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.     

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.     

Propofol and halothane versus sevoflurane in paediatric day-case surgery: induction and recovery characteristics

Background. The aim of this study was to compare the inductionand recovery characteristics associated with propofol inductionand halothane maintenance with sevoflurane anaesthesia in paediatricday surgery. Methods. In total, 322 children were assigned randomly to i.v.propofol induction and halothane/nitrous oxide maintenance orsevoflurane/nitrous oxide alone. The patients’ age, sex,and type of surgery were recorded, as were the times requiredfor anaesthetic induction, maintenance, recovery and time todischarge home. Postoperative nausea and vomiting, and the incidenceof adverse events during induction and recovery were also noted. Results. No significant differences were detected in age, sex,type of surgery performed or intraoperative opioid administration.Excitatory movement was more common during induction with sevoflurane.The mean time required for induction with propofol was 3.1 mincompared with 5 min in the sevoflurane group (P<0.001). Therecovery time was shorter in the sevoflurane group comparedwith propofol/halothane (23.2 vs 26.4 min, P<0.002). Theincidence of delirium in recovery was greater in the sevofluranegroup (P<0.001). There was no difference between groups inthe time spent on the postoperative ward before discharge home.On the postoperative ward the incidence of both nausea and vomitingwas significantly higher in the sevoflurane group (P=0.034).Five children were admitted to hospital overnight, none foranaesthetic reasons. Conclusions. The increased incidence of adverse events duringinduction, postoperative nausea and vomiting and postoperativedelirium in the sevoflurane group suggests that sevofluraneis not ideal as a sole agent for paediatric day case anaesthesia. Br J Anaesth 2003; 90: 461–6     

Propofol-alfentanil vs propofol-remifentanil for posterior spinal fusion including wake-up test

Background. Wake-up test can be used during posterior spinalfusion (PSF) to ensure that spinal function remains intact.This study aims at assessing the characteristics of the wake-uptest during propofol–alfentanil (PA) vs propofol–remifentanil(PR) infusions for PSF surgery. Methods. Sixty patients with scoliosis and candidates for PSFsurgery were randomly allocated in either alfentanil (PA) orremifentanil (PR) group. After an i.v. bolus of alfentanil 30µg kg^–1 in the PA group or remifentanil 1 µgkg^–1 in the PR group, anaesthesia was induced with thiopentaland atracurium. During maintenance, opioid infusion consistedof alfentanil 1 µg kg^–1 min^–1 or remifentanil0.2 µg kg^–1 min^–1, in the PA group and thePR group, respectively. All patients received propofol 50 µgkg^–1 min^–1. Atracurium was given to maintain therequired surgical relaxation. At the surgeon's request, allinfusions were discontinued. Patients were asked to move theirhands and feet. Time from anaesthetic discontinuation to spontaneousventilation (T₁), and from then until movement of the handsand feet (T₂), and its quality were recorded. Results. The average T₁ and T₂ were significantly shorter inthe PR group [3.6 (2.5) and 4.1 (2) min] than the PA group [6.1(4) and 7.5 (4.5) min]. Quality of wake-up test, however, didnot show significant difference between the two groups studied. Conclusion. Wake-up test can be conducted faster with remifentanilcompared with alfentanil infusion during PSF surgery.     

Etomidate-Lipuro is associated with considerably less injection pain in children compared with propofol with added lidocaine

Background. Propofol is associated with a high incidence ofinjection pain in children, even if given together with lidocaine.A new lipid formulation of etomidate (Etomidate-®Lipuro)has been found in adults to cause very little discomfort duringi.v. injection. The aim of the present prospective, double-blind,randomized trial was to compare the incidence of injection painduring i.v. induction of anaesthesia between propofol with addedlidocaine (previous standard) and this new etomidate formulationin paediatric patients. Methods. A total of 110 paediatric patients, aged 2–16years, scheduled for outpatient surgery were planned to be includedin the study. The primary end point of the study was the incidenceof injection pain during induction of anaesthesia as assessedby a four-point scale as described previously. The occurrenceof myoclonic muscular activity was registered as a secondaryend point (four-point scale). An interim analysis after 80 patientswas requested by the Ethics' Committee. Results. The study was stopped after the inclusion of 80 patients.A significantly lower incidence of injection pain was foundin the Etomidate-®Lipuro group as compared with the propofol–lidocainegroup (5.0% vs 47.5%, P<0.001). The use of etomidate wasassociated with a significantly higher incidence of myoclonicactivity compared with propofol–lidocaine (85.0% vs 15%,P<0.001). Conclusions. The use of a new lipid formulation of etomidateis associated with significantly less injection pain than propofolwith added lidocaine in children. This finding may warrant achange in clinical practice in order to avoid unnecessary painin children.     

