Duration Of Neuromuscular Block Research Articles

Low-dose sugammadex reverses moderate rocuronium-induced neuromuscular block in horses.

Neuromuscular block (NMB) during general anaesthesia has an implicit risk of inadvertent residual NMB during recovery. Reversal of NMB is commonly encouraged to decrease this risk, and has historically been performed with neostigmine/atropine, two agents with important cardiac and gastrointestinal side effects. Sugammadex is a new selective relaxant binding agent that can reverse rocuronium-induced NMB efficiently and without these complications. Recommended doses are possibly cost-prohibitive. To measure the recovery time from rocuronium-NMB after administration of low-dose sugammadex, compared with spontaneous recovery. Nonrandomised in vivo experiments. Fourteen adult horses undergoing different research procedures were anaesthetised with detomidine and isoflurane. All horses received NMB with rocuronium 0.3 mg/kg IV. Neuromuscular function was measured with acceleromyographic train-of-four (TOF) ratio. Recovery occurred spontaneously in five horses weighing (median [range]) 548 (413-594) kg and was enhanced with sugammadex 200 mg (total dose) in nine horses (433 [362-515]) kg. Recovery time from moderate NMB to a TOF ratio 1.0, and total duration of NMB were compared between groups. Cases of recurarisation (decrease in the TOF ratio <0.9 after recovery) were identified within 30 min after sugammadex. The dose of sugammadex was 0.46 (0.39-0.55) mg/kg. The recovery period lasted 21 (17-39) minutes for spontaneous and 4 (3-7) minutes for sugammadex. Total duration of NMB was 58 (41-70) minutes for spontaneous and 36 (21-43) for sugammadex (both p ≤ 0.003). There were no instances of recurarisation. Small sample size. A dose of sugammadex of approximately 0.5 mg/kg substantially shortened the recovery period from rocuronium-induced NMB from a median of 21 to 4 min, when given at a moderate depth of NMB. No recurarisation was observed within the next 30 min.

Duration of neuromuscular block is more variable and recovery time is shorter with rocuronium than cisatracurium in anesthetized dogs.

To compare the variability in the duration of action of a single dose of rocuronium or cisatracurium, and duration of subsequent top-up doses in anesthetized dogs. Thirty dogs requiring ophthalmic surgery with neuromuscular block. Neuromuscular function was monitored with train-of-four (TOF) and acceleromyography. Dogs received an initial dose of rocuronium 0.6 mg/kg, or cisatracurium 0.15 mg/kg IV, which produced complete neuromuscular block. Upon return of the first response (T1) of TOF, a third of the initial dose was repeated. The duration of the initial dose and its variability were compared between agents. Duration of subsequent top-up doses was assessed with mixed effect models. Spontaneous (from last return of T1) or neostigmine-enhanced (from administration to complete recovery) recovery times were measured for each agent. Duration of action of the initial dose was [median (range)] 25 (10-60) min with rocuronium and 35 (15-45) min with cisatracurium (p=.231). The variability of rocuronium was 3.25 times larger than cisatracurium (p=.034). Duration of top-up doses did not vary for either agent. Spontaneous recovery was shorter for rocuronium [15 (10-20) min] than cisatracurium [25 (15-45) min] (p=.02). Neostigmine-enhanced recovery times were 5 (5-25) for rocuronium and 10 (5-10) for cisatracurium (p=.491). Duration of action for a single dose is significantly more variable with rocuronium than cisatracurium. Time to spontaneous recovery was longer for cisatracurium, and cases of unexpectedly long recovery times were observed with both agents. Objective monitoring is recommended.

