The role of patient simulation and incident reporting in the development and evaluation of medical devices and the training of their users

We describe how simulation and incident reporting can be used in combination to make the interaction between people, (medical) technology and organisation safer for patients and users. We provide the background rationale for our conceptual ideas and apply the concepts to the analysis of an actual incident report. Simulation can serve as a laboratory to analyse such cases and to create relevant and effective training scenarios based on such analyses. We will describe a methodological framework for analysing simulation scenarios in a way that allows discovering and discussing mismatches between conceptual models of the device design and mental models users hold about the device and its use. We further describe how incident reporting systems can be used as one source of data to conduct the necessary needs analyses - both for training and further needs for closer analysis of specific devices or some of their special features or modes during usability analyses.

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.

Management of anaphylactic shock evaluated using a full-scale anaesthesia simulator

BACKGROUND

The diagnosis of an anaphylactic reaction during anaesthesia is not the first consideration for the anaesthetist and might be missed. The aim of this study was to describe anaesthetists' management of an anaphylactic reaction concerning diagnosing, treatment and application of anaesthesia crisis resource management (ACRM) in a full-scale anaesthesia simulator.

METHODS

Forty-two anaesthetists in teams of two attended training sessions with a critical incident of anaphylactic shock in a full-scale simulator. Trained observers from the study group evaluated the medical treatment according to a treatment sequence developed from the literature and graded the ACRM performance on a five-point scale where 1 is bad and 5 is best.

RESULTS

None of the teams made the correct diagnosis within 10 min and treatment according to the treatment sequence was not initiated. Only 6/21 teams considered the right diagnosis but first after hints from the instructor 15 min after the start of the incident. Evaluation of the use of the total ACRM concept (that is the use of all of the ACRM expressions seen in a total connection: called general impression) gave a median value of 2.0 with a range of (1-3).

CONCLUSION

Anaphylactic shock was difficult to diagnose and no structured plans were used for the treatment in the simulated incident in this study.

Pharmacokinetics of oral diclofenac and acetaminophen in children after surgery

BACKGROUND

Our aim was to study the pharmacokinetics and pain scores following administration of single oral doses of either diclofenac or high-dose acetaminophen (paracetamol).

METHODS

In the morning, the day after tonsillectomy, children 5-15 years of age were randomized in a double-blind manner to receive either diclofenac 1-2 mg.kg-1 (n=11) or acetaminophen 22.5 mg.kg-1 (n=10). Postoperative pain was assessed by self-report and blood samples were drawn every 30 min for 4 h after medication.

RESULTS

Large interindividual differences in maximum plasma diclofenac concentrations (Cmax) were found. Mean Cmax was 2.4+/-1.3 microg.ml-1 and mean tmax was 2+/-0.5 h. No significant reduction in pain score with diclofenac was seen at any of the assessments during the study period. Eight of 10 children achieved Cmax of acetaminophen within the 10-20 microg.ml-1 antipyretic range. Mean tabs was 0.7+/-0.3 h and mean Cmax and tmax were 12.7+/-3.8 microg ml-1 and 1.4+/-0.5 h, respectively. No significant reduction in pain score with acetaminophen was seen at any of the assessments during the study period.

CONCLUSIONS

The achieved concentrations of diclofenac and acetaminophen were not able to significantly reduce the children's pain score during the 5 h postingestion study period. Analgesic plasma acetaminophen concentrations may be higher than those required for antipyresis.

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.

Local infiltration with NSAIDs for postoperative analgesia: evidence for a peripheral analgesic action

BACKGROUND

In order to investigate the evidence for a peripheral analgesic effect of local infiltration with nonsteroidal antiinflammatory drugs (NSAIDs) in postoperative pain, we conducted a systematic review.

METHODS

Randomised controlled and double-blind trials were evaluated. Outcome measures were pain scores, the use of supplementary analgesics, and time to first analgesic request. Efficacy was estimated by significant difference (P<0.05) as reported in the original reports and by calculation of the weighted mean difference of pain scores between treatment groups.

