Bougie-guided insertion of the ProSeal laryngeal mask airway has higher first attempt success rate than the digital technique in children

Background. We tested the hypothesis that bougie-guided insertionof the ProSeal^TM laryngeal mask airway (ProSeal^TM LMA) has highersuccess rate than the digital technique in children. Methods. One hundred and twenty children (ASA I–II, aged1–16 yr) were randomly allocated for ProSeal^TM LMA insertionusing the digital or bougie-guided technique. The digital techniquewas performed according to the manufacturer's instructions.The bougie-guided technique involved priming the drain tubewith a bougie, placing the bougie in the oesophagus under directvision and railroading the ProSeal^TM LMA into position. Unblindeddata were collected about ease of insertion (number of attemptsand time taken to provide an effective airway), efficacy ofseal, ease of gastric tube placement, haemodynamic responsesand blood staining. Blinded data were collected about postoperativeairway morbidity. Results. The first attempt success rate was higher for the bougie-guidedtechnique (59/60 vs 52/60, P=0.015), but effective airway timewas longer (37 vs 32 s, P<0.001). There were no differencesin efficacy of seal, ease of gastric tube placement, haemodynamicresponses, blood staining or postoperative airway morbidity. Conclusion. We conclude that bougie-guided insertion of theProSeal^TM LMA has a higher first attempt success rate than thedigital technique in children. Declaration of interest. Dr Brimacombe and Dr Keller have workedas consultants for the Laryngeal Mask Company, who manufactureProSeal^TM LMA.     

Agitation and changes of Bispectral Index and electroencephalographic-derived variables during sevoflurane induction in children: clonidine premedication reduces agitation compared with midazolam

Background. This double-blind randomized study was undertakento assess agitation, Bispectral Index^TM (BIS^TM) and EEG changesduring induction of anaesthesia with sevoflurane in childrenpremedicated with midazolam or clonidine. Methods. Children were allocated randomly to receive rectalmidazolam 0.4 mg kg^–1 (n=20) or oral clonidine 4µg kg^–1 (n=20) as premedication. Rapid inductionof anaesthesia was achieved with inhalation of sevoflurane 8%in nitrous oxide 50%–oxygen 50%. After tracheal intubation,the children’s lungs were mechanically ventilated andthe inspired sevoflurane concentration was adjusted to achievean end-tidal fraction of 2.5%. The EEG and BIS^TM were recordedduring induction until 10 min after tracheal intubation. TheEEG was analysed using spectral analysis at five points: baseline,loss of eyelash reflex, 15 s before the nadir of the BIS^TM (BIS_nadir),when both pupils returned to the central position (immediatelybefore intubation), and 10 min after intubation. Results. Agitation was observed in 12 midazolam-treated andfive clonidine-treated patients (P=0.05). At baseline, EEG rhythmswere slower in the clonidine group. Induction of anaesthesiawas associated with similar EEG changes in the two groups, withan increase in total spectral power and a shift towards lowfrequencies; these changes were maximal around the end of thesecond minute of induction (BIS_nadir). When the pupils had returnedto the central position, fast EEG rhythms increased and BIS^TMwas higher than BIS_nadir (P<0.05). In both groups, agitationwas associated with an increase in slow EEG rhythms at BIS_nadir. Conclusions. Compared with midazolam, clonidine premedicationreduced agitation during sevoflurane induction. During inductionwith sevoflurane 8% (oxygen 50%–nitrous oxide 50%), thenadir of the BIS^TM occurred at the end of the second minuteof inhalation. Agitation was associated with a more pronouncedslowing of the EEG rhythms at BIS_nadir compared with inductionsin which no agitation was observed. The BIS^TM may not followthe depth of anaesthesia during sevoflurane induction in children. Br J Anaesth 2004; 92: 504–11     

Predicted values of propofol EC50 and sevoflurane concentration for insertion of laryngeal mask Classic and ProSeal