Antagonism of neuromuscular blockade but not muscle relaxation affects depth of anaesthesia

Background. Conflicting effects of neuromuscular blocking drugsand anticholinesterases on depth of anaesthesia have been reported.Therefore we evaluated the effect of atracurium and neostigmineon bispectral index (BIS) and middle-latency auditory evokedpotentials (AAI). Methods. We studied 40 patients (ASA I–II) aged 18–69yr. General anaesthesia consisted of propofol and remifentanilby target-controlled infusion and neuromuscular function wasmonitored by electromyography. When BIS reached stable values,patients were randomly assigned to one of two groups. Group1 received atracurium 0.4 mg kg^–1 and, 5 min later, thesame volume of NaCl 0.9%; group 2 received saline first andthen atracurium. When the first twitch of a train of four reached10% of control intensity, patients were again randomized: onegroup (N) received neostigmine 0.04 mg kg^–1 and glycopyrrolate0.01 mg kg^–1, and the control group (G) received onlyglycopyrrolate. Results. Injection of atracurium or NaCl 0.9% had no effecton BIS or AAI. After neostigmine–glycopyrrolate, BIS andAAI increased significantly (mean maximal change of BIS 7.1[SD 7.5], P<0.001; mean maximal change of AAI 9.7 [10.5],P<0.001). When glycopyrrolate was injected alone BIS andAAI also increased (mean maximal change of BIS 2.2 [3.4], P=0.008;mean maximal change of AAI 3.5 [5.7], P=0.012), but this increasewas significantly less than in group N (P=0.012 for BIS; P=0.027for AAI). Conclusion. These data suggest that neostigmine alters the stateof propofol–remifentanil anaesthesia and may enhance recovery.     

Fluoride excretion in children after sevoflurane anaesthesia

Background. Defluorination of sevoflurane is catalysed by thehepatic enzyme cytochrome P450 2E1 (CYP2E1). Data about theontogenesis (developmental variations in activity) of this enzymesuggest a low metabolism of sevoflurane during the first monthsof life. Methods. To test this hypothesis, 45 children less than 48 monthsof age undergoing sevoflurane anaesthesia were enrolled in aprospective open clinical trial. The 24 h urine fluoride excretionwas measured in five groups of children (A, <4 months; B,4 to <8 months; C, 8–12 months; D, >12–24months; and E, >24–48 months old). An index of sevofluranemetabolism (ISM) was calculated as the ratio of fluoride excretion,cumulative expiratory sevoflurane concentrations measured everyminute during anaesthesia, and body surface area. ISM valueswere median (IQ 25–75%). Results. ISM was lower in group A (n=9, 18.9 (11.2–29.5)than group C (n=11, 44.2 (37.5–53.5), P<0.05), groupD (n=7, 52.6 (45.8–68.4), P<0.01) and group E (n=9,53.6 (50.7–85), P<0.001). Median ISM expressed as afunction of median age, exponentially increased with a rapidincrease during the first months of life, followed by a slowerincrease after 10 months of age. Conclusion. These results suggest that, in children less than48 months, sevoflurane metabolism parallels postnatal developmentof CYP2E1. Br J Anaesth 2002; 89: 693–6     

Effects of xenon anaesthesia on the circulatory response to hypoventilation

Background. Circulatory response to hypoventilation is aimedat eliminating carbon dioxide and maintaining oxygen delivery(DO₂) by increasing cardiac output (CO). The hypothesis thatthis increase is more pronounced with xenon than with isofluraneanaesthesia was tested in pigs. Methods. Twenty pigs received anaesthesia with xenon 0.55 MAC/remifentanil0.5 µg kg^–1 min^–1 (group X, n=10) or isoflurane0.55 MAC/remifentanil 0.5 µg kg^–1min^–1 (groupI, n=10). CO, heart rate (HR), mean arterial pressure (MAP)and left ventricular fractional area change (FAC) were measuredat baseline, after 5 and 15 min of hypoventilation and after5, 15 and 30 min of restored ventilation. Results. CO increased by 10–20% with both anaesthetics,with an equivalent rise in HR, maintaining DO₂ in spite of a20% reduction in arterial oxygen content. Decreased left ventricular(LV) afterload during hypoventilation increased FAC, and thiswas more marked with xenon (0.60–0.66, P<0.05 comparedwith baseline and isoflurane). This difference is attributedto negative inotropic effects of isoflurane. Increased pulmonaryvascular resistance during hypoventilation was found with bothanaesthetics. Conclusion. The cardiovascular effects observed in this modelof moderate hypoventilation were sufficient to maintain DO₂.Although the haemodynamic response appeared more pronouncedwith xenon, differences were not clinically relevant. An increasein FAC with xenon is attributed to its lack of negative inotropiceffects.     

