Potentiation of atracurium by pancuronium and d-tubocurarine

In 60 adult patients undergoing general surgical procedures, the effect of pancuronium or d-tubocurarine "pretreatment" on the injection of a 0.1 mg X kg-1 bolus of atracurium was measured in two separate studies. In study 1, the patients received either 0.5 mg (approximately 0.007 mg X kg-1) or 1.0 mg (approximately 0.015 mg X kg-1) pancuronium, or placebo (saline) three minutes before the injection of atracurium 0.1 mg X kg-1. In study 2, the patients received 0.05 mg X kg-1 or 0.1 mg X kg-1 d-tubocurarine, or a placebo. The degree of neuromuscular blockade was assessed by evoked mechanogram (adductor pollicis muscle) using supramaximal train-of-four stimulation. Patients receiving pancuronium or d-tubocurarine pretreatment (equal to an ED5-ED15 dose) showed significantly greater inhibition of twitch (ED70-ED80) and train-of-four ratio compared with the placebo groups (ED35-ED40). Pretreatment with the larger dose of d-tubocurarine (0.1 mg X kg-1) was associated with significant neuromuscular blockade. It is concluded that pancuronium and d-tubocurarine pretreatments potentiate the clinical action of 0.1 mg X kg-1 atracurium in man by 35-100 per cent.     

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.     

Rapid tracheal intubation with atracurium--a comparison of priming intervals

To 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 X kg-1 or in an initial dose of 0.06 mg X kg-1 followed two, three or five minutes later with 0.44 mg X kg-1. When atracurium was given as a single bolus of 0.5 mg X kg-1 the time to 100 per cent twitch suppression (onset time) was 90.9 +/- 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 times were 42.2 +/- 16.5 (p less than 0.01) and 52.6 +/- 28.8 (p less than 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.     

Atracurium infusion in total intravenous anesthesia

The neuromuscular blocking effect of atracurium given as a bolus dose (0.5 mg X kg-1) followed by a maintenance infusion was studied during two different anesthetic techniques. It has been reported that benzodiazepines interact with non-depolarising neuromuscular blockers. In this study no difference was found in the effect of atracurium given with conventional fentanyl/nitrous oxide anesthesia when compared to total intravenous anesthesia using midazolam/alfentanil. More than 90% twitch depression was achieved after 123 and 137 s, respectively. Recovery time to 10% twitch height following the bolus dose was around 32 min. The dosage range for atracurium given by infusion (0.29-0.44 mg X kg-1 X h-1) was confirmed.     

Accelerated onset of pancuronium with divided doses

To determine the consequences of administering neuromuscular relaxants in divided doses, pancuronium was given either in a single dose, 0.07 mg X kg-1, or in an initial dose of 0.007 mg X kg-1 followed three minutes later with 0.063 mg X kg-1. When the drug was administered in divided dosage the onset time was reduced, the block was more intense and its duration of action was prolonged. It is suggested that such changes may be advantageous in the provision of rapid intense paralysis.     

Plasma histamine release following the intravenous administration of atracurium in man

The purpose of this study was to measure plasma histamine concentration following the intravenous bolus injection of atracurium in surgical patients and to clarify any correlation of resultant cardiovascular change with plasma histamine release. Twelve elective surgical patients of ASA-I were studied after the approved informed consent. Twenty of blood samples were collected for the assay of plasma histamine at 1 minute before as the control and 1, 3, 5, and 10 minutes after the administration of atracurium 0.6mg.kg-1 or 1.2mg.kg-1 intravenously. Plasma histamine was measured by utilization of the modified single isotope radioenzymatic assay. Blood pressure, heart rate, EKG and cutaneous signs were observed continuously during the study. Intravenous bolus administration of 0.6mg.kg-1 and 1.2mg.kg-1 atracurium which is larger than 2 times of ED95 demonstrated significant changes in heart rate, blood pressure and histamine release. A significant increase in plasma histamine, a decrease in blood pressure and an increase in heart rate occurred at 1 to 3 minutes after the injection of atracurium. Plasma histamine release and cardiovascular changes had strong correlation with the intravenous dose of atracurium.     