Background. A new laryngeal mask airway, the ProSeal^TM (PLMA),is said to be more difficult to insert than the laryngeal maskairway Classic^TM (CLMA) using propofol anaesthesia. Therefore,we expected a greater dose of propofol and sevoflurane to berequired to insert the PLMA compared with the CLMA. We determinedthe effective concentration 50% (EC₅₀) of propofol and end-tidalsevoflurane to allow insertion of the PLMA and the CLMA. Methods. Seventy-six elective female patients (aged 20–60yr and ASA I–II) were randomly assigned to one of fourgroups. Either a PLMA or a CLMA was inserted using either propofoltarget controlled infusion or sevoflurane. Both propofol andsevoflurane targets were determined with a modified Dixon’sup-and-down method. After equilibration between the predeterminedblood and effect site concentrations, which had been held steadyfor more than 10 min, LMA insertion was attempted without neuromuscularblock. Results. The predicted EC_50CLMA and EC_50PLMA for propofol were3.14 (0.33) and 4.32 (0.67) µg ml^–1. E'_CLMAand E'_PLMA of sevoflurane (mean (SD)) were 2.36 (0.22) and 2.82(0.45)% (P<0.01 and 0.05, respectively). Conclusions. The estimated concentration of propofol and thesevoflurane concentration needed to allow insertion of the ProSeal^TMare respectively 38 and 20% greater than those needed for insertionof the Classic LMA. Br J Anaesth 2004; 92: 242–5     

Correlation of the A-Line ARX index with acoustically evoked potential amplitude

Background. Automated indices derived from mid-latency auditoryevoked potentials (MLAEP) have been proposed for monitoringthe state of anaesthesia. The A-Line^TM ARX index (AAI) has beenimplemented in the A-Line^TM monitor (Danmeter, V1.4). Severalstudies have reported variable and, in awake patients, sometimessurprisingly low AAI values. The purpose of this study was toreproduce these findings under steady-state conditions and toinvestigate their causes. Methods. Ten awake unmedicated volunteers were studied understeady-state conditions. For each subject, the raw EEG and theAAI were recorded with an A-Line^TM monitor (V1.4) during threeseparate sessions of 45.0 (1.6) min duration each. MATLAB^TM(Mathworks) routines were used to derive MLAEP responses fromEEG data and to calculate maximal MLAEP amplitudes. Results. The AAI values ranged from 15 to 99, while 11.4% fellbelow levels which, according to the manufacturer, indicatean anaesthetic depth suitable for surgery. Inter-individualand intra-individual variation was observed despite stable recordingconditions. The amplitudes of the MLAEP varied from 0.8 to 42.0µV. The MLAEP amplitude exceeded 2 µV in 75.3% ofreadings. The Spearman's rank correlation coefficient betweenthe MLAEP amplitude and the AAI value was r=0.89 (P<0.0001). Conclusions. The version of the A-Line^TM monitor used in thisstudy does not exclude contaminated MLAEP signals. Previouspublications involving this version of the A-Line^TM monitor(as opposed to the newer A-Line/2^TM monitor series) should bereassessed in the light of these findings. Before exclusivelyMLAEP-based monitors can be evaluated as suitable monitors ofdepth of anaesthesia, it is essential to ensure that inbuiltvalidity tests eliminate contaminated MLAEP signals. Presented in part at the annual meeting of the European Societyof Anaesthesiologists, Lisbon, Portugal, June 5–7, 2004.     

Propacetamol augments inhibition of platelet function by diclofenac in volunteers

Background. Acetaminophen (paracetamol) enhances the analgesiceffect of non-steroidal anti-inflammatory drugs (NSAIDs). Acetaminophenis a weak inhibitor of cyclooxygenase (COX), and its combinationwith an NSAID may augment COX inhibition-related side effects. Methods. Ten healthy male volunteers (21–30 yr) were givendiclofenac 1.1 mg kg^–1 alone, a combination of propacetamol30 mg kg^–1 (which is hydrolysed to 50% acetaminophen)and diclofenac 1.1 mg kg^–1 or placebo intravenously ina double blind, crossover study. Platelet function was assessedat 5 min, 90 min and 22–24 h by photometric aggregometry,platelet function analyser (PFA-100^TM) and by measuring therelease of thromboxane B₂ (TxB₂). Analgesia was assessed withthe cold pressor test. Results. Platelet aggregation induced with arachidonic acidwas fully inhibited by both diclofenac alone and the combinationat the end of the 30-min drug infusion. Propacetamol augmentedthe inhibition by diclofenac at 90 min (P=0.014). At 22–24h, platelet function had fully recovered. TxB₂ release was inhibitedby the combination of propacetamol and diclofenac at 90 minin comparison with diclofenac alone (P=0.027). PFA-100^TM detectedno difference in platelet function between these two groups.No analgesic effect was detected with the cold pressor test. Conclusions. The combination of propacetamol and diclofenacinhibits platelet function more than diclofenac alone. Thisshould be considered when assessing the risk of surgical bleeding. Br J Anaesth 2003; 91: 357–62     

