Rapid tracheal intubation with atracurium - a comparison of priming intervals

determine the optimal interval between the administration of the priming dose and the intubating dose, atracurium was given to 44 patients either in a single dose of 0.5 mg.kg^-1 or in an initial dose of0.06mg.kg^-1 followed two, three or five minutes later with 0.44 mg.kg^-1. When atracurium was given as a single bolus of 0.5 mg. kg^-1 the time to 100 per cent twitch suppression (onset time) was90.9 ± 36 (mean ± SD) seconds. When the priming interval was two minutes, the onset time of the intubating dose was 76.6 ± 42.2 seconds (p = NS). But when the priming interval was three or five minutes, the onset timeswere42.2 ± 16.5(p<0.01)and52.6 ± 28.8(p < 0.05) seconds respectively. Waiting for five minutes after the administration of the priming dose did not improve the intubating conditions. It is concluded that three minutes appears to be the optimal time interval for the administration of atracurium in divided doses. When a priming dose of atracurium is given three minutes before the intubating dose, it can provide an alternative to succinylcholine for rapid endotracheal intubation.     

The optimal priming dose for atracurium

To determine the optimal priming dose for administration in divided doses, atracurium was given to 77 patients either in a single dose of 0.5 mg X kg-1 or in an initial dose of 0.04, 0.05, 0.06, 0.07, 0.08 or 0.09 mg X kg-1, followed three minutes later by the remainder of the 0.5 mg X kg-1 dose. Patients were anaesthetized throughout the study. When atracurium was given as a single bolus of 0.5 mg X kg-1, the mean time to complete neuromuscular block was 141.5 seconds. Administration in divided doses accelerated the onset time (p less than 0.01), that is the time from the intubating dose to the complete suppression of train-of-four (TOF) response. The TOF ratio decreased slightly but statistically significantly following the priming doses. When the priming dose was 0.05 mg X kg-1, the mean onset time was 70.9 seconds and priming with larger doses did not add any further advantage. It is concluded that 0.05 mg X kg-1 appears to be the optimal priming dose for the administration of atracurium in divided doses. When 0.05 mg X kg-1 is given three minutes before the intubating dose, tracheal intubation can be accomplished in less than 90 seconds.     

Atracurium for short surgical procedures: a comparison with succinylcholine

A comparison was made between atracurium and succinylcholine in 40 patients undergoing short gynaecological procedures of 30 minutes or less. Good intubating conditions were produced in 76.7 +/- 39.3 seconds (mean +/- S.D.) with succinylcholine 1 mg . kg-1 and 198 +/- 84 seconds with atracurium 400 micrograms . kg-1. Muscle relaxation was maintained with the initial dose of atracurium or with repeated boluses of succinylcholine. The mean time of surgery was 17.65 +/- 5.3 minutes in the atracurium group and 15.2 +/- 4.6 minutes in the succinylcholine group. Residual neuromuscular block with atracurium was reversed with neostigmine 0.036 mg . kg-1 and atropine 0.018 mg . kg-1. Recovery of neuromuscular function following reversal, assessed by return of all responses to train-of-four stimulation occurred in 5.05 +/- 4.6 minutes in the atracurium group but half the above doses of neostigmine and atropine were repeated in three patients. We conclude that a single dose of atracurium 400 micrograms . kg-1 is suitable for intubation and maintainance of muscle relaxation for short surgical procedures. However, the onset of action is slow, compared to succinylcholine. Residual neuromuscular block can be antagonised with standard doses of neostigmine, less than 20 minutes after the initial dose of relaxant. Atracurium appears to be a suitable alternative for short procedures where succinylcholine is unsuitable or contraindicated.     

