Influence of the baricity of a local anaesthetic agent on sedation with propofol during spinal anaesthesia

Background: This study examined the effect of different levels of spinalanaesthesia, induced by solutions of different baricity butcontaining the same amount of local anaesthetic agent, on therequirement for sedation with propofol. Methods: Thirty-six patients undergoing varicose vein surgery under spinalanaesthesia were randomly allocated to receive tetracaine 15mg in 3 ml of either glucose 5% (hyperbaric) or CSF (isobaric).I.V. propofol was started 5 min after the intrathecal injectionand was titrated to maintain a bispectral index (BIS) scoreof 65–75. The propofol requirements to maintain this rangein the two groups were compared every 5 min. Results: The propofol requirement was always lower in the hyperbaricgroup, with the differences becoming statistically significant20 min after the intrathecal injection. Total consumption ofpropofol over the 55 min of the study was also less in the hyperbaricgroup. Conclusion: The known difference in level of spinal anaesthetic block inducedby solutions of different baricity, but the same dose of localanaesthetic, was associated with different requirements forpropofol sedation as determined by BIS assessment.     

Multi-level approach to anaesthetic effects produced by sevoflurane or propofol in humans: 1. BIS and blink reflex

Background: The relative roles of forebrain and brainstem in producing adequateanaesthesia are unclear. Methods: We simultaneously analysed the effects of sevoflurane (GroupS; n = 18) or propofol (Group P; n = 29) on the bispectral index(BIS) and the first component of the blink reflex (R1). Thedose of anaesthetic agent was increased until loss of blinkreflex. After discontinuation and reappearance of blink reflexactivity, the amount was increased again. The area under curveR1 (area-R1) of the electromyogram of the orbicularis oculimuscle after electrical stimulation of the supraorbital nervewas measured. Using a sigmoid E_max model and a first-order rateconstant k_e0, we characterized the dose–response relationshipsfor BIS and area-R1. Results: Concentration-dependent depression of BIS and area-R1 was adequatelymodelled. The concentration that causes an effect midway betweenminimum and maximum (EC₅₀) for area-R1 was smaller than EC₅₀for BIS in both groups [0.34 (0.19) vs 1.29 (0.19) vol% and1.78 (0.65) vs 2.69 (0.67) µg ml^–1; mean (SD)].At doses of sevoflurane and propofol with equivalent depressionof BIS, sevoflurane depressed area-R1 more than propofol. Thek_e0 for area-R1 was about half that for BIS in both groups:0.24 (0.19–0.29) vs 0.48 (0.38–0.60) min^–1for Group S; 0.28 (0.23–0.34) vs 0.46 (0.40–0.54)min^–1 for Group P, geometric mean (95% CI). Conclusions: The blink reflex (brainstem function) is more sensitive to sevofluraneor propofol than BIS (forebrain function). Sevoflurane suppressesthe blink reflex more than propofol. Different k_e0s for blinkreflex vs BIS indicate different effect sites.     

Multi-level approach to anaesthetic effects produced by sevoflurane or propofol in humans: 2. BIS and tetanic stimulus-induced withdrawal reflex

