/T arm. The incidence of tachycardia was comparable between groups. Post-hoc analysis showed that E produced dose-dependent elevated heart rate values. By contrast, heart rate remained stable in patients treated with C/T. Physicians reported a higher level of treatment satisfaction with C/T, with a higher proportion of anesthetists rating treatment precision and rapidity of onset as good or very good when compared with E.

CONCLUSION

Neither drug was superior in restoring blood pressure levels; however, post-hoc analyses suggested that treatment is more goal-orientated and easier to control with C/T. Heart rate was shown to be more stable with C/T and fewer additional interventions were required to restore blood pressure, which could have contributed to the increased treatment satisfaction reported by anesthetists using C/T.

Adherence of volatile propofol to various types of plastic tubing

Propofol is an intravenous anesthetic. Currently, it is not possible to routinely measure blood concentration of the drug in real time. However, multi-capillary column ion-mobility spectrometry of exhaled gas can estimate blood propofol concentration. Unfortunately, adhesion of volatile propofol on plastic materials complicates measurements. Therefore, it is necessary to consider the extent to which volatile propofol adheres to various plastics used in sampling tubing. Perfluoralkoxy (PFA), polytetrafluorethylene (PTFE), polyurethane (PUR), silicone, and Tygon tubing were investigated in an experimental setting using a calibration gas generator (HovaCAL). Propofol gas was measured for one hour at 26 °C, 50 °C, and 90 °C tubing temperature. Test tubing segments were then flushed with N₂ to quantify desorption. PUR and Tygon sample tubing absorbed all volatile propofol. The silicone tubing reached the maximum propofol concentration after 119 min which was 29 min after propofol gas exposure stopped. The use of PFA or PTFE tubing produced comparable and reasonably accurate propofol measurements. The desaturation time for the PFA was 10 min shorter at 26 °C than for PTFE. PFA tubing thus seems most suitable for measurement of volatile propofol, with PTFE as an alternative.

Two different approaches for pharmacokinetic modeling of exhaled drug concentrations

Online measurement of drug concentrations in patient's breath is a promising approach for individualized dosage. A direct transfer from breath- to blood-concentrations is not possible. Measured exhaled concentrations are following the blood-concentration with a delay in non-steady-state situations. Therefore, it is necessary to integrate the breath-concentration into a pharmacological model. Two different approaches for pharmacokinetic modelling are presented. Usually a 3-compartment model is used for pharmacokinetic calculations of blood concentrations. This 3-compartment model is extended with a 2-compartment model based on the first compartment of the 3-compartment model and a new lung compartment. The second approach is to calculate a time delay of changes in the concentration of the first compartment to describe the lung-concentration. Exemplarily both approaches are used for modelling of exhaled propofol. Based on time series of exhaled propofol measurements using an ion-mobility-spectrometer every minute for 346 min a correlation of calculated plasma and the breath concentration was used for modelling to deliver R(2) = 0.99 interdependencies. Including the time delay modelling approach the new compartment coefficient k(e0lung) was calculated to k(e0lung) = 0.27 min(-1) with R(2) = 0.96. The described models are not limited to propofol. They could be used for any kind of drugs, which are measurable in patient's breath.

[Basic algorithm for Point-of-Care based hemotherapy: perioperative treatment of coagulopathic patients]

During perioperative treatment of coagulopathic patients the so-called Point-of-Care (POC) analyses enable more rapidly available and more comprehensive hemostatic analyses compared to routinely performed conventional coagulation testing, such as activated partial thromboplastin time (aPTT), international normalized ratio (INR), fibrinogen concentration and platelet count. In this review article a hemotherapy algorithm is presented which is based on viscoelastic and aggregometric POC measurements. The algorithm was designed double sided and consists of a general and a special part. The general part contains boxes and fields for sociodemographic data and gives general recommendations for coagulation management and therapy specifications for particular patient collectives and presents proposals for emergency reversal of anticoagulation therapy. The special part refers to basic physiological conditions for hemostasis and asks for measurement results of clot initiation, clot firmness, clot stability and platelet function analyses. Reference values were defined for each parameter and therapeutic options are presented. In cases of persistent coagulopathy despite algorithm-conform therapy, the algorithm could be run through once again. Finally, the algorithm presents therapeutic options for an ultima ratio therapy approach.

