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

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

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

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

Ketamine increases the frequency of electroencephalographic bicoherence peak on the alpha spindle area induced with propofol

Background: The reticular and thalamocortical system is known to play aprominent role in spindle wave activity, and the spindle waveis related to the sedative effects of anaesthetics. Recently,bispectral analysis of the EEG has been developed as a bettermethod to indicate nonlinear regulation including the thalamocorticalsystem linking to the cortical area. In the present study, inorder to explore the interference of ketamine with the nonlinearregulation of the sub-cortical system, we examined the effectof ketamine on spindle waves through the bispectral analysis. Methods: The study included 21 patients. Anaesthesia was induced andmaintained using a propofol-TCI system (target-controlled infusion,with target concentration 3.5 µg ml^–1). An A-2000BIS monitor was used and the raw EEG signals were collectedvia an RS232 interface on a personal computer. Bicoherence,the normalized bispectrum, and power spectrum were analysedbefore and after i.v. administration of 1 mg kg^–1 racemicketamine. Results: Propofol caused peaks in both power and bicoherence spectra,with average frequencies of 10.6 (SD 0.9) Hz and 10.7 (1.0)Hz, respectively. The addition of ketamine significantly shiftedeach peak to frequencies of 14.4 (1.4) Hz and 13.6 (1.5) Hz,respectively [P < 0.05, mean (SD)]. Conclusions: Ketamine shifted the peaks of bicoherence induced by propofolto higher frequencies. This suggests that ketamine changes the spindle rhythms through the modulation of the nonlinear sub-corticalreverberating network.     

Perioperative thermal insulation: minimal clinically important differences?

Background. Reduction of heat losses from the skin by thermalinsulation is used to avoid perioperative hypothermia. However,there is little information about the physical properties ofvarious insulating materials used in the operating room. Methods. The following insulation materials were tested usinga validated manikin: cotton surgical drape tested in two andfour layers; Allegiance drape; 3M Steri-Drape; metallized plasticsheet; Thermadrape^TM; Barkey thermcare 1 tested in one and twolayers; hospital duvet tested in one and two layers. Heat lossfrom the surface of the manikin can be described as: Q^·=h·T·Awhere Q^· is heat flux, h is the heat exchange coefficient,T is the temperature gradient between the environment and surfaceand A is the area covered. The heat flux per unit area (Q^·A^–1)and surface temperature were measured with nine calibrated heat-fluxtransducers. The environmental temperature was measured usinga thermoanemometer. T was varied and h was determined by linearregression analysis as the slope of T vs Q^·A^–1.The reciprocal of h defines the insulation. Results. The insulation value of air was 0.61 Clo. The insulationvalues of the materials varied between 0.17 Clo (two layersof cotton surgical drapes) to 2.79 Clo (two layers of hospitalduvet). Conclusions. There are relevant differences between variousinsulating materials. The best commercially available materialdesigned for use in the operating room (Barkey thermcare 1)can reduce heat loss from the covered area by 45% when usedin two layers. Given the range of insulating materials availablefor outdoor activities, significant improvement in insulationof patients in the operating room is both possible and desirable. Br J Anaesth 2004; 92: 836–40     

An isobolographic analysis of diamorphine and levobupivacaine for epidural analgesia in early labour

Background: Few data describe the pharmacological interactions between localanaesthetics and opioids. The aim of this study was to measurethe median effective concentration (MEC) of diamorphine andlevobupivacaine when given separately and as mixtures for epiduralanalgesia, and determine whether the combination is additiveor synergistic. Methods: One hundred and twenty patients were enrolled in this prospectiverandomized, two-phase, double-blind study. In the first phase,60 women were randomized to receive a fixed 20 ml volumeof either levobupivacaine or diamorphine epidurally . Dosingwas determined using up-down sequential allocation with testingintervals, respectively, of 0.01%w/v and 12.5 µg ml^–1.After estimations of the MEC of levobupivacaine and diamorphine,a further 60 patients were randomized in the second phase toone of the three mixtures: (a) diamorphine 70 µg ml^–1(fixed) and levobupivacaine (testing interval 0.004%w/v, startingat 0.044%w/v); (b) levobupivacaine 0.044%w/v (fixed) and diamorphine(testing interval 7 µg ml^–1, startingat 70 µg ml^–1); and (c) bivariate diamorphineand levobupivacaine (testing intervals of 7 µg ml^–1and 0.004%w/v starting at 70 µg ml^–1 and0.044% w/v respectively). Results: The MEC estimates from the first phase were 143.8 µg ml^–1(95% CI 122.2–165.3) for diamorphine and 0.083%w/v (95%CI 0.071–0.095) for levobupivacaine. In the second phase,the MEC and interaction index () of the three combinations were:diamorphine 65.5 µg ml^–1 (56.8–74.2), = 0.99; levobupivacaine 0.041%w/v (0.037–0.049), = 0.98;and for the fixed combination diamorphine 69.5 µg ml^–1(60.5–78.5) and levobupivacaine 0.044%w/v (0.039–0.049), = 1.02. Conclusion: The combination of diamorphine and levobupivacaine is additiveand not synergistic when used for epidural analgesia in thefirst stage of labour.     

