Acceleromyography and mechanomyography for establishing potency of neuromuscular blocking agents: a randomized-controlled trial

BACKGROUND

Acceleromyography (AMG) is increasingly being used in neuromuscular research, including in studies establishing the potency of neuromuscular blocking and reversal agents. However, AMG is insufficiently validated for use interchangeably with the gold standard, mechanomyography (MMG) for this purpose. The aim of this study was to compare AMG and MMG for establishing dose-response relationship and potency, using rocuronium as an example.

METHODS

We included 40 adult patients in this randomized-controlled single-dose response study. Anaesthesia was induced and maintained with propofol and opioid. Neuromuscular blockade was induced with rocuronium 100, 150, 200 or 250 microg/kg. Neuromuscular monitoring was performed with AMG (TOF-Watch SX) with pre-load (Hand Adapter) at one arm and MMG (modified TOF-Watch SX) on the other, using 0.1 Hz single twitch stimulation. Dose-response relationships were determined for both recording methods using log (dose) against probit (maximum block). The obtained slopes of the regression lines, ED(50), ED(95) and the maximum block were compared.

RESULTS

The ED(50) and ED(95) [95% confidence interval (CI)] for AMG were 185 microg/kg(167-205 microg/kg) and 368 microg/kg(288-470 microg/kg), compared with 174 microg/kg(159-191 microg/kg) and 338 microg/kg(273-418 microg/kg) for MMG. There were no statistically significant biases in maximum block, ED(50), ED(95) or slopes obtained with the two methods.

CONCLUSION

Our results indicate that any possible difference between AMG and MMG is so small that it justifies AMG to be used for establishing the potency of neuromuscular blocking agents. However, the wide CIs show that we cannot rule out a 13% higher ED(50) and a 26% higher ED(95) for AMG.

The undesirable effects of neuromuscular blocking drugs

Neuromuscular blocking drugs are designed to bind to the nicotinic receptor at the neuromuscular junction. However, they also interact with other acetylcholine receptors in the body. Binding to these receptors causes adverse effects that vary with the specificity for the cholinergic receptor in question. Moreover, all neuromuscular blocking drugs may cause hypersensitivity reactions. Often the symptoms are mild and self-limiting but massive histamine release can cause systematic reactions with circulatory and respiratory symptoms and signs. At the end of anaesthesia, no residual effect of a neuromuscular blocking drug should be present. However, the huge variability in response to neuromuscular blocking drugs makes it impossible to predict which patient will suffer postoperative residual curarization. This article discusses the undesirable effects of the currently available neuromuscular blocking drugs including the definitions, diagnosis and causes of hypersensitivity reactions and postoperative residual curarisation.

Prolonged residual paralysis after a single intubating dose of rocuronium

It is often argued that neuromuscular monitoring is unnecessary when only one dose of an intermediate-acting neuromuscular blocking agent is given. This case report documents that it may take more than 3.5 h before it is possible to antagonize a block caused by a normal dose of rocuronium (0.6 mg kg(-1)). Possible causes of the extremely prolonged duration of action are discussed, as is the importance of quantitative neuromuscular monitoring.

Good clinical research practice in pharmacodynamic studies of neuromuscular blocking agents II: the Stockholm revision

The set of guidelines for good clinical research practice (GCRP) in pharmacodynamic studies of neuromuscular blocking agents, which was developed following an international consensus conference in Copenhagen, has been revised and updated following the second consensus conference in Stockholm in 2005. It is hoped that these guidelines will continue to help researchers in the field and assist the pharmaceutical industry and equipment manufacturers in enhancing the standards of the studies they sponsor.

Remifentanil vs. alfentanil infusion in non-paralysed patients: a randomized, double-blind study

BACKGROUND AND OBJECTIVE

Remifentanil has a short duration of action and constant elimination, which allow administration of high doses, without prolonging recovery. Remifentanil has been compared to alfentanil, as part of a total intravenous anaesthetic technique, where remifentanil provided better anaesthetic conditions than alfentanil, without adverse effect on recovery. However, these results were obtained during anaesthesia involving neuromuscular blockade, which may mask both signs of insufficient anaesthesia and side-effects such as muscle rigidity. The aim of this study was to compare remifentanil with alfentanil for anaesthesia without neuromuscular blockade.

METHODS

We performed a prospective, randomized, double-blind, four-centre study to compare remifentanil infusion 15 microg kg(-1) h(-1) and alfentanil infusion 60 microg kg(-1) h(-1), using a total intravenous technique for non-paralysed patients, and the laryngeal mask airway for airway management. We enrolled 192 patients, 18-65 yr of age with ASA I-II, undergoing minor surgery. The primary endpoint was the number of patients having pre-defined responses to surgical stimulation. A number of secondary criteria was evaluated to assess undesirable properties of the procedures.

RESULTS

In the alfentanil group, 85% of patients responded to surgical stimulation, vs. 35% in the remifentanil group (P < 0.0001). No difference was found in recovery data, or in any other parameter than those related to insufficient anaesthesia.

CONCLUSIONS

The remifentanil-based technique provided significantly better anaesthetic conditions than the alfentanil-based technique in the setting of this study, without causing any significant adverse effects.