Background: General anaesthesia could be assessed at two sites: corticalstructures and the spinal cord. However, the practicalitiesof measurement at these two sites differ substantially. Methods: We simultaneously analysed effects of sevoflurane (Group S;n = 16) or propofol (Group P; n = 17) on bispectral index (BIS)and the tetanic stimulus-induced withdrawal reflex (TIWR). TIWRwas quantified by the area under the curve of the electromyogramof the biceps femoris muscle after electrical stimulation ofthe sural nerve. After loss of consciousness, TIWR was evokedonce per minute. The anaesthetic was increased until TIWR disappeared.After discontinuation of the anaesthetic and reappearance ofTIWR, the amount of anaesthetic was increased again. Using asigmoid E_max model and a first-order rate constant k_e0, we characterizedthe dose–response relationships for BIS and TIWR. Results: Concentration-dependent depression of TIWR was reasonably wellmodelled for sevoflurane, but poorly for propofol. TIWR wascompletely suppressed by sevoflurane, but not propofol. Sevofluranereduced TIWR to 5 mV ms (very weak movement) at 1.68 vol% end-expiredconcentration [ minimum alveolar concentration (MAC value)].The k_e0s for TIWR were smaller than those for BIS: 0.25 (0.16–0.39)vs 0.41 (0.33–0.51) min^–1 for Group S; 0.25 (0.22–0.30)vs 0.34 (0.29–0.40) min^–1 for Group P [geometricmean (95% CI)]. Conclusions: High concentrations of sevoflurane depress TIWR more than propofol.With propofol, we frequently observed a paradoxical behaviourof muscles of the lower leg. TIWR lags behind BIS, indicatingdifferent effect sites for two intended anaesthetic effects:unresponsiveness to noxious stimulation and unconsciousness.     

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     

Clonidine decreases propofol requirements during anaesthesia: effect on bispectral index

Assessment of the effect of clonidine on depth of anaesthesiais difficult because clonidine combines analgesic, sedativeand direct haemodynamic effects. We thus evaluated the influenceof clonidine on the bispectral index (BIS) and its potentialdose-sparing effect on propofol. After induction of anaesthesiawith target-controlled infusion of propofol and obtaining anunchanged bispectral index (pre-BIS), clonidine 4 µg kg^–1or placebo was administered randomly to 50 patients in a double-blindmanner. Subsequently, if there was a decrease in BIS we reducedthe target concentration of propofol until pre-BIS was reached.The pre-BIS was maintained and a remifentanil infusion was addedduring surgery. The courses of the BIS, heart rate and bloodpressure were recorded and the total amounts of intra-operativepropofol and remifentanil were determined. Assessment of implicitmemory during anaesthesia was performed with an auditory implicitmemory test consisting of item sequences. Administration ofclonidine resulted in a decrease in the BIS from 45 (SD 4) to40 (6) (P<0.001), which allowed a reduction of propofol targetconcentration from 3.3 (0.6) to 2.7 (0.7) µg ml^–1(P<0.001) and measured propofol concentration from 2.9 (0.6)to 2.5 (0.7) µg ml^–1 (P=0.009) in order tomaintain the pre-BIS value. During subsequent surgery, propofolrequirements were reduced by 20% (P=0.002) in the clonidinegroup and a similar amount of remifentanil was used in eachgroup. The increase in anaesthetic depth given by clonidinecan therefore be measured with bispectral EEG analysis and allowsreduction of the propofol dose to achieve a specific depth ofanaesthesia. Br J Anaesth 2001; 86: 627–32     

Loss of volition and pain response during induction of anaesthesia with propofol or sevoflurane

We compared the time to reach two anaesthetic end-points duringinduction of anaesthesia with a potent inhalation agent (sevoflurane)and an i.v. agent (propofol). We used a method to ensure steadybreathing during inhalation induction, and measured loss oftone in the outstretched arm and loss of response to a painfulstimulus. Thirty-eight female patients (age 39 (9) yr, weight65 (11) kg, and height 165 (8) cm) (mean (SD)) were randomlyallocated to receive either propofol or sevoflurane. The predictedinduction dose of propofol, estimated from age and weight foreach patient, was given at a rate of 1% of the induction doseper second, to a possible maximum of 2.5 times the predictedinduction dose. Sevoflurane was given with an inhaled concentrationof 8%, which was anticipated to cause loss of arm tone within90–120 s. After loss of consciousness, we applied a painfulelectrical stimulus to a finger at 15-s intervals and measuredthe time to loss of motor response. The median times and interquartilevalues for loss of arm tone were 105 (88–121) s for sevofluraneand 65 (58–80) s for propofol. This was equivalent to0.65 of the ED₅₀ of propofol. The time to loss of response topain was 226 (169–300) s for sevoflurane. The variancesof these three measurements were not significantly different,indicating that these dose–response relationships weresimilar. In contrast, only 11 of the patients given propofollost the response to pain after 2.5xED₅₀ had been given. Theseresults support previous evidence of substantial differencesbetween anaesthetic end-points, and show that this evidencecan be obtained using a simple and rapid method. Br J Anaesth 2001; 87: 283–6     