Prospective Cohort Study Comparing Varying Doses of Cisatracurium and Atracurium on Intubating Conditions in Patients Undergoing Laparoscopic Cholecystectomy

Introduction: Cisatracurium and atracurium are non-depolarising muscle relaxants belonging to benzylisoquinolinium group. Intubating dose of cisatracurium is found to be safer than atracurium owing to the histamine release and resultant respiratory and cardiac side-effects associated with the latter. However, intubating conditions of twice the ED95 dose (2xED95) of cisatracurium are not as satisfactory as equipotent dose of atracurium because of its higher potency. Aim: To compare the time of onset, intubating conditions and mean duration of action of three and four times ED95 doses (3 and 4xED95) of cisatracurium with 2xED95 dose of atracurium so as to find out an ideal intubating dose of cisatracurium that is comparable with 2xED95 of atracurium. Materials and Methods: The present study was a prospective cohort study that included 102 patients who underwent elective laparoscopic cholecystectomy. They were divided into three groups of 34 each to receive atracurium 0.5 mg/kg (group A), cisatracurium 0.15 mg/kg (group B) or cisatracurium 0.2 mg/kg (group C) for intubation. Onset and duration of neuromuscular block were assessed using Train Of Four (TOF) stimuli. Total time for intubation and mean intubation scores were also noted. Statistical analysis was done using Statistical Package for the Social Sciences (SPSS) software version 18.0. Qualitative data were compared using Chi-square test and quantitative data compared using Analysis of Variance (ANOVA). Results: Onset of neuromuscular blockade in groups A, B and C were 292.06±61.486, 204.71±39.407 and 120.88±37.284 seconds (p-value &lt;0.001), respectively. Mean intubation score was highest in group C along with least intubating time (p-value &lt;0.001). The mean duration of action in groups A, B and C were 40.44±5.275, 48.24±5.888 and 63.38±7.659 minutes, respectively (p-value &lt;0.001). Conclusion: The 3 and 4xED95 doses of cisatracurium are superior to 2xED95 dose of atracurium in providing faster onset of action, better intubating conditions, shorter intubation time and longer duration of action. The 4xED95 dose of cisatracurium may be considered for rapid intubation in two minutes.

Administration of Magnesium Sulphate Prior to Vecuronium: Effects on the Speed of Onset and Duration of Neuromuscular Block

Background: We commonly encounter surgical patients who are on magnesium therapy in the operation theatre. It is important to know the interaction of magnesium on anaesthetic drugs including neuromuscular blocking agents. Our aim is to observe and compare the onset and duration of action of vecuronium following magnesium pre-treatment. Material and Method: 50 patients were randomly divided into 2 groups. Group 1 (n = 25) received placebo (normal saline) and group 2 (n=25) received 40 mg/kg magnesium sulphate added to 100 ml of normal saline infused over a period of 15 minutes prior to induction. Following the induction of anaesthesia muscle relaxation was achieved by 0.1 mg/kg vecuronium and time for onset, duration of neuromuscularblock and vecuronium dose requirement during surgery was assessed by monitoring the tactile response to Train of four stimulation. Results: Onset of time for intubation was significantly reduced to 120.19±6.53 seconds in the magnesium group compared to 259.150±26.131 seconds in thecontrol group(P< 0.001). It was observed that the average duration of neuromuscular blockage of vecuronium was almost doubled and statistically significant (P = 0.001) in the magnesium group(26.89±2.91) as compared to the control group (42.28±1.41).The total dose of vecuronium used or required was significantly less in the magnesium group when compared to the control group (p=0.008). Duration from last dose of vecuronium to reversal of anaesthesia was prolonged in the magnesium group (40.2±3.96) compared to the control group(29.8±6.03) which is statistically significant(p<0.001). Conclusion: Magnesium sulphate administered before vecuronium significantly accelerates the onset of neuromuscular block necessary for intubation of trachea and significantly increase the time course of neuromuscular blockade. Intraoperative consumption of vecuronium was less in the magnesium group.

Onset and duration of cis-atracurium neuromuscular block during fentanyl and lidocaine infusions in isoflurane-anaesthetised dogs

BackgroundThis retrospective study assessed the onset and duration of the neuromuscular block (NMB) induced by cis-atracurium 0.15 mg/kg intravenously with and without fentanyl or lidocaine infusions in 45 isoflurane-anaesthetised dogs.MethodsDogs...

