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     

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     

Effects of sevoflurane and propofol on left ventricular diastolic function in patients with pre-existing diastolic dysfunction

Background. The effects of anaesthetics on left ventricular(LV) diastolic function in patients with pre-existing diastolicdysfunction are not well known. We hypothesized that propofolbut not sevoflurane will worsen the pre-existing LV diastolicdysfunction. Methods. Of 24 randomized patients, 23 fulfilled the predefinedechocardiographic criterion for diastolic dysfunction. Theyreceived general anaesthesia with sevoflurane 1 MAC (n=12) orpropofol 4 µg ml^–1 (n=11). Echocardiographic examinationswere performed at baseline and in anaesthetized patients underspontaneous breathing and under positive pressure ventilation.Analysis focused on peak early diastolic velocity of the mitralannulus (E_a). Results. During spontaneous breathing, E_a was higher in thesevoflurane than in the propofol group [mean (95% CI) 7.0 (5.9–8.1)vs 5.5 (4.7–6.3) cm s^–1; P<0.05], reflectingan increase of E_a from baseline only in the sevoflurane group(P<0.01). Haemodynamic findings were similar in both groups,but the end-tidal carbon dioxide content was more elevated inthe propofol group (P<0.01). During positive pressure ventilation,E_a was similarly low in the sevoflurane and propofol groups[5.3 (4.2–6.3) and 4.4 (3.6–5.2) cm s^–1, respectively]. Conclusions. During spontaneous breathing, early diastolic functionimproved in the sevoflurane but not in the propofol group. However,during positive pressure ventilation and balanced anaesthesia,there was no evidence of different effects caused by the twoanaesthetics.     

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.     

Optimization of desflurane administration in morbidly obese patients: a comparison with sevoflurane using an 'inhalation bolus' technique

Background. The concept of an ‘inhalation bolus’can be used to optimize inhaled drug administration. We investigatedthe depth of anaesthesia, haemodynamic stability, and recoverytime in morbidly obese patients resulting from bispectral index^TM(BIS^TM)-guided sevoflurane or desflurane administration andBIS-triggered inhalation boluses of sevoflurane or desfluranecombined with titration of remifentanil. Methods. Fifty morbidly obese patients undergoing laparoscopicgastroplasty received either BIS-guided sevoflurane or desfluraneanaesthesia in combination with a remifentanil target-controlledinfusion. Intraoperative haemodynamic stability and BIS controlwere measured. Immediate recovery was recorded. Results. Intraoperatively, the BIS was between 40 and 60 fora greater percentage of time in the sevoflurane (78 (13)% ofcase time) than in the desflurane patients (64 (14)% of casetime), owing to too profound anaesthesia in the desflurane patientsat the start of the procedure. However, fewer episodes of hypotensionwere found in the desflurane group, without the occurrence ofmore hypertensive episodes. During immediate recovery, eye opening,extubation, airway maintenance, and orientation occurred soonerin the desflurane group. Conclusions. Immediate recovery was significantly faster inthe desflurane group. Overall hypnotic controllability measuredby BIS was less accurate with desflurane. Overall haemodynamiccontrollability was better when using desflurane. Fewer episodesof hypotension were found in the desflurane group. The use ofthe inhalation bolus was found to be appropriate in both groupswithout causing severe haemodynamic side effects. Minimal BISvalues were significantly lower after a desflurane bolus. Br J Anaesth 2003; 91: 638–50     

Performance of entropy and Bispectral Index as measures of anaesthesia effect in children of different ages

Background. Entropy and Bispectral Index^TM (BIS^TM) have beenpromoted as EEG-based anaesthesia depth monitors. The EEG changeswith brain maturation, but there are limited published datadescribing the characteristics of entropy in children, and somedata suggest that BIS is less reliable in young children. Theaim of this study was to compare the performance of entropyas a measure of anaesthetic effect in different age groups.The performance of entropy was compared with BIS. Methods. Fifty-four children receiving a standard sevofluraneanaesthetic for cardiac catheter studies were enrolled. Theentropy and BIS were recorded pre-awakening and at 1.5%, 2%and 2.5% steady-state end-tidal sevoflurane concentrations.For analysis children were divided into four age groups: 0–1yr, 1–2 yr, 2–4 yr and 4–12 yr. Results. The pre-awakening values were obtained in 46 children.The median pre-awakening values for entropy and BIS varied significantlyacross ages with the values being lowest in the 0–1 yrage group (response entropy: 45 vs 84, 87 and 89, P=0.003; stateentropy: 36 vs 78, 74 and 77, P=0.009; BIS: 56 vs 78, 76.5 and72, P=0.02). Values were recorded at all three sevoflurane concentrationsin 48 children. Compared with older groups, the 0–1 yrage group had the least significant difference in BIS and entropywhen compared among different sevoflurane concentrations. Thecalculated sevoflurane concentrations to achieve mid-scale valuesof entropy and BIS were highest in the 1–2 yr age group,lower in the 0–1 yr age group and progressively lowerin the 2–4 and 4–12 yr age groups. Conclusions. For both entropy and BIS the measure of anaestheticeffect was significantly different for children aged <1 yrcompared with older children. There was no difference in performanceof entropy and BIS. Both should be used cautiously in smallchildren.      

