Neuromuskuläre Blockade

Currently, the main aims of using neuromuscular blocking agents during general anaesthesia are the improvement of surgical and intubation conditions. Neuromuscular blocking agents themselves are neither analgesic nor anaesthetic. All agents interact with the acetylcholinergic receptor at the neuromuscular junction and induce a blockade either through a continuous activation imitating the effect of acetylcholine or through a competitive antagonism against acetylcholine. Succinylcholine is the only depolarizing muscle relaxant that is in clinical use. Non-depolarizing neuromuscular blockers may be grouped by their chemical structure into benzylisoquinolines or aminosteroids, and cover the complete range from short and intermediate, to long acting agents. Possible adverse drug reactions to the single agents are also related to their mechanism of action. Moreover, pharmacokinetic properties and effects such as histamine liberation could play an important role when choosing a myorelaxant. The depth of a neuromuscular block and recovery from paralysis can be monitored using qualitative and quantitative techniques. Therefore, the monitoring of neuromuscular recovery plays an important role in the prevention of postoperative complications due to residual paralysis. In case of residual paralysis, cholinesterase inhibitors are suitable for reversal.

[Interaction between mivacurium and succinylcholine from a different point of view]

OBJECTIVES

Succinylcholine (SCH) may first be used and continue with mivacurium (MIV). MIV has been suggested as a pretreatment. Conflicting results arises from studies on SCH-MIV interaction. The following trial revisits this interaction.

PATIENTS AND METHODS

The patients were intubated after randomized administration of 100 microg x Kg(-1) of mivacurium (group 1) or 1 mg x Kg(-1) of succinylcholine and, after 50% recovery, 100 microg x Kg(-1) of mivacurium (group 2). A third group received the same regimen as group 2, preceded by pretreatment with 10 microg x Kg(-1) of mivacurium. Maximum effect (MAX), onset time, the 10%-25% recovery index, and duration of effect of mivacurium were determined by electromyography. In groups 2 and 3, the corrected MAX was defined as the difference between the actual MAX effect and the residual block after administration of succinylcholine, and speed of action was defined as the ratio between MAX or corrected MAX and onset time. Data were subjected to analysis of variance and Student-Newman-Keuls and t tests for bivariate comparisons. A value of P less than 0.05 was considered significant.

RESULTS

Groups 2 and 3 had significantly greater MAX effects (97% and 98%, respectively) in comparison with group 1 (93%), shorter onset times (135 and 158 seconds in groups 2 and 3 vs 279 seconds in group 1), and greater speed of action without changes in duration of effect. MAX was halved when corrected (to 47% and 49% in groups 2 and 3, respectively), and speed of action was significantly reduced (from 1.34 and 1.62 seconds/% in groups 2 and 3 respectively, to 2.69 and 3.36 seconds/%). Mivacurium pretreatment did not produce relevant clinical changes.

CONCLUSIONS

When mivacurium is used before the effects of succinylcholine disappear, a residual effect is not usually taken into consideration. This study corrected MAX and calculated speed of action, demonstrating a reduction in net block and speed of action, consistent with an antagonistic action when the 2 blockers are administered sequentially.

[Interaction of donepezil and muscular blockers in Alzheimer's disease]

A 75-years-old man with Alzheimer's disease, treated with the cholinesterase inhibitor donepezil for 14 months, was scheduled for left colectomy under general anesthesia. During the procedure, succinylcholine-induced relaxation was prolonged and the effect of atracurium besylate was inadequate even at higher doses than those indicated for the patient's weight. Cholinesterase blood tests performed 10 months, 1 month and 10 days before surgery had demonstrated a gradual decrease in the duration of activity of the enzyme. Such an effect, which has been described for cholinesterase inhibitors like neostigmine and donepezil, would explain the prolonged effect of succinylcholine. After ruling out other causes for resistance to atracurium, we conclude that donepezil or its metabolites acted on muscle plaque, blocking acetylcholine hydrolysis and antagonizing atracurium.

