Effects of SZ1677, a new non-depolarizing steroidal neuromuscular blocking drug, and rocuronium on two laryngeal muscles and the anterior tibial muscle in guinea pigs

BACKGROUND: SZ1677 is a new neuromuscular blocking drug structurally related to rocuronium. We compared the effect of an ED(90) of SZ1677 (25 microg/kg) with that of rocuronium (100 microg/kg) in guinea pig laryngeal and peripheral muscles. METHODS: Electromyography was used to quantify neuromuscular blockade at the posterior cricoarytenoid muscle, the thyroarytenoid muscle and the anterior tibial muscle after SZ1677 (n = 10) and rocuronium (n = 9). RESULTS: Maximum neuromuscular blockade was similar after SZ1677 and rocuronium (83 +/- 11% vs. 89 +/- 11%; thyroarytenoid muscle: 91 +/- 8% vs. 97 +/- 3%; anterior tibial muscle: 91 +/- 15% vs. 96 +/- 3%, respectively). Onset time of neuromuscular blockade at the laryngeal muscles was similar for the two neuromuscular blocking drugs; it was shorter at the thyroarytenoid muscle (67 +/- 32 s vs. 42 +/- 40 s) than at the posterior cricoarytenoid muscle (101 +/- 26 s vs. 102 +/- 108 s). Onset time at the anterior tibial muscle was longer after SZ1677 (114 +/- 34 s) than after rocuronium (68 +/- 46 s); P < 0.05. Neuromuscular recovery was faster after SZ1677 (interval 25%-75%: posterior cricoarytenoid muscle: 222 +/- 66 s; thyroarytenoid muscle: 192 +/- 92 s; tibial muscle 149 +/- 55 s) than after rocuronium (450 +/- 148 and 464 +/- 183 s, 292 +/- 86 s, respectively); P < 0.05. CONCLUSIONS: In guinea pigs, SZ1677 offers a rapid onset of neuromuscular blockade at a laryngeal adductor muscle with a shorter duration than rocuronium. Regardless of the drug used, the course of neuromuscular blockade differs not only between peripheral muscles and the larynx but also between antagonistic laryngeal muscles. The differences seem to be species specific.     

Simultaneous determination of neuromuscular blockade at the adducting and abducting laryngeal muscles using phonomyography

Phonomyography (PMG) is a new method for measuring neuromuscular blockade (NMB) at the larynx. In this study, we used PMG to compare NMB at the posterior cricoarytenoid (PCA) and the lateral cricoarytenoid muscle (LCA) in humans. Twelve patients were included in this study. Endotracheal intubation was performed without aid of neuromuscular blocking drugs. One small condenser microphone was inserted beside the vocal cords into the muscular process at the base of the arytenoid cartilage to record acoustic responses of the LCA (vocal cord adduction), and a second microphone was placed behind the larynx to measure NMB of the PCA (vocal cord abduction). Stimulation of the recurrent laryngeal nerve was performed using superficial electrodes placed at the neck (midline between jugular notch and cricoid cartilage) using train-of-four (TOF) stimulation every 12 s. After supramaximal stimulation, mivacurium 0.1 mg/kg was injected and onset, peak effect, and offset of NMB measured and compared using t-test (P < 0.05). The data are presented as mean (SD). Peak effect, onset time, and early recovery to 25% of control twitch height were not significantly different between PCA and LCA at 86% (13) versus 78% (16), 2.3 min (0.45) versus 2.3 min (1.0), and 9.55 min (3.05) versus 8.5 min (4.7), respectively. However, recovery to 75%, 90% of control twitch height, and recovery to a TOF ratio of 0.8 were significantly longer at the PCA than at the LCA at 14 min (4) versus 11 min (5), 17 min (5) versus 11.8 min (5.6), and 17.5 min (5.6) versus 12.3 min (5.5), respectively. The authors conclude that recovery of NMB at the PCA takes longer than at the LCA in humans after mivacurium. IMPLICATIONS: After neuromuscular blockade in humans, the recovery of the ability to open the vocal cords takes longer than the ability to close the vocal cords.     