Impact of platelets and fresh frozen plasma in contrast to red cell concentrate on unstimulated and stimulated cytokine release in an in vitro model of transfusion

Transfusion of blood may contribute to immunomodulation. Leuco-depleted standard blood products are supposed to result in less immunomodulation compared with whole blood. To determine the influence of leuco-depleted blood products on the cytokine response, red blood cell concentrates (RBC), fresh frozen plasma (FFP) and platelet concentrates (PC) were investigated in an in vitro model of blood transfusion. Leuco-depleted standard blood bank RBC, FFP and PC were mixed in vitro with AB0 compatible venous blood from healthy volunteers in ratios of 3:1, 1:1 and 1:3. Specimens were incubated in presence or absence of lipopolysaccharide, 1 mug/ml. After 24 h of incubation cytokine release of tumour necrosis factor (TNF)-alpha and interleukin-10 (IL-10) was measured in cell culture supernatants by means of enzyme-linked immunsorbent assay. Addition of RBC, FFP and PC to venous blood from healthy volunteers led to a significant and dose-dependent increase in spontaneous TNF-alpha and IL-10 release. After endotoxin stimulation, RBC, FFP and PC significantly suppressed the TNF-alpha response, while the stimulated release of IL-10 tended to increase, reaching significance only after high doses of FFP. Addition of leuco-depleted blood products changed the spontaneous and stimulated cytokine response in an in vitro model of transfusion. These data may suggest a possible contribution of transfused FFP and PC to immunomodulation after transfusion similar to RBC.

[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.

[Remifentanil-propofol versus fentanyl-midazolam combinations for intracranial surgery: influence of anaesthesia technique and intensive sedation on ventilation times and duration of stay in the ICU]

INTRODUCTION

After neurosurgery patients often need to be sedated and ventilated in the intensive care unit (ICU). However, rapid postoperative recovery and neurological examination are particularly important for the early recognition of complications. In this retrospective study two different strategies of anaesthesia technique and ICU sedation (fentanyl-midazolam versus remifentanil-propofol) were compared.

METHODS

Intraoperatively, patients received continuous infusions of either fentanyl (0.2-1.0 mg/h) and midazolam (2-10 mg/h) or remifentanil (0.2-0.5 microg/kg body weight/min) and propofol (3-6 mg/kg body weight/h). After arrival in the ICU fentanyl (0.03-0.2 mg/h) and midazolam (2-12 mg/h) or remifentanil (0.1-0.2 microg/kg body weight/min) and propofol (0.5-3 mg/kg body weight/h) were infused to reach a Ramsay score of 4. The times between termination of infusion and extubation and the length of stay in the ICU were examined.

RESULTS

A total of 60 patients (n=30 each group) undergoing supratentorial brain tumour surgery were enrolled. The groups were comparable for age, weight, ASA status (American Society of Anesthesiologists) and duration of drug administration (remifentanil-propofol 528+/-382 min versus fentanyl-midazolam 548+/-360 min). Extubation times were significantly shorter after remifentanil-propofol (47 min) than after fentanyl-midazolam (481 min), and the length of stay in the ICU was also significantly reduced (1.8 days versus 3.7 days). As a result of prolonged unconsciousness and impaired neurological assessability, a brain CT scan was necessary in 3 patients after fentanyl-midazolam to exclude neurosurgical complications.

CONCLUSION

This retrospective study demonstrates that remifentanil-propofol anaesthesia and ICU sedation are superior to the combination of fentanyl and midazolam in terms of ventilation time and length of ICU stay. Moreover, the use of fentanyl-midazolam may lead to unnecessary CT scans.

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.

[Placenta praevia totalis et increta. Cause of life-threatening haemorrhaging during a caesarean section]

Placenta increta is a rare but potentially life-threatening risk constellation after a previous caesarean section. We present the case of a 29-year-old gravida 2 para 1 patient, who developed dramatic haemorrhaging caused by this abnormal placentation, which could only be resolved by a postpartal hysterectomy. This demonstrates that in the case of a combination of the two most common predisposing factors, repeat caesarean section and placenta praevia, the possibility of a placenta increta should be considered and suitable precautions should be taken.

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.

Desfluran und Isofluran bei Niedrigflussnarkosen

BACKGROUND

In the present investigation we compared the consumption of desflurane (DES) and isoflurane (ISO) using a standardized minimal-flow protocol with a forced reduction of the fresh gas flow (FGF).