Actions of morphine on noradrenaline efflux in the rat locus coeruleus are mediated via both opioid and {alpha}2 adrenoceptor mechanisms

A recent report showed that morphine inhibited [³H]clonidinebinding to human platelet ₂ receptors. As the analgesic effectsof morphine and clonidine are clinically additive, we investigatedthe possibility that morphine might stimulate ₂ receptors or₂ mechanisms in rat locus coeruleus (LC) slices. StimulatedLC noradrenaline efflux was measured by fast cyclic voltammetry.Cumulatively applied morphine 10^–8–10^–4mollitre^–1 had no effect on noradrenaline efflux evoked bypseudo-single-pulse stimulations (20 pulses at 100 Hz) whilethe ₂ agonist dexmedetomidine 2 x 10^–10–10^–7mol litre^–1 decreased efflux of noradrenaline in a concentration-dependentmanner. Administration of single concentrations of morphine10^–6–10^–4 mol litre^–1 significantlydecreased efflux of noradrenaline (by 22% and 17%, respectively)and attenuated the effect of dexmedetomidine in a concentration-dependentfashion. Morphine 10^–6–10^–4mol litre^–1also decreased efflux of noradrenaline on long stimulus trains(50 pulses at 50 Hz). These data suggest that the analgesicpotentiation of ₂ and opioid agonists is not mediated via LC₂ receptors.     

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

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

EFFECTS OF TEMPERATURE ON THE INTERACTION OF MORPHINE WITH OPIOID RECEPTORS

The electrically stimulated guineapig ileum preparation wasused to determine the effects of temperature on the affinityof morphine for opioid receptors. The potency of morphine (expressedas the concentration which produces 50% inhibition—IC₅₀)was significantly decreased at 30C (IC₅₀ 41.0x10^–8 mollitre^–1) and increased at 40C (IC₅₀ 5.1x10^–1 mollitre^–1) when compared with its potency at 37C (IC₅₀,8.8x10^–8 mol litre^–1). Experiments carried out inthe presence of naloxone (a competitive opioid antagonist) indicatedthat the affinity of opioid receptors for this antagonist wasnot affected by temperature. Further studies using B-funaltrexamine(a mu-specific, non-reversible opioid antagonist) revealed anincrease in morphine receptor affinity when temperature wasincreased from 30 to 37C. The data demonstrated that the potencyof morphine increased with temperature; the affinity of naloxonefor opioid receptors was unaltered by temperature; and the affinityof morphine for mu-receptors reached an optimal value withinthe range 30–37C. Presented in part to the American Society of AnesthesiologistsAnnual Meeting, Las Vegas, Nevada, U.S.A., 1986.     

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     

THE ROLE OF {alpha}1-ADRENOCEPTORS IN ADRENALINE INDUCED HYPERKALAEMIA

The hyperkalaemic action of adrenaline was investigated in 44anaesthetized domestic pigs. Plasma and epicardial concentrationsof K⁺ were measured, in the latter case with an ion-selectiveelectrode. Adrenaline 10 µg kg^–1 caused a rapidincrease in the plasma concentration of K⁺ from 4.2 to 5.9 mmollitre^–1. The magnitude and the time course of epicardialconcentration of K⁺ were similar. Alpha-adrenoceptor block witheither phentolamine 5 mg kg^–1 (non-selective block) orprazosin 0.1 mg kg^–1 (selective 1-adrenoceptor block)abolished the hyperkalaemic effect of adrenaline in the plasmaand on the epicardium. The 1-adrenoceptor agonist phenylephrineincreased the K⁺ concentration, but the 2-adrenoceptor agonistUK 14.304 did not cause any change in concentration. These resultssuggest that the hyperkalaemia induced by adrenaline occursin the interstitial fluid of the myocardium and is mediatedby 1-adrenoceptors. These findings may be important in patientsat risk of hyperkalaemia, with implications, for example, inthe use of suxamethonium during induction of anaesthesia.     

