(1/520) Influence of atracurium on the diaphragm mean action potential conduction velocity in canines.

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)

(2/520) Neostigmine with glycopyrrolate does not increase the incidence or severity of postoperative nausea and vomiting in outpatients undergoing gynaecological laparoscopy.

We studied 100 healthy women undergoing outpatient gynaecological laparoscopy in a randomized, double-blind and placebo-controlled study to evaluate the effect of neostigmine on postoperative nausea and vomiting (PONV). After induction of anaesthesia with propofol, anaesthesia was maintained with sevoflurane and 66% nitrous oxide in oxygen. Mivacurium was used for neuromuscular block. At the end of anaesthesia, neostigmine 2.0 mg and glycopyrrolate 0.4 mg, or saline, was given i.v. The incidence of PONV was evaluated in the postanaesthesia care unit, on the ward and at home. The severity of nausea and vomiting, worst pain, antiemetic and analgesic use, times to urinary voiding and home readiness were recorded. During the first 24 h after operation, 44% of patients in the neostigmine group and 43% in the saline group did not have PONV. We conclude that neostigmine with glycopyrrolate did not increase the occurrence of PONV in this patient group.  (+info)

(3/520) Effects of an intubating dose of succinylcholine and rocuronium on the larynx and diaphragm: an electromyographic study in humans.

BACKGROUND: Paralysis of the vocal cords is one objective of using relaxants to facilitate tracheal intubation. This study compares the neuromuscular blocking effect of succinylcholine and rocuronium on the larynx, the diaphragm, and the adductor pollicis muscle. METHODS: Electromyographic response was used to compare the neuromuscular blocking effect of succinylcholine and rocuronium on the laryngeal adductor muscles, the diaphragm, and the adductor pollicis muscle. Sixteen patients undergoing elective surgery were anesthetized with propofol and fentanyl, and their tracheas were intubated without neuromuscular blocking agents. The recurrent laryngeal and phrenic nerves were stimulated at the neck. The electromyographic response was recorded from electrodes placed on the endotracheal tube and intercostally before and after administration of 1 mg/kg succinylcholine or 0.6 mg/kg rocuronium. RESULTS: The maximum effect was greater at the adductor pollicis (100 and 99%) than at the larynx (96 and 97%) and the diaphragm (94 and 96%) after administration of succinylcholine and rocuronium, respectively (P < or = 0.05). Onset time was not different between the larynx (58+/-10 s), the diaphragm (57+/-8 s), and the adductor pollicis (54+/-13 s), after succinylcholine (all mean +/- SD). After rocuronium, onset time was 124+/-39 s at the larynx, 130+/-44 s at the diaphragm, and 115+/-21 s at the adductor pollicis. After succinylcholine administration, time to 90% recovery was 8.3+/-3.2, 7.2+/-3.5, and 9.1+/-3.0 min at the larynx, the diaphragm, and the adductor pollicis, respectively. Time to 90% recovery after rocuronium administration was 34.9+/-7.6, 30.4+/-4.2, and 49.1+/-11.4 min at the larynx, the diaphragm, and the adductor pollicis, respectively. CONCLUSION: Neuromuscular blocking effect of muscle relaxants on the larynx can be measured noninvasively by electromyography. Although the larynx appears to be resistant to muscle relaxants, we could not demonstrate that its onset time differed from that of peripheral muscles.  (+info)

(4/520) Factors affecting the pharmacokinetic characteristics of rapacuronium.