METHODS

54 adult women were examined. After induction of anaesthesia a forced reduction of the FGF was started: 5 min 0.5 l/min O(2) + 1 l/min N(2)O, 10 min 0.5 l/min O(2) + 0.5 l/min N(2)O; finally 0.3 l/min O(2) + 0.2 l/min N(2)O up to the end of surgery. The consumption of DES/ISO was determined with a precision balance.

RESULTS

In the DES group the uptake was around 0.3 vol-%, i.e. less than 8% of the target 2/3 MAC value was taken up. For ISO the uptake was around 0.25 vol-%, i.e. the uptake was approximately 30% of the target 2/3-MAC value. The DES consumption was after 60 min 17.0+/-1.1 g, 120 min--27.3+/-1.8 g and 180 min--36.5+/-1.7 g. ISO consumption was significantly lower: 7.6+/-0.8 g, 12.4+/-1.7 g and 15.5+/-1.6 g. The use of DES yielded higher costs, i.e. 2.28 EUR for 60 min, 3.63 EUR for 120 min and 4.97 EUR for 180 min. The consumption of the inhaled anaesthetics can be calculated as: DES (g)=4.84+0.184 x duration (min) (R(2)=0.981), ISO (g)=2.049+0.0826 x duration (R(2)=0.979). The costs are: DES (EUR)=0.85+0.0323 x duration (min); ISO (EUR)=0.19+0.0077 x duration (min).

CONCLUSION

With a forced reduction of the FGF the DES consumption is still higher.

The Narcotrend monitor

The Narcotrend (MonitorTechnik, Bad Bramstedt, Germany) is an EEG monitor designed to measure the depth of anaesthesia. It has been developed at the University Medical School of Hannover, Germany, has been commercially available for 5 years and has meanwhile received US Food and Drug Administration approval. The Narcotrend algorithm is based on pattern recognition of the raw electroencephalogram (EEG) and classifies the EEG traces into different stages from A (awake) to F (increasing burst suppression down to electrical silence). The newest Narcotrend software version includes a dimensionless Narcotrend index from 100 (awake) to 0 (electrical silence). The raw EEG signal can be recorded by standard electrocardiogram electrodes for single- and double-channel registration. The Narcotrend monitor provides a vast amount of information: the actual Narcotrend stage and index, the trend ('cerebrogram'), the raw EEG signal and a power spectrum and several derived EEG parameters. Multiple clinical and validation studies are available for the Narcotrend monitor, including comparisons with the BIS monitor (Aspect Medical Systems, Natick, USA).

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.

Einfluss des Geschlechts auf Propofolverbrauch und Aufwachzeiten bei standardisierter Anästhesietiefe

INTRODUCTION

We investigated gender differences of drug consumption and recovery times for propofol-remifentanil anaesthesia.

METHODS

Adult patients scheduled for minor orthopaedic surgery were randomised to receive a propofol-remifentanil anaesthesia controlled either by EEG monitoring (Narcotrend or BIS) or solely by clinical parameters. Anaesthesia was induced with remifentanil 0.4 microg/kg/min and a propofol target-controlled infusion (TCI) at 3.5 microg/ml. After intubation remifentanil was reduced to 0.2 microg/kg/min whereas propofol TCI was adjusted according to clinical parameters or to the following EEG target values: during maintenance to "D(0)" (Narcotrend) or "50" (BIS), 15 min before the end of surgery to "C(1)" (Narcotrend) or "60" (BIS). Recovery times were recorded and average normalised propofol consumption was calculated from induction and maintenance doses.

RESULTS

A total of 60 male and 60 female patients completed the study. Gender differences were observed for recovery times (with standard practice) and for propofol consumption (with BIS monitoring). In the standard protocol group, propofol consumption was nearly identical for male and female patients whereas recovery times were significantly longer in the male group. In both EEG-guided groups propofol consumption was less for male patients while recovery times were slightly longer. In the group of female patients higher propofol TCI concentrations had to be used to reach the same BIS or Narcotrend values.

CONCLUSION

With propofol-remifentanil anaesthesia, gender has impact on recovery times and propofol consumption. If the same amounts of propofol are applied, males awake later, with BIS or Narcotrend monitoring males receive less propofol for comparable EEG effects.

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.