Effects of neuromuscular-blocking drugs in rats in vivo: direct measurements in the diaphragm and tibialis anterior muscle

BACKGROUND: Effects of neuromuscular-blocking drugs are often investigated in rodents using both the diaphragm in vitro and the tibialis anterior muscle in vivo. Differences in the properties of these muscles cannot be neglected. We evaluated the neuromuscular effects of drugs on the rat diaphragm in vivo in comparison with the tibialis anterior muscle, directly measuring twitch tension with a force transducer. METHODS: Respectively using sternotomy and an approach via the gluteal space, transducers were attached to the diaphragm and the tibialis anterior muscle. Phrenic and sciatic nerves were stimulated supramaximally by single square pulses to record isometric contraction of muscles. Pancuronium, vecuronium, or rocuronium was infused continuously at a rate adjusted repeatedly until stable tension was obtained. Effective doses for 50% (ED 50) and 90% (ED 90) depression of tension were calculated, using a cumulative infusion dosing method. RESULTS: Isometric contraction of the diaphragm could be recorded despite movements of the heart and lungs. For all three drugs, both mean ED 50 and ED 90 were more than twice as large for the diaphragm as for the tibialis anterior (P<0.05). In addition, slopes of dose-response curves for the diaphragm were significantly less steep than those of the tibialis anterior for the three drugs. CONCLUSION: Neuromuscular-blocking effects on the diaphragm can be recorded in vivo. According to direct contractile force measurement, the diaphragm is more resistant to non-depolarizing neuromuscular-blocking drugs than the tibialis anterior muscle.     

Early and late reversal of rocuronium and vecuronium with neostigmine in adults and children.

We investigated the influence of the timing of neostigmine administration on recovery from rocuronium or vecuronium neuromuscular blockade. Eighty adults and 80 children were randomized to receive 0.45 mg/kg rocuronium or 0.075 mg/kg vecuronium during propofol/fentanyl/N2O anesthesia. Neuromuscular blockade was monitored by train-of-four (TOF) stimulation and adductor pollicis electromyography. Further randomization was made to control (no neostigmine) or reversal with 0.07 mg/kg neostigmine/0.01 mg/kg glycopyrrolate given 5 min after relaxant, or first twitch (T1) recovery of 1%, 10%, or 25%. Another eight adults and eight children received 1.5 mg/kg succinylcholine. At each age, spontaneous recovery of T1 and TOF was similar after rocuronium and vecuronium administration but was more rapid in children (P < 0.05). Spontaneous recovery to TOF0.7 after rocuronium and vecuronium administration in adults was 45.7 +/- 11.5 min and 52.5 +/- 15.6 min; in children, it was 28.8 +/- 7.8 min and 34.6 +/- 9.0 min. Neostigmine accelerated recovery in all reversal groups (P < 0.05) by approximately 40%, but the times from relaxant administration to TOF0.7 were similar and independent of the timing of neostigmine administration. Recovery to T1 90% after succinylcholine was similar in adults (9.4 +/- 5.0 min) and children (8.4 +/- 1.1 min) and was shorter than recovery to TOF0.7 in any reversal group after rocuronium or vecuronium administration. Recovery from rocuronium and vecuronium blockade after neostigmine administration was more rapid in children than in adults. Return of neuromuscular function after reversal was not influenced by the timing of neostigmine administration. These results suggest that reversal of intense rocuronium or vecuronium neuromuscular blockade need not be delayed until return of appreciable neuromuscular function has been demonstrated. Implications: These results suggest that reversal of intense rocuronium or vecuronium neuromuscular blockade need not be delayed until return of appreciable neuromuscular function has been demonstrated. Although spontaneous and neostigmine-assisted recovery is more rapid in children than in adults, in neither is return of function as rapid as after succinylcholine administration.     