Acquired pseudocholinesterase deficiency after high-dose cyclophosphamide

Succinylcholine, a depolarizing neuromuscular blocking agent used in anesthesia is hydrolyzed in the plasma by the enzyme pseudocholinesterase (PSC). Conditions associated with reduced PSC activity lead to sustained action of succinylcholine and result in prolonged apnea. Cyclophosphamide is an inhibitor of PSC and its suppressive effect may be dose-dependent. We report a case of severe PSC deficiency after high-dose cyclophosphamide at 7 g/m2. The patient received succinylcholine during anesthesia 9 h after chemotherapy and developed prolonged apnea. This case highlights the potential risk of drug-induced PSC deficiency and cautions the use of depolarizing muscular relaxants soon after high-dose cyclophosphamide.

The effect of mivacurium pretreatment on intra-ocular pressure changes induced by suxamethonium

Forty patients without eye disease, undergoing elective nonophthalmic surgery, were studied in a double-blind, randomised, placebo-controlled study evaluating the efficacy of mivacurium pretreatment in attenuating the rise in intra-ocular pressure in response to suxamethonium administration, laryngoscopy and intubation. The patients were randomly allocated to receive either mivacurium 0.02 mg.kg-1 or normal saline as pretreatment 3 min before a rapid sequence induction technique using alfentanil, propofol and suxamethonium. Suxamethonium induced a significant increase in intra-ocular pressure in the control group but not in the mivacurium pretreatment group (mean (SEM) increase = 3.5 (1.2) mmHg vs. 0.4 (0.8) mmHg, p < 0.05). There was a decrease in intra-ocular pressure in both groups after laryngoscopy and intubation with no significant difference between the two groups. These results show that mivacurium pretreatment is effective in preventing the increase in intra-ocular pressure after suxamethonium administration.

Antagonism of suxamethonium-induced jaw muscle contracture in rats

Masseter muscle rigidity (MMR) induced during general anaesthesia by suxamethonium is a clinical problem that may interfere with tracheal intubation. We have investigated the relation between twitch tension and contracture response to suxamethonium in rats. Rats were anaesthetized with 1% halothane (1.35 MAC). Jaw muscle temperature was maintained at either 37 or 41 degrees C while rectal temperature was kept at 37 degrees C by radiant heat. Twitch tension was produced by nerve stimulation at 0.2 Hz. Rats were pretreated with either a low dose of vecuronium (0.03 mg kg-1) or dantrolene (0.8 mg kg-1). Thereafter suxamethonium 750 micrograms kg-1 was administrated i.v. Low-dose vecuronium pretreatment significantly (90%) decreased suxamethonium-induced jaw muscle contracture (JMC) with minimal (3%) twitch block during local hyperthermia. Low-dose dantrolene pretreatment also reduced JMC (81% at 37 degrees C and 82% at 41 degrees C) while decreasing twitch by 30% at 37 degrees C and 31% at 41 degrees C. Both vecuronium and dantrolene at doses that minimally depressed the twitch response antagonized suxamethonium-induced JMC. We speculate that pretreatment with low-dose vecuronium decreases suxamethonium-induced MMR clinically.

Comparison of rocuronium and mivacurium to succinylcholine during outpatient laparoscopic surgery

Tracheal intubating conditions and neuromuscular effects of succinylcholine, rocuronium, and mivacurium were studied in 100 healthy women undergoing outpatient laparoscopic surgery. After a standardized fentanyl-thiopental induction, tracheal intubation was facilitated with succinylcholine 1 mg/kg in Groups I (n = 23) and II (n = 25), rocuronium 0.6 mg/kg in Group III (n = 27), or mivacurium 0.2 mg/kg in Group IV (n = 25). If clinically indicated, bolus doses of rocuronium 5-10 mg (Groups I and III) or mivacurium 2-4 mg (Groups II and IV) were administered during the maintenance period. Anesthesia was maintained with desflurane and nitrous oxide 60% in oxygen. At the end of the surgery, residual neuromuscular block was reversed with edrophonium 0.5 mg/kg and atropine 10 micrograms/kg, if needed. The neuromuscular function was assessed using electromyography with a train-of-four mode of stimulation every 10 s at the wrist. Intubating conditions 90 s after succinylcholine and rocuronium were significantly better than after mivacurium. The onset time (from the end of injection until 95% suppression of the first twitch [T1]) for succinylcholine (63 +/- 21 s and 62 +/- 17 s in Groups I and II, respectively) were significantly shorter than for rocuronium (158 +/- 76 s) or mivacurium (210 +/- 93 s). Moreover, the onset times for rocuronium were significantly shorter than mivacurium. The recovery times (of T1 to 25% of the control value) were significantly shorter with succinylcholine and mivacurium than rocuronium. Significantly fewer patients needed reversal of residual neuromuscular blockade after mivacurium compared to rocuronium. One patient in Group I and six patients in Group IV displayed erythema on the upper body. Postoperative myalgia were experienced by 16% of the patients in Groups I and II compared to none in Groups III and IV. There was on difference in the incidence of postoperative nausea and vomiting among the four groups. In conclusion, rocuronium appears to be an acceptable alternative to succinylcholine for tracheal intubation. However, rocuronium's longer duration of action increases the need for reversal drugs. When rapid tracheal intubation is unnecessary, mivacurium is also an acceptable alternative to succinylcholine and is associated with a more rapid spontaneous recovery than rocuronium.