Cerebral state index: comparison between pairwise registrations from the left and the right sides of the brain

Background. Lateralization of cerebral blood flow and EEG activityis known to vary during cognition, sleep and waking. In spiteof this, electrode placement for the cerebral state index (CSI^TM)monitor is not specified to a particular side of the brain.This study is designed to determine if pairwise registrationsdiffer for CSI measured simultaneously from the left or rightsides of the brain. Methods. In total, 25 ASA I–II patients undergoing electiveday surgery under general anaesthesia were recruited. Pairwiserecordings were made every minute from two CSI^TM monitors (CerebralState Monitor, Danmeter A/S; Odense, Denmark) connected to theleft and the right side of the head. Sedation was graded accordingto the observer's assessment of alertness/sedation rating scaleand correlated with CSI. Results. A large overlap of indices, of similar magnitude, foreach side of the brain was seen between different levels ofsedation. The agreement between pairwise registrations was high,correlation between the 584 CSI pairs of recordings left/rightwas r²=0.92. Conclusions. Despite known lateralization of the EEC, this studyfound a very high correlation in CSI derived simultaneouslyfrom the left and right sides of the brain by two independentmonitors. LMA® is the property of Intavent Ltd.     

Continuous intravascular blood gas monitoring: development,current techniques,and clinical use of a commercial device

This review focuses on the development, current techniques,and clinical use of continuous intravascular blood gas monitoring(CIBM) devices in anaesthesia and intensive care. The operatingprinciples, range of application, performance, limitations,costs, and impact on patient treatment and outcome, are discussed.Studies of early and currently available CIBM devices were analysed.At present, the Paratrend 7+^® (PT7+^®) for adults andNeotrend^TM (NT^TM) for newborns are the only commercially availableCIBM systems. The PT7+^® contains three optical sensors tomeasure PO₂, PCO₂ and pH, as well as a thermocouple to measuretemperature. The NT^TM is a modification of the PT7+^® tocontinuously monitor PO₂, PCO₂, pH and temperature in newborns.Under laboratory conditions, good performance over a wide rangeof blood gas values was observed with the Paratrend 7^® (PT7^®).Performance in the clinical setting was not as satisfactory,especially for PO₂ values. However, the performance and accuracyof CIBM devices appear to be sufficient for clinical use andthey are being used clinically in selected patient groups. Severalfactors affecting the performance of CIBM are considered. Br J Anaesth 2003: 91; 397–407     

Desflurane compared with propofol for postoperative sedation in the intensive care unit

Background. We hypothesized that emergence from sedation inpostoperative patients in the intensive care unit would be fasterand more predictable after sedation with desflurane than withpropofol. Methods. Sixty patients after major operations were allocatedrandomly to receive either desflurane or propofol. The targetlevel of sedation was defined by a bispectral index^TM (BIS^TM)of 60. All patients were receiving mechanical ventilation ofthe lungs for 10.6 (SD 5.5) h depending on their clinical state.The study drugs were stopped abruptly in a calm atmosphere withthe fresh gas flow set to 6 litres min^–1, and the timeuntil the BIS increased above 75 was measured (t_BIS75, the mainobjective measure). After extubation of the trachea, when thepatients could state their birth date, they were asked to memorizefive words. Results. Emergence times were shorter (P<0.001) after desfluranethan after propofol (25th, 50th and 75th percentiles): t_BIS75,3.0, 4.5 and 5.8 vs 5.2, 7.7 and 10.3 min; time to first response,3.7, 5.0 and 5.7 vs 6.9, 8.6 and 10.7 min; time to eyes open,4.7, 5.7 and 8.0 vs 7.3, 10.5 and 20.8 min; time to squeezehand, 5.1, 6.5 and 10.2 vs 9.2, 11.1 and 21.1 min; time to trachealextubation, 5.8, 7.7 and 10.0 vs 9.7, 13.5 and 18.9 min; timeto saying their birth date, 7.7, 10.5 and 15.5 vs 13.0, 19.4and 31.8 min. Patients who received desflurane recalled significantlymore of the five words. We did not observe major side-effectsand there were no haemodynamic or laboratory changes exceptfor a more marked increase in systolic blood pressure afterstopping desflurane. Using a low fresh gas flow (air/oxygen1 litre min^–1), pure drug costs were lower for desfluranethan for propofol (95 vs 171 Euros day^–1). Conclusions. We found shorter and more predictable emergencetimes and quicker mental recovery after short-term postoperativesedation with desflurane compared with propofol. Desfluraneallows precise timing of extubation, shortening the time duringwhich the patient needs very close attention. Br J Anaesth 2003; 90: 273–80     