[The Narcotrend monitor. Development and interpretation algorithms]

The Narcotrend performs an automatic interpretation of the electroencephalogram (EEG) during anaesthesia. The classification algorithms have been developed on the basis of visually classified EEG epochs. The classification scheme which was used for these visual assessments has its origin in sleep analysis and was adapted for the EEG during anaesthesia. From the awake state to very deep anaesthesia, 15 stages (A, B(0-2), C(0-2), D(0-2), E(0-2), F(0-1)) are distinguished. The transformation of these stages into a numerical scale from 100 to 0 is a further refinement for a differentiated presentation of EEG effects. For the automatic classification multivariate discriminant functions are used. Age-related changes of the EEG were incorporated. The device contains functions for the identification of artifacts. The EEG can be recorded from a frontal channel using standard ECG electrodes, other electrode positions and types can be chosen. The device has been clinically and scientifically validated.

Bispektralindex und Desflurankonzentration unter 1�MAC

INTRODUCTION

We investigated the relationship between bispectral index (BIS, A-2000, Aspect Medical Systems, USA) and end-tidal desflurane concentrations below 1 MAC which is especially the range of interest if desflurane is combined with remifentanil for fast-track anaesthesia.

METHODS

With institutional review board approval and written informed consent we investigated 50 adult ASA I-III patients scheduled for minor orthopaedic surgical procedures. The BIS electrode (BIS-Sensor, Aspect Medical Systems, USA) was positioned on the patient's forehead as recommended by the manufacturer. All patients were premedicated with 0.15 mg x kg(-1) diazepam orally in the evening and on the morning before surgery. Induction of anaesthesia was started with a remifentanil infusion at 0.4 micro g x kg(-1) x min(-1) and 5 min later 2 mg x kg(-1) propofol was given for hypnosis. Immediately after intubation, remifentanil was reduced to 0.2 micro g x kg(-1) x min(-1), and the depth of anaesthesia was adjusted according to clinical needs by regulating the desflurane concentration. Starting 20 min after induction, a total of 1,483 data pairs, i.e. end-tidal desflurane concentrations with corresponding BIS values, was recorded. During surgery data pairs were analysed by linear regression analysis for each patient separately. During emergence from anaesthesia, desflurane effect compartment concentrations were simulated and non-linear regression analysis was applied.

RESULTS

We found a relationship between BIS ranges and mean end-tidal desflurane concentrations: A BIS range of 100-85 was related to 1.1+/-0.7 vol%, BIS 84-65 to 1.5+/-1.2 vol%, BIS 64-50 to 2.9+/-1.3 vol% and BIS 49-40 to 3.1+/-0.9 vol%. In particular, end-tidal desflurane concentrations related to these BIS ranges were significantly different from each other (ANOVA; P<0.05). Intraoperatively, we obtained a correlation coefficient of R=0.42+/-0.24 (mean+/-SD, range 0.05-0.96), during emergence from anaesthesia the correlation coefficient was R=0.84+/-0.12 (range 0.61-0.99).

CONCLUSION

We could demonstrate a relationship between bispectral index and end-tidal desflurane concentrations below 1 MAC with a BIS range of 49-40 being associated with approximately 0.5 MAC of desflurane during desflurane-remifentanil-anaesthesia.

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.

[Remifentanil. An update]

Remifentanil is a 4-anilidopiperidine mu-opioid analgesic which is rapidly metabolized by unspecific blood and tissue esterases. According to its unique pharmacokinetic profile, remifentanil-based anaesthesia combines high-dosage opioid analgesia intraoperatively with a rapid and predictable postoperative awakening. When compared with a standard fentanyl-based technique, the use of remifentanil has changed our present anaesthetic regimens. This includes the anaesthesia induction sequence, the choice and dosage of anaesthetics when used as adjuncts to remifentanil, and even more, the proper planning of postoperative pain management. The present paper was designed to review the current knowledge on remifentanil and all aspects of its use in anaesthesiology. In addition, present data on the use of remifentanil for analgesia and sedation of the critically ill patient are summarized.

[Narcotrend EEG monitoring during total intravenous anaesthesia in 4.630 patients]

INTRODUCTION

The Narcotrend is a new EEG monitor designed to measure the hypnotic component of anaesthesia; however, a major clinical evaluation is still missing. This prospective multicentre study was designed to investigate the feasibility of Narcotrend monitoring in a large number of patients under different clinical conditions and to define its impact on recovery times after propofol-based total intravenous anaesthesia.