Measuring depth of anaesthesia using changes in directional connectivity: a comparison with auditory middle latency response and estimated bispectral index during propofol anaesthesia

General anaesthesia is associated with changes in connectivity between different regions of the brain, the assessment of which has the potential to provide a novel marker of anaesthetic effect. We propose an index that quantifies the strength and direction of information flow in electroencephalographic signals collected across the scalp, assess its performance in discriminating ‘wakefulness’ from ‘anaesthesia’, and compare it with estimated bispectral index and the auditory middle latency response. We used a step-wise slow induction of anaesthesia in 10 patients to assess graded changes in electroencephalographic directional connectivity at propofol effect-site concentrations of 2 μg.ml⁻¹, 3 μg.ml⁻¹ and 4 μg.ml⁻¹. For each stable effect-site concentration, connectivity was estimated from multichannel electroencephalograms using directed coherence, together with middle latency response and estimated bispectral index. We used a linear support vector machine classifier to compare the performance of the different electroencephalographic features in discriminating wakefulness from anaesthesia. We found a significant reduction in the strength of long-range connectivity (interelectrode distance > 10 cm) (p < 0.008), and a reversal of information flow from markedly postero-frontal to fronto-posterior (p < 0.006) between wakefulness and a propofol effect-site concentration of 2 μg.ml⁻¹. This then remained relatively constant as effect-site concentration increased, consistent with a step change in directed coherence with anaesthesia. This contrasted with the gradual change with increasing anaesthetic dose observed for estimated bispectral index and middle latency response. Directed coherence performed best in discriminating wakefulness from anaesthesia with an accuracy of 95%, indicating the potential of this new method (on its own or combined with others) for monitoring adequacy of anaesthesia.     

Variation of bispectral index under TIVA with propofol in a paediatric population

BACKGROUND: In this prospective observational study, we aim to explore the relationship between age and bispectral index (BIS) values at different plasma concentrations of propofol. METHODS: Fifty children aged from 3 to 15 yr were included. Anaesthesia was induced using a target-controlled infusion of propofol with the Kataria pharmacokinetic model together with a bolus of remifentanil followed by a continuous infusion rate at 0.2 microg kg(-1) min(-1). Target plasma propofol concentration was initially stabilized to 6 microg ml(-1) and continued for 6 min. The target was then decreased and stabilized to 4 microg ml(-1) and then to 2 microg ml(-1). BIS values, plasma propofol concentration, and EEG were continuously recorded. In order to explore the relationship between variations in propofol concentration and the EEG bispectrum, we used a multiple correspondence analysis (MCA). Results are shown in median (range). RESULTS: We found no statistical difference between BIS values with propofol 6 microg ml(-1) [23 (12-40)] and 4 microg ml(-1) [28 (9-67)]. At 2 microg ml(-1), BIS was significantly different [52 (24-71)], but a significant correlation between the age of children and BIS values was found (r2=0.66; P<0.01). There was little change in children's position between 6 and 4 microg ml(-1) in the structure model of the MCA. From 4 to 2 microg ml(-1), the position of children moved only on axis 2. CONCLUSIONS: These results showed the difficulty to interpret BIS values because of the absence of significant change for higher plasma propofol concentration variation or because of the link with age for the lower plasma concentration.     