Efficacy of A-line AEP Monitor as a tool for predicting acceptable tracheal intubation conditions during sevoflurane anaesthesia

Background. It is essential for the clinical anaesthetist toknow whether patients are sufficiently anaesthetized to toleratedirect laryngoscopy and endotracheal intubation. Because ofthe lack of an accurate objective method to determine the levelof general anaesthesia, under- or overdosing of anaestheticsmay occur. Auditory evoked potential (AEP) is one of severalphysiological parameters under investigation. We aimed to determinethe clinically required depth of anaesthesia, measured by theA-line^TM AEP Monitor and expressed as A-Line ARX Index^TM (AAI)for 90% probability of acceptable conditions for endotrachealintubation. Methods. We studied 108 patients anaesthetized by mask withincreasing concentration of sevoflurane in 30% oxygen and 70%nitrous oxide. Fentanyl 1.5 µg kg^–1 and glycopyrrolate0.2 mg were administered intravenously immediately before startinginduction of anaesthesia. The monitor was programmed to givean alarm at AAI 10, 15, 20, 25 or 30 according to randomization.When the alarm sounded, the end-expiratory sevoflurane concentrationwas registered and endotracheal intubation was attempted. Intubationconditions were assessed by an observer blinded to the AAI. Results. At AAI 10 we found acceptable conditions in 91% (confidenceinterval [CI 72–99%]) of patients. The prediction probabilityvalue P_K of AAI was 0.69 (CI 0.59–0.79) and the P_K ofend-expiratory sevoflurane concentration was 0.93 (CI 0.87–0.99).ED₉₀ (the AAI with a 90% probability of acceptable intubationconditions) was calculated as 8.5 (CI 0–17.5). Conclusions. AAI indicates the depth of anaesthesia necessaryfor acceptable endotracheal intubation conditions. Under theconditions of the present study, end-expiratory sevofluraneconcentration was a better predictor and may turn out to bemore useful in the clinical setting.     

The suppression of spinal F-waves by propofol does not predict immobility to painful stimuli in humans

Background. The immobilizing effects of volatile anaestheticsare primarily mediated at the spinal level. A suppression ofrecurrent spinal responses (F-waves), which reflect spinal excitability,has been shown for propofol. We have assessed the concentration-dependentF-wave suppression by propofol and related it to the logisticregression curve for suppression of movement to noxious stimuliand the effect on the bispectral index^TM (BIS^TM). The predictivepower of drug effects on F-waves and BIS for movement responsesto noxious stimuli was tested. Methods. In 24 patients anaesthesia was induced and maintainedwith propofol infused by a target controlled infusion pump atstepwise increasing and decreasing plasma concentrations between0.5 and 4.5 mg litre^–1. The F-waves of the abductor hallucismuscle were recorded at a frequency of 0.2 Hz. BIS values wererecorded continuously. Calculated propofol concentrations andF-wave amplitude and persistence were analyzed in terms of apharmacokinetic–pharmacodynamic (PK/PD) model with a simplesigmoid concentration–response function. Motor responsesto tetanic electrical stimulation (50 Hz, 60 mA, 5 s, volarforearm) were tested and the EC_50tetanus was calculated usinglogistic regression. Results. For slowly increasing propofol concentrations, computerfits of the PK/PD model for the suppression by propofol yieldeda median EC₅₀ of 1.26 (0.4–2.3) and 1.9 (1.0–2.8)mg litre^–1 for the F-wave amplitude and persistence, respectively.These values are far lower than the calculated EC₅₀ for noxiouselectrical stimulation of 3.75 mg litre^–1. This differenceresults in a poor prediction probability of movement to noxiousstimuli of 0.59 for the F-wave amplitude. Conclusions. F-waves are almost completely suppressed at subclinicalpropofol concentrations and they are therefore not suitablefor prediction of motor responses to noxious stimuli under propofolmono-anaesthesia. Presented in part at the annual meeting of the American Societyof Anesthesiologists 2004 in Las Vegas.     