Rocuronium (ORG 9426) neuromuscular blockade at the adductor muscles of the larynx and adductor pollicis in humans

The effects of rocuronium, 0.25 or 0.5 mg.kg-1, were measured simultaneously on the adductor muscles of the larynx and adductor pollicis in 14 adult patients. Anaesthesia was induced and maintained with propofol and fentanyl. Tracheal intubation was performed without muscle relaxants. The recurrent laryngeal and ulnar nerves were both stimulated supramaximally, at the notch of the thyroid cartilage and at the wrist respectively, using train-of-four stimulation. The laryngeal response was evaluated by measuring the pressure change in the cuff of a tracheal tube positioned between the vocal cords. Onset time, intensity of blockade and duration of action were less at the larynx than at the adductor pollicis. After rocuronium, 0.25 mg.kg-1, the onset time (interval between injection and maximal T1 blockade) was 1.6 +/- 0.1 min and 3.0 +/- 0.3 min (mean +/- SEM) at the laryngeal muscles and adductor pollicis, respectively (P less than 0.01 between muscles). Maximum blockade was 37 +/- 8% and 69 +/- 8%, respectively (P less than 0.05), and time to 90% T1 recovery was 7 +/- 1 min and 20 +/- 4 min, respectively (P less than 0.05). With 0.5 mg.kg-1, the onset time was also more rapid at the vocal cords (1.4 +/- 0.1 min) than at the adductor pollicis (2.4 +/- 0.2 min, P less than 0.001). Maximum blockade was 77 +/- 5% and 98 +/- 1%, respectively (P less than 0.01), and time to 90% T1 recovery was 22 +/- 3 min and 37 +/- 4 min, respectively (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Rocuronium zur elektiven Narkoseeinleitung Verlauf der neuromuskulären Blockade und Intubationsbedingungen nach 2facher ED95 (0,6 mg/kg) und nach Dosisreduktion (0,4 mg/kg)

BACKGROUND: Rocuronium is a non-depolarising neuromuscular blocking agent structurally related to vecuronium. The compound has a rapid onset and an intermediate duration of action. The rapid onset is of importance in patients at risk for pulmonary aspiration, for elective induction of anaesthesia slower onset properties generally are accepted. In this context, we asked whether the induction dose of rocuronium may be reduced to doses smaller than 2 x ED95 in situations in which slower onset properties may be acceptable. METHODS: The time course of neuromuscular block and intubating conditions of two different doses rocuronium, 2 x ED95 (0.6 mg/kg) and 1.3 x ED95 (0.4 mg/kg), were investigated in 90 patients. We first determined the time course of neuromuscular block using electromyography (EMG), n = 15 for each group. In the second part the intubating conditions 3 min after injection of either rocuronium 0.6 mg/kg or rocuronium 0.4 mg/kg were evaluated, n = 30 for each group. RESULTS: In the present study reduction of the dose of rocuronium led to a slower onset (148 +/- 32 s vs. 220 +/- 30 s; P < 0.05) and a shorter clinical duration (21 min +/- 4 vs. 36 +/- 7 min; P < 0.05). The recovery index was modified by the dose reduction: 11 +/- 3 min after 0.6 mg/kg rocuronium and 9 +/- 2 min after 0.4 mg/kg. After both doses of rocuronium the intubating conditions were good to excellent, no difference between both rocuronium groups were found. CONCLUSION: In the present study dose reduction from 0.6 mg/kg rocuronium to 0.4 mg/kg rocuronium led to a slower onset and reduced clinical duration. However, the intubating conditions, evaluated 3 min after injection of the muscle relaxant were comparable. This offers new possibilities for muscle relaxation for surgical or diagnostic procedures of short duration and may reduce costs.     