Bias, limits of agreement, and percent errors between acceleromyography and mechanomyography in anesthetized dogs

This study compared measurements of neuromuscular function with mechanomyography (MMG) and acceleromyography (AMG) in nine anesthetized dogs receiving 0.1mg/kg vecuronium intravenously. Train-of-four (TOF) stimulation was applied to each ulnar nerve every 15s. The resulting amplitude of the first twitch (T1) and the TOF ratio were measured with both monitors. The baseline TOF ratio (prior to vecuronium), onset time (time of injection to T1<5%), recovery index (time between T1 values of 25% and 75%) and duration of neuromuscular block (injection to TOF 0.9) were recorded. The MMG TOF ratios when the AMG first reached 0.7 (AMG 0.7) and 0.9 (AMG 0.9) during recovery were also recorded. Values were compared with paired tests and individual errors>25% between monitors were identified for each dog. Bias, limits of agreement (LOA) and percentage error (PE) between methods were calculated from Bland–Altman plots for T1 and TOF ratio for the complete data set, and for TOF≥0.7 during recovery. There were no statistical differences in baseline TOF ratio, onset, recovery index, duration, AMG 0.7 and AMG 0.9. Individual errors>25% were evident in onset, recovery index, AMG 0.7 and AMG 0.9. Overall, T1 and TOF ratio had a small bias, wide LOA and PE>100%. Percent error was reduced to 30% when TOF≥0.7 was analyzed. Although there were no statistical differences between MMG and AMG in any variable of interest, individual discrepancies, wide LOA and high PE suggest that these monitors should not be used interchangeably for serial measurements on the same animals.

Predictors of the variability in neuromuscular block duration following succinylcholine: A prospective, observational study.

The duration of neuromuscular block (NMB) following succinylcholine administration is characterised by a high interindividual variability. However, this has not yet been quantified in a large sample of surgical patients. The significance of underlying clinical factors is unknown. The objective of this study was to profile the variability in NMB duration following a standard dose of succinylcholine and to investigate contributing clinical and genetic factors. A prospective, observational study. Tertiary referral centre. In a total of 1630 surgical patients undergoing a rapid sequence induction and intubation, clinical risk factors for a prolongation in NMB duration following succinylcholine were assessed. In a subset of 202 patients, additional biochemical and molecular genetic investigations of butyrylcholinesterase were performed. A standard 1 mg kg dose of succinylcholine after administration of an induction drug and an opioid. NMB duration measured as the time between administration of succinylcholine until reappearance of palpable muscular response to supramaximal transcutaneous ulnar nerve stimulation. NMB varied from 80 s to 44 min with a median duration of 7.3 min. Sixteen percent of patients had NMB duration in excess of 10 min. A multivariable survival model identified physical status, sex, age, hepatic disease, pregnancy, history of cancer and use of etomidate or metoclopramide as independent risk factors for a prolonged NMB. Three novel butyrylcholinesterase variants were identified: p.Ile5Thr; p.Val178Ile; and p.Try231Ser. Neuromuscular blockade duration in excess of 10 min occurred in 16% of a general surgical population following a single dose of succinylcholine. The multivariable model of clinical risk factors for prolonged NMB revealed a negative predictive value of 87%, thereby indicating that absence of such risk factors may reliably predict a shorter duration of NMB. In patients with clinical risk factors for a prolonged NMB or with butyrylcholinesterase mutations, an alternative to succinylcholine should be considered.

Comparison of equipotent doses of rocuronium and vecuronium.

Background:Rocuronium (R) bromide and vecuronium (V) are monoquaternary aminosteroid compounds. The aim of this study was to evaluate the onset time, conditions of intubation and duration of action of equipotent doses (3ED95) of R and V.Materials and Methods:The study was carried out in 60 adult American Society of Anesthesiologists physical status 1–2 patients of age 20–60 years. The patients were divided into two groups of 30 each and received either 0.9 mg/kg of R (Group R) or 0.168 mg/kg of V (Group V) to facilitate endotracheal intubation. Neuromuscular blockade was assessed at corrugator supercilii and adductor pollicis muscles to evaluate onset time and duration of neuromuscular block, respectively.Results:The mean onset time was significantly rapid in Group R as compared to Group V (P -0.011). Overall intubating conditions were excellent in 100% of patients in Group R as compared to 70% in Group V. The mean duration of action did not show a significant variation between the groups.Conclusion:At equipotent doses, R provides clinically acceptable intubation conditions much earlier than V without significant variation in clinical duration of action.

