Iontophoretic study of speed of action of various muscle relaxants.
(33/168)
The speed of action of nondepolarizing muscle relaxants is inversely related to potency. The hypothesis that this effect occurs at the end plate was tested in a frog (Rana pipiens) cutaneous pectoris muscle preparation. Brief acetylcholine pulses (10-100 ms) were applied iontophoretically from a central barrel of a triple-barrelled microelectrode located near an end plate. Long pulses (10-200 s) of muscle relaxant (gallamine, rocuronium, d-tubocurarine, atracurium, vecuronium, pancuronium, and doxacurium) were applied from one of two other barrels. The responses were a voltage change at the end plate, measured with an intracellular electrode. To evaluate potency, intracellular voltage changes following iontophoretic acetylcholine pulses were measured after application of various concentrations of muscle relaxants. The following were the equilibrium dissociation constants, which represent concentration of relaxant for 50% inhibition of response (mean plus or minus standard deviation): gallamine, 4.56 +/- 0.44 microM (n = 5); rocuronium, 0.71 +/- 0.09 microM (n = 6); d-tubocurarine, 0.59 +/- 0.07 microM (n = 4); atracurium, 0.31 +/- 0.03 microM (n = 4); vecuronium, 0.23 +/- 0.02 microM (n = 5); pancuronium, 0.18 +/- 0.03 microM (n = 3); doxacurium, 0.11 +/- 0.03 microM (n = 5). Both onset and offset of effect of muscle relaxant proceeded with an exponential time course.(ABSTRACT TRUNCATED AT 250 WORDS) (+info)
Modification of atracurium or vecuronium blockade and their reversal by succinylcholine in the cat.
(34/168)
The interaction between succinylcholine (SCC) and non-depolarizers, atracurium or vecuronium was investigated in 36 cats of either sex using the sciatic nerve-anterior tibialis muscle preparation. Additionally, the relation of SCC to pseudocholinesterase activity was examined. The duration of action of vecuronium (6.5 +/- 1.3 to 7.3 +/- 2.2 minutes) in cats pretreated with SCC was greater than those (2.0 +/- 0.6 minutes) in non-pretreated cats. However, SCC had no influence on the duration of atracurium. The serum pseudocholinesterase activity was decreased after the injection of atracurium or neostigmine in contrast to vecuronium. The authors conclude that the prior administration of SCC prolongs the duration of vecuronium but not that of atracurium, and pseudocholinesterase activity is not related to the prolonging effect of SCC. (+info)
Tetanus-induced changes in apparent recovery after bolus doses of atracurium or vecuronium.
(35/168)
The current study evaluated the duration and magnitude of post-tetanic effects in 56 patients recovering from a bolus dose of nondepolarizing relaxant to assess the impact of tetanus on monitoring in a common clinical setting. After induction of general anesthesia (thiopental, fentanyl, oxygen, nitrous oxide, and isoflurane), a baseline response to train-of-four (TOF) stimulation was recorded using an adductor pollicis force transducer, and the ratio of the fourth response (T4) to the first (T1) was calculated. Patients then received a bolus dose of either atracurium 0.50 mg.kg-1 (n = 28) or vecuronium 0.10 mg.kg-1 (n = 28). TOF was recorded at 12-s intervals between 25% and 75% recovery of T1 (time25-75%, first data set); then, block was reestablished with the same agent (atracurium 0.10 or vecuronium 0.02 mg.kg-1), and monitoring of time25-75% was repeated (second data set). Subjects were randomized such that none, one, or both sets had TOF monitoring interrupted by a 5-s, 50-Hz tetanic stimulus at 50% recovery (TET). For each drug, 7 patients were assigned to each of the four possible sequences: no tetanus (NOTET) set followed by NOTET set; NOTET-TET; TET-NOTET; and TET-TET. After either drug, the TET data sets demonstrated significant acceleration of recovery of T1 from 50% to 75% (time50-75%) of its baseline height (P less than 0.05 by paired t test). After atracurium, time50-75% was shortened by the tetanic stimulation from a control of 6.3 +/- 1.1 to 5.0 +/- 1.3 min (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS) (+info)
Priming doses of atracurium and vecuronium depress swallowing in humans.