Comparison of propofol/remifentanil and sevoflurane/remifentanil for maintenance of anaesthesia for elective intracranial surgery

Background. Propofol and sevoflurane are suitable agents formaintenance of anaesthesia during neurosurgical procedures.We have prospectively compared these agents in combination withthe short-acting opioid, remifentanil. Methods. Fifty unpremedicated patients undergoing elective craniotomyreceived remifentanil 1 µg kg^–1 followed by an infusioncommencing at 0.5 µg kg^–1 min^–1 reducing to0.25 µg kg^–1 min^–1 after craniotomy. Anaesthesiawas induced with propofol, and maintained with either a target-controlledinfusion of propofol, minimum target 2 µg ml^–1 orsevoflurane, initial concentration 2%_ET. Episodes of mean arterialpressure (MAP) more than 100 mm Hg or less than 60 mm Hg formore than 1 min were defined as hypertensive or hypotensiveevents, respectively. A surgical assessment of operating conditionsand times to spontaneous respiration, extubation, obey commandsand eye opening were recorded. Drug acquisition costs were calculated. Results. Twenty-four and twenty-six patients were assigned topropofol (Group P) and sevoflurane anaesthesia (Group S), respectively.The number of hypertensive events was comparable, whilst morehypotensive events were observed in Group S than in Group P(P=0.053, chi-squared test). As rescue therapy, more labetolol[45 (33) vs 76 (58) mg, P=0.073] and ephedrine [4.80 (2.21)vs 9.78 (5.59) mg, P=0.020] were used in Group S. Between groupdifferences in recovery times were small and clinically unimportant.The combined hourly acquisition costs of hypnotic, analgesic,and vasoactive drugs appeared to be lower in patients maintainedwith sevoflurane than with propofol. Conclusion. Propofol/remifentanil and sevoflurane/remifentanilboth provided satisfactory anaesthesia for intracranial surgery.     

A comparison of the SNAP II and BIS XP indices during sevoflurane and nitrous oxide anaesthesia at 1 and 1.5 MAC and at awakening

Background. Monitoring level of consciousness during anaesthesia,with the ability to predict the intentional or unintentionalreturn to consciousness, is desirable. The purpose of this studywas to compare two processed electroencephalographic depth ofanaesthesia monitors (SNAP II^TM and BIS XP^TM) during sevofluraneand sevoflurane/nitrous oxide anaesthesia. Methods. In total, 42 subjects received an interscalene block,followed by general anaesthesia with sevoflurane or sevoflurane/nitrousoxide. The indices were recorded at baseline, at 1.5 and 1.0minimum alveolar concentration (MAC) equivalents, and duringemergence. Results. The SNAP and BIS indices decreased from baseline at1.5 and 1.0 MAC equivalents, but there was no difference withingroups between subjects who received nitrous oxide and thosewho did not. The SNAP index returned to baseline by 1 min beforeawakening and was higher than baseline at eye opening, but theBIS index remained below baseline at awakening. There was abias of –1 (95% CI: –3 to 1) between the SNAP andBIS at baseline; this increased to 21 (95% CI: 19–23)during maintenance of anaesthesia and was 6 (95% CI: 4–8)at awakening. Conclusions. The SNAP index tracks loss of consciousness andemergence from sevoflurane and sevoflurane/nitrous oxide anaesthesia.There is significant bias between the SNAP and BIS indices andtherefore, the indices are not interchangeable. The SNAP indexreturns to baseline before awakening, whereas the BIS indexremains below baseline at awakening, suggesting that the SNAPindex may be more sensitive to unintentional awareness.      

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.     

