Background Many studies have indicated that acceleromyography and mechanomyography cannot be used interchangeably. To improve the agreement between the two methods, it has been suggested to use a preload and to refer all train-of-four (TOF) ratios to the control TOF (normalization) when using acceleromyography. The first purpose of this study was to test whether a preload applied to acceleromyography would increase the precision and the agreement with mechanomyography. The second purpose was to evaluate whether normalization would improve the agreement with mechanomyography. Methods Sixty patients were randomized to acceleromyography with or without a preload (Hand Adapter; Organon, Oss, the Netherlands). On the contralateral arm, mechanomyography was used. Anesthesia was induced with propofol and an opioid, and neuromuscular block with 0.6 mg/kg rocuronium. The precision and the bias and limits of agreement (with or without normalization) between the methods were evaluated using TOF stimulation. Results Preload improved the precision of acceleromyography by 21%, but it also increased the mean control TOF ratio from 1.07 to 1.13. Normalization of the acceleromyographic TOF ratios diminished the bias to mechanomyography during recovery (e.g., from 0.15 to 0.05 at TOF 0.90); when the mechanomyographic TOF values were normalized as well, the bias was eliminated. However, normalization did not exclude wide individual differences between acceleromyography and mechanomyography (+/- 0.10-0.20 at TOF 0.90). Conclusion Preload increases the precision of acceleromyography, and normalization of the TOF ratios decreases bias in relation to mechanomyography. When both acceleromyography and mechanomyography are normalized, there is no significant bias between the two methods.

This systematic review describes the evidence on the use of acceleromyography for perioperative neuromuscular monitoring in clinical practice and research. The review documents that although acceleromyography is widely used in research, it cannot be used interchangeably with mechanomyography and electromyography for construction of dose-response curves or for recording different pharmacodynamic variables after injection of a neuromuscular blocking agent. Some studies indicate that it may be beneficial to use a preload to increase the precision of acceleromyography, and to "normalize" the train-of-four ratio to decrease the bias in relation to mechanomyography and electromyography. However, currently the evidence is insufficient to support the routine clinical use of preload and "normalization." In contrast, there is good evidence that acceleromyography improves detection of postoperative residual paralysis. A train-of-four ratio of 1.0 predicts with a high predictive value recovery of pulmonary and upper airway function from neuromuscular blockade.

Background Sugammadex (Org 25969) forms a complex with steroidal neuromuscular blocking agents, thereby reversing neuromuscular block. This study investigated the dose-response relation, safety, and pharmacokinetics of sugammadex to reverse rocuronium-induced block. Methods Twenty-seven male surgical patients aged 18-64 yr were randomly assigned to receive placebo or sugammadex (0.5, 1.0, 2.0, 3.0, or 4.0 mg/kg) for reversal of 0.6 mg/kg rocuronium-induced neuromuscular block. Anesthesia was induced and maintained using intravenous fentanyl and propofol. Neuromuscular function was assessed using acceleromyography. Sugammadex or placebo was administered at reappearance of T2 of the train-of-four. The primary efficacy variable was the time required for recovery to a train-of-four ratio of 0.9. Results Sugammadex decreased median recovery time in a dose-dependent manner from 21.0 min in the placebo group to 1.1 min in the group receiving 4.0 mg/kg sugammadex. Doses of sugammadex of 2.0 mg/kg or greater reversed rocuronium-induced neuromuscular block within 3 min. A median of 59-77% of sugammadex was excreted unchanged in the urine within 16 h, mostly in the first 8 h. Sugammadex increased the proportion of the rocuronium dose excreted unchanged in the urine (from a median of 19% in the placebo group to 53% in the 4.0-mg/kg group within 16 h). Sugammadex was safe and well tolerated. No evidence of recurarization was observed in any patient. Conclusion At doses of 2.0 mg/kg or greater, sugammadex safely reversed 0.6 mg/kg rocuronium-induced neuromuscular block in a dose-dependent manner. Sugammadex enhanced renal excretion of rocuronium and was excreted unchanged by the kidneys.

Background In patients homozygous for atypical plasma cholinesterase, mivacurium causes a long-lasting neuromuscular block, but injection of human cholinesterase has been proven effective in antagonizing the block. The purpose of this study was to evaluate the pharmacodynamics and pharmacokinetics of mivacurium in such patients, as well as the effect of cholinesterase injected early or late after mivacurium. Methods Eleven patients phenotypically homozygous for the atypical variant received 0.075 mg/kg (1 patient) or 0.15 mg/kg (10 patients) mivacurium. The neuromuscular block was monitored using train-of-four nerve stimulation and mechanomyography. Cholinesterase, 2.8-10.0 mg/kg, was administered approximately 30 or 120 min after mivacurium. The times to different levels of neuromuscular recovery and the venous concentrations of the isomers of mivacurium were measured. Results Injection of cholinesterase increased plasma cholinesterase activity to normal and the clearances of the active isomers and the elimination rate constants by a factor of 10-15. The first response was seen in 13.5 min (3.7-44.2 min). Time to a train-of-four ratio of 0.8 ranged from 30 to 60 min (n = 6). Neostigmine injected after cholinesterase shortened recovery further, and a train-of-four ratio of 0.8 was reached in 10-30 min. Conclusion As expected, the duration of action of mivacurium is markedly prolonged in homozygous atypical patients. Injection of cholinesterase significantly increases the metabolism of mivacurium, leading to a shorter duration of action. Injection of neostigmine after the administration of cholinesterase speeds up recovery.

Background Mivacurium is hydrolyzed by the butyrylcholinesterase enzyme, and patients with hereditary changes of the enzyme often have prolonged duration of action of mivacurium. In this study, the authors investigated the significance of the most commonly occurring variant, the Kalow (K) variant, established using DNA analysis, for the response to mivacurium. Methods A total of 58 patients carrying either the wild-type butyrylcholinesterase or different combinations of the atypical (A) variant and the K variant were included. Patients who were homozygous for the A variant were given 0.03 mg/kg mivacurium. All other patients received 0.2 mg/kg mivacurium. The neuromuscular block was measured using train-of-four nerve stimulation and mechanomyography. Genotyping was performed with complete nucleotide sequencing. Results Heterozygosity of the K variant prolonged the time to train-of-four 0.70 from 26.6 to 34.5 min (30%; not significant) as compared with the wild type. Heterozygosity of the K variant linked to the A variant prolonged the corresponding time from 32 to 42.7 min (33%; P = 0.03) as compared with patients who were heterozygous for solely an A allele. For eight patients who were homozygous for both the A and K variants, the time to 25% recovery was 78-89 min as compared with 44-57 min in patients who were homozygous for the A variant or had only one linked K variant. Conclusion The K variant prolongs the duration of action of mivacurium. The current results indicate that the effect is modest when the K variant occurs heterozygously with the wild type or the A variant but is marked in patients who are homozygous for both the A and K variants.

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.

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.