Evaluation of the timing principle with small priming doses of vecuronium]

The intubating conditions using the timing principle combined with small priming doses of vecuronium were evaluated in forty patients who underwent elective surgery. They were randomly assigned to one of two groups: 1) timing, 2) timing with priming. In timing group, vecuronium 0.15 mg.kg-1 was administered, and at the onset of clinical muscle weakness, thiopental 4-5 mg.kg-1 was given promptly. Sixty seconds after thiopental, patients were intubated. In the timing with priming group, vecuronium 0.005 mg.kg-1 was administered as priming doses. Four minutes later vecuronium 0.15 mg.kg-1 was given. The administration of thiopental and the intubation were done in the same way as in timing group. The time to onset of clinical weakness after the administration of vecuronium 0.15 mg.kg-1 was significantly shorter in the timing with priming group than that in the timing group (46.1 +/- 4.8 vs. 57.6 +/- 7.8, P < 0.01). There were no significant differences in intubating score, T1, TR, onset time, and duration between the two groups. We conclude that the timing principle combined with small priming doses of vecuronium might be safe and useful for rapid tracheal intubation.     

Facilitation of rapid endotracheal intubations with divided doses of nondepolarizing neuromuscular blocking drugs

The authors sought to determine whether prior administration of a small, subparalyzing dose of nondepolarizing muscle relaxant would shorten the onset time of an intubating dose of muscle relaxant. Initially, in 60 anesthetized patients, twitch response of adductor pollicis to ulnar nerve stimulation was studied after a small dose of pancuronium 0.015 mg . kg-1, metocurine 0.03 mg . kg-1, or d-tubocurarine 0.04 mg . kg-1, followed 3 min later by pancuronium 0.08 mg . kg-1 or atracurium 0.4 mg . kg-1 administered iv. After 60 s, the minimum neuromuscular block, in all patients was 79.0 +/- 5.0%. A 95% depression or twitch tension occurred between 59.1 +/- 5.3 and 86.1 +/- 5.9 s. In another 60 patients, intubating conditions under similar regimen were studied, except the small dose of muscle relaxant was given immediately prior to induction of anesthesia. At the end of 60 s, good to excellent intubating conditions were present in 100% of the patients following the second dose of pancuronium and in 83% of the patients following atracurium. In 17% of the patients, after atracurium intubating conditions were fair. When nondepolarizing neuromuscular blocking drugs are administered in divided doses, neuromuscular blockade adequate for endotracheal intubation is achieved in less than 90 s. This facilitates rapid endotracheal intubation in a time comparable to using succinylcholine, without undesirable effects of the depolarizing neuromuscular blocking drugs.     

Neuromuscular blockade for rapid tracheal intubation in children: comparison of succinylcholine and pancuronium

To compare the effectiveness of succinylcholine and pancuronium for rapid intubation in children, 49 healthy children ages two to eight years were studied. After induction of anaesthesia with thiopentone and atropine, and administration of droperidol, fentanyl, nitrous oxide, and oxygen, each child received one of the following muscle relaxants: succinylcholine 1.5 mg X kg-1 (n = 12), succinylcholine 1.0 mg X kg-1 (n = 13), pancuronium 0.15 mg X kg-1 (n = 11), or pancuronium 0.10 mg X kg-1 (n = 13). The force of thumb adduction was measured by stimulating the ulnar nerve with repetitive supramaximal single twitches (0.15 Hz). The time to 95 per cent twitch depression (mean +/- S.D.) was most rapid with succinylcholine 1.5 mg X kg-1 (40.8 +/- 3.0 seconds) and succinylcholine 1.0 mg X kg-1 (51.8 +/- 14.0 seconds), slowest with pancuronium 0.10 mg X kg-1 (150.9 +/- 38.0 seconds), and intermediate with pancuronium 0.15 mg X kg-1 (80.3 +/- 21.8 seconds) (p less than 0.005). The intubating conditions were excellent in 100% of the children who received succinylcholine 1.5 and 1.0 mg X kg-1, and pancuronium 0.15 mg X kg-1, but were excellent in only 69 per cent of those who received pancuronium 0.10 mg X kg-1. We conclude that succinylcholine 1.5 mg X kg-1 produces the most rapid onset of excellent intubating conditions in children. In children in whom succinylcholine is contra-indicated, pancuronium 0.15 mg X kg-1 provides excellent intubating conditions within 80 seconds.     