Effect of an intravenous infusion of lidocaine on cisatracurium-induced neuromuscular block duration: a randomized-controlled trial

Effect of an intravenous infusion of lidocaine on cisatracurium-induced neuromuscular block duration: a randomized-controlled trial

Reversal of rocuronium-induced neuromuscular block by sugammadex is independent of renal perfusion in anesthetized cats

Sugammadex is a selective relaxant binding agent designed to encapsulate the aminosteroidal neuromuscular blocking agent rocuronium, thereby reversing its effect. Both sugammadex and the sugammadex-rocuronium complex are eliminated by the kidneys. This study investigated the effect of sugammadex on recovery of rocuronium-induced neuromuscular block in cats with clamped renal pedicles, as a model for acute renal failure. Twelve male cats were divided into two groups and anesthetized with medetomidine, ketamine, and alpha-chloralose. The cats were intubated and ventilated with a mixture of oxygen and air. Neuromuscular monitoring was performed by single twitch monitoring. Rocuronium 0.5mg/kg i.v. was administered. After spontaneous recovery from neuromuscular block, both renal pedicles were ligated. A second dose of rocuronium 0.5mg/kg i.v. was given. One minute after disappearance of the twitches, in Group 1 placebo (0.9% saline) and in Group 2 sugammadex 5.0mg/kg i.v. was administered. Onset time, duration of neuromuscular block, and time to recovery to 25, 50, 75, and 90% were determined. After renal pedicle ligation, sugammadex reversed rocuronium-induced neuromuscular block significantly faster than spontaneous recovery. Mean time (SEM) to 90% recovery of the twitch response was 4.7 (0.25)min (Group 2) versus 31.1 (5.0)min (Group 1) (p<0.0001). No signs of recurrence of neuromuscular block were observed for 90min after complete twitch restoration. Sugammadex caused no significant cardiovascular effects. Sugammadex rapidly and effectively reversed rocuronium-induced neuromuscular block in anesthetized cats, even when both renal pedicles were ligated and renal elimination of the drugs was no longer possible.

Neostigmine injected 5 minutes after low-dose rocuronium accelerates the recovery of neuromuscular function

Study Objective To determine whether neostigmine 5 minutes after 0.4 mg/kg rocuronium accelerates reversal. Design Prospective, randomized, comparative open-label study. Setting Operating room. Patients 60 ASA physical status I and II patients, aged 18 to 65 years. Interventions Patients received 0.4 mg/kg rocuronium during nitrous oxide (N 2O)-propofol-opioid anesthesia. Reversal of neuromuscular blockade was achieved with neostigmine, either at 0.03 mg/kg or 0.05 mg/kg intravenously (IV), together with glycopyrrolate administered 5 minutes after relaxant and compared with spontaneous recovery. Onset, depth, and duration of neuromuscular block, as well as recovery of train-of-four (TOF) to 0.8 and 0.9 were evaluated. Main Results Times to achieve TOF ratios of 0.8 and 0.9 were significantly shorter when 0.03 mg/kg or 0.05 mg/kg neostigmine was administered 5 minutes after administration of rocuronium (20.2 ± 5 min and 22.6 ± 5.9 min or 17.8 ± 4.8 min and 19.4 ± 5.1 min, respectively) compared with controls (36.2 ± 8.5 min and 39.0 ± 8.7 min; P < 0.01). Duration to spontaneous T1 25% recovery after rocuronium was 15.5 ± 6.5 min versus 9.3 ± 2.3 min and 7.7 ± 1.6 min in the treatment groups ( P < 0.01). Recovery index (T1 from 25% to 75%) was significantly shorter after neostigmine (7.1 ± 2.4 min and 5.7 ± 4.0 min) versus controls (13.3 ± 8.3 min; P < 0.01). Speed of reversal did not differ significantly between IV neostigmine doses of 0.03 mg/kg or 0.05 mg/kg. Conclusion Neostigmine accelerates recovery when administered 5 minutes after injection of IV rocuronium 0.4 mg/kg.