Scandinavian research in anaesthesiology 1981-2000: visibility and impact in EU and world context

BACKGROUND

We wished to assess the development in number and impact of publications in anaesthesiology and intensive care medicine from 1981 to 2000 in the four Scandinavian countries: Sweden, Norway, Finland, and Denmark. For comparison, we also analyzed data from the UK and the Netherlands.

METHODS

Publication and citation data from 1981 to 2000 were gathered from National Science Indicators (2001), covering 33 journals indexed in Current Contents. Data were analyzed in running 5-year periods. The following informetric indicators were used: absolute number of publications; absolute number of citations; absolute citation impact (average number of citations per publication per 5-year period); citation impact relative to the European Union and the world; and the percentage of cited papers from each country.

RESULTS

The annual number of publications from Denmark was stable over the 20-year period. Sweden increased its production by 35%, while the remaining four countries showed increases from 100% to 146%. Thus, Sweden and Denmark lost visibility within the European Union (EU) and in world context. The EU and world citation shares of Finland and Norway increased slightly, whereas those of Sweden, Denmark, the UK, and the Netherlands all declined significantly. The absolute citation impact (ACI) increased for all the four Scandinavian countries. The ACI of the Netherlands did not change and was surpassed by all the Scandinavian countries by 1994-98, while the UK finished below the other five countries.

CONCLUSIONS

(1) The annual number of publications from Sweden, Norway, Finland, the UK, and the Netherlands increased after the late eighties, whereas the net publication output from Denmark was stagnant over the 20-year period investigated; (2) the international publication and citation visibility of Finland and Norway increased slightly, as opposed to the significant decrease seen by the other four countries; (3) judging from the increase in absolute and relative citation impact and in the percentage of cited papers, the recognition of publications from the four Scandinavian countries increased over the past 20 years.

Pharmacokinetics and pharmacodynamics of mivacurium in patients phenotypically heterozygous for the usual and atypical plasma cholinesterase variants (UA)

BACKGROUND

Mivacurium is hydrolyzed by plasma cholinesterase (pChe). The purpose of this study was to evaluate the pharmacodynamics and the pharmacokinetics of the three isomers of mivacurium in patients phenotypically heterozygous for the usual and the atypical pChe variant (UA).

METHODS

Thirty-two patients were included in a dose-response study, in which the patients received one of four doses of mivacurium. An additional bolus dose of mivacurium, to a total of 0.1 mg kg-1, was given followed by a continuous infusion adjusted to maintain 91-99% neuromuscular block. The times to different levels of recovery following the infusion were measured using mechanomyography and train-of-four (TOF) nerve stimulation. Twelve of the patients with an estimated duration of anaesthesia of more than 90 min were (randomly) selected for the pharmacokinetic part of the study. Venous samples were taken for determination of the three isomers of mivacurium. These results were compared with results from a previous study in phenotypically normal patients (UU).

RESULTS

The estimated ED50 and ED95 were 24 and 69 microg kg-1, respectively. The median (range) infusion rate was 3.7 microg kg-1 min-1 (1.2-2.9) and the time to a TOF ratio of 0.7 was 29.8 min (16.1-44.8). The median clearances of the cis-cis, cis-trans and trans-trans isomers were 3.7, 29 and 28 ml kg-1 min-1, respectively. The elimination half-lives of the isomers were 45, 6.7 and 6.3 min, respectively.

CONCLUSION

In patients heterozygous for the usual and the atypical variant (UA), the potency of mivacurium is higher, the infusion requirements lower and the rate of spontaneous recovery prolonged, compared with phenotypically normal patients. The clearances of the active isomers are significantly lower and the elimination half-lives longer in heterozygous patients than in phenotypically normal patients (UU). The pharmacokinetics of the inactive cis-cis isomer was not affected.

Rapid simultaneous genotyping of the frequent butyrylcholinesterase variants Asp70Gly and Ala539Thr with fluorescent hybridization probes

BACKGROUND

The clinically important variants of butyrylcholinesterase (BChE) are the A- (Asp70Gly) and K-variants (Ala539Thr), which are common among Caucasians. These variants are associated with abnormal drug metabolism during anaesthesia, which leads to a prolonged neuromuscular block following administration of the neuromuscular blocking agents, mivacurium and succinylcholine. In addition, the K-variant has been proposed to be associated with Alzheimer's disease together with apolipoprotein E epsilon4. To facilitate diagnostics, we set out to establish a rapid and simple method for simultaneous genotyping of the A- and K-variants.

METHODS

Using the LightCycler, a rapid-cycle duplex PCR is combined with generation of allele-specific fluorescent probe melting profiles. This allows simultaneous detection of both of the mutations in the BChE gene. The results were compared with direct sequencing and phenotyping results.

RESULTS

Samples from 80 subjects were genotyped. The genotypes determined using the LightCycler were identical to those obtained by direct sequencing of conventional polymerase chain reaction products and was more accurate than phenotyping based on biochemical assays.

CONCLUSIONS

A high-speed and easy to perform mutation detection assay has been established for the two most common mutations, Asp70Gly and Ala539Thr, in BChE, using the LightCycler technology and melting curves.