Intubating conditions after vecuronium and atracurium given in divided doses (the priming technique)

Intubating conditions have been assessed at 60 s following administration of vecuronium 0.1 mg kg-1 or atracurium 0.5 mg kg-1 given either as a single dose after induction of anaesthesia with thiopentone or in divided doses; vecuronium 0.015 mg kg-1 followed 4 or 6 min later by 0.085 mg kg-1, or atracurium 0.075 mg kg-1 followed 4 or 6 min later by 0.425 mg kg-1. In the divided dose groups the smaller initial (priming) dose was given prior to induction of anaesthesia. Onset and duration of clinical relaxation were assessed using a peripheral nerve stimulator. The intubating conditions at 60 s improved significantly, with the use of relaxants in divided doses being acceptable in 80 and 70% of patients, respectively, with vecuronium and atracurium, but the conditions are not as good as those commonly found using suxamethonium. Priming at 6 min has no advantage over priming at 4 min. The onset of complete block was accelerated with priming, but the difference was not significant. The duration of clinical relaxation of vecuronium was significantly prolonged by giving it in divided doses. Unpleasant awareness of muscle weakness was observed in 15 patients, requiring early induction of anaesthesia in five of them.     

Priming with atracurium: improving intubating conditions with additional doses of thiopental

The effects of different intubating doses of atracurium on the time of onset, and the effect of an additional dose of thiopental on intubating conditions, were studied in 72 patients divided into six groups (n = 12 in each). Stratified sampling was used to obtain an even sex distribution. Groups I, III, and V (controls) received atracurium as a single bolus dose of 0.4, 0.5 or 0.6 mg/kg respectively. Groups II, IV, and VI received an initial (priming) dose of 0.05 mg/kg followed 3 min later by 0.35, 0.45, or 0.55 mg/kg respectively. The time of onset, that is the time from the intubating dose to complete suppression of the train-of-four (TOF) response, was significantly accelerated after administration of atracurium in divided doses. Increasing the intubating dose of atracurium after an initial 0.05 mg/kg from 0.35 to 0.55 mg/kg did not result in further significant acceleration of the onset time, but resulted in prolongation of the duration of neuromuscular blockade. When divided doses of atracurium were given, administration of 2 mg/kg thiopental (in addition to the 5 mg/kg used for induction) before the injection of the intubating dose resulted in improvement of intubating conditions as reflected by statistically significant changes in intubating scores. This result was probably due to the increase by thiopental in the depth of anesthesia. Therefore, when thiopental is given as supplement, the priming technique can be made to provide better conditions for tracheal intubation in less than 90 sec.     

Comparison of the effects of succinylcholine and atracurium on intracranial pressure in monkeys with intracranial hypertension

The effects of succinylcholine (1.5 mg X kg-1 IV) administered five minutes after a defasciculating dose of curare (0.05 mg X kg-1 IV), were compared with the effects of atracurium (0.5 mg X kg-1 IV) on intracranial pressure (ICP) in 13 cynomolgus monkeys with intracranial hypertension (ICP approximately 25 mmHg). Neither succinylcholine nor atracurium increased ICP during general anaesthesia with 60 per cent N2O/O2, 0.5-1 per cent halothane. During a rapid sequence induction and intubation with thiopentone 5 mg X kg-1 IV, ICP increased equally with intubation following both atracurium (25 +/- 1 to 32 +/- 2 mmHg) and succinylcholine (25 +/- 1 to 31 +/- 2 mmHg) (p less than 0.05). Intubation was also associated with significant increases in PaCO2, CVP and MAP. We conclude that in this primate model of intracranial hypertension, neither atracurium nor succinylcholine (when given following a defasciculating dose of curare) elevates ICP. In terms of the elevation of ICP associated with intubation, atracurium was found to offer no advantage over succinylcholine.     