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     

Cerebral haemodynamic changes during propofol-remifentanil or sevoflurane anaesthesia: transcranial Doppler study under bispectral index monitoring

Background. Sevoflurane or propofol–remifentanil-basedanaesthetic regimens represent modern techniques for neurosurgicalanaesthesia. Nevertheless, there are potential differences relatedto their activity on the cerebrovascular system. The magnitudeof such difference is not completely known. Methods. In total 40 patients, treated for spinal or maxillo-facialdisorders, were randomly allocated to either i.v. propofol–remifentanilor inhalational sevoflurane anaesthesia. Transcranial Dopplerwas used to assess changes in cerebral blood flow velocity,carbon dioxide reactivity, cerebral autoregulation and the bispectralindex to assess the depth of anaesthesia. Results. Time-averaged mean flow velocity (MFV) was significantlyreduced after induction of anaesthesia in both sevoflurane andpropofol–remifentanil groups (P<0.001). At deeper levelsof anaesthesia, MFV increased in the sevoflurane group, suggestingan uncoupling flow/metabolism, whereas it was further reducedin the propofol–remifentanil group (P<0.001). Indicesof cerebral autoregulation were reduced in patients with high-dosesevoflurane whereas autoregulation was preserved in patientsanaesthetized with propofol–remifentanil (P<0.001).Higher CO₂ concentrations impaired cerebral autoregulation inthe sevoflurane group but not in patients anaesthetized withpropofol–remifentanil. Conclusions. Propofol–remifentanil anaesthesia induceda dose-dependent low-flow state with preserved cerebral autoregulation,whereas sevoflurane at high doses provided a certain degreeof luxury perfusion.     

Plasma lidocaine concentrations following insertion of 2% lidocaine gel into the uterine cavity after uterine balloon thermal ablation

Background. Uterine balloon thermal ablation is used to treatmenorrhagia. We thought that intrauterine application of 2%lidocaine gel could reduce postoperative pain after this procedure.Before using this technique we wished to establish how muchlidocaine is absorbed systemically from the uterine cavity afterthermal ablation. Methods. Ten ASA I–II patients (age 38–50 yr) underwentuterine balloon thermal ablation under general anaesthesia.They each had 11 ml of 2% lidocaine gel (Instillagel^TM) insertedinto the uterine cavity at the end of the procedure. Blood sampleswere taken at 5, 15, 30 and 60 min after insertion and lidocaineconcentrations were measured using high-performance liquid chromatography. Results. Mean (range) plasma lidocaine concentrations at 5,15, 30 and 60 min were 40.3 (0–221.9), 66.3 (0–271.9),64.9 (0–208) and 75 (0–212) ng ml^–1, respectively. Conclusion. There was minimal systemic absorption of lidocainefrom the uterus following uterine balloon thermal ablation.Measured concentrations were well below the toxic plasma concentrationfor lidocaine (8–10 µg ml^–1). Br J Anaesth 2002; 89: 846–8     

Reflex pupillary dilatation in response to skin incision and alfentanil in children anaesthetized with sevoflurane: a more sensitive measure of noxious stimulation than the commonly used variables

Background. Estimation of analgesia in anaesthetized childrenis often imprecise, and consequently, anaesthesiologists commonlyevaluate children's response to surgical stimulation by movementor haemodynamic changes. In adults reflex pupillary dilatationhas been demonstrated to be a very sensitive measure of noxiousstimulation, correlated with opioid concentrations. The autonomicnervous control changes with age, raising the hypothesis thatmechanisms involved in pupillary autonomic functions regardingboth sympathetic and parasympathetic components may also differbetween adults and children. In this pilot study, we testedthe hypothesis that the pupillary reflex dilatation might allowassessment of noxious stimulation and analgesic effect of alfentanilin children under sevoflurane anaesthesia, as an alternativeto haemodynamic and bispectral measures. Methods. After sevoflurane induction, 24 children were maintainedin steady-state conditions at 1.5 MAC of sevoflurane in O₂–N₂O(50–50). An intense noxious stimulation was provided bystandardized skin incision on the lower limb. A bolus of alfentanil(10 µg kg^–1) was administered either 1 min (n=16)or 2 min (n=8) after skin incision. Haemodynamic values, bispectralindex (BIS) and pupillary diameter (PD) were recorded just beforestimulation and at 30–60 s intervals during 4 subsequentminutes. Results. In all children PD increased significantly after noxiousstimulation [+200 (40)%, at 60 s]. In contrast, mean heart rateand blood pressure increased only 11 (7)% and 10 (8)% respectively,60 s after stimulation. BIS did not change significantly. Inall children, alfentanil injection induced a rapid decreaseof PD and restored pre-incision values in 2 min. Conclusion. PD is a more sensitive measure of noxious stimulationthan the commonly used variables of heart rate, arterial bloodpressure and BIS in children anaesthetized with sevoflurane.     