Differential neuromuscular effects of vecuronium on the adductor and abductor laryngeal muscles and tibialis anterior muscle in dogs

We have studied in dogs the neuromuscular blocking effects ofvecuronium on the cricothyroid (CT) (a tensor muscle of thevocal folds) and posterior cricoarytenoid (PCA) (sole abductormuscle of the vocal folds) muscles of the larynx and the tibiaIis anterior (TA) muscle. The lungs of the animals were ventilatedmechanically with 0.2% halothane and oxygen. Electromyography(EMG) was performed on the CT, PCA and TA muscles by insertingfine wire electrodes. The evoked compound EMG responses of thethree muscles were measured simultaneously in an identical mannerby stimulating supramaximally the superior laryngeal, recurrentand sciatic nerves at 0.1 Hz and 0.2 ms. Vecuronium was infusedcontinuously at a rate of 0.01 mg kg^–1 min^–1 for8 min. Vecuronium produced more intense neuromuscular blockin the CT than in the PCA and TA muscles. The rate of recoverywas significantly slowly in the CT compared with the PCA andTA muscles. This study confirms the difference in sensitivitybetween laryngeal and peripheral muscles, demonstrating thatthe intrinsic laryngeal muscles do not all behave similarlyafter administration of vecuronium. (Br. J. Anaesth. 1994; 72:321–323)     

Low doses of rocuronium during remifentanil-propofol-based anesthesia in children: comparison of intubating conditions

BACKGROUND : In this prospective double-blind study, intubation conditions were compared at 90 s following two different low doses of rocuronium during remifentanil and propofol anesthesia in children undergoing ambulatory procedures. METHODS : Forty-four children (ASA I-II, aged 3-12 years) undergoing day case ENT surgery were premedicated with midazolam 0.5 mg x kg(-1). Following atropine 10 microg x kg(-1), remifentanil infusion 0.5 microg x kg(-1) x min(-1) was started. After 60 s, anesthesia was induced with propofol 2.5 mg x kg(-1). Immediately after a bolus dose of propofol, the children received rocuronium doses of 0.15 mg x kg(-1) (group I, n = 22) or 0.3 mg x kg(-1) (group II, n = 22) in a randomized manner, after which an infusion of propofol 6 mg x kg(-1) h(-1) was added to the infusion of remifentanil 0.5 microg x kg(-1) min(-1) for maintenance of anesthesia. Intubating conditions were evaluated 90 s after rocuronium administration applying the Copenhagen Scoring System which included components of laryngoscopy, vocal cord movement and reaction to intubation. Hemodynamic values were recorded at predetermined time intervals. RESULTS : Excellent, good and poor intubation conditions were 18.2, 40.9 and 40.9% in group I and 40.9, 54.5 and 4.5% in group II. Clinically acceptable intubating conditions (excellent and good) were significantly higher in group II (95.5%) than in group I (59.1%) (P = 0.004). Mean values of heart rate and blood pressure did not differ significantly between groups. No children required any intervention for hemodynamic instability and/or muscle rigidity. CONCLUSIONS : The results suggest that 0.3 mg x kg(-1) of rocuronium may be a better low dose than 0.15 mg x kg(-1) of rocuronium for clinically acceptable intubating conditions in pediatric ambulatory surgery during remifentanil-propofol-based anesthesia at the doses used in the study.     

Abductor vocal cord spasm

The purpose of this study is twofold. First, to introduce a new phenomenon--abductor vocal cord spasm, or abductor laryngospasm. Second, to reconcile a longstanding discrepancy involving the effect of lung inflation on vocal cord position. Abductor laryngospasm was induced in six anesthetized, tracheotomized dogs by the administration of continuous positive airway pressure (CPAP) after occlusion of the trachea for 60 seconds. Abductor laryngospasm was characterized by sustained vocal cord abduction with concomitant massive, continuous posterior cricoarytenoid muscle (PCA) electromyography (EMG) activity and little or no laryngeal adductor muscle EMG activity. Vocal cord opening was sustained for up to 90 seconds. In the same dogs, administration of CPAP, after hyperventilation of the animal, resulted in adductor laryngospasm. Adductor laryngospasm was characterized by steady apposition of the vocal cords, massive laryngeal adductor muscle EMG activity, and silent PCA EMG activity. Abductor laryngospasm appears to be the physiologic converse of adductor laryngospasm. The results of this study show that lung inflation can produce either vocal cord abduction or adduction, depending on whether the dog is hypoventilated or hyperventilated before administration of CPAP.     

