Evaluation of the time course of action of maintenance doses of rocuronium (ORG 9426) under halothane anaesthesia

Newer neuromuscular blocking agents: how do they compare with established agents?

Rapacuronium bromide (rapacuronium; ORG-9487) is a nondepolarising muscle relaxant (NMBA) with a low potency [90% effective dose (ED90) 1 mg/kg], which to some extent is responsible for its rapid onset of action. Because of the high plasma clearance (5.3 to 11.1 mg/kg/min) of rapacuronium, its clinical duration of action following single bolus doses up to 2 mg/kg in adults is short (i.e. <20 minutes). Rapacuronium forms a pharmacologically active 3-desacetyl metabolite, ORG-9488, which may contribute to a delay in spontaneous recovery after repeat bolus doses or infusions. After rapacuronium 1.5 mg/kg clinically acceptable intubating conditions are achieved within 60 to 90 seconds in the majority of adult and elderly patients undergoing elective anaesthesia. However, in a rapid-sequence setting. intubating conditions are less favourable after rapacuronium 1.5 to 2.5 mg/kg than after succinylcholine. The most prominent adverse effects of rapacuronium (tachycardia, hypotension and bronchospasm) are dose-related, and in particular pulmonary adverse effects are observed more frequently under conditions of a rapid-sequence induction in adults. Therefore, it seems worthwhile to consider only doses of rapacuronium < or = 1.5 mg/kg to facilitate rapid tracheal intubation, and to use succinylcholine or rocuronium rather than rapacuronium in a rapid-sequence setting. Rapacuronium, however, is a suitable alternative to mivacurium chloride (mivacurium) and succinylcholine for short procedures (e.g. ambulatory anaesthesia). Rocuronium bromide (rocuronium) is a relatively low-potent, intermediateacting NMBA. Its main advantage is the rapid onset of neuromuscular block whereby good or excellent intubating conditions are achieved within 60 to 90 seconds after rocuronium 0.6 mg/kg (2 x ED95), and within 60 to 180 seconds after smaller doses (1 to 1.5 x ED95). Larger doses of rocuronium (> or = 1 mg/kg) seem to be suitable for rapid-sequence induction under relatively light anaesthesia. However, it is still a matter of controversy whether, in the case of an unanticipated difficult intubation, the long duration of rocuronium administered in such large doses outweighs the many adverse effects of succinylcholine. Rocuronium has mild vagolytic effects and does not release histamine, even when administered in large doses. Rocuronium is primarily eliminated via the liver and its pharmacokinetic profile is similar to that of vecuronium bromide (vecuronium). Unlike vecuronium, rocuronium has no metabolite. Cisatracurium besilate (cisatracurium), the IR-cis, 1'R-cis isomer of atracurium besilate (atracurium) is approximately 4 times more potent than atracurium. The onset time of cisatracurium is significantly slower than after equipotent doses of atracurium. The recommended intubating dose is 0.15 to 0.2 mg/kg (3 to 4 times ED95). Over a wide range of clinically relevant doses the recovery properties of cisatracurium are affected by neither the size of the bolus dose nor by the duration of infusion. Unlike atracurium, cisatracurium does not trigger histamine release. Like atracurium, cisatracurium undergoes Hofmann elimination. In contrast to atracurium, cisatracurium does not undergo hydrolysis by nonspecific plasma esterases. Moreover, about 77% of the drug is cleared by organ-dependent mechanisms.

[Assessment of intubation time and conditions under the influence of rocuronium]

PURPOSE

To evaluate the tracheal intubating conditions when intubation time is determined by the onset time of the neuromuscular block either of the adductor pollicis (AP) or of the orbicularis oculi muscle (OO).

METHODS

In this prospective, double blind, randomised study, 40 adults ASA I-II undergoing general anaesthesia with tracheal intubation were allocated to two groups (n = 20) according to the reference muscle (AP or OO) used to determine the appropriate intubation time. Induction of anaesthesia was achieved with 5-7 mg.kg-1 thiopentone, 1.5-2.5 micrograms.kg-1 fentanyl and 0.9 mg.kg-1 rocuronium (3 x ED95) for muscular relaxation. Supramaximal train of four stimulation of the ulnar and facial nerve every 10 sec was used to monitor the neuromuscular block. After visual loss of AP or OO contraction, tracheal intubation and quality of intubation assessment were performed by two independent anaesthetists. Data are expressed as mean and standard error of the mean (X +/- SEM).

RESULTS

Curarisation time of the OO was shorter (110 +/- 4.9 sec) than that of the AP (144 +/- 5.5 sec; P < 0.0001). Intubation conditions were excellent in 95% and good in 5% of the patients in the AP group whereas in the OO group only 65% of the patients had excellent and 20% good intubation conditions (P < 0.05). Coughing was observed in 15% of patients in the OO group during tracheal intubation.

CONCLUSION

Monitoring neuro-muscular activity of the AP using TOF to determine the appropriate tracheal intubation time and conditions in patients paralysed with rocurorium is more clinically relevant than monitoring the OO muscle.