Remifentanil vs. alfentanil for direct laryngoscopy: a randomized study comparing two total intravenous anaesthesia techniques. TIVA for direct laryngoscopy

The ideal anaesthesia for direct laryngoscopy is profound and yet brief. The present study sought to determine whether a new anaesthetic technique based on infusion of the ultra short-acting opioid remifentanil was superior to our routine alfentanil multiple-dose technique in terms of haemodynamic stability, stress responses and recovery. A total of 58 patients were randomized to receive propofol and either remifentanil or alfentanil as part of a total intravenous anaesthesia. In the remifentanil group, systolic blood pressure during anaesthesia remained significantly lower than baseline values, while it increased significantly in the alfentanil group. None of the patients receiving remifentanil showed stress responses (hypertension, tachycardia, somatic or autonomic responses), compared to 22 patients (79%) in the alfentanil group (P < 0.0001). In the remifentanil group, hypotension or bradycardia requiring intervention arose in 5 (18%) and 3 patients (11%); neither response was seen in the alfentanil group. The period from the end of propofol infusion until extubation was 5 min longer in the remifentanil group (P < 0.0001), whereas the time from extubation until discharge was similar in the two groups. Thus, neither technique showed sufficient haemodynamic stability, and further studies are needed to determine optimal dosages of propofol and opioid.

Mortality among anesthesiologists in Denmark, 1973-95

BACKGROUND

Preliminary data from Sweden indicating that anesthesiologists have a high mortality risk has caused a lot of concern in Denmark. The aim of this study therefore was to compare mortality between consultant anesthesiologists and other consultants in Denmark.

METHODS

A historical prospective cohort study based on the membership register of the Danish Medical Association from 1973 to 1992. The study population consisted of 6854 consultants who were members of the Association of Medical Specialists, 406 of whom were anesthesiologists. The all-cause mortality between the two groups was compared during the period 1972-95 using Cox's proportional hazard regression model.

RESULTS

The study covered approximately 86000 person-years. A total of 1205 deaths occurred within the period studied, 41 of whom were anesthesiologists. The relative risk for all-cause mortality among the anesthesiologists compared with all the other consultants was 1.0 (95% confidence limit: 0.7-1.4).

CONCLUSION

In Denmark there is no evidence of a high mortality risk in consultant anesthesiologists compared with other consultants.

Acceleromyography of the orbicularis oculi muscle II: comparing the orbicularis oculi and adductor pollicis muscles

BACKGROUND

The orbicularis oculi (OO) muscle has been recommended for neuromuscular monitoring when the adductor pollicis (AP) muscle is not available. We investigated whether neuromuscular block could be measured reliably from the orbital part of the OO muscle by the use of acceleromyography.

METHODS

During propofol, fentanyl, and alfentanil anaesthesia two TOF-Guards (Organon Teknika NV, Boxtel, the Netherlands) with acceleration transducers placed on the distal phalanx of the thumb and over the middle of the eyebrow, respectively, were used to measure neuromuscular block simultaneously in 23 patients during vecuronium-induced and neostigmine-antagonized neuromuscular block. For both muscles, the simultaneously recorded first response (T1) in the train-of-four (TOF) and TOF-ratio were measured both during onset and recovery of the block. Furthermore, both the AP muscle T1 and TOF-ratio responses were plotted against 10% intervals of the OO muscle responses during onset and recovery, respectively.

RESULTS

The orbicularis oculi muscle had a shorter latency and a faster recovery to TOF-ratio 0.80 compared with the AP muscle. During onset and recovery, pronounced variations of the AP muscle T1 and TOF-ratio responses were observed when compared with the OO muscle.

CONCLUSION

A significant clinical disagreement exists between the degree of paralysis measured at the OO and the AP muscles. It is impossible to obtain a reasonable estimate of the degree of block at the AP muscle when the block is measured from the OO muscle with acceleromyography. If used, there is substantial risk of overlooking a residual block, and adequate recovery of the block should be confirmed by a final AP muscle measurement.

Acceleromyography of the orbicularis oculi muscle I: significance of the electrode position

BACKGROUND

This study aimed to establish the best position of the stimulating electrodes for facial nerve stimulation during acceleromyographic monitoring from the orbital part of the orbicularis oculi muscle.

METHODS

In 59 anaesthetised patients, an acceleration transducer was positioned over the middle of the eyebrow. In 47 patients, supramaximal train-of-four (TOF) stimulation was established for four electrode pairs with different positions along the facial nerve and behind the ear. The electrode pair with the lowest, the intermediate, and the highest supramaximal stimulating current based on first response (T1) in TOF was found in each patient. A possible response from direct muscle stimulation was evaluated during complete vecuronium block. In 12 patients, supramaximal stimulation was established using a stimulation sequence different from the one used in the first part of the study.

RESULTS

The best positions for the stimulating electrodes were either with both electrodes just lateral to the eye, or with one electrode lateral to the eye and one in front of the ear. In most patients, supramaximal stimulation was obtained at these positions at 20-60 mA. However, in 10-21% of the patients, supramaximal stimulation could not be obtained. During complete block, 1-4 responses with a twitch height of 3-11% were recorded in 80% of the patients.

CONCLUSION

The best placements of the stimulation electrodes are either just lateral to the eye or along the zygomatic arch. However, supramaximal stimulation may often not be obtainable, and activation of other facial muscles may be a confounding factor that may impede correct evaluation of the degree of neuromuscular block.

Plasma cholinesterase activity and duration of action of mivacurium in phenotypically normal patients

BACKGROUND

The short duration of action of mivacurium is due to its rapid hydrolysis by plasma cholinesterase (pChe). In patients with normal phenotype, low pChe activity because of, for instance, disease or intake of drugs may prolong the duration of action of mivacurium. The purpose of this study was to evaluate the relationship between pChe activity and the duration of action of mivacurium 0.2 mg/kg in phenotypically normal patients.