Cerebral autoregulation in children during sevoflurane anaesthesia

Introduction. Little is known about cerebral autoregulationin children. The aim of this study was to examine cerebral autoregulationin children. Methods. Cerebral autoregulation testing was performed duringless than 1 MAC sevoflurane anaesthesia in children (from 6months to 14 yr) and in adults (18–41 yr). Mean middlecerebral artery flow velocities (V_MCA) were measured using transcranialDoppler ultrasonography. Mean arterial pressure (MAP) was increasedto whichever was greater: 20% above baseline or (i) 80 mm Hgfor less than 9 yr, (ii) 90 mm Hg for 9–14 yr, and (iii)100 mm Hg for adults. Cerebral autoregulation was consideredintact if the autoregulatory index was     

Comparison of 1% and 2% lidocaine epidural anaesthesia combined with sevoflurane general anaesthesia utilizing a constant bispectral index

Background. The authors compared the effects of epidural anaesthesiawith lidocaine 1% and lidocaine 2% on haemodynamic variables,sevoflurane requirements, and stress hormone responses duringsurgery under combined epidural/general anaesthesia with bispectralindex score (BIS) kept within the range 40–50. Methods. Thirty-three patients undergoing lower abdominal surgerywere randomly divided into two groups to receive lidocaine 1%or 2% by epidural with sevoflurane general anaesthesia. Sevofluranewas adjusted to achieve a target BIS of 40–50 during maintenanceof anaesthesia with nitrous oxide 60% in oxygen. Measurementsincluded the inspired (FI_SEVO) and the end-tidal sevofluraneconcentrations (E'_SEVO), blood pressure (BP), and heart rate(HR) before surgery and every 5 min during surgery for2 h. Plasma samples were taken immediately before and duringsurgery for measurements of catecholamines, cortisol, and lidocaine. Results. During surgery, both groups were similar for HR, BPand BIS, but FI_SEVO and E'_SEVO were significantly higher andmore variable with lidocaine 1% than with 2%. Intraoperativeplasma concentrations of epinephrine and cortisol were foundto be higher with lidocaine 1% as compared with 2%. Conclusions. To maintain BIS of 40–50 during combinedepidural/general anaesthesia for lower abdominal surgery, sevofluraneconcentrations were lower and less variable with lidocaine 2%than with 1%. In addition, the larger concentration of lidocainesuppressed the stress hormone responses better. Br J Anaesth 2003; 91: 825–9     

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     

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.     

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.     

Awareness and the EEG power spectrum: analysis of frequencies

Background. Power spectral analysis is a well-established methodfor the analysis of EEG signals. Spectral parameters can beused to quantify pharmacological effects of anaesthetics onthe brain and the level of sedation. This method, in numerousvariations, has been applied to depth of anaesthesia monitoringand has been incorporated into several commercially availableEEG monitors. Because of the importance of EEG spectral analysis,we evaluated the performance of each frequency in the powerspectrum regarding detection of awareness. Methods. Ninety artefact-free EEG segments of length 8 s wereobtained from a database that contains perioperatively recordedEEG data. For the present analysis, EEG data were selected from39 patients with propofol–remifentanil or sevoflurane–remifentanilanaesthesia with a period of awareness. Half of the EEG segmentswere recorded during periods of awareness as defined by an adequateresponse to the command ‘squeeze my hand’. The otherhalf were from unresponsive patients. The power spectral densitywas calculated for each segment. The performance of each frequencybin of the power spectrum as a detector of awareness was assessedwith a remapped prediction probability rP_K, i.e. the predictionprobability P_K mapped to a range of 0.5–1. Results. The remapped prediction probability was high (rP_K>0.8)for low frequencies (<15 Hz) and for high frequencies (>26Hz), with a minimum (rP_K<0.55) at 21 Hz. Indentations inthe ‘performance spectrum’ occur at the power-linefrequency (50 Hz) and its harmonics and at 78 Hz, probably causedby the continuous impedance measurement of another device usedin parallel. With the exception of the indentations, the remappedprediction probability of the high frequencies (>35 Hz) was>0.95. Conclusions. The best performance for the detection of awarenesswas achieved by EEG power spectral frequencies from >35 Hzup to 127 Hz. This frequency band may be dominated by muscleactivity. The frequency band between 15 and 26 Hz may be oflimited value, as reflected by lower rP_K values.     