Comparative evaluation of the cerebral state index and the bispectral index during target-controlled infusion of propofol

Background. Cerebral state index (CSI) has recently been introducedas an intra-operative monitor of anaesthetic depth. We comparedthe performance of the CSI to the bispectral index (BIS) inmeasuring depth of anaesthesia during target-controlled infusion(TCI) of propofol. Methods. Twenty Chinese patients undergoing general anaesthesiawere recruited. CSI and BIS, and predicted effect-site concentrationof propofol were recorded. The level of sedation was testedby Modified Observer's Assessment of Alertness/Sedation Scale(MOAAS) every 20 s during stepwise increase (TCI, 0.5 µgml^–1) of propofol. The loss of verbal contact (LVC) andloss of response (LOR) were defined by MOAAS values of 2–3and less than 2, respectively. Baseline variability and theprediction probability (P_K) were calculated for the BIS andCSI. The values of BIS₀₅ and CSI₀₅, BIS₅₀ and CSI₅₀, BIS₉₅ andCSI₉₅ were calculated at each end-point (LVC and LOR). Results. Baseline variability of CSI was more than that of BIS.Both CSI and BIS showed a high prediction probability for thesteps awake vs LVC, awake vs LOR, and LVC vs LOR, and good correlationswith MOAAS values. Conclusion. Despite larger baseline variation, CSI performedas well as BIS in terms of P_K values and correlations with stepchanges in sedation.     

Target-controlled infusion of propofol and remifentanil in cardiac anaesthesia: influence of age on predicted effect-site concentrations

Background. Propofol-anaesthesia administrated via target-controlledinfusion (TCI) has been proposed for cardiac surgery. Age-relatedchanges in pharmacology explain why propofol dose requirementis reduced in elderly patients. However, the Marsh pharmacokineticmodel incorporated in the Diprifusor propofol device does nottake age into account as a covariable. In the absence of depthof anaesthesia monitoring, this limitation could cause adversecardiovascular effects resulting from propofol overdose in olderpatients. We assessed the influence of age on effect-site propofolconcentrations predicted by the Diprifusor and titrated to thebispectral index score (BIS) during cardiac anaesthesia. Methods. Forty-five patients received propofol by Diprifusorand remifentanil by software including Minto model. Propofoland remifentanil effect-site concentrations were adapted toBIS (40–60) and haemodynamic profile, respectively. Theinfluence of age on effect-site concentrations was assessedby dividing patients into two groups: young (<65 yr) andelderly (     

Cerebrospinal fluid and blood propofol concentration during total intravenous anaesthesia for neurosurgery

Background. The aim of this paper is to compare the propofolconcentration in blood and cerebrospinal fluid (CSF) in patientsscheduled for different neurosurgical procedures and anaesthetizedusing propofol as part of a total intravenous anaesthesia technique. Methods. Thirty-nine patients (ASA I–III) scheduled forelective intracranial procedures, were studied. Propofol wasinfused initially at 12 mg kg^–1 h^–1 and thenreduced in steps to 9 and 6 mg kg^–1 h^–1. Duringanaesthesia, bolus doses of fentanyl and cis-atracurium wereadministered as necessary. After tracheal intubation the lungswere ventilated to achieve normocapnia with an oxygen-air mixture(FI_O2=0.33). Arterial blood and CSF samples for propofol examinationwere obtained simultaneously directly after intracranial drainageinsertion and measured using high-performance liquid chromatography.The patients were divided into two groups depending on the typeof neurosurgery. The Aneurysm group consisted of 13 patientswho were surgically treated for ruptured intracranial aneurysm.The Tumour group was composed of 26 patients who were undergoingelective posterior fossa extra-axial tumour removal. Results. Blood propofol concentrations in both groups did notdiffer significantly (P>0.05). The propofol concentrationin CSF was 86.62 (SD 37.99) ng ml^–1 in the Aneurysm groupand 50.81 (26.10) ng ml^–1 in the Tumour group (P<0.005). Conclusions. Intracranial pathology may influence CSF propofolconcentration. However, the observed discrepancies may alsoresult from quantitative differences in CSF composition andfrom restricted diffusion of the drug in the CSF. Br J Anaesth 2003; 90: 84–6     