RESULTS

Sixteen studies with data from 844 patients were considered appropriate for analysis. The NSAIDs were administered as intra-articular injections, as components of intravenous regional anaesthesia (IVRA), and by wound infiltration and were compared with systemic administration or placebo. In the four studies comparing intra-articular NSAIDs with systemic administration a statistically significant effect in favour of intraarticular NSAIDs was found. Only one study compared IVRA NSAID with systemic administration, showing a significant effect in favour of IVRA administration. No more than two of the five studies comparing intrawound NSAIDs with systemic administration showed significant effect after intrawound administration. Most of the studies comparing local infiltration with placebo showed significant effect in favour of local infiltration.

CONCLUSION

There is evidence for a clinically relevant peripheral analgesic action of intra-articular NSAIDs while results of IVRA and wound infiltration with NSAIDs in postoperative pain are inconclusive. Trials without a systemic control group were not considered to provide evidence for a local effect.

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.

Diclofenac or acetaminophen for analgesia in paediatric tonsillectomy outpatients

BACKGROUND

In order to establish an effective drug regimen, we compared the analgesic efficacy of oral diclofenac and high-dose acetaminophen on pain after tonsillectomy.

METHODS

In this randomised, double-blind study 48 children, 5 to 15 years of age, following tonsillectomy were assigned to receive either diclofenac 2-3 mg kg(-1) 24 h(-1) (n=24) or acetaminophen 90 mg kg(-1) 24 h(-1) (n=24) for the first three days after surgery. Postoperative pain was assessed by self-report each day before scheduled medication at 7 h, 12 h, 18 h and 23 h.

RESULTS

The number of children rating severe pain was high in both the diclofenac group, 5-50%, and in the acetaminophen group, 12-58% during the three day study period. Pain scores in the diclofenac group were only significantly lower at 12 h on day 1-3 compared to pain scores in the acetaminophen group (P<0.05). None of the children in the diclofenac group experienced any episodes of nausea/vomiting compared to 9 children in the acetaminophen group on day 1. The incidences of nausea/vomiting increased with pain (P<0.05). None of the 48 children experienced any episodes of bleeding.

CONCLUSIONS

This study indicates that diclofenac was no more effective than high-dose acetaminophen (90 mg vs. 60 mg kg(-1) 24 h(-1)) for analgesia, but resulted in a lower incidence of nausea and vomiting in patients following tonsillectomy.

Analgesic efficacy and safety of preoperative versus postoperative ketorolac in paediatric tonsillectomy

BACKGROUND

Tonsillectomy is a common procedure in childhood resulting in significant morbidity due to pain. The aim of this study was to evaluate the analgesic efficacy and safety of a single dose of ketorolac i.v. given before or after tonsillectomy, compared to placebo.

METHODS

A randomized, double-blind, placebo-controlled study was performed in 60 children, 5 to 15 years of age, admitted for tonsillectomy. Patients were allocated to receive ketorolac 1 mg.kg-1 i.v. or placebo. Postoperative pain was assessed by self-report 1.5, 3, 5, and 24 h after surgery.

RESULTS

Pain scores were significantly lower for both ketorolac groups compared to the placebo group 1.5, 3, and 5 h after surgery (P = 0.05). Pain scores were lowest in the preoperative ketorolac group 1.5 to 5 h after surgery, and significantly fewer children in this group had fentanyl 0 to 1.5 hr after surgery. But no significant differences were found between pain scores of the preoperative and postoperative ketorolac groups in the first 24 h after surgery. Acetaminophen consumption during the first 5 h after surgery was significantly less in patients receiving ketorolac (P < 0.05). Patients in the preoperative ketorolac group had a significantly lower incidence of postoperative vomiting (P < 0.05). There were no significant differences in the incidence of postoperative bleeding between groups. Three children in the preoperative, 5 children in the postoperative ketorolac group and 5 children in the placebo group experienced postoperative haemorrhage.

CONCLUSION

This study indicates that a single dose of ketorolac 1 mg.kg-1 i.v. administered either before or immediately after surgery improves postoperative analgesia in children after tonsillectomy without evidence of increased incidence of bleeding.

Tracheal administration of atropine in children--effect on heart rate

Forty-one ASA I patients, aged 2-6 years, anaesthetized for elective ear, nose and throat surgery, were studied in a double blind and randomized fashion in order to examine the effect of tracheally administered atropine 0.02 mg.kg-1 or saline 0.9% on heart rate. In patients receiving atropine heart rate increased 8.8 beats.min-1 (8.7%) and 16.2 beats.min-1 (16.0%) after 3 and 5 min respectively. No increase in heart rate was seen in the saline group. Because of the late onset of action and only moderate increase in heart rate it is concluded that tracheal administration of atropine 0.02 mg.kg-1 to children is insufficient in emergency situations.