Effects of magnesium sulphate on suxamethonium-induced complications during rapid-sequence induction of anaesthesia

Twenty patients were studied in a double-blind manner to investigate whether magnesium sulphate, when given during a rapid-sequence induction of anaesthesia, lessens the side effects caused by suxamethonium. Patients were randomly allocated to two groups; equal volumes of either magnesium sulphate (40 mg.kg-1) or saline were given during rapid-sequence induction of anaesthesia, after thiopentone but before the administration of suxamethonium (1.5 mg.kg-1). The changes in the serum potassium concentration, the degree of muscle fasciculations and the presence of postoperative myalgia were recorded. The mean serum potassium concentration increased by 0.08 mmol.l-1 in the magnesium group and by 0.1 mmol.l-1 in the control group at 2 min after injection of suxamethonium; in neither group was there a significant increase from baseline values. The systolic blood pressure and heart rate increased in both groups after tracheal intubation. The incidence of fasciculations was significantly lower in the magnesium group. Magnesium did not clinically prolong muscle relaxation. There was no difference between the groups in the incidence of myalgia after surgery (one patient in each group). Since no significant increase in the serum potassium concentration was demonstrated, no assessment could be made of the effect of magnesium sulphate on the serum potassium concentration after administration of suxamethonium.

Effects of diltiazem on calcium ion translocation: a study on isolated frog rectus abdominis muscle

Diltiazem, a calcium channel blocker was studied to observe its effects on the acetylcholine contractile responses of isolated frog rectus abdominis muscle. This response was modified in a dual manner i.e., initial potentiation, followed by inhibition. Diltiazem may not have anticholinesterase like mechanism, as it potentiated the responses to both acetylcholine and succinylcholine. Rectus muscle preparation, incubated in calcium free frog Ringer, showed dose dependent inhibition of acetylcholine contractile responses by diltiazem. The study suggests that diltiazem inhibits calcium ion influx across receptor operated calcium channels and may also inhibit calcium ion release from intracellular structures.

Neuromuscular interactions between succinylcholine and esmolol in the rat

To study the neuromuscular interactions between succinylcholine (Sch) and esmolol, we determined the dose-response relationship of Sch and the neuromuscular actions of the 3xED90 dose of Sch, both prior to and following esmolol pretreatment. Twenty rats were anaesthetized with urethane. Train-of-four stimulation was applied every 12 s to the sciatic nerve, and the electromyogram (EMG) of the tibialis anterior muscle was measured. The results showed that the potency of Sch decreased with esmolol pretreatment. The ED50 of Sch increased significantly, from 191 ug/kg to 227 ug/kg after esmolol infusion, p < 0.05. The duration of EMG depression achieved by the 3xED90 dose of Sch decreased significantly with esmolol pretreatment (12 min vs 14 min p < 0.05), and also the onset time was significantly longer (43 sec vs 28 sec, p < 0.05). There were no significant difference between groups with regard to the maximal block or recovery index. The results of two methods of study demonstrated that the pharmacological interaction between Sch and esmolol is antagonistic instead of potentiating.