BACKGROUND: Rapacuronium is a new nondepolarizing muscle relaxant with rapid onset and offset. As part of a study to determine its neuromuscular effects, the authors sampled plasma sparsely to determine the influence of age, gender, and other covariates on its pharmacokinetic characteristics. METHODS: Of 181 patients receiving a single bolus dose of 0.5-2.5 mg/kg rapacuronium, 43 (aged 24-83 yr) had plasma sampled 3 or 4 times to determine plasma concentrations of rapacuronium and its metabolite, ORG9488. Pharmacokinetic analysis was performed using a population approach (mixed-effects modeling) to determine the influence of demographic characteristics and preoperative laboratory values on the pharmacokinetic parameters. RESULTS: Rapacuronium's weight-normalized plasma clearance was 7.03 x (1 - 0.0507 x (HgB - 13)) ml x kg(-1) x min(-1), where HgB is the patient's preoperative value for hemoglobin (g/100 ml); however, rapacuronium's blood clearance (11.4+/-1.4 ml x kg(-1) x min(-1), mean +/- SD) did not vary with hemoglobin. Rapacuronium's weight-normalized pharmacokinetic parameters were not influenced by age, gender, or other covariates examined. Plasma concentrations of ORG9488 were typically less than 14% those of rapacuronium during the initial 30 min after rapacuronium administration. CONCLUSIONS: In this patient population, neither age nor gender influence elimination of rapacuronium. This finding contrasts to an age-related decrease in plasma clearance observed in a study of 10 healthy volunteers and in a pooled analysis of the pharmacokinetic data from 206 adults in multiple clinical studies. Even if ORG9488 has a potency similar to that of rapacuronium, its plasma concentrations after a single bolus dose of rapacuronium are sufficiently small to contribute minimally to neuromuscular blockade.  (+info)

(5/520) Antagonism of vecuronium-induced neuromuscular block in patients pretreated with magnesium sulphate: dose-effect relationship of neostigmine.

We have investigated the dose-effect relationship of neostigmine in antagonizing vecuronium-induced neuromuscular block with and without magnesium sulphate (MgSO4) pretreatment. Neuromuscular block was assessed by electromyography with train-of-four (TOF) stimulation. First, we determined neostigmine-induced recovery in patients pretreated with MgSO4 (group A) or saline (group B) (n = 12 each). The height of T1, 5 min after neostigmine, was 43 (7)% in group A and 65 (6)% in group B (P < 0.01). Respective values after 10 min were 59 (7)% and 83 (5)% (P < 0.01). TOF ratio, 5 min after neostigmine, was 29 (6)% in group A and 29 (5)% in group B. Respective values after 10 min were 38 (11)% and 51 (7)% (P < 0.01). To gain insight into the mechanisms leading to delayed recovery after MgSO4, we calculated assisted recovery, defined as neostigmine-induced recovery minus mean spontaneous recovery. Spontaneous recovery was assessed in another 24 patients. Patients in group C received MgSO4/vecuronium and patients in group D vecuronium only (n = 12 each). Five minutes after neostigmine, assisted recovery was 22 (7)% in the MgSO4 pretreated patients and 28 (6)% in controls (P < 0.05). Ten minutes after neostigmine, values were 24 (7)% and 22 (6)%. Maximum assisted recovery was not influenced by MgSO4 pretreatment (27 (6)% in group A and 32 (6)% in group B) and time to maximum effect was comparable between groups: 6 (4-10) min and 7 (5-8) min, respectively. We conclude that neostigmine-induced recovery was attenuated in patients treated with MgSO4. This was mainly a result of slower spontaneous recovery and not decreased response to neostigmine.  (+info)

(6/520) Augmentation of the rocuronium-induced neuromuscular block by the acutely administered phenytoin.

BACKGROUND: The effects of an acute administration of phenytoin on the magnitude of the rocuronium-induced neuromuscular block were evaluated. METHODS: Twenty patients (classified as American Society of Anesthesiologists physical status I or II) scheduled for craniotomy were studied: 15 received phenytoin during operation (10 mg/kg), and the others served as controls. Anesthesia was induced with thiopental and fentanyl and maintained with nitrous oxide (65%) in oxygen and end-tidal isoflurane (1%). The ulnar nerve was stimulated supramaximally and the evoked electromyography was recorded using a neuromuscular transmission monitor. Continuous infusion of rocuronium maintained the neuromuscular block with first twitch (T1) between 10 and 15% for 45 min before the start of an infusion of either phenytoin or NaCl 0.9%. Twitch recordings continued for 60 min thereafter. Arterial blood samples were collected at the predefined time points (four measurements before and four after the start of the infusion) to determine the concentrations of phenytoin and rocuronium and the percentage of rocuronium bound to plasma proteins. RESULTS: The first twitch produced by an infusion of rocuronium remained constant during the 15 min before and the 60 min after the start of the saline infusion. After the phenytoin infusion, the twitch decreased progressively, but the plasma concentrations and the protein-bound fraction of rocuronium did not change. CONCLUSION: Phenytoin acutely augments the neuromuscular block produced by rocuronium without altering its plasma concentration or its binding to plasma proteins.  (+info)