METHODS

After legal authority approval and patients'informed consent had been obtained, total intravenous anaesthesia was induced and maintained with propofol and an opioid analgesic at the discretion of the attending anaesthesiologist. In the first 10-15 patients of each centre the anaesthesiologist was blinded to the Narcotrend recordings and propofol was dosed according to clinical needs. In the following patients propofol was infused at a rate sufficient to achieve a target Narcotrend stage of D or E. With termination of propofol infusion,recovery times were recorded and analysed for the patients with or without Narcotrend monitoring; in addition, recovery times were analysed depending on the Narcotrend stage at the moment of termination of propofol infusion.

RESULTS

In total, 4,630 adult patients were studied at 46 institutions, 521 without and 4,109 with Narcotrend monitoring. Demographic data and duration of anaesthesia were comparable. Emergence from anaesthesia was significantly shorter in Narcotrend monitored patients, e.g.opening eyes after 9.8+/-5.9 (mean+/-SD) vs.11.8+/-7.1 min. In addition,awakening was significantly more rapid when the propofol infusion was stopped at a lower level of hypnosis as indicated by Narcotrend monitoring, e.g.opening eyes after 7.1+/-4.5 min with stage C instead of 17.0+/-7.4 min with stage F.

CONCLUSIONS

The EEG monitor Narcotrend can be used for adult patients of different ages and during various surgical procedures.Narcotrend monitoring facilitates a reduction of recovery times after propofol-based total intravenous anaesthesia,presumably by allowing for an individual titration of the propofol dosage. Moreover, it appears that the profile of recovery can be optimised when at the end of surgery,the propofol infusion is controlled to Narcotrend stage C instead of D, E, or F.

[Narcotrend stages and end-tidal desflurane concentrations. An investigation during recovery from desflurane/remifentanil anaesthesia]

OBJECTIVE

[corrected] As indicated by the manufacturer the EEG monitor Narcotrend trade mark (MonitorTechnik, Bad Bramstedt) can be used to analyse EEG effects of volatile anaesthetics, however, published data are missing. This study evaluated the emergence from a desflurane/remifentanil anaesthetic and was designed to investigate the relationship between Narcotrend stages (version 2.0 AF) and end-tidal desflurane concentrations and to identify the pattern of changes of the Narcotrend stages during recovery.

METHODS

Adult patients scheduled for orthopaedic surgery were premedicated with 0.15 mg/kg diazepam orally in the evening and on the morning before surgery. Narcotrend EEG electrodes were positioned on the patient's forehead as recommended by the manufacturer. For induction of anaesthesia, remifentanil was infused at 0.4 microgram/kg/min and propofol 2 mg/kg was given for hypnosis. After neuromuscular blockade and orotracheal intubation, remifentanil was reduced to 0.2 microgram/kg/min, and desflurane in O(2)/air was added according to clinical needs. After termination of surgery, administration of anaesthetics was discontinued and simultaneously, the fresh gas flow was increased to 10 l/min of O(2) while the respirator pattern was left unchanged. Narcotrend stages and end-tidal desflurane concentrations were recorded as data pairs at intervals of 1 min during emergence from anaesthesia; data evaluation included the last 7 min before extubation.

RESULTS

A total of 50 patients (mean age +/-SD 44.4+/-13.0 years) were studied and 400 data pairs were obtained. A decreasing depth of anaesthesia as indicated by the Narcotrend was associated with significantly lower end-tidal desflurane concentrations: for E (general anaesthesia with deep hypnosis) 3.6+/-1.0 vol%, for D (general anaesthesia) 1.7+/-0.8 vol%, for C (light anaesthesia) 0.7+/-0.3 vol% and for A and B (awake or sedated) 0.5 vol%. A reduction of end-tidal desflurane concentrations was accompanied by a shift of Narcotrend stages from C/D/E to A/B/C.

CONCLUSION

During emergence from desflurane/remifentanil anaesthesia, a reduction of end-tidal desflurane concentrations was detected by the EEG monitor Narcotrend and classified as a typical change of distribution of Narcotrend stages.

Comparison of the effects of remifentanil or fentanyl on anaesthetic induction characteristics of propofol, thiopental or etomidate

BACKGROUND AND OBJECTIVE

This prospective, randomized, double-blinded study was designed to compare the effects of remifentanil or fentanyl on anaesthetic induction characteristics of propofol, thiopental or etomidate.