Specialty practice of family practice residency graduates, 1969 through 1993. A national study

OBJECTIVE

To describe demographic and practice characteristics of physicians who graduated from family practice residency training programs.

DESIGN

Information was obtained from the databases of the American Academy of Family Physicians, the American Board of Family Practice (ABFP), and the American Medical Association. Data sets were cross-referenced, and quantitative data from medical membership organizations and the certifying board were summarized. Information regarding medical school graduation and family practice residency completion was reported by the participating residency programs, and data on practice specialty were self-designated by the participating physicians.

SUBJECTS

Physician graduates of Accreditation Council for Graduate Medical Education-accredited family practice residency programs from 1969 through 1993.

MAIN OUTCOME MEASURES

Practice specialty designation by graduates of family practice residency programs.

RESULTS

Of the 38659 physicians who graduated from family practice residency programs from 1969 through 1993, 8780 (23%) were women, 2181 (6%) were graduates of colleges of osteopathic medicine, 4777 (12%) were international medical graduates, and 33484 (87%) were certified by the ABFP. Of the 36088 family practice residency graduates who designated a practice specialty, 32764 (91%) identified their specialty as family practice, including 32608 physicians who identified family practice, 129 general practice, 21 family practice-geriatric medicine, and six family practice-sports medicine. Among the 3324 family practice residency graduates (9%) who identified themselves as practicing in another specialty, the most common specialties were emergency medicine (1446 physicians [4%]) and preventive medicine (386 physicians [1%]). No other practice specialty was designated by more that 0.5% of family practice residency graduates.

CONCLUSION

The vast majority of family practice residency graduates are self-designated as practicing family medicine. These data suggest that family practice residency programs are an effective mechanism for the production of generalist physicians.

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.

Update on newer neuromuscular blocking drugs

The development of new non-depolarizing neuromuscular blocking drugs starting with the introduction of the intermediate-acting agents atracurium and vecuronium has made it possible to avoid the use of succinylcholine for elective cases. Recently 4 new drugs have become available; the short-acting mivacurium, the intermediate-acting rocuronium and the 2 long-acting drugs doxacurium and pipecuronium. The pharmacokinetic and pharmacodynamic profile of these drugs are reviewed in this paper.

Mivacurium-induced neuromuscular blockade in patients with atypical plasma cholinesterase

The duration of action of mivacurium was evaluated during a modified neurolept anaesthesia in 17 patients heterozygous for the usual and the atypical plasma cholinesterase (pChe) gene (E1uE1a) and in five patients homozygous for the atypical gene (E1aE1a). The response to train-of-four nerve stimulation was recorded using a Myograph 2000. Five heterozygous patients were given a small dose of mivacurium 0.03 mg kg bw-1 intravenously (Group 1). The mean (range) suppression of the first twitch in the train-of-four response (T1) was 91% (69-100%). The time to 90% T1 recovery was 23.9 min (14.0-31.3 min). Twelve other heterozygous patients (Group 2) received mivacurium 0.2 mg kg bw-1 (2.5 x ED95). In these patients the time to 100% T1 suppression was 1.4 min (1.1-2.0 min). The time to reappearance of the T1 response, to 90% T1 recovery, and the recovery index (25.3 min (14.5-34.5), 45.5 min (30.9-59.2), and 9.8 min (6.8-19.6), respectively) were significantly longer than reported in phenotypically normal patients. Five patients homozygous for the atypical gene (Group 3) were given 0.03 mg kg bw-1 mivacurium. The time to reappearance of T1 response following this low dose of mivacurium ranged from 26-128 min. In all five patients the neuromuscular block was successfully antagonized with neostigmine preceded by atropine. In conclusion, mivacurium-induced neuromuscular blockade was moderately prolonged in patients heterozygous for the usual and the atypical gene for plasma cholinesterase. Patients homozygous for the atypical plasma cholinesterase gene appear to be markedly sensitive to mivacurium.