(36/168)
The administration of low doses of muscle relaxant may cause peripheral muscular weakness including difficulty in swallowing. In the present study, the effect of priming doses of atracurium and vecuronium on swallowing was studied. Sixty patients undergoing elective surgery under general anesthesia were divided randomly into four groups of 15 patients and received as a priming dose either vecuronium (10 or 15 micrograms/kg) or atracurium (50 or 75 micrograms/kg). Swallowing muscle activity was measured by electromyography using submental surface electrodes. Swallowing was initiated by administration of 0.3 ml distilled water through an oral catheter. Swallowing reflex was determined by measuring the latency time (i.e., time from water administration to start of EMG activity of glossal muscles). Swallowing activity was determined by integration of the EMG of glossal muscles during swallowing. Peripheral muscle strength was determined by hand grip strength. Swallowing reflex activity and peripheral muscle strength were measured before and 3 and 6 min after administration of vecuronium or atracurium. Latency time remained unchanged after any of the priming doses. Integrated EMG decreased significantly (P < .001) 3 and 6 min after all priming doses tested (42-75% of baseline value). Only after atracurium 75 micrograms/kg was the hand grip strength significantly decreased (P < .01). These results suggest that owing to its effect on swallowing, the priming dose should be used with caution. (+info)
Mechanism of action of atracurium on airways.
(37/168)
Histamine-releasing drugs may produce significant effects on airways in high-risk populations. To determine if clinically relevant doses of atracurium produce adverse effects on airways, we measured changes in airway resistance in the lung periphery of anesthetized Basenji-Greyhound dogs before and after intravenous (iv) administration of atracurium. A wedged bronchoscope technique was used to measure collateral system resistance (Rcs). After a stable baseline was obtained, atracurium (1.2 or 0.5 mg/kg) or histamine (200 micrograms) were administered as an iv bolus, and percent increase in Rcs was calculated. On separate days dogs were pretreated with the histamine 1 receptor antagonist, chlorpheniramine (0.2 mg/kg iv), with or without atropine (0.2 mg/kg iv) and ranitidine (0.75 mg/kg iv) and the experiment repeated. Histamine (200 micrograms) increased Rcs 97 +/- 24% at 30 s (8 sublobar segments), whereas a second dose increased Rcs 77 +/- 15%. Pretreatment with chlorpheniramine (0.2 mg/kg iv) totally prevented increases in Rcs (9 sublobar segments). Atracurium (1.2 mg/kg) increased Rcs to 174 +/- 35% at 3 min (14 sublobar segments), whereas 0.5 mg/kg had little effect (10 sublobar segments). A second bolus of atracurium (1.2 mg/kg) increased Rcs to only 54 +/- 14% (P less than 0.01). Chlorpheniramine pretreatment (0.2 mg/kg iv) reduced the response to the initial dose of atracurium to only 26 +/- 14% (10 sublobar segments). Pretreatment with a combination of atropine and chlorpheniramine (4 sublobar segments), or ranitidine and chlorpheniramine (5 sublobar segments), did not attenuate the increase in Rcs significantly more than chlorpheniramine pretreatment alone.(ABSTRACT TRUNCATED AT 250 WORDS) (+info)
Central command is capable of modulating sweating from non-glabrous human skin.