Reanimation of paralyzed laryngeal muscles by electrical stimulation synchronized with inspiration.

OBJECTIVE: To determine the effects of electrical stimulation on denervated cat posterior cricoarytenoid (PCA) muscle. STUDY DESIGN AND SETTING: This study was conducted on six cats with PCA muscle denervation. All animals were sacrificed 12 weeks after surgery and the glottal area in the live animals and the fiber diameters of PCA muscle were obtained. RESULTS: Signals synchronized with inspiration were recorded and transmitted to stimulate PCA muscle. The abduction of the paralyzed vocal cord during inspiration was observed; this allows enough flow of air through the larynx to maintain the respiration. The stimulated fiber diameters of PCA muscle were different from that of nonstimulated (P < 0.01). Although all denervated muscles were degenerated, electrical stimulation was used to prevent muscular atrophy. CONCLUSIONS: This study indicates that electrical stimulation of the PCA muscle synchronized with inspiration could restore the abduction of a paralyzed vocal cord and prevent the denervated muscles from atrophying. SIGNIFICANCE: Electrical stimulation synchronized with inspiration may lead to reanimation of paralyzed laryngeal muscles.     

Investigation of fading responses induced by non-depolarising muscle relaxants in the evoked EMG of the gastrocnemius muscle of the cat

BACKGROUND: During partial neuromuscular blockade indirect repetitive nerve stimulation causes fade in the response of the muscle. We studied the intensity of the fade induced by intravenous administration of three steroidal muscle relaxants, and investigated the mechanism of fade by comparing with results obtained during partial blockade with animal toxins and vesamicol. METHODS: In 60 cats, we measured the fade in the compound action potentials of the gastrocnemius muscle evoked by repetitive sciatic nerve stimulation at 100 Hz during partial neuromuscular blockade with rocuronium, vecuronium, pancuronium, alpha-bungarotoxin, mu-conotoxin and vesamicol, respectively. RESULTS: Profound fade was induced by all three non-depolarising muscle relaxants (rocuronium=vecuronium相似文献   

A comparison between anterior and posterior monitoring of neuromuscular blockade at the diaphragm: both sites can be used interchangeably

We present a novel site of monitoring neuromuscular blockade of the diaphragm at the patient's back. After the induction of anesthesia, 12 patients were orotracheally intubated. Two Ag/AgCl-electrodes were attached at the right seventh or eighth intercostal space between the midclavicular and anterior axillary line; two Ag/AgCl-electrodes were paravertebrally attached on the right side lateral to vertebrae T12-L1 or L1-2. Two Ag/AgCl-skin-electrodes were placed over the right thenar area for an electromyography recording of the adductor pollicis (AP) muscle, and two Ag/AgCl-skin-electrodes were used to stimulate the ulnar nerve. Onset and offset of neuromuscular blockade after rocuronium 0.6 mg/kg were determined, and significant differences between diaphragm and AP muscle and agreement between the two methods were determined. Mean maximum block was more than 96% at all sites. Lag time, onset 50, and onset time were not significantly different between the diaphragm and the AP. However, time to reach 25% of control twitch was significantly longer at the AP muscle than at the diaphragm (P < 0.001). The difference of the means and limits of agreement between the anterior and the posterior site of diaphragmatic monitoring were 0 +/- 11 s, 3 +/- 9 s, 0 +/- 19 s, and -2% +/- 5% for lag, onset 50, onset time, and peak effect, respectively, and -2 +/- 2 min for the time to reach 25% of control twitch of neuromuscular blockade. We conclude that anterior and posterior diaphragmatic monitoring can be used interchangeably to determine neuromuscular blockade after rocuronium. IMPLICATIONS: We present a novel site of monitoring neuromuscular blockade of the diaphragm at the patient's back, which shows good agreement with the conventional anterior site at the seventh or eighth intercostal space.     

