Blood pressure manipulation during awake carotid surgery to reverse neurological deficit after carotid cross-clamping

We describe the management of three patients undergoing awakecarotid surgery who developed signs of cerebral ischaemia aftercarotid cross-clamping. Drug treatment to increase arterialblood pressure above baseline reversed the neurological deficitand an internal carotid artery shunt was not needed. Shunt insertionis less frequent with regional rather than general anaesthesia,and blood pressure control can reduce this even more. Coincidentally,one of the patients, who gave a history of angina of effortafter walking 100 m, complained of chest pain after cross-clamprelease. This was treated successfully with sublingual nitroglycerinbefore ST segment changes became apparent on the ECG. Thesereports suggest that regional anaesthesia for carotid surgeryallows potential complications to be identified earlier thanunder general anaesthesia using reports from the patient, sothat treatment may be modified to prevent morbidity and evenmortality. Br J Anaesth 2001; 87: 641–4     

Relationship between nocturnal hypoxaemia, tachycardia and myocardial ischaemia after major abdominal surgery

Background. Episodic hypoxaemia, cardiac arrhythmias, and myocardialischaemia may be related after major abdominal surgery. Methods. We studied 52 patients on the second and third nightsafter major abdominal operations, using continuous pulse oximetryand Holter ECG. We recorded the amount of time spent with oxygensaturation values less than 90, 85, and 80% during the night,and noted episodes of hypoxaemia, tachycardia, bradycardia,and ST-segment changes. Results. In 87 study nights there were 2403 (individual range1–229) episodes of hypoxaemia, 3509 (individual range1–234) episodes of tachycardia, and 265 (individual range1–73) episodes of ST segment deviation. Of the 52 patients,50 had episodes of hypoxaemia and tachycardia, and 19 patientshad one or more episodes of ST segment deviation. For 38% ofthe episodes of ST deviation, there was an episode of hypoxaemiaat the same time and in 16% there was an episode of tachycardia.ST deviation was only noted in 4% of the episodes of hypoxaemiaand in 1% of the episodes of tachycardia. Conclusion. Episodes of hypoxaemia and tachycardia frequentlyoccur together after surgery but are rarely associated withST deviation. Hypoxaemia or tachycardia is often present atthe same time as ST deviation occurs.     

Dose-dependent prophylactic effect of nicorandil, an ATP-sensitive potassium channel opener, on intra-operative myocardial ischaemia in patients undergoing major abdominal surgery

Nicorandil, a nicotinamide nitrate derivative, relaxes vascularsmooth muscle and reduces cardiac muscle contractility by increasingmembrane potassium conductance, probably by activating ATP-sensitivepotassium channels. In this prospective, randomized, double-blind,placebo-controlled clinical study, we examined the dose-dependentprophylactic effect of nicorandil on intra-operative myocardialischaemia in 248 patients who had pre-operative risk factorsfor ischaemic heart disease and were undergoing major abdominalsurgery. Patients in group HD (n=81) received a bolus dose ofnicorandil 0.08 mg kg^–1 and a continuous infusion of 0.08mg kg^–1 h^–1. Patients in group LD (n=87) receivednicorandil 0.04 mg kg^–1 and 0.04 mg kg^–1 h^–1.Patients in the placebo (P) group (n=80) received the same volumesof saline. The patients were monitored with a three-lead clinicalECG monitor with an ST trending device from arrival in the operatingtheatre to the end of anaesthesia. Intra-operative myocardialischaemia occurred significantly less frequently in the HD group(one patient, 1.2%) than in the LD (11 patients, 12.6%) andP groups (21 patients, 26.3%) (P<0.01), and in group LD significantlyless than in group P (P<0.05). Administration of nicorandilhad little effect on the patients’ heart rate or arterialpressure. Three patients in group P and none in either treatmentgroup developed myocardial infarction after surgery. Br J Anaesth 2001; 86: 332–7     