(38/168)
Isometric handgrip exercise (IHG) increases sweating rate without changing core or skin temperatures. The contribution of central command resulting in increases in sweating rate during IHG is unknown. To investigate this question, seven subjects performed IHG (35 % maximum voluntary contraction (MVC) for 2 min) followed by 2-min of post-exercise ischaemia (PEI), with and without partial neuromuscular blockade (PNB). PNB was performed to augment central command during the IHG bout. These trials were conducted while the subject was normothermic, mildly heated, and moderately heated. On the non-exercising arm, forearm sweating rate was monitored over a microdialysis membrane perfused with neostigmine (acetylcholinesterase inhibitor), and at an adjacent untreated site. In normothermia with PNB, despite reduced force production during IHG (17 +/- 9 versus 157 +/- 13 N; P < 0.001), the elevation in sweating rate at the neostigmine-treated site was greater relative to the control IHG bout (P < 0.05). During subsequent PEI, for the PNB trial mean arterial blood pressure (MAP) and sweating rate returned towards pre-IHG levels, while during the control trial these variables remained elevated. During IHG while mildly heated, the elevation in sweating rate was greater during the PNB trial relative to the control trial. In contrast, during moderate heating sweating increased during IHG for both trials, however the elevation in sweating rate during the PNB trial was not greater than during the control trial. These results suggest that central command is capable of modulating sweating rate in all thermal conditions, however its effect is reduced when body temperatures and/or sweating rate are substantially elevated. (+info)
Atracurium, cisatracurium, vecuronium and rocuronium in patients with renal failure.
(39/168)
AIM: The cumulative index, the recovery, the onset and the duration of action, of atracurium, cisatracurium, vecuronium and rocuronium in uremic patients undergoing kidney transplantation compared to healthy patients undergoing general surgery were studied. METHODS: In all patients (64 uremic vs 62 "healthy" patients) after anesthesia induction, atracurium 0.5 mgxkg(-1) or cisatracurium 0.15 mgxkg(-1) or vecuronium 0.1 mgxkg(-1) or rocuronium 0.6 mgxkg(-1) were administered, and at the end of surgery when T1 reached 25% neostigmine 0.05 mgxkg(-1) was given. Neuro-muscu-lar transmission was monitored by accelerometry (TOF-GUARD, Organon). RESULTS: Cumulative index of vecuronium (1.3+/-0.1 vs 1.06+/-0.11, p<0.001) and rocuronium (1.45+/-0.18 vs 1.04+/-0.16, p<0.001), recovery index (time of T1 25-75) of atracurium (14.2+/-5 vs 9+/-4, p<0.005), cisatracurium (18.7+/-3 vs 9.1, p<0.001), vecuronium (18.5+/-3 vs 12.5+/-3, p<0.001) and rocuronium (18+/-6 vs 11+/-4, p<0.001) and interval T1 25% to TOF 0.8 of cisatracurium (20.5+/-1.2 vs 16+/-2.1, p<0.001) and vecuronium (27+/-6.3 vs 20+/-3.3, p<0.001) were longer in uremic patients. The onset time and the duration of action of atracurium, cisatracurium, vecuronium and rocuronium were similar in all groups compared to controls one. CONCLUSION: In patients with renal failure the use of atracurium, cisatracurium, vecuronium and rocuronium is suitable and predictable in terms of onset, and duration of action. Care has to be taken to vecuronium and rocuronium cumulative index. Neuromuscular trasmission has to be always monitored. (+info)
Acute motor axonal polyneuropathy after a cisatracurium infusion and concomitant corticosteroid therapy.
(40/168)
A 40-yr-old male was admitted to the intensive care unit following blunt chest trauma. He had multiple rib fractures, bilateral pneumothoraces, and acute respiratory failure requiring mechanical ventilation. Sedation was achieved with midazolam and morphine, and later with propofol. The patient was paralysed with a continuous infusion of cisatracurium 1.42-5.75 micro g kg(-1) min(-1). Methylprednisolone 125 mg i.v. every 12 h was also started. After discontinuation of the cisatracurium infusion 7 days later, the patient manifested a flaccid quadriplegia with absence of deep-tendon reflexes. No sensory deficits were observed. Electromyography (EMG), repetitive nerve stimulation testing, and single fibre EMG (SFEMG) were performed at regular intervals after stopping cisatracurium. Clinical symptoms and electrophysiological examinations supported the diagnosis of acute motor axonal polyneuropathy related to concomitant administration of cisatracurium and corticosteroid therapy. (+info)