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© Borgis - Anaesthesiology Intensive Therapy 1/2001
Ewa Wojcieszek, Hanna Misiołek, Hanna Kucia
Comparison of mivacurium chloride and vecuronium bromide for muscle relaxation during general anaesthesia in maxillofacial surgery
Department of Clinical Anaesthesiology in Zabrze, Chair & Department of Anaesthesiology and Intensive Therapy,
Head: prof. A. Dyaczyńska-Herman, Silesian Medical Academy, Katowice, Poland
Summary
We have assessed the usefulness of mivacurium chloride and vecuronium bromide in thirty adult patient, scheduled for maxillofacial surgery. Neuromuscular transmission was assessed tactilly and visually using twitch and double burst stimulation at the posterior tibial nerve. We have noted onest time, first supplementary dose administration time and mean interval time (time between supplementary doses). Relaxation with mivacurium was significantly shorter. Both drugs provided satisfactory relaxation, both for intubation and surgery. Both drugs can be safely used for maxillofacial surgery. Neuromuscular transmission monitoring increases safety of anaesthesia.
Anaesthesia for maxillofacial surgery, especially for trauma of the mandible and maxilla, constitute a challenge to the anaesthesiologist in terms of choice of the method and perioperative management of the patient [1,2]. Surgical treatment of mandibular trauma, with reconstruction of the correct occlusion requires securing of the patient's airways without obstructing the operative field. To meet these requirements, endotracheal intubation is necessary [1, 2, 3, 4].
In patients with maxillofacial trauma this procedure may be very difficult [1, 3, 4, 5]. To obtain optimal conditions for tracheal intubation, short- or medium-long acting depolarising or non-depolarising muscle relaxants are used [3, 4, 5]. The new generation of non-depolarising short acting muscle relaxants is represented by mivacurium chloride. Its time of action places it between ultra-short acting suxamethonium and medium-long acting nondepolarizing agents such as vecuronium bromide [6].
The aim of the study was to compare the conditions for tracheal intubation and the degree of muscle relaxation following mivacurium chloride and vecuronium bromide administration for maxillofacial surgery.
METHODS
The study was performed in 30 patients scheduled for mandible or maxilla osteosynthesis. The patients were randomly assigned to 2 groups: 15 patients received mivacurium chloride (group I), 15 - vecuronium bromide (group II).
The patients belonged to ASA group I, II or III.
The difficulties in endotracheal intubation were classified according to the four-grade Mallampati scale [7]. The difficulty of intubation were assessed during direct laryngoscopy according to the Cormack-Lehan scale [8], and conditions of intubation - to the Krieg scale [4].
As premedication, 45 minutes before surgery, the patients received midazolam 0.1 mg/kg and atropine 0.015 mg/kg i.m. Induction to anaesthesia was performed with methohexital 1.5 mg/kg and fentanyl (5 mg/kg) or etomidate 0.2 mg/kg and fentanyl.
For intraoperative monitoring of neuromuscular blockade, a peripheral nerve stimulator (MS-IIIA Professional Instruments, Live-Tech Inc., USA) placed on the patient's calf was used. After the induction of anaesthesia the nerve was stimulated with single twitch of 0.1-1.0 Hz frequency, in order to calibrate the supramaximal impulse. Then the induction dose of mivacurium chloride or vecuronium bromide (0.1 mg/kg) was injected. Naso-tracheal intubation was performed under direct vision control after disappearance of any reaction to double burst stimulation (DBS). The response to stimulation was assessed visually and by palpation. The measured time intervals (in minutes) included: time from the injection of induction dose to the complete disappearance of response (T1); mean time from the induction dose to the first maintenance dose (T2); mean time between consecutive maintenance doses (T3). The results were noted in both groups and were compared using the Student's t-test. Maintenance doses were administered after the return of muscular response to DBS. These doses were 0.1 mg/kg for mivacurium chloride and 0.04 mg/kg for vecuronium bromide. ECG, non-invasive blood pressure, heart rate, haemoglobin oxygen saturation (pulsoximetry) and capnometry were monitored during anaesthesia. Extubation was performed after the return of full response to DBS and clinical signs of muscle strength (raising the head, frowning, protruding the tongue. Cholinesterase inhibitors were not used.
RESULTS
In group I the patient's age ranged from 18 to 60 years (mean: 39), in group II - from 21 to 62 years (mean: 36) and body weight - from 46 to 88 kg (Tab. I).
The difficulties in endotracheal intubation, according to the Mallampati and Cormack-Lehan scales are presented in tables II and III. No special problems were encountered. Table IV presents the conditions of intubation according to the Krieg scale. In table V the mean duration of procedure and anaesthesia, as well as mean induction doses, are presented.
T1 was similar in both groups (difference not significant).
T2 and T3 were significantly shorter in patients of group I (p<0.05) (Tab. V).