MATERIAL

Forty-three adult patients with normal pChe phenotype and low or normal pChe activity, undergoing a variety of surgical procedures were included in the study with their informed consent and Ethics Committee approval. The neuromuscular block was monitored using TOF stimulation every 12 s and mechanomyography. The time to reappearance of the first response to TOF stimulation was measured.

RESULTS

The patients pChe activities ranged from 45 to 1272 U/l (normal range 660-1620 U/l) and the time to first response to TOF from 8.1 to 62.7 min. An inverse relationship between enzyme activity and duration of action of mivacurium was found. The relationship was described by the equation: log10 (time) =alpha- beta log10 (pChe), where alpha (SD) is 2.547 (0.186) and beta (SD) 0.454 (0.069).

CONCLUSION

In patients with phenotypically normal pChe, prediction of the duration of action of mivacurium is possible from the patients actual pChe activity. In patients with pChe activities below the normal range, the time to reappearance of the first response to TOF stimulation may vary from 10 to 180 min Only patients with pChe activities <220 U/l had a significantly prolonged duration of action of mivacurium.

Pharmacokinetics and pharmacodynamics of mivacurium in young adult and elderly patients

BACKGROUND

Mivacurium is hydrolyzed by plasma cholinesterase, and is therefore less dependent on liver metabolism and renal elimination than other neuromuscular blocking drugs. This might favor the use of mivacurium in elderly patients. The purpose of this study was to compare the pharmacodynamics and the pharmacokinetics of the three isomers of mivacurium and their metabolites in young adult and elderly patients.

METHODS

Sixty-four patients were included in a dose-response study, in which 32 young adults and 32 elderly patients received one of four doses of mivacurium. An additional bolus dose of mivacurium to a total of 0.1 mg/kg was given followed by a continuous infusion adjusted to maintain a 91-99% neuromuscular block. The times to maximum block and different levels of recovery were measured using mechanomyography and train-of-four (TOF) nerve stimulation. Thirty-two patients were randomly selected for the pharmacokinetic study. Venous samples were taken for determination of the three mivacurium isomers and the metabolites.

RESULTS

The estimated ED95 were 0.053 and 0.061 mg/kg in young adults and elderly patients, respectively (NS). The median infusion rate did not differ, but duration to a TOF ratio of 0.7 was significantly longer in elderly patients than in young adult patients (21.0 vs. 16.5 min). No statistically significant difference between the age groups in clearance and elimination half-life of the isomers was seen. The half-lives of the metabolites were significantly prolonged in the elderly patients.

CONCLUSION

There were no significant differences in the potency or infusion requirements between the adult and elderly patients, but the rate of recovery was significantly, though only moderately prolonged, in the elderly patients. No significant difference in clearance was seen but the elimination half-lives of the metabolites was longer in the elderly patients.

The pharmacodynamics and pharmacokinetics of mivacurium in children

BACKGROUND

In children, onset time and duration of action of mivacurium are shorter than in adults. Some suggest that this is due to differences in plasma cholinesterase (pChe), whereas others indicate that there is no difference. The purpose of this study was to evaluate the pharmacodynamics and pharmacokinetics of mivacurium in phenotypically normal children aged 3-6 and 10-14 years old, respectively.

METHODS

Ten children aged 3-6 years and 10 children aged 10-14 years were studied during halothane anaesthesia. Before induction of anaesthesia, a blood sample was drawn to measure the pChe activity and phenotype. The neuromuscular block was monitored at the thumb using train-of-four (TOF) nerve stimulation every 12 s and mechanomyography. The times to different levels of neuromuscular recovery following mivacurium 0.2 mg/kg were recorded. The concentrations in venous blood of the three isomers and the metabolites of mivacurium were measured.

RESULTS

No statistically significant difference was found in pChe activity or in the pharmacodynamics of mivacurium. The onset time was 1.4 min (0.8-1.9) median (range) and 1.3 min (1.1-1.9) and the time to first response to TOF nerve stimulation was 9.6 min (6.5-12.6) and 10.5 min (7.0-14.0) in young and older children, respectively. The pharmacokinetic data were too sparse to allow analysis of the two age groups separately (8 and 8 patients), hence the data were pooled. The median clearances of the cis-cis, the cis-trans, and the trans-trans isomer were 5.5, 51.0 and 30.5 ml/kg/min, respectively.

CONCLUSION

Our data indicate that there are no major differences in pharmacodynamics or pharmacokinetics of mivacurium between young (3-6 years) and older (10-14 years) children.

Postoperative muscle paralysis after rocuronium: less residual block when acceleromyography is used

BACKGROUND

Residual muscle paralysis after anesthesia is common after pancuronium, but less common following the intermediate-acting drugs vecuronium and atracurium. Therefore, many anesthetists do not monitor neuromuscular function when using an intermediate-acting agent. The purpose of this prospective, randomised and double-blind study was to establish the incidence and degree of postoperative residual block following the use of rocuronium in patients not monitored with a nerve stimulator, and to compare it with results obtained in patients monitored using acceleromyography (AMG).