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

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

PHARMACOKINETICS OF ATRACURIUM IN ANAESTHETIZED INFANTS AND CHILDREN

The pharmacokinetics of atracurium were studied in infants andchildren anaesthetized with isoflurane and nitrous oxide inoxygen. There were no significant differences in volume of distribution(area) (139 v. 152 ml kg^–1), clearance (5.1 v. 5.3 mlkg^–1 min^–1), T (2.1 v. 2.0 mim), or T^ß(19.1 v. 20.3 min) between children with normal hepatic andrenal function and those with moderately impaired hepatic functionpresenting for hepatic transplantation. There were significantdifferences in volume of distribution (area) (176 v. 139 mlkg^–1) and in clearance of atracurium (9.1 v.5.1 ml kg^–1min^–1) between infants and children with normal excretoryfunction. In infants the clearance of atracurium in ml m^–1min^–1 (153 v. 133) tended to be greater and the T andT^ß tended to be shorter (1.0 v. 2.0 and 13.6 v. 19.1)than in children with normal excretory function; however, thesetrends did not reach statistical significance. Plasma laudanosineconcentration was around 100 ng ml^–1 greater in patientswith liver disease than in normal children from 15–45min following a bolus of atracurium 0.5 mg kg^–1.     

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     

Anaesthetics and cardiac preconditioning. Part I. Signalling and cytoprotective mechanisms

Cardiac preconditioning represents the most potent and consistentlyreproducible method of rescuing heart tissue from undergoingirreversible ischaemic damage. Major milestones regarding theelucidation of this phenomenon have been passed in the lasttwo decades. The signalling and amplification cascades fromthe preconditioning stimulus, be it ischaemic or pharmacological,to the putative end-effectors, including the mechanisms involvedin cellular protection, are discussed in this review. Volatileanaesthetics and opioids effectively elicit pharmacologicalpreconditioning. Anaesthetic-induced preconditioning and ischaemicpreconditioning share many fundamental steps, including activationof G-protein-coupled receptors, multiple protein kinases andATP-sensitive potassium channels (K_ATP channels). Volatile anaestheticsprime the activation of the sarcolemmal and mitochondrial K_ATPchannels, the putative end-effectors of preconditioning, bystimulation of adenosine receptors and subsequent activationof protein kinase C (PKC) and by increased formation of nitricoxide and free oxygen radicals. In the case of desflurane, stimulationof - and ß-adrenergic receptors may also be of importance.Similarly, opioids activate - and -opioid receptors, and thisalso leads to PKC activation. Activated PKC acts as an amplifierof the preconditioning stimulus and stabilizes, by phosphorylation,the open state of the mitochondrial K_ATP channel (the main end-effectorin anaesthetic preconditioning) and the sarcolemmal K_ATP channel.The opening of K_ATP channels ultimately elicits cytoprotectionby decreasing cytosolic and mitochondrial Ca²⁺ overload. Br J Anaesth 2003; 91: 551–65     

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.      

Absorption of carbon dioxide during laparoscopy in children measured using a novel mass spectrometric technique

Background. Carbon dioxide (CO₂) is absorbed during pneumoperitoneumand may cause adverse haemodynamic effects. The aim of thisstudy was to measure the elimination of exogenous CO₂ duringlaparoscopy in children. Methods. Ten children [27.6 (56.5) months; mean (SD)] undergoinglaparoscopic and nine [24.5 (17.3) months] undergoing open surgerywere studied. Breath samples were collected at the line forend-tidal CO₂ and analysed for ¹³CO₂/¹²CO₂ ratio expressed asPDB (difference from standard), by isotope-ratio mass spectrometry.The proportion of absorbed CO₂ was calculated comparing exhaled¹³CO₂/¹²CO₂ before and during CO₂ pneumoperitoneum. Results. ¹³CO₂/¹²CO₂ in medical CO₂ was –32.7 (2.1) PDB.¹³CO₂/¹²CO₂ in breath of patients undergoing open procedureswas –24.3 (2.4) PDB at the start of operation and didnot change during the operation (P > 0.2). ¹³CO₂/¹²CO₂ inbreath of patients undergoing laparoscopy was –21.5 (5.4)PDB at the start of insufflation, and decreased during pneumoperitoneumby 2.5 (1.6) PDB, indicating absorption of exogenous CO₂. Thepercentage of expired CO₂ absorbed rose to 15.5 (7.7)% after30 min of pneumoperitoneum and decreased rapidly after desufflation. Conclusion. After 10 min of laparoscopy 10–20% of expiredCO₂ derives from the exogenous CO₂. CO₂ absorption can be measuredusing a simple mass spectrometric technique.     