Clinical pharmacology of atracurium besylate (BW 33A): a new non-depolarizing muscle relaxant

Atracurium, a new non-depolarizing neuromuscular blocking agent, was studied in 70 patients anesthetized with fentanyl, thiopental, and nitrous oxide-oxygen. The dose found to produce 95% twitch inhibition (ED95) was 0.2 mg/kg. The onset time from injection to maximum depression of twitch was 4.0 minutes at this dose; the duration to 95% recovery was 44.1 minutes. Twice the ED95 dose (0.4 mg/kg) had an onset time of 1.7 minutes and a duration of 63.5 minutes. No cardiovascular effects were observed in this dosage range. At higher doses (0.5 and 0.6 mg/kg) arterial pressure decreased 13% and 20% and heart rate increased 5% and 8%, respectively. Sixteen patients received at least four successive doses of atracurium. No clinically significant cumulative effect could be shown when recovery from 25% to 75% of control twitch height was compared for initial and final doses in the series. Atracurium spontaneously decomposes at physiologic pH via the Hofmann elimination reaction and may also undergo ester hydrolysis independent of plasma cholinesterase. These proposed pathways of inactivation may explain the lack of cumulative effect and the drug's intermediate duration of action. Based on the results of this study, atracurium offers several clinical advantages and should undergo more extensive clinical trials.     

Atracurium infusions in major ophthalmic surgery

Fifteen patients who were undergoing major ophthalmic surgery were anaesthetized using controlled ventilation with nitrous oxide, oxygen, midazolam and fentanyl after induction with thiopentone. Each was then given a bolus dose of 0.6 mg kg-1 atracurium followed immediately by an infusion of the drug at the rate of 0.6 mg kg-1 h-1, neuromuscular function being monitored throughout. Even slight movement can jeopardize the success of this type of surgery but good control of neuromuscular blockade was achieved without inhalational supplementation. The mean duration of the atracurium infusion was 118 min (range 30-247 min). The mean time from stopping the infusion to recovery of the first twitch of the train of four (TOF) to 20% was 25 min (range 11-44 min). Atropine (1.2 mg) and 5.0 mg neostigmine were then given in divided doses and a rapid and complete recovery was achieved. This technique can be used safely even in bad-risk patients but the infusion should be discontinued about 25 min before the end of surgery.     

Détermination de la courbe dose-effet du dibésylate d''atracurium chez l''homme adulte anesthésié

The mechanical response of the adductor pollicis to a 0.15 Hz stimulation of the ulnar nerve was studied in 35 unpremedicated adult patients (mean age 38 yr) under general anaesthesia using thiopentone, fentanyl and a N2O/O2 mixture under mechanical ventilation. PaCO2, pH, K, Ca, Mg plasma levels and temperature were in the normal range. Each patient received a single bolus of atracurium dibesylate: 0.10 mg . kg-1 (n = 11), 0.15 mg . kg-1 (n = 10), 0.20 mg . kg-1 (n = 11) or 0.30 mg . kg-1 (n = 4). The dose-response curve was constructed using the log-probit method for 0.10, 0.15, 0.20 mg . kg-1 doses, giving neuromuscular blocks greater than 0% and less than 0.20 mg . kg-1. The 0.20 mg . kg-1 dose had an onset time of 6.1 +/- 0.6 min, duration 0-90% of 34.3 +/- 3.2 min and a recovery index 25-75% of 10.9 +/- 1.0 min. The 0.3 mg . kg-1 dose resulted in onset time of 4.7 +/- 1.3 min, duration of 39.9 +/- 3.7 min and a recovery index of 10.7 +/- 1.8 min. Thus atracurium dibesylate seemed to be an agent of intermediate potency. Onset time was approximately the same as that for other non-depolarizing neuromuscular blocking drugs, but duration of action and recovery index were quite shorter, except for vecuronium bromide.     