METHODS

During propofol/opioid anesthesia, 120 adult patients were randomised to two groups, one monitored with AMG, the other using only clinical criteria without a nerve stimulator. Postoperatively, TOF-ratio was measured with mechanomyography; a TOF-ratio < 0.80 indicated residual muscle paralysis.

RESULTS

Residual muscle paralysis was found in 10 patients in the group without neuromuscular monitoring (16.7%) (95% confidence interval, 12-21%) and in two patients in the AMG-monitored group (3%) (95% CI, 0-8%); (P = 0.029, Fisher's exact test). Time from end of surgery to tracheal extubation was significantly longer in the AMG-monitored group (12.5 min) than in the group not monitored with AMG (10 min).

CONCLUSION

Clinical evaluation of recovery of neuromuscular function does not exclude significant residual paralysis following the intermediate-acting muscle relaxant rocuronium, but the problem of residual block can be minimized by use of AMG.

Neuromuscular monitoring

This review summarizes recent reports on the techniques and the use of methods for monitoring neuromuscular function during anaesthesia. The latest news on the use of acceleromyography in the face and hand, on laryngeal and diaphragmal surface electromyography, on acoustic myography, on evaluation of intense neuromuscular block, and on postoperative residual curarization is presented and discussed. It is concluded that available evidence suggests that more attention should be paid by the anaesthetist to the problems of residual curarization and hence to proper monitoring of neuromuscular function using objective methods.

[Research in Danish departments of anesthesiology at the turn of the century. A bibliometric analysis]

INTRODUCTION

This investigation was based on the surmise that the scientific activity in the specialty of anaesthesiology and intensive care medicine in Denmark is declining.

MATERIAL AND METHODS

A quantitative and qualitative analysis of the development in Danish anaesthesiological research during the seven-year period of 1992-1998 was performed with bibliometrical methods and a count of the PhD and doctoral theses produced by Danish anaesthesiologists during that period.

RESULTS

In the period investigated, a total of 906 scientific articles were published, of which 749 (83%) originated from university hospitals. Total production decreased by 15% between the two-year periods of 1992-1993 and 1997-1998, whereas the output from university hospitals alone decreased by 10%. The number of scientific publications per anaesthesiologist decreased by 34%, corresponding to 6.7% per year. The quality of the research published, as examined by the cumulative and average impact, showed a slight increase. The number of PhD and doctoral theses per year showed no change.

DISCUSSION

Research activity in Danish anaesthesiology is declining, and the specialty seems to be losing scientific ground, both nationally and internationally.

Response to mivacurium in a patient compound heterozygous for a novel and a known silent mutation in the butyrylcholinesterase gene: genotyping by sequencing

BACKGROUND

Patients who are homozygous for the atypical mutation, compound heterozygous for atypical and silent mutations, or homozygous for silent mutations (SS) respond to mivacurium with extensively prolonged neuromuscular block. Although important, exact phenotyping of these patients is difficult. This article presents the pharmacodynamics and pharmacokinetics of a normal dose of mivacurium in a patient with phenotype SS, including a pedigree analysis and delineation of the molecular genetic method used to identify the genotype.

METHODS

The neuromuscular block following administration of mivacurium, at a dose of 0.14 mg/kg, was monitored in a 30-yr-old healthy man with use of a mechanosensor and mechanomyography, and times to different levels of recovery were measured. Venous samples for determination of the mivacurium isomers were collected during the interval 134-494 min after administration of mivacurium, and the terminal half-lives were calculated. Butyrylcholinesterase activity, phenotype, and genotype were determined for both the patient and the family. Complete nucleotide sequencing was used to identify the genotype.

RESULTS

A train-of-four ratio of 0.75 was reached 469 min after the injection of mivacurium. The terminal elimination half-lives of the mivacurium isomers, cis-trans and trans-trans, were 90 min. Complete nucleotide sequencing revealed two point mutations, the known silent variant S7 and a previously undescribed mutation of amino acid residue 170 introducing a stop codon.

CONCLUSIONS

The patient was compound heterozygous for silent mutations in the butyrylcholinesterase gene. The response to mivacurium was an extensively prolonged duration of action. Identification of the rare silent mutations presupposes access to modern molecular genetic methods such as complete nucleotide sequencing.

Pharmacokinetic studies of neuromuscular blocking agents: good clinical research practice (GCRP)

In September 1997, an international consensus conference on standardization of studies of neuromuscular blocking agents was held in Copenhagen, Denmark. Based on the conference, a set of guidelines for good clinical research practice (GCRP) in pharmacokinetic studies of neuromuscular blocking agents is presented. Guidelines include: design of the study; relevant patient groups to investigate; test drug administration, sampling and analysis; pharmacokinetic analysis; pharmacokinetic/pharmacodynamic modeling; population pharmacokinetics; statistics; and presentation of pharmacokinetic data. The guidelines are intended to aid those working in this research area; it is hoped that they will assist researchers, editors of scientific papers, and pharmaceutical companies in improving the quality of pharmacokinetic studies.

The influence of drug-induced low plasma cholinesterase activity on the pharmacokinetics and pharmacodynamics of mivacurium

BACKGROUND

The short duration of action of mivacurium results from its rapid hydrolysis by plasma cholinesterase. Bambuterol, an oral bronchodilator, has an inhibiting effect on plasma cholinesterase. The purpose of this study was to evaluate the effect of bambuterol-induced low plasma cholinesterase activity on the pharmacokinetics and pharmacodynamics of mivacurium.