Curare modification of suxamethonium blockade

Tubocurare (0.125 mg.kg-1 or 0.25 mg.kg-1) was injected 10 s before 1 mg.kg-1 suxamethonium in patients anaesthetised with enflurane 1-1.5%. Measurement of electromyographic response was recorded using a 0.2 Hz train-of-four every 20 s. The modified blocks were slower in onset, of lesser intensity, and of shorter duration than that of suxamethonium alone, but were much closer to those of suxamethonium than of tubocurare. However, the train-of-four fade observed during onset of the modified blocks were similar to that of their tubocurare controls and significantly different from the suxamethonium group. We conclude that effective amounts of tubocurare are present in the neuromuscular junction within the 30 s following intravenous injection of the drugs, and this affects the onset of action of the suxamethonium block. The presence of train-of-four fade during a predominantly agonist block is difficult to explain on the basis of diminished acetylcholine release and a postsynaptic site of action of suxamethonium.

Neuromuscular interactions between suxamethonium and magnesium sulphate in the cat

In order to study the neuromuscular interactions between suxamethonium and magnesium sulphate (MgSO4), we have determined the dose-response relationship of suxamethonium and the neuromuscular actions of 1.25 x ED50 dose of suxamethonium, both before and after pretreatment with MgSO4. We have also compared the effect of 1.25 x ED50 dose of suxamethonium in the absence and in the presence of 50% neuromuscular block, established previously by infusion of MgSO4. Twenty-one cats were anaesthetized with urethane. Train-of-four stimulation was applied every 12 s to the sciatic nerve and the force of contraction of the tibialis anterior muscle was measured. The potency of suxamethonium decreased in each instance with pretreatment with MgSO4. The ED50 of suxamethonium increased significantly from mean 21.0 (SEM 1.9) micrograms kg-1 before MgSO4 to 25.6 (2.3) micrograms kg-1 after MgSO4 60 mg kg-1 and to 26.6 (2.2) micrograms kg-1 after MgSO4 90 mg kg-1 (P < 0.05). Twitch depression produced by 1.25 x ED50 dose of suxamethonium decreased significantly with MgSO4 pretreatment, from 76.7 (2.6)% before MgSO4 to 61.7 (6.4)% after MgSO4 60 mg kg-1 and 48.7 (7.5)% after MgSO4 90 mg kg-1 (P < 0.05). With stable 50% neuromuscular block, established previously by infusion of MgSO4, the 1.25 x ED50 dose of suxamethonium produced more twitch augmentation (133 (6.3)% vs 108.3 (1.3)%; P < 0.05) and less twitch depression (31.6 (9.6)% vs 74.1 (0.6)%, P < 0.05) than in the absence of MgSO4. The results of all three methods demonstrated that the pharmacological interaction between suxamethonium and magnesium was antagonistic.

Use of mivacurium during laparoscopic surgery: effect of reversal drugs on postoperative recovery

We studied the influence of mivacurium on the recovery profile following outpatient laparoscopic tubal ligation in 60 healthy, nonpregnant women. After administration of midazolam 2 mg intravenously (IV), anesthesia was induced with fentanyl, 2 micrograms/kg, and thiopental, 4 mg/kg, IV. When the patient became unresponsive (loss of eyelid reflex), either succinylcholine 1 mg/kg, IV (Group I), or mivacurium 0.2 mg/kg, IV (Groups II and III), was administered to facilitate tracheal intubation. Anesthesia was maintained with isoflurane (0.5%-2% inspired concentration) in combination with 67% N2O in oxygen. Muscle relaxation was maintained in all three groups with intermittent bolus doses of mivacurium, 2-4 mg, IV. In Group III, residual neuromuscular block was reversed with a combination of neostigmine, 2.5 mg, and glycopyrrolate, 0.5 mg, IV, at the end of the operation. In the postanesthesia care unit (PACU), patients in Group III had a significantly increased incidence of postoperative nausea and vomiting compared to Group II. The use of succinylcholine (versus mivacurium) was also associated with more frequent postoperative nausea and vomiting. However, these emetic sequelae did not delay postoperative recovery times. In addition, a comparable number of patients in each treatment group required analgesic medication for postoperative pain. Although patients who received succinylcholine complained of significantly more neck pain during the 24-h period after discharge, nausea, vomiting, and shoulder pain were similar in all three groups during this period. We conclude that neostigmine and glycopyrrolate may contribute to the development of postoperative emesis when used for reversal of residual neuromuscular block.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cholinesterase inhibitors on the neuromuscular blocking action of suxamethonium