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), whichis a dimensionless number scaled from 100 (awake) to 0. Thisstudy was designed to compare AAI and BIS^TM (Aspect, USA, versionXP) values at different levels of anaesthesia. Methods. Adult female patients were premedicated with diazepam0.15 mg kg^–1 orally on the morning of surgery. Electrodesfor BIS and Alaris AEP monitoring and a headphone to give auditorystimuli were applied as recommended by the manufacturers. Anaesthesiawas induced with remifentanil (0.4 µg kg^–1 min^–1)and a propofol target-controlled infusion (Diprifusor^TM TCI,AstraZeneca, Germany) to obtain a predicted concentration ofinitially 3.5 µg ml^–1. After loss of consciousnessthe patients were given 0.5 mg kg^–1 of atracurium. Aftertracheal intubation, remifentanil was given at 0.2 µgkg^–1 min^–1 and the propofol infusion was adjustedto obtain BIS target values of 30, 40, 50, and 60. AAI and BISvalues were recorded and matched with the predicted propofoleffect-site concentrations. Prediction probability was calculatedfor 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 anaesthesiawere 95 (4), range 99–82 for BIS and 85 (12), range 99–55for AAI. With loss of eyelash reflex both values were significantlyreduced to 64 (13), range 83–39 for BIS (P<0.05) and61 (22), range 99–15 for AAI (P<0.05). The predictionprobability P_K for consciousness vs unconsciousness (i.e. lossof 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 correspondingAAI values were 15 (6), 20 (8), 28 (11), and 40 (16), and thesewere significantly different. Conclusions. During propofol-remifentanil anaesthesia a decreaseof the depth of anaesthesia as indicated by BIS monitoring isaccompanied by corresponding effects shown by the AAI. However,wide variation in the awake values and considerable overlapof AAI values between consciousness and unconsciousness, suggestsfurther improvement of the AAI system is required. Br J Anaesth 2003; 91: 336–40     

Entropy indices vs the bispectral index for estimating nociception during sevoflurane anaesthesia

Background. It is now possible to acquire and process raw EEGand frontal EMG signals to produce two spectral-entropy-basedindices (response entropy and state entropy) reflective of analgesicand hypnotic levels during general anaesthesia (with the Datex-OhmedaS/5 Entropy Module, Datex-Ohmeda, Helsinki, Finland). However,there are no data available on the accuracy of the Entropy Modulein estimating nociception during sevoflurane anaesthesia. Methods. Forty female patients were enrolled in the presentstudy. Each patient was allocated randomly to one of four end-tidalsevoflurane concentration (ET_sev) groups (1.3, 1.7, 2.1 or 2.5%).A BIS Sensor^TM (Aspect Medical Systems, Newton, MA) and an EntropySensor^TM (Datex-Ohmeda) were applied side-by-side to the forehead.The bispectral index (A-2000 BIS Monitor, version 3.4, AspectMedical Systems), response entropy, state entropy and patientmovement were observed after electrical stimulation (20, 40,60 and 80 mA, 100 Hz, 5 s) and after skin incision during sevofluraneanaesthesia (1.3, 1.7, 2.1 or 2.5%). Accuracy of the EEG variablesin differentiating the intensity of electrical stimulation wasestimated by the prediction probability (P_K) values. Results. Response entropy and state entropy [median, (range)]before skin incision were significantly lower in patients whodid not move [29 (15–41) and 24 (14–41)] than inthose that did [38 (24–53) and 37 (24–52)], butthere was no significant difference in BIS. All EEG variablesincreased significantly (P<0.0001 for all) with increasesin the intensity of electrical stimulation. The difference betweenresponse entropy and state entropy increased with increasesin the electrical stimulation (P<0.0001). However, no EEGvariables could differentiate the intensity of the electricalstimulations accurately because of low P_K-values (P_K<0.8). Conclusion. Noxious stimulation increased the difference betweenresponse entropy and state entropy. However, an increase inthe difference does not always indicate inadequate analgesiaand should be interpreted carefully during anaesthesia.     

