Influence of atracurium on the diaphragm mean action potential conduction velocity in canines. (1/168)

BACKGROUND: It has been shown that progressive neuromuscular blockade (NMB) affects the electromyogram power spectrum and compound muscle action potential duration in skeletal muscle. These measures are linked to the mean muscle action potential conduction velocity (APCV), but no studies have confirmed a relation between the mean APCV and NMB. The aim of this study was to determine whether diaphragm mean APCV is affected by NMB. METHODS: The effects of NMB on diaphragm mean APCV were evaluated in five mongrel dogs. Progressive NMB was induced by slow intravenous infusion of atracurium. During spontaneous breathing, the diaphragm mean APCV was determined by electromyogram signals, in the time and frequency domains. The magnitude of NMB was quantified by the amplitude of the compound muscle action potential and by changes in muscle shortening during supramaximal stimulation of the phrenic nerve. RESULTS: Progressive NMB was associated with a decrease in diaphragm mean APCV. At approximately 70% reduction in the compound muscle action potential amplitude, diaphragm mean APCV had decreased more than 20%. Recovery after NMB was characterized by a restoration of the mean APCV to control values. CONCLUSION: This study shows that progressive NMB paralyzes motor units within the diaphragm in an orderly manner, and the blockade first affects muscle fibers with high APCV before it affects fibers with lower APCV.  (+info)

The infusion rate of mivacurium or atracurium for cesarean section compared with gynecological procedures. (2/168)

Mivacurium is mainly metabolized by plasma cholinesterase, whereas atracurium is removed by Hofman elimination. The purpose of this study was to compare the infusion rate of atracurium and mivacurium in maintaining surgical relaxation, and to compare their recovery indices between parturients and non-pregnant women. Muscle relaxation was maintained by the continuous infusion of relaxants to retain the first response of train-of-four (TOF) at 5% of control. When mivacurium was used, Bolus-T5 (duration from the end of mivacurium bolus injection to 5% single twitch recovery) was measured. After discontinuing the infusion, the recovery index was measured. The infusion rate of mivacurium, not atracurium, was significantly lower in parturients and Bolus-T5 of parturients was significantly longer than that of non-pregnant women. There was no significant difference in the recovery indices of both relaxants. The authors concluded that the infusion rate of mivacurium in maintaining muscle relaxation in parturients should be reduced compared to the rate in non-pregnant women and measuring Bolus-T5 may be helpful in determining the infusion rate to maintain muscle relaxation.  (+info)

Comparison of a new piezoelectric train-of-four neuromuscular monitor, the ParaGraph, and the Relaxometer mechanomyograph. (3/168)

The ParaGraph is a new device for monitoring neuromuscular function using a piezoelectric motion sensor. In 20 patients, monitoring of neuromuscular block produced by cisatracurium 0.1 mg kg-1 was compared using the ParaGraph and a Relaxometer 2 mechanomyograph. The ParaGraph was quick to set up, and easy to operate and interpret. There were no significant differences in the time to 100% depression of T1/T0, time to 25% recovery of T1/T0 or time to recovery of T1/T0 from 25% to 75%, measured by the two monitors. When the difference between the two monitors was plotted against the average of the two measurements, the limits of agreement for T1/T0 (-42.95, +53.98%) and the train-of-four ratio, T4/T1 (-0.28, +0.21) were too wide to allow the values given by the two monitors for individual patients to be used interchangeably.  (+info)

Cisatracurium neuromuscular block at the adductor pollicis and the laryngeal adductor muscles in humans. (4/168)

We have compared the dose-response relationship (n = 30) and time course of neuromuscular block (n = 20) of cisatracurium at the laryngeal adductor and the adductor pollicis muscles. ED95 values for cisatracurium were 66.8 (95% confidence interval 61.3-72.3) micrograms kg-1 at the larynx and 45.2 (42.1-48.3) micrograms kg-1 at the adductor pollicis muscle (P < 0.0001). After administration of cisatracurium 0.1 mg kg-1, onset time was 2.7 (2.2-3.2) min at the larynx and 3.9 (3.0-4.8) min at the adductor pollicis (P < 0.0001). Time to 95% recovery of the first twitch of the TOF was 26.9 (20.1-33.7) min and 45.6 (39.7-51.5) min, respectively (P < 0.0001). We found that the laryngeal adductors were more resistant to the action of cisatracurium than the adductor pollicis muscle, but onset and recovery were faster at the larynx.  (+info)