Coronary artery spasm induced by carotid sinus stimulation during neck surgery

We observed four transient episodes of marked ST-segment elevationin a 58-yr-old man with no history of coronary artery diseaseundergoing resection of a metastatic neck mass under generalanaesthesia. Elevations of the ST segment were abrupt, withno change in arterial pressure or heart rate, and resolved spontaneously.When the carotid sinus was compressed directly, ST-segment elevationwas noted 1 min after the onset of stimulation. After surgery,coronary angiography showed diffuse, slight narrowing of thedistal bed of the posterolateral branch of the right coronaryartery. Ergonovine caused total occlusion of the posterolateralbranch of the right coronary artery with chest pain and ST-segmentelevation, confirming the diagnosis of variant angina. The coronaryartery spasm seems to have been provoked by vagal activationfrom carotid sinus stimulation during general anaesthesia. Br J Anaesth 2003; 90: 391–4     

Vectorcardiographic changes during laparoscopic cholecystectomy may mimic signs of myocardial ischaemia

Background: Laparoscopic surgery involves the use of intra-ab-dominal carbon dioxide insufflation (pneumoperitoneum). The increased intra-abdominal pressure causes marked haemodyn-amic changes, which may influence electrocardiographic monitoring. The aim of the present study was to elucidate the influence of pneumoperitoneum on vectorcardiographic recordings.
Methods: Vectorcardiographic changes (QRS vector difference= QRSVD, QRS loop area, QRS magnitude, ST vector magnitude, spatial ST vector change) were recorded continuously applying computerized vectorcardiography in 12 anaesthetised cardio-vascularly healthy patients, scheduled for laparoscopic cholecystectomy.
Measurements were made before and during pneumoperitoneum in three different body positions (supine, Trendelenburg and reversed Trendelenburg), also employing transesophageal echo-cardiography and invasive blood pressure monitoring. Results: Pneumoperitoneum significantly increased QRSVD, in parallel with an enlargement in loop area and magnitude. The magnitude was significantly increased in the transversal and frontal planes and there was a tendency to increase the magnitude in the sagittal plane. The increase in QRS-VD reached levels previously associated with the development of myocardial ischaemia in patients with coronary artery disease. The ST-variables were not changed by the pneumoperitoneum. The positional changes also influenced QRSVD significantly.
Conclusions: When computerized vectorcardiography is used for ischaemia monitoring during pneumoperitoneum, the ST-variables seem reliable. However, vectorcardiographic QRS changes should be interpreted with caution, as the QRS alterations found during pneumoperitoneum mimic the changes seen during myocardial ischaemia.     

General anaesthesia for the cocaine abusing patient. Is it safe?

Background. Commonly, cocaine abusing patient are scheduledfor elective surgery with a positive urine test for cocainemetabolites. As many of these patients were clinically non-toxic[normal arterial pressure and heart rate, normothermic, anda normal (or unchanged from previous) ECG, including a QTc interval<500 ms], we have recently proceeded with elective surgeryrequiring general anaesthesia in this patient group. Methods. Forty urine cocaine positive patients were comparedwith an equal number of drug-free controls in a prospective,non-randomized, blinded analysis. Intraoperative mean arterialblood pressure, ST segment analysis, heart rate and body temperaturewere recorded and compared. Results. Cardiovascular stability during and after general anaesthesiain cocaine positive, non-toxic patients was not significantlydifferent when compared with an age and ASA matched drug-freecontrol group. Conclusions. These results demonstrate that the non-toxic cocaineabusing patient can be administered general anaesthesia withno greater risk than comparable age and ASA matched drug-freepatients.     

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     

Changes in cortical electrical activity during induction of anaesthesia with thiopental/fentanyl and tracheal intubation: a quantitative electroencephalographic analysis

Background. There are regional differences in the effects ofanaesthetics agents and perioperative stimuli on the EEG. Westudied the topography of the EEG during induction of anaesthesiaand intubation in patients receiving thiopental and fentanylto document regional electrical brain activity. Methods. EEG was recorded in 25 patients in the awake state,after pre-medication, during induction, at loss of consciousnessand after intubation. Eight bipolar recordings were made andthe relative power of the frequency bands delta, theta, alpha,and beta were used (after z-score transformation for age) tomeasure changes in regional EEG activity. Results. Noxious stimulation during tracheal intubation partiallyreversed the slowing of the EEG caused by anaesthesia. Duringinduction of anaesthesia alpha activity was most reduced intemporal and occipital regions. The most prominent EEG changesafter intubation were an increase in alpha and a decrease indelta power (P<0.001). The largest changes were in the frontaland temporal leads for alpha and in the frontal and centralleads for delta. Heart rate and arterial pressure remained constantduring intubation. Conclusions. Changes in alpha and delta power were identifiedas the most sensitive EEG measures of regional changes in electricalbrain activity during anaesthesia and noxious stimulation. Br J Anaesth 2004; 92: 33–8     

Is morphine-induced sedation synonymous with analgesia during intravenous morphine titration?