Bispectral index is a topographically dependent variable in patients receiving propofol anaesthesia

Background. As very strong agreement has been reported betweenbispectral index (BIS) values measured from the occipital andfrontal skull areas, we compared BIS values measured from centraland parietal areas with those from frontal area to investigatewhether BIS is really a topographically dependent or topographicallyindependent variable. Methods. Twenty patients, ASA I–II, non-obese, aged 18–62yr and with no neurological disorders were enrolled. Based onthe 10–20 international landmarks, five silver dome electrodeswere positioned: F7, C3, P7, Cz (common reference) and Fp1 (ground).Using frontal (F7–Cz), central (C3–Cz) and parietal(P7–Cz) electrode montages, the corresponding BIS valueswere simultaneously recorded with an Aspect A-1000 monitor (softwarev3.12). The BIS values were recorded at the propofol concentrationallowing laryngeal mask insertion, which was maintained duringthe 10 min data collection period in absence of additional externalstimuli. Data were analysed using the Kruskall–Wallis,Wilcoxon paired sign with Bonferroni correction, Bland–Altmanand linear correlation tests. Results. At the predicted effect target propofol concentration4–8 µg ml^–1, the 10 min mean BIS (median [min–max])were 32 [20–44], 46 [28–68] and 58 [41–72]for the frontal, central and parietal leads, respectively. Differencesbetween these BIS recordings were statistically significant(P<0.0001, Kruskall–Wallis; P<0.005, Wilcoxon pairedsign test). Conclusions. The present results provide evidence that BIS indexis a topographically dependent variable in patients receivingpropofol anaesthesia.     

Remifentanil target-controlled infusion vs propofol target-controlled infusion for conscious sedation for awake fibreoptic intubation: a double-blinded randomized controlled trial

BACKGROUND: Awake fibreoptic intubation (AFOI) is a technique used in patients with difficult airways. This study compares the suitability of remifentanil target-controlled infusion (TCI) to propofol TCI for conscious sedation during AFOI in patients with bona fide difficult airways. METHODS: We recruited 24, ASA I-III patients, who were undergoing sedation for elective AFOI. Patients were randomized to one of the two groups, Group P (n=10) received propofol TCI and Group R (n=14) received remifentanil TCI. Primary outcome measures were conditions achieved at endoscopy, intubation, and post-intubation, which were graded using scoring systems. Other parameters measured were the endoscopy time, intubation time, and number of attempts at intubation. A postoperative interview was conducted to determine recall of events and level of patient satisfaction. RESULTS: Endoscopy scores (0-5) and intubation scores (0-5) were significantly different [Group P 3 (1-4) vs Group R 1 (0-3) P<0.0001, Group P 3 (2-4) vs Group R 1 (0-3) P<0.0001, respectively]; with much better conditions in Group R, endoscopy times and intubation times were also significantly different, being shorter in Group R (P<0.007 and P<0.023, respectively). Patient tolerance of the procedure, judged by the discomfort scores (P<0.004) and the post-intubation scores (P<0.08), was significantly better in Group R. The level of recall for events was higher in Group R. However, there were no significant differences in the patient satisfaction scores. CONCLUSIONS: Remifentanil TCI appears to provide better conditions for AFOI when compared with propofol TCI. The disadvantage of remifentanil in this setting may be a higher incidence of recall.     