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     

Closed-loop control of propofol anaesthesia using bispectral index: performance assessment in patients receiving computer-controlled propofol and manually controlled remifentanil infusions for minor surgery

Background. In a previous study we used the bispectral index(BIS)^TM for automatic control of propofol anaesthesia, usinga proportional-integral-differential control algorithm. As controlwas less than optimal in some patients, we revised the constantsof the control algorithm. The aim of the current study was tomeasure the performance of the revised system in patients undergoingminor surgery under propofol and remifentanil anaesthesia. Methods. Twenty adult patients scheduled for body surface surgerywere enrolled. Anaesthesia was manually induced with target-controlledinfusions (TCI) of propofol and remifentanil. After the startof surgery, when anaesthesia was clinically adequate, automaticcontrol of the propofol TCI was commenced using the revisedclosed-loop system. For patients 11–20, effect-site steeringwas also incorporated into the closed-loop control algorithm.Adequacy of anaesthesia during closed-loop control was assessedclinically, and by calculating the median performance error(MDPE), the median absolute performance error (MDAPE) and themean offset of the control variable. Results. The system provided adequate operating conditions andstable cardiovascular values in all patients during closed-loopcontrol. The mean MDPE and MDAPE were –0.42% and 5.63%,respectively. Mean offset of the BIS^TM from setpoint was –0.2.No patients reported awareness or recall of intraoperative events. Conclusions. The system was able to provide clinically adequateanaesthesia in all patients, with better accuracy of controlthan in the previous study. There was a tendency for more accuratecontrol in those patients in whom the control algorithm incorporatedeffect-site steering. Br J Anaesth 2003; 90: 737–41     

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     

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     

Sevoflurane preconditions stunned myocardium in septic but not healthy isolated rat hearts

Background. Recent evidence indicates that sevoflurane treatmentbefore prolonged ischaemia reduces infarct size in normal hearts,mimicking ischaemic preconditioning. We examined whether exposureto sevoflurane before brief ischaemia, inducing a ‘stunnedmyocardium’, provided such protective effects in an isolatedworking heart from normal or septic rats. Methods. With institutional approval, 91 rats were randomlyallocated into one of either caecal-ligation and perforation(CLP: n=50) or sham (Sham: n=41) procedure groups 24 h beforethe study. After determination of baseline measurements, includingcardiac output (CO), myocardial oxygen consumption (mV^·O₂)and cardiac efficiency (CE; COxpeak systolic pressure/mV^·O₂),each isolated heart was perfused with or without 2% sevofluranefor 15 min before global ischaemia (pre-ischaemia). After 15min ischaemia and 30 min reperfusion, all hearts were assessedfor functional recovery of myocardium (post-reperfusion). Results. During the pre-ischaemia period, 2% sevoflurane causeda significant reduction of CO in the CLP group compared withthe Sham group. During the post-reperfusion period, both CO(16.9 vs 11.0 ml min^–1) and CE (11.2 vs 7.7 mm Hg ml^–1(µl O₂)^–1) was higher in the sevoflurane-treatedvs -untreated hearts from CLP rats, and was accompanied by lowerincidence of reperfusion arrhythmia compared with control hearts(8 vs 32%). In contrast, 2% sevoflurane did not provide cardioprotectiveeffects in normal rats. Conclusions. The current study demonstrates that pre-treatmentwith sevoflurane minimizes myocardial dysfunction and the incidenceof reperfusion arrhythmia after brief ischaemic insults in septichearts. Br J Anaesth 2002; 89: 896–903     

Comparison of the role of endothelin, vasopressin and angiotensin in arterial pressure regulation during sevoflurane anaesthesia in dogs

Background. In this study we aimed to clarify the role of endothelinin arterial pressure regulation during anaesthesia with increasingconcentrations of sevoflurane (1–3 MAC) and compare itwith those of vasopressin and angiotensin. Methods. After an awake control period, on different days, sixdogs underwent each of the following four interventions: sevofluraneanaesthesia alone (1–3 MAC), sevoflurane after block ofeither endothelin receptors using tezosentan (3 mg kg^–1followed by 3 mg kg^–1 h^–1), vasopressinV_1a receptors using [d(CH₂)₅Tyr(Me²)]AVP (40 µg kg^--1)or angiotensin receptors using losartan (6 mg kg^–1 h^–1).Plasma concentrations of endothelin, big endothelin, vasopressinand renin were measured. Effects of sevoflurane in the presenceand absence of the respective receptor block were analysed andcompared using analysis of variance for repeated measures (ANOVAfollowed by Fisher’s PLSD (protected least significantdifference) (P<0.05)). Results. Mean arterial pressure decreased in a dose-dependentmanner with sevoflurane during all interventions. At 1 MAC,this decrease was greatest during angiotensin receptor block(mean (SEM), –41 (3) mm Hg), intermediate duringvasopressin and endothelin receptor block (–31 (4) and–30 (2) mm Hg respectively), and least during sevofluranealone (–24 (3) mm Hg). The course of systemic vascularresistance mirrored the course of arterial pressure, while cardiacoutput did not differ between groups. Plasma concentrationsof endothelin, big endothelin and renin did not change duringany intervention, whereas vasopressin concentration increasedfrom