A comparison of continuous infusion of vecuronium and atracurium in midline and paramedian laparotomies. (5/168)

This was a study to compare continuous intravenous infusion of atracurium with continuous intravenous infusion of vecuronium for intraoperative muscle relaxation in 62 ASA I / II patients. Scheduled for laparotomies and pelvic surgeries under general anaesthesia. They were randomly allocated in two groups to receive either vecuronium infusion of 50 microg/kg/hour following a bolus dose of 0.1 microg/kg, or atracurium infusion of 400 microg/kg/hour following a bolus dose of 0.5 microg/kg. The mean infusion dose of atracurium was 478 +/- 44.11 microg/kg/hour and that of vecuronium was 63.2 +/- 74 microg/kg/hour for adequate muscle relaxation. The depth of neuromuscular blockade was monitored by using peripheral nerve stimulator so that only one twitch of train of four was present, resistance to ventilation, surgical relaxation and haemodynamic changes. Vecuronium infusions produced more haemodynamic stability than atracurium infusions. Vecuronium produced lesser change in systolic blood pressure (mean change of 3. 46 +/- 3.33%) from baseline values as compared to atracurium (mean change of 5.81 +/- 3.73%) from baseline values ( p < 0.01) which was statistically significant. The difference in mean pulse rate change from baseline value in the atracurium group (4.78 +/- 2.745%) was less than that in the vecuronium group (5.99 +/- 2.67%), which was not statistically significant. Spontaneous recovery was faster with vecuronium (540.94 +/- 76.46 seconds) as compared to atracurium (596. 33 +/- 72.48 seconds). 84.4% of patients who received vecuronium fell within good to very good category of muscle relaxation as compared to 63.3% in atracurium group. There were no cost benefits when either agents were used in infusion form.  (+info)

The incidence and mechanisms of pharyngeal and upper esophageal dysfunction in partially paralyzed humans: pharyngeal videoradiography and simultaneous manometry after atracurium. (6/168)

BACKGROUND: Residual neuromuscular block caused by vecuronium alters pharyngeal function and impairs airway protection. The primary objectives of this investigation were to radiographically evaluate the swallowing act and to record the incidence of and the mechanism behind pharyngeal dysfunction during partial neuromuscular block. The secondary objective was to evaluate the effect of atracurium on pharyngeal function. METHODS: Twenty healthy volunteers were studied while awake during liquid-contrast bolus swallowing. The incidence of pharyngeal dysfunction was studied by fluoroscopy. The initiation of the swallowing process, the pharyngeal coordination, and the bolus transit time were evaluated. Simultaneous manometry was used to document pressure changes at the tongue base, the pharyngeal constrictor muscles, and the upper esophageal sphincter. After control recordings, an intravenous infusion of atracurium was administered to obtain train-of-four ratios (T4/T1) of 0.60, 0.70, and 0.80, followed by recovery to a train-of-four ratio of more than 0.90. RESULTS: The incidence of pharyngeal dysfunction was 6% during the control recordings and increased (P < 0.05) to 28%, 17%, and 20% at train-of-four ratios 0.60, 0.70, and 0.80, respectively. After recovery to a train-of-four ratio of more than 0.90, the incidence was 13%. Pharyngeal dysfunction occurred in 74 of 444 swallows, the majority (80%) resulting in laryngeal penetration. The initiation of the swallowing reflex was impaired during partial paralysis (P = 0.0081). The pharyngeal coordination was impaired at train-of-four ratios of 0.60 and 0.70 (P < 0.01). A marked reduction in the upper esophageal sphincter resting tone was found, as well as a reduced contraction force in the pharyngeal constrictor muscles. The bolus transit time did not change significantly. CONCLUSION: Partial neuromuscular paralysis caused by atracurium is associated with a four- to fivefold increase in the incidence of misdirected swallowing. The mechanism behind the pharyngeal dysfunction is a delayed initiation of the swallowing reflex, impaired pharyngeal muscle function, and impaired coordination. The majority of misdirected swallows resulted in penetration of bolus to the larynx.  (+info)