Histamine-release haemodynamic changes produced by rocuronium, vecuronium, mivacurium, atracurium and tubocurarine

We have examined the effects of different benzyl-isoquinolinium and steroidal neuromuscular blocking compounds on plasma concentrations of histamine, heart rate and arterial pressure in surgical patients. A single, rapid (5-s) bolus of mivacurium 0.2 mg kg-1, atracurium 0.6 mg kg-1, tubocurarine 0.5 mg kg-1, vecuronium 0.1 mg kg-1 or rocuronium 0.6 mg kg-1 was administered to 75 patients (n = 15 in each group). Anaesthesia was induced with thiopentone 6 mg kg-1 i.v. and maintained with isoflurane and 70% nitrous oxide in oxygen. Venous blood samples were obtained before induction, 1 min after thiopentone and 1, 3 and 5 min after administration of the neuromuscular blocking drug. Mivacurium, atracurium and tubocurarine caused 370%, 234% and 252% increases in plasma histamine concentrations at 1 min, respectively. Corresponding values at 3 min were 223%, 148% and 157%, respectively. These changes were significant (P < 0.01) at 1 and 3 min. In contrast, the rocuronium and vecuronium groups had no significant changes in either plasma histamine concentrations or haemodynamic variables.      

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.     

Atracurium: neuromuscular blockade in repeated administration

The neuromuscular blocking action of repeated injections of atracurium and vecuronium was studied in 74 surgical patients during balanced anaesthesia (methohexitone or etomidate, intubation after suxamethonium, fentanyl, droperidol, N2O). The initial bolus dose (ID) of atracurium was 0.25 mg/kg and of vecuronium 0.05 mg/kg followed by repeated increments (RD) of atracurium 0.1 mg/kg and vecuronium 0.0125 mg/kg when neuromuscular function (EMG) had recovered to about 30% of pre-relaxant control. Dose-response relationships revealed atracurium to be about 1/5 as potent as vecuronium; the ED50 of atracurium was 0.13 +/- 0.03 mg/kg and of vecuronium 0.023 +/- 0.007 mg/kg. The ID of both relaxants produced a neuromuscular blockade of about 90% within 4 min. The duration from the time of injection to 30% recovery was slightly longer in atracurium 26 +/- 9 min. In all patients the RD produced within 3.5 min satisfactory muscle relaxation with a neuromuscular block of about 85%. The mean duration of atracurium (18 min) was 5-10 min longer than of vecuronium (12 min). To maintain good surgical relaxation (more than 70% blockade) atracurium 0.32 mg/kg X h and vecuronium 0.056 mg/kg X h were required. No cumulation could be measured after repeated injections. The recovery time of atracurium and vecuronium at the end of anaesthesia was 10-12 min. Neither cardiovascular side-effects nor signs of histamine release were observed after both relaxants in our particular dose range. It is concluded, that atracurium is a favourable blocker for anaesthetic practice: The time of onset is approximately the same compared with vecuronium. The duration of action, however, is slightly longer but still truly intermediate long.(ABSTRACT TRUNCATED AT 250 WORDS)     

Maintenance of surgical muscle relaxation by repeat doses of vecuronium and atracurium at three different dose levels.

The time-course of the neuromuscular effects of vecuronium (n = 25) and atracurium (n = 25) has been compared at three different levels of maintenance dose in anaesthetized patients. Following intubation with vecuronium 0.1 mg kg-1 or atracurium 0.5 mg kg-1, surgical muscle relaxation was maintained by using increments of equipotent maintenance doses equivalent to 0.5, 1.0 and 1.5 x ED95 for each drug. Repeat doses were administered each time the twitch height, depressed by the previous dose, returned to 25% of its control value. The apparent increase in the duration of action, i.e. the difference between the duration of the last and the first maintenance dose, did not reach statistical significance and approximated 3 +/- 2, 6 +/- 4, 11 +/- 5 and 3 +/- 2, 8 +/- 13, 5 +/- 7 min following the low, medium and high maintenance doses of vecuronium and atracurium, respectively.     