Effect of nitrous oxide on cerebrovascular reactivity to carbon dioxide in children during sevoflurane anaesthesia

Background. Sevoflurane and nitrous oxide have intrinsic cerebralvasodilatory activity. To determine the effects of nitrous oxideon cerebrovascular reactivity to carbon dioxide (CCO₂R) duringsevoflurane anaesthesia in children, middle cerebral arteryblood flow velocity (V_mca) was measured over a range of end-tidalcarbon dioxide concentrations (E'_CO2), using transcranial Doppler(TCD) ultrasonography. Methods. Ten children aged 1.5–6 yr were anaesthetizedwith sevoflurane and received a caudal block. Patients wereallocated randomly to receive either air–nitrous oxideor nitrous oxide–air. Further randomization determinedthe sequence of E'_CO2 (25, 35, 45, and 55 mm Hg) and sevoflurane(1.0 then 1.5 MAC or 1.5 then 1.0 MAC) concentrations. Oncesteady state had been reached, three measurements of V_mca, meanarterial pressure (MAP), and heart rate (HR) were recorded. Results. Cerebrovascular carbon dioxide reactivity was reducedin the 25–35 mm Hg E'_CO2 range on the addition of nitrousoxide to 1.5 MAC, but not 1.0 MAC sevoflurane. A plateau inCCO₂R of 0.4–0.6% per mm Hg was seen in all groups betweenE'_CO2 values of 45 and 55 mm Hg. Mean HR and MAP remained constantthroughout the study period. Conclusions. Cerebrovascular carbon dioxide reactivity is reducedat and above an E'_CO2 of 45 mm Hg during 1.0 and 1.5 MAC sevofluraneanaesthesia. The addition of nitrous oxide to 1.5 MAC sevofluranediminishes CCO₂R in the hypocapnic range. This should be takeninto consideration when hyperventilation techniques for reductionof brain bulk are being contemplated in children with raisedintracranial pressure. Br J Anaesth 2003; 91: 190–5     

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.      

Comparative efficacy and safety of remifentanil and fentanyl in 'fast track' coronary artery bypass graft surgery: a randomized, double-blind study

This multi-centre, parallel group, randomized, double-blindstudy compared the efficacy and safety of high-dose remifentaniladministered by continuous infusion with an intermittent bolusfentanyl regimen, when given in combination with propofol forgeneral anaesthesia in 321 patients undergoing elective coronaryartery bypass graft surgery. A significantly lower proportionof the patients who received remifentanil had responses to maximalsternal spread (the primary efficacy endpoint) compared withthose who received fentanyl (11% vs 52%; P<0.001). More patientswho received remifentanil responded to tracheal intubation comparedwith those who received fentanyl (24% vs 9%; P<0.001). However,fewer patients who received remifentanil responded to sternalskin incision (11% vs 36%; P<0.001) and sternotomy (14% vs60%; P <0.001). Median time to extubation was longer in thesubjects who received remifentanil than for those who receivedfentanyl (5.1 vs 4.2 h; P=0.006). There were no statisticallysignificant differences between the two groups in the timesfor transfer from intensive care unit or hospital dischargebut time to extubation was significantly longer in the remifentanilgroup. Overall, the incidence of adverse events was similarbut greater in the remifentanil group with respect to shivering(P<0.049) and hypertension (P<0.001). Significantly moredrug-related adverse events were reported in the remifentanilgroup (P=0.016) There were no drug-related adverse cardiac outcomesand no deaths from cardiac causes before hospital dischargein either treatment group. Br J Anaesth 2001; 87: 718–26     

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     

Remifentanil or propofol for sedation during carotid endarterectomy under cervical plexus block

Background. During carotid endarterectomy under regional anaesthesia,patients often require medication to control haemodynamic instabilityand to provide sedation and analgesia. Propofol and remifentanilare used for this purpose. However, the benefits, side-effects,and optimal dose of these drugs in such patients are unclear. Methods. Sixty patients were included in a prospective, randomized,single blinded study. All patients received a deep cervicalplexus block with 30 ml ropivacaine 0.75% and were randomizedto receive either remifentanil 3 µg kg^–1 h^–1or propofol 1 mg kg^–1 h^–1. The infusions were startedafter performing the regional block and were stopped at theend of surgery. Arterial pressure, ECG, ventilatory rate, andPa_CO2 were measured continuously and recorded at predeterminedtimes. Twenty-four hours after surgery, patient comfort, andsatisfaction were also evaluated. Results. In three patients, the infusion of remifentanil hadto be stopped because of severe respiratory depression or bradycardia.No significant differences were found between the two groupsin haemodynamic variables or sedative effects, but there wasa significantly greater decrease in ventilatory frequency andincrease in Pa_CO2 in the remifentanil group. The patient’ssubjective impressions and pain control were excellent in bothgroups. Conclusion. As a result of the higher incidence of adverse respiratoryeffects with remifentanil and similar sedative effects, propofolis preferable for sedation during cervical plexus block in elderlypatients with comorbid disease at the dosage used. Br J Anaesth 2002; 89: 637–40