Edrophonium priming for antagonism of atracurium neuro-muscular blockade

Edrophonium administered in divided doses has been reported to accelerate antagonism of neuromuscular blockade, i.e., a "priming" effect. Since measured onset times can be affected by the type of stimulation used, this effect was studied using both train-of-four (TOF) and single twitch (ST) stimulation. During thiopentone-nitrous oxide-enflurane anaesthesia 20 adults were given atracurium 0.5 mg.kg-1. Both ulnar nerves were stimulated with TOF every 12 sec until one per cent recovery of first twitch (T1). At this time, ST stimulation was applied to one arm, selected at random. When the mean value of T1 and ST reached ten per cent of control, edrophonium, 1 mg.kg-1, preceded by atropine was given either as a single dose, or in two doses consisting of 0.2 mg.kg-1 followed by 0.8 mg.kg-1 three minutes later. No statistically significant differences were observed between T1 and ST for the next ten minutes, whether edrophonium had been given in single or divided doses. Giving edrophonium in divided doses did not improve recovery significantly, measured with either T1, ST or train-of-four ratio (T4/T1). Five minutes after the first administration of edrophonium, T1 was (mean +/- SEM) 86 +/- 3 and 86 +/- 2 per cent control in the single and divided dose groups respectively. Corresponding values for ST were 89 +/- 1 and 89 +/- 2 per cent (NS), and for TOF, 49 +/- 3 and 57 +/- 3 per cent (NS), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparative evaluation of intubating doses of atracurium,d-tubocurarine,pancuronium and vecuronium in children

To determine the onset and recovery times and haemodynamic effects of intubating doses of atracurium (0.4 mg.kg-1), d-tubocurarine (0.8 mg.kg-1), pancuronium (0.12 mg.kg-1), and vecuronium (0.07 mg.kg-1), sixty-seven children aged one to eight years were studied under halothane and nitrous oxide anaesthesia. The time to maximum twitch depression and the time to recovery to T1/Tc 25 per cent were recorded with an integrated evoked EMG recorder. The heart rate and systolic blood pressure were recorded for five minutes after drug administration and prior to intubation. There was no difference in onset times between drugs. The recovery time to T1/Tc 25 per cent following vecuronium (25.5 +/- 6.3 min) was shorter than following atracurium (37.5 +/- 7.0 min). Recovery times for d-tubocurarine and pancuronium were greater than sixty minutes. Elevation of heart rate occurred after administration of pancuronium (+29.8 per cent to +38.6 per cent) and d-tubocurarine (+31 per cent to +34.9 per cent), but no change was observed after atracurium or vecuronium. Elevation of blood pressure was greatest following pancuronium (+10.8 to +14.8 per cent). No significant change was observed following atracurium or vecuronium. A transient lowering of blood pressure (-9.3 per cent) occurred following d-tubocurarine.     

“Priming” with neostigmine: failure to accelerate reversal of single twitch and train-of-four responses

Train-of-four stimulation can shorten the apparent onset time of neuromuscular blocking drugs. This study was designed to verify whether the same occurred with neostigmine-assisted recovery, and whether this apparent acceleration could explain the previously reported effectiveness of the priming technique for reversal agents. Fourteen adults received atracurium, 0.5 mg.kg-1, during a thiopentone-nitrous oxide-enflurane anaesthetic. The ulnar nerves of both arms were stimulated with train-of-four stimulation every 12 seconds until 1 per cent recovery of first twitch, at which time stimulation in one arm was switched to single twitch. When mean first twitch height reached 10 per cent of control, neostigmine, 0.04 mg.kg-1, was administered either as a single bolus, or as a "priming" dose of 0.01 mg.kg-1, followed 3 min later by 0.03 mg.kg-1. No statistically significant differences were observed between single twitch in one arm and first twitch height of the train-of-four in the other arm for the next 10 min. With priming, first twitch height was 45 +/- (SEM) 5 per cent at 5 min and 85 +/- 6 per cent at 10 min, compared with 72 +/- 5 per cent (p less than 0.05) and 91 +/- 2 per cent (NS) respectively without priming. Train-of-four ratio was 28 +/- 3 per cent at 5 min and 65 +/- 5 per cent at 10 min with priming, versus 53 +/- 4 per cent (P less than 0.05) and 73 +/- 3 per cent (NS) respectively without priming.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intubation conditions following rocuronium: influence of induction agent and priming