Prospective randomised double-blind comparative study of rocuronium and pancuronium in adult patients scheduled for elective 'fast-track' cardiac surgery involving hypothermic cardiopulmonary bypass

The majority of cardiac anaesthetists in the UK use pancuronium for fast-track cardiac surgery. We compared the duration of action of pancuronium and rocuronium in patients undergoing fast-track hypothermic cardiopulmonary bypass and cardiac surgery. We determined whether patients would have had residual neuromuscular blockade at extubation. Twenty patients were randomly allocated to receive either pancuronium 0.1 mg x kg(-1) or rocuronium 1 mg x kg(-1). Neuromuscular function was assessed by acceleromyography; spontaneous recovery was evaluated by the train-of-four ratio measured at the adductor pollicis longus muscle. Median times to recover train-of-four ratio of 0.9 were 3 h 38 min for rocuronium and 7 h 52 min for pancuronium. The median difference in recovery times was 4 h 15 min (95% CI 2 h 30 min to 6 h 20 min; p = 0.0003 by Mann-Whitney test). None of the patients in the rocuronium group and seven of 10 patients in the pancuronium group had their extubations delayed because of residual neuromuscular blockade. Unless fast-track patients have neuromuscular function assessed before extubation, pancuronium should not be used.     

Immobilités laryngées unilatérales après chirurgie de la glande thyroïde

Background

The authors studied a cohort of 154 patients with unilateral vocal cord paresis following thyroidectomy, analyzing the pathogenesis, symptomatology, spontaneous evolution, and management of this complication.

Objective

This retrospective study distinguished between vocal cord paresis due to recurrent laryngeal nerve injury or due to injury of the cricoarytenoid articulation. We assessed the influence multiple variables on therapeutic management. The results and complications of currently-employed surgical techniques to remedy unilateral vocal cord paresis were defined.

Patients and methods

Injury to the recurrent laryngeal nerve was the cause of vocal cord paresis in 98% of cases; injury to the cricoarytenoid articulation accounted for only 2% of cases. When the recurrent laryngeal nerve had not been actually transected, spontaneous recovery of vocal cord function occurred in 36% of cases. No spontaneous recovery was noted when the nerve had been divided. The interval to recovery of cord function ranged from 2 to 15 months (median: 4 months). Spontaneous recovery of vocal cord function had occurred in 90% of these patients by the 9th postoperative month. Three factors significantly influenced the decision to perform a median transposition of the injured vocal cord: known transection of the recurrent laryngeal nerve, the interval to consultation with an ENT specialist, and the severity of dysphonia. Medial transposition of the injured vocal cord resulted in an immediate improvement in the quality of voice and speech with no major complications.

Conclusion

Unilateral vocal cord paresis occurring after thyroidectomy is not always symptomatic and is not uniformly due to injury of the recurrent laryngeal nerve. Management does not always require surgical reintervention. The practical and medico-legal consequences of these injuries are discussed.     

Atracurium and vecuronium: repeated bolus injection versus infusion.

The purpose of this study was to compare the characteristics of recovery from neuromuscular blockade after either atracurium or vecuronium given by intravenous infusion or by repeated injection. Four groups of 10 patients each were studied during nitrous oxide narcotic anesthesia. An initial intravenous dose of 2 x ED95 of either muscle relaxant was followed by an intravenous infusion started at 5% recovery of control twitch tension and adjusted for 95% block or by repeated injection of 0.6 x ED95 administered whenever twitch tension had returned to 25% of control. There were no significant differences between the maintenance doses required based on method of administration: atracurium repeated injection, 1.6 +/- 0.3 x ED95 h-1; atracurium infusion, 1.7 +/- 0.3 x ED95 h-1; vecuronium repeated injection, 1.8 +/- 0.5 x ED95 h-1; and vecuronium infusion, 1.6 +/- 0.4 x ED95 h-1. Nevertheless, differences of up to 20 min were noted in the recovery indices in the following order: atracurium repeated injection = atracurium infusion less than vecuronium repeated injection less than vecuronium infusion. A single dose of neostigmine (7 micrograms/kg) significantly reduced the recovery indices, thereby eliminating their differences.     