Table I. Demographic data
 TotalGroup IGroup II
Number301515
Age (years) 
mean
18-6218-52
39
21-61
36
Body weight
 (kg)
46-88,546-7354-88,5
Table II. Tracheal intubation conditions according to the Mallampati scale
 Number of patients
group Igroup II
86
II°53
III°24
IV°02
Table III. Tracheal intubation conditions according to the Cormack-Lehan scale
 Number of patients
group Igroup II
106
II°45
III°12
IV°00
Table IV. Tracheal intubation conditions according to the Krieg's scale
 ValuationScore (points)
LaryngoscopyEasy
Fair
Difficult
Impossible
1
2
3
4
Vocal cordsOpened
Moving
Closing
Closed
1
2
3
4
CoughingAbsent
Diaphragmatic only 
Mild
Severe
1
2
3
4
Evaluation of conditionsExcellent
Good
Fair
Bad
1
2
3
4
Number of patients (group I)IntubationconditionsNumber of patients (group II)
8Excellent9
5Good4
2Fair1
0Bad0
Table V. Comparison of mean duration of action of the investigated muscle relaxants
 Group I (mean ± SD)Group II (mean ± SD)Statistical significance
Mean duration of surgery (min)58.5 ± 30.7470.6 ± 26.61NS
Mean duration of anaesthesia (min)67.5 ± 31.478.3 ± 25.82NS
Mean dose of muscle relaxant drug (mg)13,646.8 
T1-mean time from the initial dose to the disappearance of response (min)2.8 ± 0.473.1 ± 0.48NS
T2-mean time from the initial dose to the first maintenance dose (min)15.64 ± 1.624.92 ± 0.90p <0.05
T3-mean time interval between maintenance doses (min)15.0 ± 4.9825.0 ± 4.22p <0.05
DISCUSSION
Introducing of a new generation of short-acting, non-depolarising drugs to everyday clinical anaesthesiological practice markedly increased the patient's safety and reduced indications to suxamethonium use [9]. Nasotracheal intubation for maxillofacial surgery often poses problems, as the fracture of the mandibular condyles or bilateral mandible fracture make opening the mouth difficult. This results from the limitation of mandibular joint movements caused by pain and muscular strain. This is why 2 patients were classified as grade IV, and 6 - as grade III in the Mallampati scale. Muscle relaxant drugs, to a great extent, alleviate these difficulties [1]. In all patients the endotracheal intubation was successful, and the intubation conditions, according to Krieg's scale, were in most cases excellent.
Monitoring of the neuromuscular blockade is not widely used, as many anaesthesiologists do not consider it a valuable tool. In part, it may be caused by confidence in own experience, but economic factors cannot be neglected [10, 11].
In the present study the monitoring of neuromuscular function was assessed by stimulation of the posterior tibial nerve, provoking plantar flexion of the toe. Although most authors stimulate the ulnar nerve (more seldom - fibular or facial nerves) [10, 11, 12] the chosen placement proved efficient and did not disturb surgical nor anaesthetic procedures. The stimulation was begun with single impulses of 0.1-1.0 Hz frequency. This proved a useful method during monitoring, as it shortens the time to elicit a supramaximal twitch [10, 12]. The patients were extubated after the return of full response to DBS. This method also enables the precise assessment of, even minimal, persistent neuromuscular blockade by palpation. Such a monitoring, does not require recording devices and enables the fairly accurate assessment of responses. It is also gaining popularity because of the low cost of the equipment needed [10, 12]. It is suggested that the palpation evaluation of response to DBS should always be accompanied by clinical testing of the muscle strength [10, 12, 14]. This increases the safety of neuromuscular function return and limits the need to use anticholinesterase drugs [10, 14].
It is widely accepted that both agents compared in this study, produce good conditions for endotracheal intubation[4, 5, 15, 16, 17]. In maxillofacial surgery specific difficulties in intubation may be encountered. Both mivacurium and atracurium provide good intubation conditions [18].
The mean time elapsed from the initial dose to tracheal intubation was comparable in both groups, although it was longer than reported by other authors [14,16]. The mean time interval between the initial dose and the first maintenance dose, as well as between consecutive maintenance doses, was significantly longer after vecuronium bromide than mivacurium chloride. These observations are consistent with reports published elsewhere [15, 16, 17, 18].
The wide choice of muscle relaxants and the possibility of monitoring the neuromuscular block increase the safety of anaesthesia, by enabling the precise dosing of relaxant drugs. However in patients, in whom special difficulties in intubation are anticipated, the use of muscle relaxants of long onset - and long duration - time must be cautious [1, 4, 14, 16, 19, 20].
CONCLUSIONS
1. Both mivacurium chloride and vecuronium bromide seem equally useful for muscle relaxation in maxillofacial surgery.
2. The use of a simple peripheral nerves stimulator enables the correct dosing of relaxant drugs and diminishes the risk of residual neuro-muscular block, increasing the safety of anaesthesia.

Originally published in Anestezjologia Intensywna Terapia 31; (3), 167-170, 1999.
Piśmiennictwo
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Adres do korespondencji:
Rymera Str. 18; 41-800 ZABRZE, Poland

Anaesthesiology Intensive Therapy 1/2001