Genotyping the Butyrylcholinesterase in Patients with Prolonged Neuromuscular Block after Succinylcholine

Succinylcholine remains the standard neuromuscular blocking drug for tracheal intubation in emergency situations. The short duration of action is due to its rapid hydrolytic degradation by butyrylcholinesterase (plasmacholinesterase). Multiple variants of this enzyme are known (A, F, S, H, J, K variants) with different effects on enzyme activity. This study was undertaken to evaluate the use of molecular genetic methods in patients with clinically prolonged neuromuscular block. Nine patients with a neuromuscular block of 14 min to 5 h were selected. All four exons of the butyrylcholinesterase were amplified by polymerase chain reaction and analyzed by automated sequencing. Molecular genetic results were compared with clinical relaxation time and with biochemical test results (total butyrylcholinesterase activity, dibucaine and fluoride inhibition). Seven of nine patients were mutation carriers. Five of these had more than one mutation. The A and K variants were the most frequent variations. Three of four patients who were homozygous for the A variant were also carriers of the K allele. The authors identified one novel mutation (G1294T) introducing a stop codon at amino acid position 432. The duration of neuromuscular block was substantially different between patients with identical butyrylcholinesterase genotypes. Variations in the genetic sequence of butyrylcholinesterase are frequent in patients with prolonged duration of action of succinylcholine. Direct sequencing of the whole butyrylcholinesterase gene is an appropriate method for genotyping and, accordingly, should be used in future clinical studies with drugs metabolized by this enzyme (e.g., succinylcholine, mivacurium).

Prolonged neuromuscular block after rocuronium in postpartum patients.

Postpartum patients have not completely lost the weight gained during pregnancy. Drug dosing according to total body weight (TBW) can cause exaggerated effects and dosing by lean body mass (LBM) may provide a more consistent response despite the increased weight. We compared the duration of a rocuronium neuromuscular block in 22 women undergoing postpartum tubal ligation 31--79 h after delivery, with that in 22 women undergoing gynecological surgery. Anesthesia was induced and maintained with propofol and alfentanil. Half of the patients in each of the Postpartum and Control groups received a bolus dose of rocuronium 0.6 mg/kg TBW and the remaining half received rocuronium 0.6 mg/kg LBM. Neuromuscular block was monitored by electromyography and the ulnar nerve was stimulated transcutaneously using a train-of-four pattern. When rocuronium was given by TBW, median (range) duration of neuromuscular block until 25% recovery of the first twitch response was longer in the Postpartum group, 35.3 (29.7--48.7) min, compared with the Control group, 24.8 (21.5--28.6) min (P < 0.001). After dosing by LBM, the duration of block was similar between groups. The prolonged block with rocuronium in the Postpartum patients can be explained by relative drug overdose when dose calculation is based on their temporarily increased body weight. Neuromuscular block is prolonged in the postpartum period after standard doses of rocuronium. Drug administration according to lean body mass will produce a more consistent duration of block.

Neuromuscular interactions between mivacurium and esmolol in rabbits.