Influence of plasma cholinesterase activity on recovery from mivacurium-induced neuromuscular blockade in phenotypically normal patients

The significance of plasma cholinesterase (pChe) activity for the duration of action of mivacurium in phenotypically normal patients was evaluated in 35 patients during neurolept anaesthesia. The response to train-of-four nerve stimulation was recorded using a Myograph 2000. Ten patients with normal pChe (Group I) and five patients with decreased pChe activity (Group 2) were given a small test dose of mivacurium 0.03 mg kg-1. Mivacurium 0.1 mg kg-1 was administered following spontaneous recovery from the first dose. The mean suppression of the height of the first (T1) of the train-of-four responses following mivacurium 0.03 mg kg-1 patients with normal and decreased enzyme activity was 40% and 56%, respectively, and the mean T1 suppression after mivacurium 0.1 mg kg-1 was 100% in both groups. The times to different levels of twitch height recovery following the 0.1 mg kg-1 dose did not differ between the two groups of patients. Another 20 patients with normal or decreased pChe activity (Group 3) were given mivacurium 0.2 mg kg-1. In this group the time to maximum block was 1.4 min (1.0-4.0) mean (range) and the time to reappearance of the T1 response was 15.0 min (7.4-22.7) (range). An inverse relationship was found between the patients' pChe activity and the time to first response. It is concluded that mivacurium is short-acting in patients with normal pChe phenotype and normal to low-normal pChe activity. No patient with very low pChe activity was included in the study. A prolonged response to mivacurium may, however, be expected in these patients.

Pretreatment with pancuronium before suxamethonium administration in patients heterozygous for the usual and the atypical plasma cholinesterase gene

The object of this study was to investigate whether pretreatment with pancuronium before i.v. injection of suxamethonium could cause prolonged neuromuscular blockade in patients heterozygous for the usual and the atypical plasma cholinesterase gene (E1uE1a). Forty-three patients, 23 with genotype E1uE1a and 20 with normal genotype (E1uE1u), were pretreated with pancuronium 0.01 mg.kg-1 followed by suxamethonium 1.5 mg.kg-1, and received either neurolept anaesthesia or halothane anaesthesia. Seven patients (E1uE1a) were given suxamethonium 1.5 mg.kg-1 without pretreatment. The duration and type of neuromuscular block were evaluated using train-of-four (TOF) nerve stimulation. Type of anaesthesia did not significantly influence the results. The duration of block following pretreatment was significantly longer in heterozygous patients than in normal patients. Time to 90% twitch height recovery was 10.7 +/- 1.2 min (mean +/- s.d.) in genotypically normal patients, and 18.0 +/- 4.2 min in patients with genotype E1uE1a. Pretreatment with pancuronium caused a significantly slower recovery of the TOF ratio (phase II block). Thus, a TOF ratio of 0.7 was always reached within 13 min in genotypically normal patients. In genotypically abnormal patients, the same TOF ratio was reached within 20 min in all but three patients. In these three patients time to 90% twitch height recovery was prolonged (18-31 min), and TOF ratio did not return to normal, but stabilized at about 0.35, 0.50, and 0.65, respectively. Injection of edrophonium restored normal neuromuscular function in 10 min. It is concluded that in patients heterozygous for the usual and the atypical gene, pretreatment with pancuronium in combination with an increased dose of suxamethonium may cause a phase II block and thus a prolonged neuromuscular block.

Reversal of intense neuromuscular blockade following infusion of atracurium

In order to evaluate reversal time from very intense neuromuscular blockade caused by a continuous infusion of atracurium, the time course of neostigmine induced reversal from different levels of neuromuscular blockade was evaluated using the post-tetanic count (PTC) and the train-of-four (TOF) in 30 patients anesthetized with nitrous oxide, fentanyl, and thiopental. Reversal time (time from administration of neostigmine at different PTC levels to a TOF ratio of 0.7) was found to depend upon the degree of blockade at the time of reversal. Median reversal time from a PTC of 1-2, 3-4, 5-6, 7-8, 9-10, 11-12, and greater than 13 (but less than 10% twitch height) to a TOF ratio of 0.7 was 31, 23, 19, 18, 14, and 13 min, respectively. Spontaneous recovery from PTC level of 1-2, when atracurium infusion was stopped, to a PTC level at which antagonism was induced and reversal time were both correlated to the square root of the PTC. Total recovery time (spontaneous recovery plus reversal time) was not shortened by an early injection of neostigmine. It is concluded that neostigmine administration during intense neuromuscular blockade following atracurium infusion does not shorten total recovery time and offers no clinical advantages.