Surfacevs intramuscular laryngeal electromyography

PURPOSE: To compare surface and intramuscular laryngeal electromyography (EMG) with adductor pollicis muscle EMG after 0.1 mgxkg(-1) cisatracurium. METHODS: This prospective study included ten patients undergoing surgery with risk of damage to the recurrent laryngeal nerve (RLN). The tracheas were intubated after fentanyl/propofol without the aid of muscle relaxation. A surface laryngeal electrode was attached to the tube and placed amidst the vocal cords; two straight needles were inserted endoscopically into the left lateral cricoarytenoid muscle. Single twitch stimulation of the left RLN (0.1 Hz) was performed transcutaneously; skin EMG of the left adductor pollicis muscle was performed at 0.1 Hz. After supramaximal stimulation for 10 min, 0.1 mgxkg(-1) cisatracurium was injected. Lag, onset time and peak effect were measured and compared. RESULTS: Good correlation (r = 0.9, 0.8, P < 0.005) and good comparability of the two methods of laryngeal EMG (mean difference and limits of agreement: 0 +/- 28 sec for lag time, -2 +/- 84 sec for onset time) was shown. The mean surface laryngeal lag and onset times were 67 +/- 22 sec and 198 +/- 72 sec, compared with the adductor pollicis muscle (98 +/- 30 sec and 242 +/- 59 sec) at P < 0.01. Peak effects at larynx (92 +/- 9%) and adductor pollicis muscle (95 +/- 3%) were similar. CONCLUSION: Surface laryngeal EMG is comparable to intramuscular laryngeal EMG to determine degree and onset of the neuromuscular blockade. Increasing muscle relaxation does not cause the surface electrode to lose contact with the vocal cords and therefore underestimate onset time and peak effect.     

Variability of duration of action of neuromuscular-blocking drugs in elderly patients

BACKGROUND: Steroid-based, non-depolarizing neuromuscular-blocking (NMB) drugs (e.g. rocuronium, vecuronium) are characterized by organ-dependent elimination and significantly longer durations of action in elderly compared to young patients. Cisatracurium is a benzylisoquinolinium NMB drug with a duration of action not altered by ageing. The objective of the study was to determine if elderly patients had less variability in duration of action with 2 x ED95 of cisatracurium compared to equipotent doses of rocuronium or vecuronium. METHODS: Informed consent was obtained from 66 elderly patients with normal renal and liver function. Preoperative midazolam (1 mg) was given IV. The anaesthestic induction was with 5 mg kg(-1) thiopental and 2 microg kg(-1) fentanyl. The patients received 0.6 mg kg(-1) rocuronium, 0.1 mg kg(-1) vecuronium or 0.1 mg kg(-1) cisatracurium. Anaesthetic maintenance was with sevoflurane in oxygen/nitrous oxide. Neuromuscular-blocking duration of action was defined as the return of T1 twitch height to 25% of control. Variability was determined by subtracting the actual duration of action from the mean duration of action for each drug. RESULTS: The durations of action (range, min) were: cisatracurium, 37-81; vecuronium, 35-137; and rocuronium, 33-119. The median of the variability of duration was significantly less with cisatracurium (7 min) compared to vecuronium (18 min) and rocuronium (18 min) (P < 0.05). CONCLUSION: When used with sevoflurane/N(2)O, there was a two-fold greater variability of duration of neuromuscular blockade in elderly patients receiving rocuronium or vecuronium compared with cisatracurium.     