Background. Postoperative morphine titration frequently inducessedation. The assumption is made that patients sleep when theirpain is relieved. Some patients complain of persistent painwhen they awake. We studied the time-course of sedation andanalgesia to understand the determinants of patients’sleep during morphine titration. Methods. Seventy-three patients requiring morphine titrationin a post-anaesthetic care unit after major surgery, were studied.Fifty-two patients slept (Sleep group) and 21 did not (Awakegroup). When a patient slept during titration, morphine wasdiscontinued. Visual analogue pain scale (VAS), Ramsay score(RS), and the bispectral index (BIS) were recorded at the beginningof titration (STonset), at sleep onset (STsleep), then 5, 10,20, and 30 min afterwards (ST4). Results. In the Sleep group, mean (SD) RS increased from 1.7(0.4) to 2.4 (0.6) (P<0.05 vs STonset) and BIS decreasedfrom 95 (5.0) to 89.8 (10.2) between STonset and STsleep (P<0.05),RS remained stable thereafter. Conversely, RS and BIS remainedunaltered in the Awake group. The reduction in VAS was comparablebetween groups (from 78 (17) to 39 (21), and from 64 (16) to30.4 (11), respectively). Even though mean (SD) VAS was 39 (21)at ST4 in the Sleep group, 13 patients (25%) maintained a VASabove 50 mm. Conclusion. We observed dissociated effects of morphine on thetime-course of sedation and analgesia with sedation occurringfirst, followed by analgesia. Therefore, morphine-induced sedationshould not be considered as an indicator of an appropriate correctlevel of analgesia during i.v. morphine titration. Br J Anaesth 2002; 89: 697–701     

Progressive changes in arterial oxygenation during one-lung anaesthesia are related to the response to compression of the non-dependent lung

Background. Arterial oxygenation can change during one-lungventilation for reasons that are not fully understood. Methods. We studied patients during anaesthesia and one-lungventilation, with an inspiratory oxygen fraction of 0.8. Arterialblood gas values were recorded every 10 s with a continuousintra-arterial sensor. The non-dependent lung was compressedseveral times during the surgical procedure, using a retractor.The change in Pa_O2 during and after compression of the non-dependentlung was measured. Results. Pa_O2 increased significantly when the non-dependentlung was compressed, and decreased when the compression wasreleased. The first compression of the non-dependent lung transientlyincreased Pa_O2, but the effect of the second compression onoxygenation was more marked and persistent. Pa_O2 increased bymore than 13 kPa at 10 min after the second compression in fourpatients (responder group). Arterial oxygenation improved markedlyin patients in this group during the surgical procedure. Conclusion. Oxygenation can improve during one-lung ventilationin some patients. This improvement is partly related to a markedincrease in Pa_O2 during compression of the non-dependent lung. Br J Anaesth 2003; 90: 21–6     

Randomized double-blind clinical trial comparing topical and sub-Tenon's anaesthesia in routine cataract surgery