A small priming dose of rocuronium can shorten the onset time of neuromuscular blockade. Induction agents with less cardiovascular depression also reduce the onset time. We hypothesized that ketamine, compared to thiopentone, would reduce onset time and improve intubating conditions following priming. Sixty patients ASA I to II, randomized by computer-generated sequence to four groups were investigated in a double-blind controlled trial. In the two groups with priming, 0.04 mg/kg of rocuronium was followed by three minutes of priming interval. Induction was followed by an intubation dose of 0.4 mg/kg of rocuronium. After 30 seconds, intubation was attempted within a further 20 seconds. In the two control groups, the same sequence was repeated except sham priming (saline) was given. For induction, S-ketamine (1 mg/kg) or thiopentone (4 mg/kg) were administered. Intubating conditions were graded as excellent, good, poor, or not possible. Neuromuscular transmission was monitored by acceleromyography of the thumb. There were no measured differences in onset time of neuromuscular block or in haemodynamics between the groups. The proportion of good to excellent intubating conditions was higher when ketamine was preceded by priming compared to ketamine without priming (87% vs 20%; P<0.05). In both priming and control groups intubating conditions were improved when using ketamine compared to thiopentone (P<0.05). The mechanism of this effect was not clear from this study.     

Accelerated reversal of atracurium blockade with divided doses of neostigmine

The hypothesis that administration of neostigmine in divided doses might accelerate the antagonism of neuromuscular blockade was investigated. Neostigmine 0.05 mg X kg-1 was administered either in a single bolus dose (Group I, n = 16) or in an initial dose of 0.01 mg X kg-1 followed three minutes later by 0.04 mg X kg-1 (Group II, n = 16) for antagonism of atracurium-induced blockade. Reversal was attempted at 10 per cent spontaneous recovery of twitch height. The mean time (+/- SD) from the first injection of the drug until the train-of-four (TOF) ratio value had reached 0.75 was significantly shorter in Group II (p less than 0.05) than in Group I (391.8 +/- 83.3 and 468.6 +/- 150.3 seconds respectively). The rate of TOF ratio recovery was 2.5 times faster after neostigmine administration in divided doses. It is concluded that administration of neostigmine in divided doses, as described in this study, produced a significantly faster reversal of residual atracurium-induced neuromuscular blockade as compared to a single bolus administration.     

Priming with vecuronium and atracurium--a comparison

Vecuronium (V) and atracurium (A) were compared in a randomised study in premedicated patients undergoing laparoscopy for gynecological pathology. Both groups contained ten patients. Anesthesia was induced with fentanyl (0.1 mg) and thiopentone (1 mg/kg initially and subsequently 4 mg/kg). A priming dose of vecuronium (20 micrograms/kg) or atracurium (100 micrograms/kg) was given one minute before the intubating dose (60 micrograms/kg for vecuronium and 300 micrograms/kg for atracurium). Ninety seconds thereafter intubation was performed. Maintenance of anesthesia consisted of isoflurane at an inspiratory concentration of 1% in a mixture of O2/N2O (50%/50%) with small supplements of fentanyl. Neuromuscular block was monitored with the Datex Relaxograph. Results show that neither drug offers major clinical advantages over the other: there is no difference in speed of onset (V:T190sec 14.6 +/- 4.3%; A:T190sec 23.5 +/- 6.5%; Mean +/- SEM) and duration of neuromuscular block (V:T150sec 34.2 +/- 3.5 min; A:T150sec 41.3 +/- 2.8 min; Mean +/- SEM) and intubation conditions are almost identical.     