Unconscious learning during surgery with propofol anaesthesia

Background. Learning during anaesthesia has been demonstrated,but little is known about the circumstances under which it mayoccur. This study investigated the hypothesis that learningduring anaesthesia occurs during, but not before, surgical stimulation. Methods. Words were played through headphones to 64 day-surgerypatients during propofol anaesthesia. Fourteen words were playedrepeatedly (15 times) for 1 min each either before (n=32) orduring (n=32) surgical stimulation. The depth of anaesthesiawas estimated using the bispectral index^TM (BIS^TM). Heart rate,ventilatory frequency, mean arterial pressure, end-tidal carbondioxide concentration, and infusion rate of propofol were recordedat 1 min intervals during word presentation. On recovery, memorywas assessed using an auditory word stem completion test andword recognition test. Results. The mean BIS^TM, arterial pressure, end-tidal carbondioxide and heart rate during word presentation did not differbetween the groups. The infusion rate of propofol and the ventilatoryfrequency were significantly greater in the during-surgicalstimulation group. There was no evidence for explicit recallor recognition, nor of awareness during anaesthesia (medianmean-BIS^TM=38 in the before-surgical stimulation group and 42in the during-surgical stimulation group). Only patients whowere played words during surgical stimulation showed significantimplicit memory on recovery (mean score=0.08, P<0.02) However,their scores were not significantly higher than those of thebefore-surgical stimulation group (mean score=0.01). Conclusions. Learning during anaesthesia seems more likely tooccur during rather than before surgical stimulation at comparableanaesthetic depth. We hypothesize that surgical stimulationfacilitates learning during anaesthesia, independently of itseffects on anaesthetic depth. Br J Anaesth 2004; 92: 171–7     

Comparison of effects of anandamide at recombinant and endogenous rat vanilloid receptors

Background. Anandamide, an endogenous lipid, activates bothcannabinoid (CB₁) and vanilloid (VR1) receptors, both of whichare co-expressed in rat dorsal root ganglion (DRG) cells. Activationof either receptor results in analgesia but the relative contributionof CB₁ and VR1 in anandamide-induced analgesia remains controversial.Here we compare the in vitro pharmacology of recombinant andendogenous VR1 receptors using calcium imaging, in clonal andDRG cells, respectively. We also consider the contribution ofCB₁ and VR1 receptors to anandamide-induced analgesia. Methods. Using a Flurometric Imaging Plate Reader (FLIPR^TM),calcium imaging has been used to study the effects of severalvanilloid and cannabinoid ligands in rat VR1-transfected HEK293(rVR1-HEK) cells and in DRG cells. The effect of pre-exposureof several vanilloid and cannabinoids has also been comparedin DRG cells. Results. The VR1 agonists capsaicin, olvanil, (N-(4-hydroxyphenyl-arachinoylamide)(AM404) and anandamide caused a concentration-dependent increasein intracellular calcium concentration ([Ca²⁺]_i), with similartemporal profiles in both rVR1-HEK and DRG cells, and potency(pEC₅₀) values of 8.25 (SEM 0.11), 8.37 (0.04), 6.96 (0.06),5.85 (0.01) and 7.45 (0.10), 7.55 (0.07), 6.10 (0.13), approximately5.5, respectively. These responses were inhibited by the VR1antagonist capsazepine (1 µM). In contrast, applicationof synthetic cannabinoid antagonists failed to inhibit the anandamide-inducedincrease in [Ca²⁺]_i. Reapplication of VR1 agonists significantlyinhibited a subsequent challenge to either capsaicin or anandamidein either cell type, whilst pre-exposure to cannabinoid agonistswere without effect. Conclusion. Here we provide evidence that the pharmacology ofrecombinant rVR1 receptors is similar to those endogenouslyexpressed in DRG cells. Moreover, we have shown that VR1, butnot CB₁, receptors are involved in anandamide-induced responsesin dorsal root primary neurones in vitro. Therefore, the analgesicproperties of anandamide are likely to be mediated, at leastin part, by VR1 activation in DRG cells in vivo. Br J Anaesth 2002; 89: 882–7     

Use of a ProSeal laryngeal mask airway for airway maintenance during emergency Caesarean section after failed tracheal intubation

We report the use of the ProSeal^TM laryngeal mask airway toestablish and maintain the airway during emergency Caesareansection when tracheal intubation had failed with conventionallaryngoscopy and mask ventilation was difficult. The ProSeal^TMlaryngeal mask allowed controlled ventilation without gas leakand facilitated drainage of the stomach. Br J Anaesth 2004; 92: 144–6     

Comparability of Narcotrend index and bispectral index during propofol anaesthesia