Background. Several local anaesthetic techniques are availablefor cataract surgery. Recently, topical anaesthesia has gainedin popularity. A randomized trial was designed to compare patientdiscomfort and intraoperative complications following routinecataract surgery under topical or sub-Tenon's anaesthesia. Methods. A randomized double-blinded placebo-controlled clinicaltrial of 210 patients assigned to either a sub-Tenon's group(sub-Tenon's anaesthesia with placebo topical balanced saltsolution, n=140) or a topical anaesthesia group (topical anaesthesiawith placebo sub-Tenon's injection of balanced salt solution,n=70) was carried out. All patients underwent phacoemulsificationwith intraocular lens implantation. Patients in the sub-Tenon'sgroup received a single injection (3 ml) of a combination oflidocaine 2% (2 ml) and bupivacaine 0.75% (1 ml), and four dosesof topical placebo (balanced salt solution). Patients in thetopical anaesthesia group received four doses of topical proxymethocaine0.5% and a placebo sub-Tenon's injection (3 ml) of balancedsalt solution. No intracameral injection of local anaestheticwas given. A 10-point visual analogue pain scale was used preoperativelyand for postoperative pain assessment immediately after theoperation and 30 min postoperatively. The intraoperative complicationsin the two groups were recorded. Results. The mean pain score immediately after surgery was 2.42(SD 2.2) in the sub-Tenon's group and 3.44 (2.3) in the topicalanaesthesia group (P=0.0043). The mean pain score 30 min aftersurgery was 1.24 (1.7) in the sub-Tenon's group and 2.25 (2.2)in the topical anaesthesia group (P=0.0009). Conclusions. Patients undergoing cataract surgery under topicalanaesthesia experience more postoperative discomfort than patientsreceiving sub-Tenon's anaesthesia. Surgery-related complicationswere similar in both groups.      

Spinal anaesthesia indirectly depresses cortical activity associated with electrical stimulation of the reticular formation

Background. Neuraxial blockade reduces the requirements forsedation and general anaesthesia. We investigated whether lidocainespinal anaesthesia affected cortical activity as determinedby EEG desynchronization that occurs following electrical stimulationof the midbrain reticular formation (MRF). Methods. Six goats were anaesthetized with isoflurane, and cervicallaminectomy performed to permit spinal application of lidocaine.The EEG was recorded before, during and after focal electricalstimulation (0.1, 0.2, 0.3 and 0.4 mA) in the MRF while keepingthe isoflurane concentration constant. Results. During lidocaine spinal anaesthesia, the spectral edgefrequency (SEF) after MRF electrical stimulation (13.6 (SD 1.0)Hz, averaged across all stimulus currents) was less than theSEF during control and recovery periods (18.6 (3.6) Hz and 17.2(2.2) Hz, respectively; P<0.05). Bispectral index valueswere similarly affected: 69 (10) at control compared with 55(6) during the spinal block (P<0.05). Conclusions. These results suggest that lidocaine spinal anaesthesiablocks ascending somatosensory transmission to mildly depressthe excitability of reticulo–thalamo–cortical arousalmechanisms. Br J Anaesth 2003; 91: 233–8     

Is prolongation of the QTc interval during isoflurane anaesthesia more prominent in women pretreated with anthracyclines for breast cancer?

Background. Inhalation anaesthetics and anthracycline chemotherapeuticdrugs may both prolong the QT interval of the electrocardiogram.We investigated whether isoflurane may induce or augment QTcprolongation in patients who had previously received cancerchemotherapy including anthracycline drugs. Methods. Forty women undergoing surgery for breast cancer wereincluded in the study. They were divided into two groups: (A)women previously treated with anthracyclines (n=20); and (B)women not treated with antineoplastic drugs (n=20). All patientsreceived a standardized balanced anaesthetic in which isoflurane0.5 vol% was used. The QT and corrected QT intervals were measuredbefore anaesthesia, after induction and tracheal intubation,after 1, 5, 15, 30, 60 and 90 min of anaesthesia, and duringrecovery. Results. In both groups we observed a tendency to QTc prolongation,but statistically significant differences among baseline valuesand values observed during isoflurane-containing anaesthesiawere seen only in group A. During anaesthesia, significant differencesin QTc values between the two groups were observed. Conclusion. In female patients pretreated with anthracyclinesfor breast cancer, the tendency to QTc prolongation during isoflurane-containinggeneral anaesthesia was more strongly expressed than in patientswithout previous chemotherapy. Br J Anaesth 2004; 92: 658–61     

Analgesic and antacid properties of i.m. tramadol given before Caesarean section under general anaesthesia