METHODS

Fourteen patients received 20 mg bambuterol and 14 patients received placebo orally 2 h before induction of anesthesia. During anesthesia the neuromuscular block was monitored at the thumb using train-of-four nerve stimulation every 12 s and mechanomyography. The times to different levels of neuromuscular recovery after 0.2 mg/kg mivacurium were measured. The concentrations in venous blood of the three isomers and the metabolites of mivacurium were measured using high-performance liquid chromatography.

RESULTS

Plasma cholinesterase activity was inhibited a median of 90% (range, 67-97%) after bambuterol. The time to first response to train-of-four nerve stimulation was 15 min (range, 9-21 min) and 59 min (range, 32-179 min) in patients receiving placebo and bambuterol, respectively. The estimated clearances of the isomers were significantly lower and the elimination half-lives of all three isomers significantly prolonged in patients receiving bambuterol. No difference was seen in elimination half-lives of the metabolites. The elimination rate constant from the effect compartment and the potency of mivacurium was not affected by bambuterol.

CONCLUSION

A 90% inhibition of plasma cholinesterase activity significantly reduced clearance of the isomers of mivacurium. Correspondingly, the duration of action of 0.2 mg/kg mivacurium was prolonged three- to fourfold, compared with patients not administered bambuterol.

Why should I change my practice of anaesthesia: neuromuscular blocking agents

BACKGROUND

Recently, four neuromuscular blocking agents have been introduced into clinical practice. The drug companies claim that these new drugs offer several important advantages. But is this true? Do the new neuromuscular blocking agents add anything to our clinical practice, and will their introduction really benefit our patients? Or will it only benefit the economy of the companies?

PURPOSE OF THE LECTURE

In this lecture I shall try to update you on these new drugs and give you my personal bias on when to use the different (new and old) neuromuscular blocking agents.

Why, how and when to monitor neuromuscular function

BACKGROUND

Traditionally, anaesthetists evaluate the effect of neuromuscular blocking agents clinically. We observe the fasciculations following injection of succinylcholine, the movements of the reservoir bag, the spontaneous movements of the patient, headlift etc. However, with the advent of new fast acting neuromuscular blocking agents and the increasing awareness of the problems of postoperative residual neuromuscular block there is an mounting understanding of the importance of a more objective assessment of the neuromuscular function during anaesthesia.

PURPOSE OF LECTURE

In this lecture I shall give my personal bias on whether or not routine monitoring of neuromuscular function during anaesthesia is essential. Also, I shall try to answer the question "why, how and when should we monitor neuromuscular function during clinical anaesthesia?"

Tactile evaluation of the response to double burst stimulation decreases, but does not eliminate, the problem of postoperative residual paralysis

BACKGROUND

Routine perioperative monitoring with accelero-myography might prevent residual block, whereas routine tactile evaluation of the response to train-of-four (TOF) nerve stimulation does not. The purpose of this prospective, randomised and blinded study was to evaluate the effect of manual evaluation of the response to double burst stimulation (DBS3.3) upon the incidence of residual block.

METHODS

Sixty adult patients scheduled for elective abdominal surgery were included in the study. Pancuronium 0.08 to 0.1 mg kg-1 was given for relaxation and tracheal intubation. For maintenance of neuromuscular block, pancuronium 1-2 mg was administered. The patients were randomly allocated into two groups. In group DBS (double burst stimulation) the degree of block during anaesthesia was assessed by manual evaluation of the response to TOF nerve stimulation. During reversal, when no fade was detectable in the TOF response, the stimulation pattern was changed to DBS3.3. The trachea was extubated when the anaesthetist judged the neuromuscular function to have recovered adequately and no fade in the DBS3.3 response could be felt. In group CC (clinical criteria) patients were managed without the use of a nerve stimulator, and the level of neuromuscular block and reversal were evaluated solely on the basis of clinical criteria. In both groups, the TOF ratio was measured by mechanomyography immediately after tracheal extubation. Also, the ability to sustain head lift for 5 s, to protrude the tongue, to open the eyes, and to lift one arm to the opposite shoulder were tested.

RESULTS

The TOF ratio, as measured immediately after tracheal extubation, was significantly lower in group CC than in group DBS (means: 0.68 and 0.78, respectively), and the incidence of residual neuromuscular block defined as a TOF ratio < 0.7 was significantly higher in group CC than in group DBS (57 and 24%, respectively). The time from the first TOF measurement until the TOF ratio reached 0.8 was significantly longer in group CC than in group DBs (means: 11.5 and 6.2 min, respectively). No significant differences between the two groups of patients were found in duration of anaesthesia, in times from end of surgery to injection of neostigmine, tracheal extubation or TOF ratio 0.8, in dose of pancuronium, or in any other postoperative variable.

CONCLUSION

Routine perioperative manual evaluation of the responses to TOF and DBS3.3 decreased the incidence and the degree of residual block following the use of pancuronium. It did not, however, exclude clinically significant residual paralysis, nor did it influence the amount of pancuronium used during the operation, the duration of anaesthesia or the time from end of surgery to tracheal extubation or to sufficient recovery of neuromuscular function (TOF = 0.8).