Entropy of EEG during anaesthetic induction: a comparative study with propofol or nitrous oxide as sole agent

Background. The search continues for an anaesthetic monitorthat can define the level of anaesthesia in an individual patientirrespective of anaesthetic agent(s) used. Studies of availablemonitors based on bispectral analysis or evoked auditory potentialsshow the complexity of the problem. We assessed a new monitor,based on the entropy of the EEG, during induction of anaesthesiawith either propofol or nitrous oxide. Methods. In an open, randomized study (two groups; n=10) ofday surgical patients, we induced loss of response with incrementalboluses of propofol. The other group was given propofol 30 mgand then increasing concentrations of nitrous oxide until lossof response. We measured entropy with the M-Entropy Module S/5^TM(Datex-Ohmeda) using forehead electrodes and recorded responseentropy (RE; including frontal electromyogram) and state entropy(SE; only the cortical EEG). Values are median (range). Results. Baseline values were RE 98 (96–100), SE 89 (87–91)and RE 98 (96–99), SE 89 (87–91) for the propofoland nitrous oxide patients, respectively. During propofol induction,both entropy indices decreased with increasing sedation, withRE 40 (23–76) and SE 34 (17–70) at loss of response.Neither RE nor SE decreased during nitrous oxide inhalation,and at loss of response using nitrous oxide, RE and SE wereunchanged at 98 (96–100) and 88 (85–91) respectively. Conclusions. The entropy monitor of anaesthetic depth showsa successive decrease with propofol but loss of consciousnesswith nitrous oxide is not associated with change in entropyindices. Br J Anaesth 2004; 92: 167–70     

Mid-latency auditory evoked response during propofol and alfentanil anaesthesia

Background. Propofol has been shown to affect the mid-latencyauditory evoked response (MLAER) in a dose-dependant manner.Few studies have investigated the addition of alfentanil. Myogenicresponses, such as the post-auricular responses (PAR), can confoundthe MLAER but there has been little investigation as to whichelectrode site reduces this interference. Methods. We studied the MLAER in 27 women. They received aninfusion of alfentanil 15 µg kg^–1 h^–1, followedby either a high or low infusion regimen of propofol (finalinfusion rates 6 and 3 mg kg^–1 h^–1). We comparedthe results with those of our study using propofol alone. Wecollected the data from two electrode sites: vertex–inionand vertex–mastoid. We evaluated the occurrence of thePAR and the shape of the MLAER at each electrode site. Results. The infusion rate of propofol associated with lossof the eyelash response in 50% of subjects was 3.3 mg kg^–1h^–1. This was significantly lower than using propofolalone (5.8 mg kg^–1 h^–1). Nb latency was the bestMLAER discriminator of unconsciousness (sensitivity 94%, specificity88%), with a threshold of 46 ms (propofol alone was 53 ms).The addition of alfentanil did not alter the relationship betweenpropofol infusion rate and MLAER. The vertex–inion electrodesite gave the best protection against PAR in awake subjects(P=0.0003), and after 30 min of propofol infusion (P=0.06).The magnitude of the MLAER obtained from the vertex–mastoidelectrodes was larger than from the other site, although theincrease was not consistent throughout the waveform (brain stem100%, Nb 14%). Conclusions. Addition of alfentanil lowers the propofol infusionrate required to produce unconsciousness and the Nb latencythat predicts it. The better of the two sites to reduce theincidence of PAR is the vertex–inion electrode site. Br J Anaesth 2004; 92: 25–32     

Effect of an intubation dose of rocuronium on Spectral Entropy and Bispectral Index responses to laryngoscopy during propofol anaesthesia