Background. Intramuscular (i.m.) tramadol increases gastricpH during anaesthesia similar to famotidine. We investigatedthe antacid analgesic value of a single dose of i.m. tramadolgiven 1 h before elective Caesarean section performed undergeneral anaesthesia. Methods. Sixty ASA I parturients undergoing elective Caesareansection were included in a randomized double-blind study. Thepatients were randomly allocated to receive i.m. tramadol 100mg (n=30) or famotidine 20 mg (n=30) 1 h before general anaesthesia. Results. At the beginning and the end of anaesthesia, patientsreceiving tramadol had a median gastric fluid pH of 6.4, whichwas not significantly different from those treated with famotidine(median 6.3). The infant well-being, as judged by Apgar score,cord blood gas analysis, and neurobehavioural assessment showedno significant difference between the two groups. Nalbuphineconsumption in the first 24 h after operation was reduced by35% in the tramadol group. Pain intensity score on sitting andsedation were significantly greater in famotidine group up to24 h after surgery. There was no significant difference in incidenceand severity of nausea and vomiting between the two groups. Conclusion. A single i.m. dose of tramadol is useful pre-treatmentto minimize the risk of acid aspiration during operation, andin improving pain relief during 24 h after surgery.     

Saliva cyclic GMP increases during anaesthesia

Background. Cyclic GMP (cGMP) has been implicated in modulatingthe effects of general anaesthesia. Changes in cGMP in humansundergoing anaesthesia have not been reported previously. Methods. In this pilot study we measured cGMP in the salivaof six healthy volunteers and eight patients undergoing generalanaesthesia for minor gynaecological procedures. Samples wereobtained using a commercially available sampling device andcGMP was determined with an enzyme immunoassay and results expressedas a cGMP per mg protein. Results. There was no statistically significant variation insalivary cGMP either day-to-day or between time points in healthyvolunteers. Analysis of variance of salivary cGMP of patientsundergoing general anaesthesia showed that cGMP increased significantlyintraoperatively and returned to preoperative levels after surgery(P=0.03). Conclusions. This is the first time that real time in vivo changesin salivary cGMP levels during general anaesthesia in humanshave been demonstrated and may allow an alternative techniquefor measuring depth of anaesthesia in the future. Br J Anaesth 2002; 89: 635–7     

Perioperative use of the modified nasal trumpet in 346 patients

Background. The modified nasal trumpet (MNT) is a prepackagednasopharyngeal airway modified with distal holes and fittedwith a 15 mm adaptor allowing connection to an anaesthesia circuit.It may be useful for airway management during anaesthesia. Methods. After applying a spray to constrict the nasal mucosa,we used the MNT in 346 spontaneously breathing patients forthree indications: alone as an airway device during generalanaesthesia, to provide supplemental oxygen immediately afterextubation instead of by facemask, and to facilitate fibreopticintubation during general anaesthesia. Results. The device was successful for giving supplemental oxygenafter extubation (n=244) and facilitating fibreoptic intubation(n=28). When used as an airway for general anaesthesia, it wasonly successful without manipulation in 33 of 74 patients (45%).The MNT was easy to insert in awake patients. We encounteredsix complications: one MNT folded in the pharynx, and five patients(1.4%) experienced nosebleeds. Conclusions. The MNT was disappointing as a primary airway deviceunder general anaesthesia but was useful for giving oxygen afterextubation and for facilitation of fibreoptic intubation. Itcan cause nosebleeds. Br J Anaesth 2004; 92: 694–6     

Patient well-being after general anaesthesia: a prospective, randomized, controlled multi-centre trial comparing intravenous and inhalation anaesthesia