Prolonged neuromuscular block occurs when suxamethonium is given after neostigmine or pyridostigmine; however, studies of edrophonium and suxamethonium have yielded conflicting results. We have studied, therefore, interactions between suxamethonium and all three anticholinesterases in rats anaesthetized with pentobarbitone. After recovery from an initial bolus of suxamethonium, saline, edrophonium, pyridostigmine or neostigmine was administered and a second dose of suxamethonium was then given. All three anticholinesterases prolonged the duration of neuromuscular block (90% suppression to 50% twitch recovery) to 127 (SEM 9)%, 127(10)% and 138 (11)% of baseline for edrophonium, pyridostigmine and neostigmine, respectively. Recovery index (25% to 75% twitch recovery) was increased also to 125 (9)%; 149 (10%) and 185 (15)% of baseline, respectively for the three drugs.

Interaction between succinylcholine and ranitidine in rats

The hypothesis that the histamine H2 receptor blocker ranitidine potentiates neuromuscular paralysis during anaesthesia was tested in vivo in urethane anaesthetised and mechanically ventilated rats. Succinylcholine was administered as a bolus and constant-rate infusion to maintain 48.5% (+/- 2.5 SEM) tibialis anterior muscle paralysis in 14 rats. Ranitidine 2.5, 5, 10, or 20 mg.kg-1 iv, was then administered into groups of three or five rats. Ranitidine produced an immediate potentiation of neuromuscular paralysis followed by a transient reversal and then a continued steady-state potentiation. Peak potentiation occurred within 20 (+/- 3.3) sec and was maintained in all the rats to steady-state. Peak reversal was evident 70 (+/- 8.1) sec after ranitidine administration. There was an excellent relationship (r2 = 0.98, P < 0.001) between peak potentiation and serum ranitidine concentration with 50% potentiation occurring at 25.8 (+/- 1.1) micrograms.ml-1. There was a weak relationship (r2 = 0.39, P < 0.05) between peak reversal and serum ranitidine but potentiation at steady-state was not correlated to serum ranitidine concentration (r2 = 0.19, P > 0.05). These results show that ranitidine alters the neuromuscular action of succinylcholine in rats in a similar manner to cimetidine.

Phenytoin reduces suxamethonium-induced myalgia

A prospective, randomised trial was undertaken in 60 healthy adults to determine the efficacy of intravenously administered phenytoin in doses of 5 mg.kg-1 for the prevention of suxamethonium-induced fasciculations, a rise in serum K+ and myalgia. This was compared with tubocurarine pretreatment and no pretreatment (control group). Phenytoin pretreatment significantly reduced myalgia from 45% (nine patients) in the control group to 10% (two patients) (p less than 0.05). It also decreased the duration and mean intensity of fasciculations. Incidentally, phenytoin was also found to decrease significantly mean serum Na+ levels (p less than 0.001) both at 5 and 20 min after administration. Tubocurarine pretreatment (3 mg) resulted in a significant decrease in fasciculations, but myalgia, which occurred in five patients, remained the same. No significant correlation was found between muscle fasciculations, postoperative myalgia and K+ changes, but patients with myalgia had a significant decrease in mean serum Na+ levels at 5 and 20 min after suxamethonium (p less than 0.01).

Alfentanil inhibits muscle fasciculations caused by suxamethonium in children and in young adults

The effect of alfentanil on suxamethonium-induced muscle fasciculations was studied in a double-blind study in 34 children (mean age 6.8 years) and in 30 adults (mean age 20 years). After pretreatment with either alfentanil 50 micrograms kg-1 or saline, each patient was anaesthetized with a sleep dose of thiopental followed by suxamethonium 1.5 mg kg-1 for endotracheal intubation. Compared to the control groups, alfentanil significantly decreased the intensity of visible muscle fasciculations caused by suxamethonium. In children, the duration of muscle fasciculations was shorter in the alfentanil than in the control group. In adults, the intensity rather than the duration of fasciculations was attenuated by alfentanil. The inhibition of fasciculations caused by alfentanil was also demonstrated in children in the surface electromyogram recorded on the biceps. There was no circulatory response to endotracheal intubation in the groups pretreated with alfentanil.