Clinical recovery and train-of-four ratio measured mechanically and electromyographically following atracurium

Indices of clinical recovery were compared with mechanically (adductor pollicis muscle) and electromyographically (first dorsal interosseal muscle) recorded train-of-four (TOF) ratios during antagonism of atracurium blockade in 23 healthy neurolept anesthetized patients. Clinical recovery was evaluated from the ability to lift the head, sustain headlift for 5 or 10 s, protrude the tongue, open the eyes, and the presence of ptosis of the eyelids. In all patients the mechanical TOF ratio was recorded. In 17 patients TOF ratios based on measurements of the potential area and the amplitude of the major negative deflection of the compound EMG response were recorded as well. At each TOF ratio interval of 0.05 from a TOF ratio of 0.5-0.85, the number of patients being able to perform the individual tests was recorded. Further, the mechanical TOF ratio during recovery was compared with the EMG TOF ratios. Headlift could not be sustained for 5 s in any patient at a TOF ratio of 0.5, whether recorded mechanically or by EMG, and TOF ratio had to recover to 0.8 before all patients could sustain headlift for 5 s. All patients could open the eyes and protrude the tongue at a TOF ratio of 0.65, and ptosis remained present during the entire testing period. There was no statistically significant difference between the mechanical and the EMG methods with regard to the TOF ratios at which the tests could be performed. During recovery a linear relationship was found between mechanical TOF ratios and the square root of the EMG TOF ratios.(ABSTRACT TRUNCATED AT 250 WORDS)

Adverse reactions and interactions of the neuromuscular blocking drugs

The adverse reactions seen following administration of neuromuscular blocking agents are mainly cardiovascular. Due to the lack of specificity for the nicotinic receptor at the neuromuscular junction, these agents may interact with receptors in autonomic ganglia and muscarinic receptors in the heart. Furthermore, muscle relaxants may have histamine-releasing properties. The cardiovascular effects vary with potency and specificity of the drug, depending mainly on the chemical structure. Pancuronium, fazadinium and especially gallamonium block cardiac muscarinic receptors, and tachycardia may be seen. Atracurium, metocurine and in particular d-tubocurarine have histamine-releasing properties and may cause flushing, hypotension and tachycardia. Vecuronium has no effect on the cardiovascular system. The effect of succinylcholine on heart rate differs between children, where bradycardia is seen, and adults in whom tachycardia may follow. However, bradycardia may occur in adults following a single dose. Succinylcholine increases plasma potassium, especially in patients with nerve damage, and arrhythmias may be observed. The neuromuscular adverse effects of succinylcholine, such as fasciculations and increased gastric and intraocular pressure, may be prevented by precurarisation. Many drugs interact with neuromuscular blocking agents and there is often a potentiation of the neuromuscular effect. This is of clinical importance in the case of antibiotics, inhalational anaesthetics, lithium and cyclosporin. Difficulty in reversing the block may occur with calcium channel blockers and polymyxin. However, some drugs, such as phenytoin, carbamazepine and lithium, may cause resistance to neuromuscular blocking agents. Furthermore, clinically important interactions exist between individual neuromuscular blocking drugs. Precurarisation with a non-depolarising drug prolongs the onset of succinylcholine, and conversely a prolonged effect of non-depolarising drugs is seen following succinylcholine. The effect of succinylcholine is markedly prolonged if the drug is administered during recovery from pancuronium blockade or following neostigmine for reversal. Succinylcholine is hydrolysed by plasma cholinesterase, and drugs which decrease the activity of this enzyme may produce a prolonged block, i.e. contraceptive pills, cyclophosphamide, echothiopate and organophosphate.