Background. The aim of this study was to assess postoperativepatient well-being after total i.v. anaesthesia compared withinhalation anaesthesia by means of validated psychometric tests. Methods. With ethics committee approval, 305 patients undergoingminor elective gynaecologic or orthopaedic interventions wereassigned randomly to total i.v. anaesthesia using propofol orinhalation anaesthesia using sevoflurane. The primary outcomemeasurement was the actual mental state 90 min and 24 h afteranaesthesia assessed by a blinded observer using the AdjectiveMood Scale (AMS) and the State-Trait-Anxiety Inventory (STAI).Incidence of postoperative nausea and vomiting (PONV) and postoperativepain level were determined by Visual Analogue Scale (VAS) 90min and 24 h after anaesthesia (secondary outcome measurements).Patient satisfaction was evaluated using a VAS 24 h after anaesthesia. Results. The AMS and STAI scores were significantly better 90min after total i.v. anaesthesia compared with inhalation anaesthesia(P=0.02, P=0.05, respectively), but equal 24 h after both anaesthetictechniques (P=0.90, P=0.78, respectively); patient satisfactionwas comparable (P=0.26). Postoperative pain was comparable inboth groups 90 min and 24 h after anaesthesia (P=0.11, P=0.12,respectively). The incidence of postoperative nausea was reducedafter total i.v. compared with inhalation anaesthesia at 90min (7 vs 35%, P<0.001), and 24 h (33 vs 52%, P=0.001). Conclusion. Total i.v. anaesthesia improves early postoperativepatient well-being and reduces the incidence of PONV. Br J Anaesth 2003; 91: 631–7     

Safety of oral nicorandil before coronary artery bypass graft surgery

Nicorandil is a K_ATP channel opener used to treat angina. Itis cardioprotective and a vasodilator. We conducted a prospective,randomized, double-blind, placebo-controlled study to assessoral nicorandil in patients undergoing coronary artery bypassgrafting (CABG) with cardiopulmonary bypass (CPB). Twenty-twopatients received nicorandil (10 mg twice a day) and 23patients received placebo. Haemodynamic data were recorded beforeinduction of anaesthesia (T0), 5 and 20 min after startingmechanical ventilation (T1, T2), before aortic cannulation (T3),after 30 min of CPB (T4), 10 min after CPB (T5) andafter 3, 8 and 18 h in the intensive care unit (T6, T7,T8). Serum proteins (creatine kinase metabolite and cardiactroponin I) were measured before and 8 and 18 h after surgery.Haemodynamic values did not differ between the two groups. Therewas no tachycardia during the study, no significant differencein hypotensive episodes, ST segment changes and no changes incardiac enzymes. Myocardial infarction after surgery was similarin the two groups. Vasoactive therapy was similar in the twogroups. Nicorandil can be continued safely up to premedicationwithout deleterious haemodynamic consequences, but a myocardialprotective effect of nicorandil in CABG surgery was not found. Br J Anaesth 2001; 87: 848–54     

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.     

Effect of three anaesthetic techniques on isometric skeletal muscle strength

Background. Our aim was to quantify human involuntary isometricskeletal muscle strength during anaesthesia with propofol, sevoflurane,or spinal anaesthesia using bupivacaine. Methods. Thirty-three healthy patients undergoing anaesthesiafor elective lower limb surgery were investigated. Twenty-twopatients received a general anaesthetic with either propofol(n=12) or sevoflurane (n=10); for the remaining 11 patientsspinal anaesthesia with bupivacaine was used. We used a non-invasivemuscle force assessment system before and during anaesthesiato determine the contractile properties of the ankle dorsiflexormuscles after peroneal nerve stimulation (single, double, triple,and quadruple stimulation). We measured peak torques; contractiontimes; peak rates of torque development and decay; times topeak torque development and decay; half-relaxation times; torquelatencies. Results. Males elicited greater peak torques than females, medians6.3 vs 4.4 Nm, respectively (P=0.0002, Mann-Whitney rank-sumtest). During sevoflurane and propofol anaesthesia, muscle strengthdid not differ from pre-anaesthetic values. During spinal anaesthesia,torques were diminished for single-pulse stimulation from 3.5to 2.0 Nm (P=0.002, Wilcoxon signed rank test), and for double-pulsefrom 7.6 to 5.6 Nm (P=0.02). Peak rates of torque developmentdecreased for single-pulse stimulation from 113 to 53 Nm s^–1and for double pulse from 195 to 105 Nm s^–1. Torque latencieswere increased during spinal anaesthesia. Conclusions. At clinically relevant concentrations, propofoland sevoflurane did not influence involuntary isometric skeletalmuscle strength in adults, whereas spinal anaesthesia reducedstrength by about 20%. Muscle strength assessment using a devicesuch as described here provided reliable results and shouldbe considered for use in other scientific investigations toidentify potential effects of anaesthetic agents. Br J Anaesth 2004; 92: 367–72