Cardiovascular effects of non-depolarizing neuromuscular blockers in patients with aortic valve disease

To compare haemodynamic responses associated with equipotent doses of neuromuscular blockers and high-dose fentanyl (50 micrograms.kg-1), 40 patients with aortic valve stenosis (AS) and 20 patients with aortic insufficiency (AI) were randomized to four study groups to receive the following: (1) pancuronium 0.12 mg.kg-1, (2) vecuronium 0.12 mg.kg-1, (3) atracurium 0.4 mg.kg-1, or (4) pancuronium-metocurine mixture (0.4 mg + 1.6 mg/ml): 1 ml/10 kg). Neuromuscular blockers were injected at the same time with the fentanyl; haemodynamics were recorded with the patients awake (baseline), at two minutes post-induction, and at two and five minutes after intubation. In patients with AS, pancuronium increased heart rate more than vecuronium or atracurium; heart rates were also higher with the pancuronium-metocurine mixture than with vecuronium. Although there were no ECG signs of ischaemia, one patient given pancuronium developed severe hypotension associated with tachycardia. Reductions in SVR after atracurium allowed small but significant (p less than 0.01) decreases in MAP which were well tolerated; one patient, however, did develop severe hypotension. Intubation resulted in significant (p less than 0.01) increases in MAP in the pancuronium-metocurine mixture group. Vecuronium permitted the most stable overall haemodynamic course at all measurement times. In contrast, patients with AI showed stable haemodynamics after vecuronium, pancuronium and the pancuronium-metocurine mixture; one patient became tachycardic following vecuronium. Atracurium caused unexplained elevations in diastolic and mean arterial pressures which were significant when compared to vecuronium (p less than 0.01). These results in increases in PCWP; mean PA pressures and CVP were also increased. These effects of atracurium inpatients with Al need further evaluation.     

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.     

Quantitation of the interaction between atracurium and succinylcholine using closed-loop feedback control of infusion of atracurium

The authors used closed-loop feedback control of infusion of atracurium to study the effect of prior administration of succinylcholine on neuromuscular blockade induced by atracurium in patients undergoing otolaryngologic surgery. Anesthesia was maintained with nitrous oxide in oxygen, flunitrazepam, and fentanyl. Of 14 patients given atracurium, seven were given prior administration of succinylcholine and seven were not. Interaction between the two drugs was quantified by determining the asymptotic steady-state rate of infusion necessary to produce a constant 90% neuromuscular blockade. This was accomplished by applying nonlinear curve-fitting to data on the cumulative dose requirement during anesthesia. The neuromuscular blocking effect of atracurium was found to be greater after prior administration of succinylcholine. The asymptotic steady-state rate of infusion (+/- SD) for atracurium was 0.27 +/- 0.06 mg.kg-1.h-1 for patients given succinylcholine and 0.38 +/- 0.10 mg.kg-1.h-1 for those not given succinylcholine. The clinical implication of this study is that the clinician should be aware of the fact that an induction dose of 1 mg/kg of succinylcholine does reduce atracurium requirement for 90% neuromuscular blockade by approximately 30%.     

USE OF ATRACURIUM DURING GENERAL SURGERY MONITORED BY THE TRAIN-OF-FOUR STIMULI

The use of atracurium in 25 patients undergoing general surgicalprocedures is described, neuromuscular function being monitoredby the "train-of-four" stimuli. An initial dose of atracurium0.5 mg kg^–1 proved to be clinically acceptable, givinggood conditions for endotrachea] intubation and adequate musclerelaxation for about 40 min Comparison of the results with thosefrom 15 patients given suxamethomum 50 mg showed that atracunumin this dosage took longer to produce complete ablation of thetwitch responses but that it lasted longer (about 40 min). Incrementaldoses of atracurium (of 0.2 mg kg-1) gave relaxation for about30 min and there was no evidence of a cumulative effect. Reversalof the neuromuscular block with neostigmine was prompt and adequate.Using simple clinical means no evidence of an important changein heart rate or arterial pressure was found. There were noadverse reactions to the drug.     