Pretreatment technique for fast intubation with vecuronium: intubation conditions and unwanted effects

In eighty patients 15 micrograms kg-1 of vecuronium was given 3 minutes before induction of anesthesia and 50 micrograms kg-1 was given at the time of induction. The trachea was intubated 60 seconds after the second dose. A wide spread of twitch depression was found. The 80 patients were divided into 4 groups retrospectively with respect to the degree of neuromuscular blockade during intubation. Tracheal intubation was performed when the mean twitch depression was 48.8 +/- 11.8 (SD)% and the conditions were satisfactory in 89% of the cases. Intubating conditions were different significantly between the four sub-groups (p less than 0.01). Ptosis occurred in 77 patients, diplopia in 13 patients and dyspnea in 2 patients between the first injection of vecuronium and induction of anesthesia. The administration of vecuronium in divided doses gives satisfactory intubating conditions in the majority of the patients, but close observation between the priming dose and the induction of anesthesia is mandatory. The method is not considered suitable for obese and is probably not indicated in severely ill patients.     

Comparative clinical studies of vecuronium, atracurium and pancuronium

The new relaxants vecuronium (Norcuron) and atracurium (Tracrium) have been compared with pancuronium (Pavulon) with respect to onset and duration of action and intubating conditions under clinical situations. A variant of the balanced anaesthesia technique with flunitrazepam, fentanyl and N2O/O2 was used. The following doses were considered equipotent (mg/kg body weight): vecuronium 0.07/0.10; atracurium 0.35/0.50; pancuronium 0.08/0.115. The degree of neuromuscular block was assessed in a semiquantitative manner, using the train of four. No difference between the three relaxants in onset of action was found. After the high doses, however, full paralysis developed 60 s earlier. The same is true of intubating conditions. Good or very good intubating conditions were obtained in the majority of cases 3 minutes after injection of the drug. Following the higher dose, good intubating conditions are achieved approximatively 1/2-1 min sooner. Both new relaxants allow for relatively rapid intubation without the inconvenience of a long duration of action. After a low initial dose the following time for recovery to 25% was noted (means +/- S.D., min): vecuronium 20.3 +/- 7.0; atracurium 28.0 +/- 3.1; pancuronium 53.3 +/- 14.8. The early recovery phase (from 5% to 25% recovery) was 6.1 +/- 2.4 after vecuronium, 8.3 +/- 1.7 after atracurium, 17.2 +/- 10.8 after pancuronium. There is a good correlation between our semiquantitative results, using the train of four, and quantitative recordings of muscle contractions reported in the literature. Both drugs show no cumulative effect after five repeated administrations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Is the priming principle both effective and safe?

This study determined the priming dose of vecuronium (V), pancuronium (P) and atracurium (A) that resulted in the most rapid onset of neuromuscular blockade (NMB) in 150 patients given either V 0.08 mg/kg, P 0.1 mg/kg or A 0.6 mg/kg. Patients were further divided (n = 10 per group) to receive no prime or 5%, 10%, 15% or 20% of the total dose as a prime followed 5-7 minutes later by the remaining (intubating) dose. A further 10 patients received 0.04 mg/kg d-tubocurarine followed by 1.5 mg/kg succinylcholine (S). Priming significantly shortened the onset of NMB. The priming doses producing the most rapid onset were 0.012 mg/kg for V, 0.015 mg/kg for P and 0.09 mg/kg for A. The S resulted in significantly greater NMB at 60 sec than any priming dose of A, V or P. There was no difference between the three nondepolarizing neuromuscular blockers in shortening the onset of NMB produced by priming. To evaluate both the effect of the "optimal" priming dose in awake patients and the effect of increasing intubating doses on NMB an additional 40 patients were given V 0.012 mg/kg followed by V 0.08, 0.1, 0.12 or 0.15 mg/kg. Increasing the intubating dose did not improve onset of NMB. The "optimal" priming dose, however, resulted in a high incidence of symptoms of muscle weakness. We conclude that priming shortens the onset of NMB similarly between V, P and A but the priming dose producing the most rapid onset of NMB also results in a high incidence of side effects and therefore the priming principle should be used with caution.     