Double burst stimulation (DBS): a new pattern of nerve stimulation to identify residual neuromuscular block

We present a new pattern of nerve stimulation--double burst stimulation (DBS)--to detect residual neuromuscular block manually. The DBS consists of two short lasting, 50-Hz tetanic stimuli or bursts separated by a 750-ms interval. The response to this pattern of stimulation is two single separated muscle contractions of which the second is less than the first during nondepolarizing neuromuscular blockade. The ability to identify fade manually at different train-of-four (TOF) ratios was compared in four DBS patterns in which different numbers of impulses in the individual bursts were combined. The DBS with three impulses in each burst (DBS3,3) was considered to be the most sensitive and the least painful and thus most suitable for clinical use. The degree of fade in TOF and DBS3,3 was almost identical at any level of blockade (correlation coefficient 0.96), and the major post-DBS3,3 effect was a depression of the first twitch in TOF lasting less than 15 s. It is concluded that the DBS is more sensitive than the TOF in manual detection of residual block.

Half-life of plasma cholinesterase

The half-life of plasma cholinesterase (acylcholine acylhydrolase EC 3.1.1.8) was determined in three patients homozygous for the atypical gene for plasma cholinesterase by measuring the rate of disappearance of enzyme activity following intravenous injection of concentrated human cholinesterase. Half-life values of 10.9, 11.1, and 11.3 days were estimated. The distribution volume was estimated to be 18.0, 18.2, and 13.8% of body weight, respectively.

A new infusion design for atracurium and vecuronium

An infusion technique, designed to reduce the duration of period of no response to nerve stimulation following atracurium (Group I) and vecuronium (Group 2), was studied in 30 patients during neurolept anaesthesia. For intubation a combination of a small bolus injection of the relaxant (ED50) and a continuous infusion were administered. The tactile response to nerve stimulation was used to quantify the degree of relaxation and to adjust the speed of infusion. On the other arm the mechanical twitch was recorded blindly for control. Good to excellent intubation conditions were obtained in 4.3 min with atracurium and in 4.0 min with vecuronium. The total dose given for intubation was 0.36 mg kg-1 atracurium (0.24-0.49 mg kg-1) and 0.064 mg kg-1 vecuronium (0.046-0.084 mg kg-1). The period of no response was zero in seven patients in Group I and in four patients in Group 2. In the remaining patients in Group I the period of no response ranged from 5.0-25.0 min, median 10.9 min, and in Group 2 from 2.5-15.6 min, median 9.5 min. At the time of extubation the train-of-four ratio was 0.71 and 0.72 in Group I and 2, respectively. It is concluded that it is possible to achieve a stable, adjustable, and easily reversible block with this technique, even during surgery of short duration.

The influence of fentanyl on the cardiovascular effect of suxamethonium

The influence of fentanyl on the cardiovascular effect of a single dose of suxamethonium was evaluated during thiopentone N2O/O2 anaesthesia. Sixty adult patients were randomly allocated to three groups. In one group (control group) no fentanyl was given. In two groups fentanyl 0.002 mg/kg and 0.004 mg/kg, respectively, was given before induction of anaesthesia. Three minutes after the injection of suxamethonium 1 mg/kg, both heart rate (HR) and mean arterial pressure (MAP) in the two groups receiving fentanyl were significantly lower than in the control group. However, the absolute changes were small and no dose-related effect was seen. An estimation of the change in HR following suxamethonium was made using as predictors initial HR before induction of anaesthesia, age, sex, and the injection of fentanyl. The higher the initial HR, the greater was the chance of a decrease in HR following suxamethonium. Injection of fentanyl lowered the threshold HR above which a decrease was to be expected following injection of suxamethonium. This effect was most pronounced among the younger patients. It is concluded that injection of fentanyl potentiates the decrease in HR sometimes seen after a single dose of suxamethonium and that this effect is influenced by HR before induction of anaesthesia and by age of the patient.

Edrophonium and neostigmine for reversal of the neuromuscular blocking effect of vecuronium

The effect of edrophonium for reversal of the non-depolarizing neuromuscular blockade produced by a continuous infusion of vecuronium was compared to that of neostigmine in 20 adult patients during neurolept anaesthesia. When antagonism was attempted at 10% twitch height recovery, reversal time to a train-of-four ratio of 0.7 was significantly shorter following neostigmine 0.04 mg/kg than after edrophonium 0.75 mg/kg (9.8 min and 18.7 min, respectively) but the same after edrophonium 1.5 mg/kg (10.3 min). There was no statistically significant difference in reversal time between neostigmine 0.04 mg/kg given at 10% twitch height and edrophonium 0.75 mg/kg given at 25% twitch height recovery (6.0 min). Additional doses of atropine were necessary following edrophonium 1.5 mg/kg.