Dose requirements of infusions of cisatracurium or rocuronium during hypothermic cardiopulmonary bypass. (7/168)

We investigated the influence of mild hypothermic cardiopulmonary bypass (CPB) on the dose requirements of cisatracurium or rocuronium used as a continuous infusion. We studied eight patients given cisatracurium and nine given rocuronium. They were ASA class III and IV and scheduled for elective coronary artery bypass grafting. Neuromuscular transmission was monitored electromyographically. After recovery of T1/T0 to 10%, a cisatracurium infusion or a rocuronium infusion was started at a rate of 1.5 or 10 micrograms kg-1 min-1, respectively, and adjusted to maintain T1/T0 at 15%. Infusion rate and duration were recorded before, during and after CPB in each patient and the mean infusion rates were calculated. One-way ANOVA showed a statistically significant difference between the cisatracurium infusion rates before, during and after CPB: A T1/T0 of 15% could be achieved with a mean infusion rate of 1.1, 0.75 and 0.98 micrograms kg-1 min-1 before, during and after CPB, respectively. There was no significant difference between the rocuronium infusion rates before, during and after CPB. The mean rocuronium infusion rate required to maintain T1/T0 at 15% throughout the procedure was 4.1 micrograms kg-1 min-1. Cisatracurium infusion rates should be halved during CPB. Even after CPB, requirements are reduced. The same tendency occurs with rocuronium, but the changes in infusion rate were not statistically significant.  (+info)

Preanesthetic train-of-four fade predicts the atracurium requirement of myasthenia gravis patients. (8/168)

BACKGROUND: The most sensitive diagnostic criterion of myasthenia gravis is a decrement in the muscular response to repetitive stimulation. The authors hypothesized that myasthenia gravis patients who show a train-of-four ratio (T4/T1) < 0.9 in the preanesthetic period will have increased sensitivity to nondepolarizing neuromuscular blocking agents compared with myasthenia gravis patients with preanesthetic T4/T1 > or = 0.9. METHODS: After institutional review board approval was obtained, 20 electrophysiologically documented myasthenia gravis patients were studied. Current pyridostigmine therapy was continued until the morning of surgery. Before induction of anesthesia, neuromuscular transmission was recorded from the hypothenar muscles using electromyography with train-of-four stimulation of the ulnar nerve. According to the T4/T1 ratio, patients were assigned to the "normal" group (T4/T1 > or = 0.9) or the "decrement" group (T4/T1 < 0.9). After induction of intravenous anesthesia, the effective dose to achieve a 95% neuromuscular blockade (ED95) for atracurium was assessed with a cumulative bolus technique. Postoperatively, pyridostigmine was titrated to obtain a T4/T1 > 0.75 and to treat residual myasthenic symptoms. RESULTS: In 14 patients, preanesthetic T4/T1 was > or = 0.9 (normal), whereas 6 patients presented with T4/T1 < 0.9 (decrement). Decrement patients had a lower ED95 of 0.07 +/- 0.03 mg/kg atracurium (mean +/- SD) compared with normal patients with an ED95 of 0.24 +/- 0.11 mg/kg atracurium (P = 0.002). All patients were extubated within 30 min after surgery. Postoperative pyridostigmine infusion did not differ significantly between groups. CONCLUSIONS: The requirement for atracurium is significantly reduced in myasthenia gravis patients with a T4/T1 ratio < 0.9 before anesthesia. This study indicates that routine neuromuscular monitoring in myasthenia gravis patients should be extended into the preinduction period to identify patients who require less atracurium.  (+info)

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