Neuromuscular effects of succinylcholine on the vocal cords and adductor pollicis muscles

To quantify the effects of succinylcholine at the laryngeal adductor muscles and the adductor pollicis, 17 adult patients were studied during propofol-fentanyl anesthesia. Train-of-four stimulation was applied to the ulnar nerve at the wrist and the recurrent laryngeal nerve at the notch of the thyroid cartilage. Laryngeal response was measured as pressure changes in the cuff of the tracheal tube positioned between the vocal cords. The force of contraction of the laryngeal adductor muscles and of the adductor pollicis were compared after administration of 0.25 or 0.5 mg/kg of succinylcholine. With 0.25 mg/kg, maximum blockade of first twitch (T1) was 66% +/- 10% (mean +/- SEM) and 45% +/- 13% at the vocal cords and the adductor pollicis, respectively (P less than 0.01). After 0.5 mg/kg, maximum blockade at the vocal cords (93% +/- 2%) and the adductor pollicis (84% +/- 6%) did not differ significantly. For both doses, time to maximal blockade was shorter for the vocal cords (0.9 +/- 0.1 min) than for the adductor pollicis (1.7 +/- 0.2 min; P less than 0.01). Time to 90% recovery of T1 after a bolus of 0.5 mg/kg was similar at the vocal cords (4.3 +/- 0.5 min) and the adductor pollicis (5.2 +/- 0.8 min) (NS). The ED50 was less at the laryngeal adductors (0.170 mg/kg) than at the adductor pollicis (0.278 mg/kg). It is concluded that, in adults, succinylcholine-induced blockade is more rapid and more intense at the laryngeal muscles than at the adductor pollicis.     

Opening and closing mechanisms of the larynx

Opening and closing of the larynx are determined by the intrinsic and extrinsic muscles acting on the elastic forces in the tongue, pharynx, larynx, and trachea. The pharynx is opened or closed by two mechanisms: (1) Contractions of the cricothyroid and of the intrinsic muscles of the larynx open and close the vocal cords. (2) The false cords, ventricle, and true cords accordion open or close in a bellows mechanism. We conclude that the posterior cricoarytenoid opens the laryngeal airway. The cricothyroid together with the posterior cricoarytenoid accentuates this opening. The larynx is also opened by the geniohyoid, mylohyoid, sternothyroid, and middle constrictor. The thyrohyoid, cricothyroid, sternohyoid, and inferior constrictor close the laryngeal airway. Abnormalities in the soft tissues of the neck or of the innervation of the larynx, pharynx, and neck muscles may severely interfere with patency of the laryngeal airway. This occurs in such conditions as vocal cord paralysis, sleep apnea, multiple sclerosis, amyotrophic lateral sclerosis, spastic dysphonia, mandibular fractures or hypodevelopment, and cerebrovascular disease.     

The pharmacodynamics of vecuronium on the musculature of the vocal cords and the ball of the thumb. Preliminary report

During endolaryngeal microsurgery, an attempt was made to quantify laryngeal muscle relaxation by electromyographic recording of evoked responses from the vocal cord musculature in 5 patients. Both mechanographic and electromyographic recordings from the adductor pollicis were obtained simultaneously. Following a bolus dose of vecuronium (60 micrograms/kg, n = 3, and 100 micrograms/kg, n = 2), nearly total (97%-100%) suppression of evoked responses at the peripheral muscle site was observed; the vocal cords, however, did not show complete neuromuscular (nm) blockade, but rather varying degrees of nm depression ranging from 61%-92%. The present results clearly show that quantitative information as to duration and degree of neuromuscular depression in the vocal musculature may be obtained by electromyographic recordings of evoked potentials in the clinical setting; it is impossible however, to quantitatively estimate the extent of intrinsic laryngeal muscle relaxation from peripheral nm depression. The pharmacodynamic differences observed might be due to the varying acetylcholine receptor density of the muscle groups studied.