Comparison of the cardiovascular effects of cisatracurium and vecuronium in patients with coronary artery disease

PURPOSE

Cisatracurium besylate (Nimbex Injection, Glaxo Wellcome Inc., Research Triangle Park, NC) is an intermediate-acting bis-benzylisoquinolinium neuromuscular blocking drug that is one of the stereoisomers of atracurium. At doses < or = 8 x ED95, it caused no clinically important cardiovascular side effects or histamine release in healthy patients. The purpose of the present study was to investigate the haemodynamic effects of high doses of cisatracurium in patients with coronary artery disease.

METHODS

One hundred patients undergoing myocardial revascularization participated in a pilot study (seven patients) and a double-blinded, randomized, controlled trial comparing the haemodynamic effects of cisatracurium with vecuronium at three centres. The patients were anaesthetized using oxygen 100%, with etomidate, fentanyl and a benzodiazepine, and tracheal intubation was facilitated using succinylcholine. After baseline haemodynamic measurements, the study drug was administered over 5-10 sec according to group assignment: Group A (pilot) cisatracurium, 0.20 mg.kg-1 (4 x ED95), (n = 7); Group B-cisatracurium, 0.30 mg.kg-1 (6 x ED95), (n x ED95), (n = 31); Group C-vecuronium, 0.30 mg.kg-1 (6 x ED95), (n = 31); Group D cisatracurium, 0.40 mg.kg-1 (8 x ED95), (n = 21); Group E-vecuronium, 0.30 mg.kg-1 (6 x ED95), (n = 10). The haemodynamic measurements were repeated at 2, 5, and 10 min after cisatracurium or vecuronium.

RESULTS

Two patients in Group D had > 20% decreases in MAP, but only one required therapy for hypotension. The haemodynamic changes from pre- to post-injection in the cisatracurium patients were minimal and similar to patients receiving vecuronium.

CONCLUSIONS

In patients with coronary artery disease, rapid cisatracurium (4-8 x ED95) boluses and vecuronium (6 x ED95) result in minor, clinically insignificant haemodynamic side effects.

Pharmacokinetics of bambuterol in subjects homozygous for the atypical gene for plasma cholinesterase

AIMS

It has been assumed that both plasma cholinesterase (EC 3.1.1.8) and oxidative enzymes are needed for optimum formation of the bronchodilator terbutaline from its biscarbamate prodrug bambuterol. The present study aimed at investigating the fate of bambuterol in subjects with deficient plasma cholinesterase but with normal oxidative (CYP2D6) capability.

METHODS

The pharmacokinetics of bambuterol and terbutaline were studied in four healthy subjects (two men and two women) being homozygous for the atypical gene for plasma cholinesterase. Their oxidative metabolism was apparently good as they were all rapid metabolizers of debrisoquine. Bambuterol hydrochloride 20 mg was given orally once daily for 10 days, and plasma and urine samples were taken for 1.5 days (plasma) and 4.5 days (urine) after administration of the last dose.

RESULTS

The pharmacokinetic parameters in the present study were grossly similar to those found in a study of bambuterol in subjects with normal plasma cholinesterase activity (N). However, subjects with atypical cholinesterase had a shorter terminal half-life of bambuterol (a measure of uptake rate), 4.8-12.6 h vs 8.3-22.3 h in N, and slightly higher plasma concentrations of bambuterol (average concentrations 1.9-3.7 nmol l(-1) vs 1.5-3.1 nmol l(-1) in N). Peak/trough terbutaline plasma concentrations ratios (2.1-3.2) were somewhat increased, but average plasma concentrations (8.3-14.5 nmol l(-1)) and terminal half-life (16.5-21.8 h) of terbutaline did not differ.

CONCLUSIONS

In Caucasian populations, one subject out of 2500 is homozygous for the atypical gene for plasma cholinesterase. The atypical enzyme has a much lower affinity for bambuterol than the normal enzyme. Nevertheless, the subjects with atypical cholinesterase were able to produce terbutaline as efficiently as normal subjects. This might be explained by an altered uptake and metabolism in the absence of plasma cholinesterase, or the importance of this enzyme for the formation of terbutaline from bambuterol in vivo may have been overestimated.

Residual neuromuscular block is a risk factor for postoperative pulmonary complications. A prospective, randomised, and blinded study of postoperative pulmonary complications after atracurium, vecuronium and pancuronium

BACKGROUND

After anaesthesia involving pancuronium a high incidence of both residual neuromuscular block and postoperative pulmonary complications (POPC) has been reported. The aim of this study was to compare the incidence of POPC following the use of pancuronium, atracurium, and vecuronium, and to examine the effect of residual neuromuscular block on the incidence of POPC.

METHODS

A total of 691 adult patients undergoing abdominal, gynaecological, or orthopaedic surgery under general anaesthesia were randomised to receive either pancuronium, atracurium, or vecuronium. Perioperatively, the response to train-of-four (TOF) nerve stimulation was evaluated manually. Postoperatively, the TOF ratios were measured mechanomyographically, and through a 6-day follow-up the patients were examined for pulmonary complications.

RESULTS

The incidence of residual block, defined as a TOF ratio < 0.7, was significantly higher in the pancuronium group (59/226: 26%) than in the atracurium/vecuronium groups (24/450: 5.3%). In the pancuronium group, significantly more patients with residual block developed POPC (10/59: 16.9%) as compared to patients without residual block (8/167: 4.8%). In the atracurium/vecuronium groups, the incidence of POPC was not significantly different in patients with (1/24: 4.2%) or without (23/426: 5.4%) residual block. Multiple regression analysis indicated that abdominal surgery, age, long-lasting surgery, and a TOF ratio < 0.7 following the use of pancuronium were potential risk factors for the development of POPC.