Background. The spectral entropy of the electroencephalogramhas been proposed to monitor the depth of anaesthesia. StateEntropy (SE) reflects the level of hypnosis. Response Entropy(RE), computed from electroencephalogram and facial muscle activity,reflects the response to nociceptive stimulation. We evaluatedthe effect of rocuronium on Bispectral Index^TM (BIS) and entropyresponses to laryngoscopy. Methods. A total of 25 patients were anaesthetized with propofolusing a target-controlled infusion. At steady state, they randomlyreceived 0.6 mg kg^–1 rocuronium (R) or saline (S). After3 min, a 20 s laryngoscopy was applied. BIS, RE and SE wererecorded continuously and averaged over 1 min during baseline,at steady state, 2 min after R or S administration (R/S+2) and0, 1, 2 and 3 min after laryngoscopy (L0, L1, L2, L3). Results. At R/S+2, the RE–SE gradient was higher in GroupS than in Group R. Laryngoscopy provoked an increase in BIS,RE and SE. Comparing R/S+2 and L0 values in Groups R and S,BIS increased from 43 (6) to 49 (8) and 42 (9) to 51 (15), SEincreased from 43 (7) to 50 (8) and 41 (10) to 55 (12), andRE increased from 46 (8) to 54 (9) and 47 (12) to 66 (15), respectively.BIS and SE did not differ between groups. At L0, RE and RE–SEwere higher in Group S [66 (15) and 11 (4), respectively] thanin Group R [54 (9) and 4 (2), respectively]. Conclusions. Rocuronium alters the RE–SE gradient andthe RE and RE–SE responses to laryngoscopy. Muscle relaxationmay confound interpretation of entropy monitoring.     

Comparing the effects of stimulation and propofol infusion rate on implicit and explicit memory formation

Doubt remains about the conditions under which learning persistsdespite anaesthesia. This study investigated the relative importanceof dose of anaesthetic and stimulation for learning during propofolinfusion before surgery. Thirty-six patients were randomly assignedto three groups. Group 1 received two word lists (category examplesand nonsense words) during infusion of propofol to a targetconcentration of 2 µg ml^–1. Groups 2 and3 received the word lists during infusion of propofol 5 µg ml^–1.Group 2 received nonsense words before tracheal intubation andcategory examples during intubation; Group 3 heard categoryexamples before and nonsense words during intubation. Bispectralindex was recorded as a measure of depth of sedation/anaesthesia.We assessed explicit memory on recovery using a structured interviewand a recognition test. We assessed implicit memory using acategory generation test and a preference rating task. To establishbaseline, a control group of 12 patients completed the categorygeneration test without receiving the category examples duringanaesthesia. Overall, there was no evidence for learning duringpropofol infusion, though the category generation task showeda trend towards more implicit memory for words presented duringintubation than during anaesthesia. We conclude that learningdoes not occur during anaesthesia without surgery. Br J Anaesth 2001; 86: 189–95     

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     

Effects of intramuscular administration of lidocaine or bupivacaine on induction and maintenance doses of propofol evaluated by bispectral index

Background. Interest in combining local and general anaesthesiahas lead to studies investigating possible interactions. Ina prospective, randomized, double-blind study, we tested whetherlocal anaesthetics administered i.m. potentiate the hypnoticeffect of propofol. Methods. Sixty patients (three groups, n=20) undergoing lowerabdominal surgery with total i.v. propofol anaesthesia wereinvestigated. Patients in Group B received i.m. bupivacaine(5 mg ml^–1) 1 mg kg^–1, patients in Group Lreceived i.m. lidocaine (100 mg ml^–1) 2 mg kg^–1and patients in Group C received i.m. saline 5 ml beforeoperation. Hypnosis was measured with bispectral index (BIS). Results. The induction (BIS <45), and the maintenance dosesof propofol (BIS between 40 and 50) were significantly lessin Group B and Group L compared with the control group. Inductiondoses were 1.58 (SD 0.39), 1.56 (0.24) and 2.03 (0.33) mg kg^–1respectively; P<0.0001. Maintenance doses were 6.33 (2.06),7.08 (1.23) and 9.95 (2.02) mg kg^–1 respectively in thefirst hour; P<0.0001. Groups B and L were associated withan attenuated haemodynamic response to both induction and intubation. Conclusion. I.M. administered local anaesthetics are associatedwith a decrease in both the induction and maintenance dosesof propofol during total i.v. anaesthesia and a reduction inhaemodynamic responses. Br J Anaesth 2002; 89: 849–52     

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