Accelerated onset of non-depolarizing neuromuscular blocking drugs: pancuronium, atracurium and vecuronium. A comparison with succinylcholine

The time of onset and degree of neuromuscular blockade (NMB) in 80 anaesthetized patients, following either a single bolus injection of pancuronium 0.95 mg kg-1, atracurium 0.53 mg kg-1 or vecuronium 0.07 mg kg-1, or divided doses of pancuronium 0.15 mg kg-1, atracurium 0.07 mg kg-1 or vecuronium 0.01 mg kg-1 administered 3 min or 5 min before the second dose of pancuronium 0.08 mg kg-1, atracurium 0.46 mg kg-1 or vecuronium 0.06 mg kg-1, were determined and compared to the same parameters measured following succinylcholine administration (1 mg kg-1). The time to maximum NMB (100%) following the administration of succinylcholine was 58.1 +/- 5.3 s, whereas the time to maximum NMB (100%) following a single bolus injection of either pancuronium, atracurium or vecuronium was 130.6 +/- 22.2, 93.0 +/- 6.4, 127.5 +/- 13.0 s, respectively. These values for time to maximum NMB are significantly longer than the time required for succinylcholine to achieve maximal blockade. The time to attain maximum NMB following divided doses of pancuronium, atracurium or vecuronium separated by 3 min decreased significantly to 77.9 +/- 4.3, 77.5 +/- 7.6, 89.0 +/- 8.6 s, respectively. However, when the two doses of drug were separated by 5 min, only small, non-significant further decreases occurred in the time required to achieve maximum blockade. Although the time to maximum NMB following divided doses of pancuronium, atracurium or vecuronium is significantly longer than that for succinylcholine, divided dosing significantly decreases the time required to reach maximal NMB.     

Clinical use in adults of 2 new muscle relaxants: atracurium and vecuronium

115 general and urologic surgery adult patients, ASA class I-II, were divided in four groups according to initial bolus and relaxant used: group A atracurium 0.6 mg X kg-1, group B 0.5 mg X kg-1, group C vecuronium 0.1 mg X kg-1 and group D pancuronium 0.1 mg X kg-1. When the single twitch recovered to 25% of control height (T25), subgroups were individualized depending on whether repeat doses of 1/3 of initial bolus were given or not, and whether reversal was spontaneous or obtained by a standard dose of neostigmine 2.5 mg and atropine 1.25 mg. By ulnar nerve stimulation at the wrist, the force of thumb adduction was recorded on a polygraph; single twitch (tw), train of four (tof) and ratio tof 4/1 (Rtof) were measured. Anaesthesia was induced with thiopentone and fentanyl without premedication and maintained with fentanyl and N2O in oxygen; the trachea was intubated once the block was at its maximum. The onset time of maximal block was 5 min for groups A, B and C, and 7.9 min for group D. T25 was 39.9 +/- 8.5 min for group A, 34.4 +/- 9.7 min for group B, 28.9 +/- 9.9 min for group C and 70.7 +/- 25.9 min for group D. A Rtof equal to 75% was achieved in less than 65 min with atracurium and vecuronium, but much later with pancuronium. Reversal at T25 was efficient, but not really required, for atracurium and vecuronium, but necessary and useful for pancuronium.(ABSTRACT TRUNCATED AT 250 WORDS)