CONCLUSION

Postoperative residual block caused by pancuronium is a significant risk factor for development of POPC.

A comparison of remifentanil and alfentanil in patients undergoing major abdominal surgery

The efficacy and safety of remifentanil and alfentanil for patients undergoing major abdominal surgery were compared. Premedicated patients received a loading dose of remifentanil (1.0 microgram.kg-1; n = 116) and a continuous infusion of 0.5 microgram.kg-1.min-1, or a loading dose of alfentanil (25 micrograms.kg-1; n = 118) and a continuous infusion of 1.0 microgram.kg-1.min-1. Propofol was administered (10 mg every 10 s) until loss of consciousness. Patients' lungs were ventilated with 66% nitrous oxide and 0.5% (end-tidal) isoflurane in oxygen. The study drug infusion rate was reduced by 50% 5 min after intubation. Alfentanil was discontinued 15 min before the end of surgery, whereas remifentanil was continued in the immediate postoperative period at a reduced dose. Responses to intubation (28%) and skin incision (17%) occurred approximately twice as often in the alfentanil group (15% and 8%; p = 0.014 and p = 0.037, respectively). More patients receiving alfentanil had one or more responses to surgery (72% vs. 57%; p = 0.016). The time to spontaneous respiration, adequate respiration, response to verbal command and time to recovery room discharge were similar. However, owing to decreased variability, the time to extubation was shorter with remifentanil than with alfentanil (p = 0.048). There was a similar overall incidence of adverse events in both groups, 82% and 75% of patients, respectively. Adverse events associated with remifentanil were rapidly controlled by dose reductions. The incidence of intra-operative hypotension and bradycardia was higher in the remifentanil group (p < or = 0.033). An initial remifentanil infusion rate of 0.1 microgram.kg-1.min-1 titrated to individual need provided postoperative pain relief in the presence of adequate respiration in 71% of patients. When using remifentanil in the immediate postoperative setting, rapid administration of bolus doses and infusion rate increases resulted in a relatively high incidence of muscle rigidity, respiratory depression and apnoea. Changing the postoperative regimen to avoid rapid changes in remifentanil blood concentration resulted in more effective analgesia and dramatically reduced the incidence of adverse events during this period. In patients undergoing major abdominal surgery, remifentanil appears to offer superior intra-operative haemodynamic stability during stressful surgical events compared with alfentanil without compromising recovery from anaesthesia. Remifentanil can be administered as a postoperative analgesic agent at a starting dose of 0.1 microgram-.kg-1.min-1; however, it should only be used in the presence of adequate supervision and monitoring of the patient. Administration of bolus doses is not recommended in this setting.

Timing of tracheal intubation: monitoring the orbicularis oculi, the adductor pollicis or use a stopwatch?

The most suitable time for tracheal intubation, following vecuronium 0.1 mg kg-1, was estimated in 120 patients. The trachea was intubated at cessation of the visually observed response of the orbicularis oculi muscle to facial nerve stimulation (group 1; n = 30), or of the manually detected response of the adductor pollicis to ulnar nerve stimulation (group 2; n = 30), or after waiting 3 min (group 3; n = 30), or 4 min (group 4; n = 30). There were no significant differences in intubation scores between the four groups of patients. Loss of response to train-of-four stimulation occurred significantly sooner in group 1 (orbicularis oculi) than in group 2 (adductor pollicis) P = 0.021). However, intubating conditions were poor in four patients (14%) in group 1, compared with none in group 2 and one in groups 3 and 4, respectively. Thus, contrary to expectations, the cessation of the response of the orbicularis oculi muscle did not guarantee good or even satisfactory intubating conditions. The results suggest that in fit adult patients it is as good to wait 3 min after injection of vecuronium 0.1 mg kg-1 before tracheal intubation, as to use a nerve stimulator.

Good clinical research practice (GCRP) in pharmacodynamic studies of neuromuscular blocking agents

Based on an international consensus conference held in Copenhagen in the autumn of 1994, a set of guidelines for Good Clinical Research Practice (GCRP) in pharmacodynamic studies of neuromuscular blocking agents are presented. The guidelines are intended to be a help for people working in this research field, and it is hoped that the guidelines will assist researchers, editors, and drug companies to enhance the quality of their pharmacodynamic studies of neuromuscular blocking agents.

Dose-response relationship for mivacurium in patients with phenotypically abnormal plasma cholinesterase activity

During thiopentone-fentanyl-nitrous oxide anaesthesia and using a cumulative design, we studied the dose-response relationship of mivacurium in 8 patients: 7 patients phenotypically homozygous for the atypical plasma cholinesterase gene and 1 patient homozygous for the silent gene. The estimated mean ED50 and ED95 were 15 and 20 micrograms.kg.bw-1 in patients homozygous for the atypical gene, and 13 and 16 micrograms.kg.bw-1 in the patient homozygous for the silent gene, respectively. The results indicate that mivacurium is 4-5 times more potent in patients homozygous for the atypical or the silent gene than in patients with normal plasma cholinesterase activity and phenotype.