We compared the dose-response relationship and the neuromuscular blocking effects of mivacurium during infusions of esmolol in 40 anaesthetised rabbits. Train-of-four stimuli were applied every 10 s to the common peroneal nerve and the force of contraction of the tibialis anterior muscle was measured. Plasma cholinesterase activity decreased by 13% after esmolol infusion. The ED95 of mivacurium increased significantly from 29 (4.8) micrograms.kg-1 with placebo to 61 (9.8) micrograms.kg-1 during esmolol 100 micrograms.kg-1.min-1, 49 (8.2) micrograms.kg-1 during esmolol 300 micrograms.kg-1.min-1 and 54 (7.3) micrograms.kg-1 during esmolol 500 micrograms.kg-1.min-1, respectively (p < 0.001). The duration of neuromuscular block with mivacurium 0.16 mg.kg-1 was prolonged by 30% with esmolol due to diminished plasma cholinesterase activity (p < 0.05). Heart rate and mean arterial blood pressure decreased by 15% with esmolol (p < 0.05). The results of this study show that, in rabbits, esmolol decreased plasma cholinesterase activity, antagonised the neuromuscular blocking potency of mivacurium and prolonged its neuromuscular blocking effect.

Postpartum patients have slightly prolonged neuromuscular block after mivacurium.

Postpartum patients have decreased plasma cholinesterase activity, which may slow the metabolism of mivacurium. We compared the duration of a mivacurium neuromuscular block in 11 women undergoing postpartum tubal ligation 36-99 h after delivery with that in 11 control women undergoing gynecological surgery. Anesthesia was induced with propofol and fentanyl and maintained with propofol and nitrous oxide. Neuromuscular block was monitored by electromyography, and the ulnar nerve was stimulated transcutaneously using a train-of-four pattern. Patients received a bolus dose of mivacurium 0.15 mg/kg. The median (range) duration of neuromuscular block until 25% recovery of the first twitch response was longer in the postpartum group, 19.4 (15.6-25.2) min, compared with the control group, 16.3 (11.0-23.4) min (P = 0.04). The median (range) plasma cholinesterase activity was decreased in the postpartum group, 4.0 (0.1-5.5) kU/L, compared with the control group, 7.1 (6.2-10.0) kU/L (P < 0.001). The duration of neuromuscular block was inversely correlated with cholinesterase activity (Kendall rank correlation tau = -0.43, P = 0.005). The slight prolongation of neuromuscular block should not be significant clinically. Postpartum patients have decreased amounts of the plasma cholinesterase enzyme. This would slow the metabolism of the muscle relaxant mivacurium. However, the duration of muscle paralysis is only prolonged by approximately 3 min, which would not normally cause any significant problems.

Administration of magnesium sulphate before rocuronium: effects on speed of onset and duration of neuromuscular block

The speeds of onset of pancuronium, atracurium and vecuronium are increased by prior administration of magnesium sulphate. A prospective, randomized, double-blind, controlled, clinical study was performed to examine the effects of prior i.v. administration of magnesium sulphate 60 mg kg-1 on the neuromuscular blocking effects of rocuronium 0.6 mg kg-1 during isoflurane anaesthesia. Neuromuscular function was measured electromyographically (Relaxograph) in 30 patients who received either magnesium sulphate 60 mg kg-1 or normal saline, 1-min before rocuronium 0.6 mg kg-1. Mean onset times were similar in the two groups (magnesium sulphate 71 (SD 20) s; normal saline 75 (23) s), but times to initial, 10% and 25% recovery from neuromuscular block were significantly longer in the magnesium sulphate group (42.1 (16.3), 49.0 (12.4) and 56.5 (13.2) min, respectively) than in the saline group (25.1 (9.1), 33.0 (11.1) and 35.6 (13.2) min, respectively) (P < 0.05 in all three cases). Administration of magnesium sulphate was not associated with adverse haemodynamic effects. Prior administration of magnesium sulphate, under the study conditions described, prolonged rocuronium-induced neuromuscular block but did not increase speed of onset.