Background. The dimensionless Narcotrend^TM (NCT) index (MonitorTechnik,Germany, version 4.0), from 100 (awake) to 0, is a new indexbased on electroencephalogram pattern recognition. Transferringguidelines for titrating the Bispectral Index^TM (BIS, AspectMedical Systems, USA, version XP) to the NCT index depends ontheir comparability. We compared the relationship between BISand NCT values during propofol anaesthesia. Methods. Eighteen adult patients about to have radical prostatectomywere investigated. An epidural catheter was placed in the lumbarspace and electrodes for BIS and NCT were applied as recommendedby the manufacturers. After i.v. fentanyl 0.1 mg, anaesthesiawas induced with a propofol infusion. After intubation, patientsreceived bupivacaine 0.5% 15 ml via the epidural catheter. Forty-fiveminutes after induction, the propofol concentration was increasedto substantial burst suppression pattern and then decreased.This was done twice in each patient, and BIS and Narcotrendvalues were recorded at intervals of 5 s. The efficacy of NCTand BIS in predicting consciousness vs unconsciousness was evaluatedusing the prediction probability (P_K). Results. We collected 38 629 artefact-free data pairs of BISand NCT values from the respective 5-s epochs. Because of artefacts,another 5008 epochs had been excluded from data analysis (3855epochs for the NCT index alone, 245 epochs for the BIS aloneand 908 epochs for both indices). Mean (SD) values in awakepatients were 94 (6) for Narcotrend and 91 (8) for BIS. Withloss 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 P_K value for loss of eyelash reflex was similarfor BIS (0.95) and NCT (0.93). Decreasing BIS values coincidedwith 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 indexin a BIS range between 100 and 50. For BIS values lower than50, a second sigmoid model with a correlation of r=0.83 wasapplied [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 sigmoidmodel: NCT index=265/(1+exp((–BSR+108)/–49); r=0.73. Conclusions. We found a sufficient correlation between BIS andNCT index, but deviations from the line of identity in someranges require attention. Therefore, a simple 1:1 transfer fromBIS to NCT values is not adequate. Our results might serve asa blueprint for the rational translation of BIS into NCT values.     

Relation between fentanyl dose and predicted EC50 of propofol for laryngeal mask insertion

Background. This study sought to determine the effective concentrationfor 50% of the attempts to secure laryngeal mask insertion (predictedEC_50LMA) of propofol using a target-controlled infusion (Diprifusor^TM)and investigated whether fentanyl influenced these requiredconcentrations, respiratory rate (RR) and bispectral index (BIS). Methods. Sixty-four elective unpremedicated patients were randomlyassigned to four groups (n = 16 for each group) and given saline(control) or fentanyl 0.5, 1 or 2 µg kg^–1.Propofol target concentration was determined by a modificationof Dixon’s up-and-down method. Laryngeal mask airway insertionwas attempted without neuromuscular blocking drugs after equilibrationhad been established for >10 min. Movement was defined aspresence of bucking or gross purposeful muscular movement within1 min after insertion. EC_50LMA values were obtained by calculatingthe mean of 16 patients in each group. Results. Predicted EC_50LMA of the control, fentanyl 0.5, 1 and2 µg kg^–1 groups were 3.25 (0.20), 2.06 (0.55),1.69 (0.38) and 1.50 (0.54) µg ml^–1 respectively;those of all fentanyl groups were significantly lower than thatof control. RR was decreased in relation to the fentanyl doseup to 1 µg kg^–1. BIS values after fentanyl1 and 2 µg kg^–1 were significantly greaterthan in the control and 0.5 µg kg^–1 groups. Conclusions. A fentanyl dose of 0.5 µg kg^–1is sufficient to decrease predicted EC_50LMA with minimum respiratorydepression and without a high BIS value. Br J Anaesth 2004; 92: 238–41     

The LMA CTrach, a new laryngeal mask airway for endotracheal intubation under vision: evaluation in 100 patients

Background. The LMA CTrach^TM is a new laryngeal mask systemconsisting of an LMA CTrach^TM Airway with integrated fibreopticchannels, and a detachable LMA CTrach^TM Viewer. This systemenables viewing of the larynx and aids endotracheal intubationthrough a laryngeal mask airway. Method. We used and evaluated this system in 100 adult patientsundergoing general anaesthesia for elective surgery. Our primaryoutcomes were the success rates of LMA CTrach^TM Airway insertionand endotracheal intubation with this system. Results. We were able to insert the LMA CTrach^TM Airway in andto ventilate all 100 patients. We were successful in endotrachealintubation, either under vision or blind, in 96 patients. Wewere able to view the larynx in 84 patients, but the qualityof the best view obtained was very variable. The median (interquartile range) time for the complete intubation process was166 (114–233) s. The system allowed nearly continuousventilation and oxygenation during the process. Conclusions. The LMA CTrach^TM system has potential advantagesover the LMA Fastrach^TM system, including the ability to alignthe LMA outlet with the larynx and a high first intubation attemptsuccess rate. However, it was difficult to view the larynx withthe LMA CTrach^TM compared with direct laryngoscopy, and expectationsmust be moderated.     