METHODS

Seventy-two patients were enrolled in six groups of 12 individuals each. In three groups, fentanyl was given as a bolus dose of 1.5 microg kg(-1), whereas the others received a remifentanil infusion at 0.5 microg kg(-1) min(-1). Five minutes later, propofol, thiopental or etomidate were titrated to a state of unresponsiveness. Assessment included the amounts of drug necessary for induction, haemodynamics and the times to apnoea, loss of eyelash reflex, and the release of a water-filled syringe held in the patient's hand.

RESULTS

Induction times to loss of the eyelash reflex were significantly shorter in the remifentanil than in the fentanyl groups: with propofol 50.7 +/- 13.6s (mean +/- SD) versus 74.9 +/- 27.0s (P < 0.01), with thiopental 42.9 +/- 16.8s versus 77.2 +/- 27.8s (P < 0.01) and with etomidate 54.7 +/- 17.6s versus 72.3 +/- 24.0s (P < 0.05). The times to respiratory arrest or for the syringe to fall were significantly shorter with remifentanil than with fentanyl for propofol and for thiopental, but not for etomidate. In terms of dosages per kg body weight necessary to achieve unresponsiveness, less propofol (-29%, P < 0.05), thiopental (-25%, P < 0.05) or etomidate (-32%, P < 0.01) was necessary with remifentanil than with fentanyl. Haemodynamic responses to tracheal intubation were controlled more effectively with remifentanil. However, within the remifentanil groups, mean arterial pressure significantly decreased during induction: -26% with propofol, -181% with thiopental and -14% with etomidate (all P < 0.01).

CONCLUSIONS

During anaesthetic induction, a remifentanil infusion of 0.5 microg kg(-1) min(-1) over 5 min is a suitable alternative to a 1.5 microg kg(-1) bolus dose of fentanyl: induction times are shorter with reduced amounts of propofol, thiopental or etomidate.

The Narcotrend--a new EEG monitor designed to measure the depth of anaesthesia. A comparison with bispectral index monitoring during propofol-remifentanil-anaesthesia

INTRODUCTION

The Narcotrend is a new EEG monitor designed to measure the depth of anaesthesia based on a 6-letter classification from A (awake) to F (general anaesthesia with increasing burst suppression) and divided into 14 substages (A, B0-2, C0-2, D0-2, E0,1, F0,1). This study was designed to investigate the assessment of the depth of anaesthesia as measured by the Narcotrend in comparison with bispectral index monitoring (BIS).

METHODS

Both BIS and Narcotrend EEG electrodes were positioned on the patient's forehead as recommended by the manufacturers. All patients were premedicated with diazepam 0.15 mg/kg orally in the evening and on the morning before surgery. Induction of anaesthesia was started with a remifentanil infusion at 0.4 microgram/kg/min; 5 min later propofol was given for hypnosis using a target-controlled infusion initially started at 3.5 micrograms/ml. After loss of consciousness patients received 1.2 mg/kg of suxamethonium. Immediately after intubation, remifentanil was reduced to 0.2 microgram/kg/min, and the depth of anaesthesia was adjusted according to clinical needs by regulating the propofol target-controlled-infusion. BIS values and Narcotrend stages were recorded as data pairs in intervals of 1 min during anaesthetic induction and emergence, and in intervals of 5 min during maintenance of anaesthesia.

RESULTS

Fifty patients undergoing orthopaedic surgery were studied and 2031 data pairs were obtained. An increasing depth of anaesthesia as indicated by the Narcotrend was associated with significantly lower mean BIS values. With BIS values between 100 and 85 (representing awake patients), 95.5% of all data pairs indicated a Narcotrend stage A or B. In case the BIS was found to be 65-40 (representing general anaesthesia) the corresponding Narcotrend stages were measured as D (52.4%) or E (41.1%). No patient complained of intraoperative recall when interviewed on the 1st and 3rd postoperative day.

CONCLUSIONS

We could demonstrate that an increase of the hypnotic component of anaesthesia as indicated by BIS is accompanied by corresponding effects as displayed by the Narcotrend during propofol-remifentanil anaesthesia. The Narcotrend stages D or E are assumed equivalent to BIS values between 64 and 40 indicating general anaesthesia.