A.251 Recovery rate of mivacurium used alone or after atracurium after a similar clinical duration of neuromuscular block

A.251 Recovery rate of mivacurium used alone or after atracurium after a similar clinical duration of neuromuscular block

Recovery from neuromuscular block in warm hands is five times faster than in cold hands

The effect of temperature on the duration of neuromuscular block is controversial. Peripheral hypothermia prolongs relaxation time. We investigated the effect of peripheral temperature on the recovery time after intra-arterial vecuronium 5 μg kg−1, with approval from the Institutional Ethics Committee. Eleven consented and overnight fasted volunteers (age 18-36 years) participated in a two-phase experiment: First, they were surface-cooled until peripheral skin temperatures and electromyographical responses to train-of-four (TOF) stimuli were stabilized and relaxed. After full recovery of neuromuscular transmission they were rewarmed to a steady peripheral temperature and relaxed again. Recovery intervals 25-75% were measured during both recoveries and compared. In the cold hands, the mean skin temperature at first dorsal interosseal muscle was 25.9±0.8°C (mean±95% C.I.) and the first TOF response showed a recovery index 25-75% in 19.1±1.0 min. In the warm hands (35±0.8°C), the respective recovery index was 3.8±0.3 min. These differences were significant (P<0.0001). In conclusion, recovery from arterially induced neuromuscular block was five times faster in warm hands than in cold hands. This finding suggests that the actual muscle or surface temperatures should be reported in neuromuscular recovery studies. The difference in recovery times may arise from disparate muscle perfusion (redistribution from the biophase into the blood with presumably very low relaxant concentrations) in the warm and cold hands or differences in receptor kinetics.

Different priming techniques, including mivacurium, accelerate the onset of rocuronium

Different priming sequences of equipotent doses of rocuronium and mivacurium on the onset of maximum neuromuscular block and intubating conditions were compared with those obtained after succinylcholine. During thiopentone-fentanylnitrous oxide anaesthesia, 70 patients were randomly assigned into seven groups. Group I received mivacurium 0.15 mg.kg-1 as a single bolus dose. Group II received a priming dose of mivacurium 0.015 mg.kg-1 followed three minutes later by mivacurium 0.135 mg.kg-1. Group III received rocuronium 0.6 mg.kg-1 as a single bolus dose, and Group IV received an initial dose of rocuronium 0.06 mg.kg-1 followed by rocuronium 0.54 mg.kg-1. Group V received a priming dose of mivacurium 0.015 mg.kg-1 followed by rocuronium 0.54 mg.kg-1. Group VI received an initial dose of rocuronium 0.06 mg.kg-1 followed by mivacurium 0.135 mg.kg-1. Group VII received succinylcholine 1.0 mg.kg-1. Groups I, III, and VII received a placebo injection before the administration of the neuromuscular blocking drug. Additional thiopentone 2 mg.kg-1 iv was given 30 sec before intubation. Onset times (mean (95% confidence interval)) after priming a rocuronium block with either rocuronium (73 (57-90) sec) or mivacurium (58 (47-69) sec) were similar to those after succinylcholine (54 (40-68) sec), and were shorter (P < 0.01) than that observed in other groups. Intubating conditions were not different between the groups. The duration of neuromuscular block was shortest with succinylcholine. It is concluded that priming a rocuronium block with either mivacurium or rocuronium resulted in a neuromuscular block comparable to that of succinylcholine in both the onset of action and intubating conditions.

NEUROMUSCULAR BLOCK BY SUXAMETHONIUM FOLLOWING TREATMENT WITH HISTAMINE TYPE 2 ANTAGONISTS OR METOCLOPRAMIDE

We have examined the effect of preoperative i.v. administration of three different histamine type 2 (H2) antagonists (cimetidine 400 mg, ranitidine 80 mg and famotidine 20 mg) or metoclopramide 10 mg i.v. on the duration of neuromuscular block produced by an intubating dose (1 mg kg-1) of suxamethonium. The study was conducted blindly in 70 post partum patients, weighing between 45 and 120 kg, scheduled for tubal ligation. The duration of neuromuscular block following suxamethonium was measured from a chart recording of train-of-four (TOF) electromyographic responses. The time from onset of 95% block to 25% recovery ("block time") was not significantly different between the groups receiving cimetidine (A), ranitidine (B), famotidine (C), and control (E). However, there was prolongation of neuromuscular block in patients receiving suxamethonium and metoclopramide (D).