Clinical pharmacology of mivacurium chloride: a review.

Mivacurium chloride (Mivacron) is a new benzylisoquinolinium choline-like diester neuromuscular blocking drug with an onset of action at equipotent doses that is comparable to atracurium and vecuronium but slower than succinylcholine. Its clinical duration (injection-25% recovery and injection-95% recovery) is twice that of succinylcholine but one-half to one-third that of atracurium and vecuronium. Mivacurium is easy to use as a continuous infusion and when used this way its recovery characteristics are unchanged. It is readily antagonized by anticholinesterase drugs. The ED95 in adults under narcotic-based anesthesia is 0.07-0.08 mg/kg. At twice the ED95 (0.15 mg/kg) onset time is about 2 to 3 minutes, duration to 25% recovery is 15 to 20 minutes, and 5-95% recovery time about 14 minutes. The mean infusion rate in adults is 6 micrograms/kg/min (range 2-15) with a 5-95% recovery time of 14 minutes. Enflurane and isoflurane require a 20-30% decrease in dosage; halothane, enflurane, and isoflurane prolong the duration of mivacurium 25-30%. The ED95 in children 2 to 12 years of age is slightly higher (0.09-0.11 mg/kg) with a faster onset and shorter duration. In these young patients, a dose of 0.2 mg/kg has an onset comparable to succinylcholine. Being chemically related to atracurium, mivacurium may cause histamine release. When administered rapidly at doses of 0.2 mg/kg or greater in adults, histamine release and transient hypotension have been observed. Doses of 0.2 mg/kg or higher are not recommended by the manufacturer. Mivacurium is metabolized by plasma cholinesterase. In vitro, the rate is about 70% that of succinylcholine. In patients with normal or slightly less than normal plasma cholinesterase activity, no prolonged durations of action have been observed. In patients heterozygous for the atypical gene and at a dose of 0.2 mg/kg, 50% prolongation has been shown. Those individuals homozygous for the atypical gene are exquisitely sensitive to mivacurium and have a markedly prolonged blockade that is readily reversible. In these patients and those with acquired deficiencies, mivacurium should not be used. The duration of action in elderly patients is comparable to that in the young, while in prerenal transplant patients, its duration is prolonged by about 50%, and in prehepatic transplant patients, duration of block is increased threefold. Mivacurium possesses the advantages of short duration, unchanged recovery characteristics following infusions (without phase II block or tachyphylaxis), and precise control.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of atracurium on intraocular pressure during steady state anaesthesia and rapid sequence induction: a comparison with succinylcholine

The effects of atracurium 0.5 mg X kg-1 or succinylcholine 1.0 mg X kg-1 on intraocular pressure (IOP) were studied in ten patients during steady state nitrous oxide-oxygen-fentanyl anaesthesia. IOP was unchanged following atracurium but, one minute after succinylcholine, it had increased significantly (p less than 0.025) from 5.6 mmHg to 13.2 mmHg and remained significantly above control for 3 min. Twenty additional patients received either atracurium 0.75 mg X kg-1 or succinylcholine 1.0 mg X kg-1 as part of a rapid sequence induction, atracurium being administered prior to, and succinylcholine after, thiopentone. Intubating conditions were acceptable in all patients in both groups. Administration of thiopentone was associated with a significant (p less than 0.025) decrease in IOP. Although IOP increased in both groups as a result of laryngoscopy and intubation (from 8.0 mmHg to 12.1 mmHg in the atracurium Group and from 7.5 mmHg to 14.5 mmHg in the succinylcholine group) it did not exceed pre-induction IOP in the former. In the succinylcholine group, IOP after intubation exceeded pre-induction values for 2 min, although this increase was significant (p less than 0.05) only at the immediate post-intubation reading. It is concluded that atracurium in a dose of 0.75 mg X kg-1 is a suitable relaxant for use in rapid sequence induction.