(7/520) Deep sedation and mechanical ventilation without paralysis for 3 weeks in normal beagles: exaggerated resistance to metocurine in gastrocnemius muscle.

BACKGROUND: Patients in the intensive care unit may have muscle weakness in the recovery phase, and disuse atrophy may play a role in this weakness. To assess this problem, the authors measured changes in the potency of the nondepolarizing neuromuscular blocking agent metocurine in a canine model that involved 3 weeks of intensive care, nonparalyzing anesthesia with pentobarbital, and positive-pressure ventilation. METHODS: Six dogs were anesthetized with pentobarbital to a sufficient depth that spontaneous and reflex muscle movements were absent. Their tracheas were intubated, their lungs were mechanically ventilated, and they received round-the-clock intensive medical and nursing care for 3 weeks. Transduced gastrocnemius muscle responses to metocurine were determined weekly. A 4- to 15-min infusion of 148-4,300 microg/min (longer durations and greater concentrations on progressive weeks) yielded more than 80% paralysis. Serial metocurine plasma concentrations during the onset of the block and recovery provided data to determine pharmacokinetics using NONMEM. Metocurine plasma concentrations and the degree of paralysis were used to model the effect compartment equilibration constant, and the Hill equation was used to yield the slope factor and potency within the effect compartment. RESULTS: The metocurine effect compartment concentration associated with a 50% diminution of twitch height after 3 weeks was 1,716+/-1,208 ng/ml (mean +/- SD), which was significantly different from 257+/-34 ng/ml, the value on day 0. There were no pharmacokinetic differences. CONCLUSION: The absence of muscle tone and reflex responsiveness for 3 weeks was associated with exaggerated resistance to the neuromuscular blocker metocurine.  (+info)

(8/520) Early reversal of rapacuronium with neostigmine.

BACKGROUND: Rapacuronium is a rapid-onset, short-acting neuromuscular relaxant. This multiple-center study determined neuromuscular recovery when neostigmine was given 2 or 5 min after rapacuronium. METHODS: One hundred seventeen patients were randomized to receive two different doses of rapacuronium and to receive neostigmine in two different doses and at two different times. During propofol anesthesia with nitrous oxide, oxygen, and fentanyl, 1.5 or 2.5 mg/kg rapacuronium was given 1 min before tracheal intubation. Neuromuscular block was measured by train-of-four ulnar nerve stimulation every 12 s: The adductor pollicis force of contraction was recorded mechanomyographically. Two or five minutes after rapacuronium was administered, 0.05 or 0.07 mg/kg neostigmine was administered and recovery was compared with that of control patients who received no neostigmine. RESULTS: Both doses of rapacuronium produced 100% block in all but one patient, who exhibited 97% block. Neostigmine accelerated recovery in all groups. After 1.5 mg/kg rapacuronium, the time to 25% T1 twitch recovery decreased from a mean of 16 min in control patients to mean values of 8-10 min in the treatment groups: The time to train-of-four ratio of 0.7 decreased from 38 min to 17-19 min. After 2.5 mg/kg rapacuronium, the time to 25% T1 was reduced from 23 min to 11-12 min, and the time to train-of-four ratio of 0.7 decreased from 54 min to 26-32 min. Recovery was not different among the the groups that received different doses and timing of neostigmine. CONCLUSIONS: Recovery of intense rapacuronium block was accelerated by early neostigmine administration. When given 2 min after rapacuronium, neostigmine was as effective as after 5 min, and 0.05 mg/kg neostigmine was comparable to 0.07 mg/kg neostigmine.  (+info)