VENTILATORY EFFECTS AND PLASMA CONCENTRATION OF MORPHINE IN MAN

The relationship between the plasma concentration of morphineand morphine-induced changes in ventilation and the ventilatoryresponse to carbon dioxide was studied in 17 healthy adultsundergoing elective surgery under general anaesthesia. Eachsubject was given morphine sulphate 0.15 mg kg^–1 i.m.;ventilation (E), end-tidal Pco₂(PE'_CO2), mixed venous PV_CO2(P_CO2)and ventilatory response to carbon dioxide (E/P_CO2) were measured before and within 90 min afterinjection. Mixed venous P_CO2 and E/P_CO2were measured by standard rebreathing methods; plasma morphineconcentration was measured by radioimmunoassay. Maximum plasmamorphine ranged from 30 to 120 ng ml^–1, between 4 and60 min after injection. There was a significant increase inmixed venous PE'_CO2 (P<0.001), and PE'_CO2 (P<0.01) aftermorphine while E decreased insignificantly. Morphine displaced the carbon dioxide responsecurve to the right (P<0.01) and E/P_CO2decreased from 12.3 to 10.0 litre min^–1 kPa^–1 (P<0.05).The magnitude of changes in E and E/P_CO2 were not relatedto the peak plasma concentration of morphine or to the meanconcentration immediately before and after the carbon dioxideresponse measurement. Plasma concentrations of morphine, underthe conditions of the present study, are not an objective indicatorof pharmacological activity between one patient and another. Presented in part at the VI World Congress of Anaesthesiology,MexicoCity, Mexico, April 1976     

NEUROMUSCULAR BLOCKING EFFECTS OF VECURONIUM AND PANCURONIUM DURING HALOTHANE ANAESTHESIA

The neuromuscular blocking properties of vecuronium (Org NC45) and pancuronium were compared in 40 patients during halothaneanaesthesia. Onset time was found to be dose-dependent, butno significant difference was found between the two drugs. Theduration of action of vecuronium was significantly shorter thanpancuronium. Times to 90 recovery of twitch height followingvecuronium 0.03 mg kg^–1 and 0.057 mgkg^–1 were 32.0min and 44.9 min, respectively, compared with 72.9 min and 124.7min following equipotent doses of pancuronium (0.042 mg kg^–1and 0.08 mg kg^–1). Recovery indices following both dosesof vecuronium (10.0 min and 11.8 min) were significantly shorterthan after pancuronium (31.0 min and 46.9 min). The reversaltimes of vecuronium (times from 10 to 90 twitch height recovery)were significantly shorter than those of pancuronium (7.9 minand 7.3 min, respectively, compared with 17.1 min and 17.7 min).     

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

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

IN VITRO DISPLACEMENT OF VASOACTIVE MEDIATORS FROM PLASMA PROTEINS: A POSSIBLE MECHANISM FOR PSEUDO-ALLERGIC REACTIONS TO NEUROMUSCULAR BLOCKING DRUGS

We have studied the re/ease of prostaglandin F₂ (PGF₂ and histaminefrom serum proteins by neuromuscular blocking drugs using equilibriumdialysis, with tracer quantities of radio-labelled mediatorsas probes. Small concentrations (0.05–0.25 mmol litre^–1)of competitive neuromuscular blocking drugs displaced 16–67%of bound histamine. Greater concentrations of suxamethonium(2 mmol litre^–1) were required for histamine displacement(19%). There was a significant release of PGF2^* by atracurium1 mmol litre^–1 and pan–curonium 0.69 mmol litre^–1.These findings suggest an alternative mechanism of histaminerelease by neuromuscular blocking drugs which may be relevantto adverse reactions during use. (Br. J. Anaesth. 1992;69:508–510)