Can final EMG baseline be used as a reference to calculate neuromuscular recovery?

BACKGROUND

Investigations recording recovery times of muscle relaxants have used initial or final baseline of a neuromuscular trace, or both, as a reference for data analysis. We evaluated the use of final baseline of EMG traces as a reliable reference to calculate recovery times.

METHODS

We analyzed EMG traces from 82 children who had full spontaneous neuromuscular recovery following a single dose of mivacurium. Times from administration of mivacurium to 25, 50, 75, and 90% EMG recoveries were measured using both initial and final baselines as a reference. EMG traces with final baseline of 100 +/- 10% of the initial baseline were regarded as optimal. Recovery times from all other traces were compared to the times obtained from these optimal traces. Poor final baseline was defined as that of < 80% of initial baseline. Inter-group comparisons were made using Kruskal-Wallis test followed by Mann-Whitney U tests.

RESULTS

EMG recovery times were similar for optimal traces whether the reference was the initial or the final baseline of the EMG trace. If the final baseline was used as the reference, then traces with poor final EMG baseline also showed similar neuromuscular recovery times. If the initial baseline was used as the reference for EMG traces with poor final baseline, then neuromuscular recovery times became 24-55% longer (P < 0.05).

CONCLUSIONS

We conclude that the final baseline of an EMG trace can be used as a reference for calculations of neuromuscular recovery times following a bolus injection of mivacurium.

Time course of action and intubating conditions following vecuronium, rocuronium and mivacurium

The purpose of this study was to compare the time course of action and tracheal intubating conditions of vecuronium, rocuronium and mivacurium in anaesthetised patients. Anaesthesia consisted of thiopentone, fentanyl, N2O/O2 and isoflurane. After a 2 x ED90 dose the first attempt at tracheal intubation was made at 90 s. If required, maintenance doses of 0.5 x ED90 were administered. The intubating conditions after rocuronium were significantly better than those after vecuronium and mivacurium. The average onset times of rocuronium (172 s) and vecuronium (192 s) were significantly shorter than that of mivacurium (229 s). The clinical duration and recovery time were significantly shorter after mivacurium (13 and 6 min, respectively) than with vecuronium (33 and 14 min, respectively) and rocuronium (28 and 11 min, respectively). We conclude that rocuronium might be of advantage whenever the interval between the administration of the muscle relaxant and tracheal intubation must be short, whereas mivacurium may be of benefit if fast spontaneous recovery is required.

Pharmacodynamics of rocuronium with and without prior administration of succinylcholine

STUDY OBJECTIVES

To compare succinylcholine (S) and rocuronium (R) used for endotracheal intubation, and to assess the possible action of S on subsequently administered R.

DESIGN

Double-blind, randomized, phase III study.

SETTING

University Medical Center.

PATIENTS

24 ASA physical status I and II patients, ages 28 to 65, undergoing general anesthesia for abdominal procedures.

INTERVENTION

Double-blind administration of R 600 mcg/kg (Group A) or S 1 mg/kg was achieved with open label R 150 mcg/kg. Standardized general anesthetic technique with sodium thiopental, fentanyl, and nitrous oxide in oxygen was administered.

MEASUREMENTS AND MAIN RESULTS

Neuromuscular junction was tested by ulnar nerve stimulation and mechanomyograph. Intubation was attempted at 80% first twitch depression of train-of-four. Heart rate and blood pressure were recorded throughout. Onset times were 74 +/- 37 seconds for S and 130 +/- 46 seconds for R. Intubation times were 76 +/- 29 seconds for S and 85 +/- 23 seconds for R (no significant difference). Good to excellent intubation conditions were achieved in both groups. S given prior to R decreased onset time and increased duration of R, when compared with R given alone. No drug related cardiovascular events were noted.

CONCLUSION

Rapid intubation conditions can be obtained after both S and R. Given its overall safety profile, R can be used when S is contraindicated, or in healthy patients with no apparent difficult airway, when procedures are expected to last more than 25 minutes.

The use of rocuronium (ORG 9426) in patients with chronic renal failure

The pharmacodynamics of an initial dose of 0.6 mg.kg-1 rocuronium followed by three maintenance doses of 0.15 mg.kg-1 were studied during nitrous oxide/oxygen/isoflurane anaesthesia in patients with normal renal function (n = 12) and chronic renal failure (n = 12). The mean (SD) duration (min) of block after the initial dose was 28.0 (5.5) and 25.6 (11.7) respectively. The mean (SD) duration (min) of the effect of the three maintenance doses was 15.3 (4.0) and 14.2 (7.0); 17.3 (3.2) and 17.4 (8.7); 18.1 (2.8) and 19.1 (10.1) for the normal and renal failure patients respectively. The induced and spontaneous recovery indices were 3.7 (0.7) and 17.1 (6.9) in the normal group compared with 3.9 (0.5) and 19.0 (12.5) in the renal failure group and these values did not differ between the two groups. In this small study rocuronium appears to be suitable for patients with chronic renal failure. There is no evidence of prolonged block even when the drug is given in repeated doses for maintenance.