Onset and duration of mivacurium-induced neuromuscular block in patients with Duchenne muscular dystrophy

Background. To determine the response to mivacurium, we prospectivelystudied onset time and complete spontaneous recovery from mivacurium-inducedneuromuscular block in patients with Duchenne muscular dystrophy(DMD). Methods. Twelve boys with DMD, age 5–14 yr, seven of themwheelchair-bound, ASA II–III, and 12 age- and sex-matchedcontrols (ASA I) were enrolled in the study. Anaesthesia wasinduced with fentanyl 2–3 µg kg^–1 and propofol3–4 mg kg^–1 titrated to effect, and maintained bycontinuous i.v. infusion of propofol 8–12 mg kg^–1and remifentanil as required. The lungs were ventilated withoxygen in air. Neuromuscular transmission was assessed by acceleromyographyusing train-of-four (TOF) stimulation every 15 s. After baselinereadings, a single dose of mivacurium 0.2 mg kg^–1 wasgiven. The following variables were recorded: (i) lag time;(ii) onset time; (iii) peak effect; (iv) recovery of first twitchfrom the TOF response to 10, 25 and 90% (T₁₀, T₂₅, T₉₀) relativeto baseline; (v) recovery index (time between 25 and 75% recoveryof first twitch); and (vi) recovery time (time between 25% recoveryof first twitch and recovery of TOF ratio to 90%). For comparisonbetween the groups the Mann–Whitney U-test was applied. Results. There were no differences between the groups in lagtime, onset time and peak effect. However, all recorded recoveryindices were significantly (P<0.05) prolonged in the DMDgroup. The median (range) for time points T₁₀, T₂₅ and T₉₀ inthe DMD and control group was 12.0 (8–16) vs 8.4 (5–15)min, 14.1 (9–20) vs 10.5 (7–17) min and 26.9 (15–40)vs 15.9 (12–23) min, respectively. The recovery indexand recovery time were similarly prolonged in the DMD group. Conclusions. These results support the assumption that mivacurium-inducedneuromuscular block is prolonged in patients with DMD. This study was presented at the Annual Meeting of the AmericanSociety of Anaesthesiologists, Las Vegas, October 2004. These authors contributed equally to this work.     

Randomized evaluation of the performance of single-use laryngoscopes in simulated easy and difficult intubation

Background. Single-use laryngoscopes are becoming used morewidely. Methods. We compared six types of single-use laryngoscope withthe standard Macintosh laryngoscope using the Laerdal SimMan^TMpatient simulator. Twenty anaesthetists attempted to intubatethe simulator with standardized airway settings allowing a fullview of the vocal cords (‘easy intubation’). Theairway settings were then changed so that only the posteriorpart of the glottis was visible (‘difficult intubation’)and the anaesthetists were asked to intubate the simulator again. Results. The time to intubate with the standard laryngoscopewas less in both easy (P<0.05) and difficult (P<0.01)intubations. The performance of five laryngoscopes during easyintubation (P<0.01) and four during difficult intubation(P<0.001) was significantly worse than that of the Macintosh.There was a significant difference in Cormack and Lehane gradingbetween the laryngoscopes tested in both easy (P<0.05) anddifficult (P<0.05) intubation. The percentage of glotticopening visible (POGO score) also differed between laryngoscopesin both the easy (P<0.01) and difficult (P<0.001) groups.The highest POGO scores were obtained with the Macintosh laryngoscope.During the difficult intubation simulation, the reusable Macintoshlaryngoscope needed less use of a bougie and had fewer failedintubations than the single-use laryngoscopes, but these differencesdid not reach statistical significance. Conclusions. Of the laryngoscopes tested, the standard reusableMacintosh laryngoscope performed best. The Europa^TM was thebest single-use laryngoscope. Some single-use laryngoscopestested were significantly inferior to the Macintosh. This raisesconcern over their use in clinical practice, particularly ifintubation is difficult. Br J Anaesth 2003; 90: 8–13