Pathogenesis of suxamethonium-induced muscle damage in the biventer cervicis muscle in the chick

Muscle damage induced by suxamethonium, and the influence of halothane on it, has been examined by measuring the efflux of creatine kinase (CK) in the biventer cervicis muscle of the chick. Whereas halothane and suxamethonium alone did not increase the enzyme efflux significantly, the combination of the two was associated with significant increase in the concentration of CK in the bathing medium by 59-157%. The increase in CK was prevented by adding chlorpromazine 100 mumol litre-1 to the medium, suggesting the involvement of phospholipases in the pathogenesis of suxamethonium-induced muscle damage.

Effects of neuroleptic agents on rat skeletal muscle contracture in vitro

The purpose of this investigation was to examine and compare the effects of both in vivo pretreatment and in vitro treatment with the neuroleptic agents droperidol, haloperidol, and trifluoperazine on skeletal muscle contracture using an in vitro model. Strips of normal rat diaphragm were challenged with succinylcholine and halothane (halothane: 1% and 3%) subsequent to either in vitro administration (10-100 microM) or in vivo pretreatment (0.35-2.80 mg/kg) with droperidol, haloperidol, or trifluoperazine. After equilibration, maximum increases in tension were recorded and mean data analyzed by analysis of variance (P less than 0.05). When either droperidol or trifluoperazine was administered in vivo, contracture values after exposure to succinylcholine and halothane were significantly decreased. After in vivo pretreatment with haloperidol or in vitro administration of droperidol, succinylcholine-induced contractures were significantly reduced; contractures subsequently induced by halothane did not significantly differ from that of controls. In vitro treatment with haloperidol and trifluoperazine, however, produced significant increases in tension in muscles exposed to succinylcholine and halothane. This study provides evidence that droperidol may be considered a safe anesthetic adjunct in malignant hyperthermia-susceptible patients, and, additionally, that caution should be exercised when interpreting results from studies in which contracture testing is performed on muscle from patients treated with neuroleptic agents.

Pretreatment with d-tubocurarine, vecuronium, and pancuronium attenuates succinylcholine-induced increases in plasma norepinephrine concentrations in humans

We studied in patients the effect of d-tubocurarine, which has sympathetic ganglion blocking action, on succinylcholine-induced increases in plasma levels of catecholamines, and compared it with the effects of vecuronium and pancuronium, which have little sympathetic ganglion blocking action. Thirty-two patients were divided into five groups: seven were given 3 mL saline; seven received 1 mg/kg succinylcholine; and six, seven, and five patients were given 0.08 mg/kg d-tubocurarine, 0.01 mg/kg vecuronium, and 0.01 mg/kg pancuronium, respectively, all of which were injected 5 min before 1 mg/kg succinylcholine. Succinylcholine alone significantly increased plasma norepinephrine concentrations, systolic blood pressure, and heart rate from 187 +/- 39 pg/mL (mean +/- SEM), 93 +/- 2 mm Hg, and 77 +/- 4 beats/min to 429 +/- 61 pg/mL, 120 +/- 7 mm Hg, and 102 +/- 6 beats/min, respectively, with onset of fasciculations. Pretreatment with d-tubocurarine, vecuronium, and pancuronium significantly and equally attenuated both the fasciculations and the cardiovascular responses to succinylcholine. These results suggest that the sympathetic ganglion blocking action of neuromuscular relaxants when given before succinylcholine is not an important factor in attenuation of succinylcholine-induced increases in plasma levels of catecholamines.

A defasciculating dose of d-tubocurarine causes resistance to succinylcholine

Forty-four patients, ASA physical status I or II, undergoing thiamylal, fentanyl, N2O/O2 anaesthesia were studied to determine the dose-response to succinylcholine (Sch) without prior defasciculation (24 pt - Group 1), or three minutes following d-tubocurarine (dTC), 0.043 mg.kg-1 (20 pt - Group 2). The individual log dose-logit response curve for each patient was determined using a cumulative dose plus infusion technique and integrated EMG monitoring of the first dorsal interosseous muscle. The mean (+/- SEM) ED50, ED90 and ED95 values for Sch in Group 1 were 0.13 +/- 0.01, 0.19 +/- 0.01 and 0.22 +- 0.01 mg.kg-1, and in Group 2 were 0.16 +/- 0.01, 0.25 +/- 0.01 and 0.29 +/- 0.02 mg.kg-1, respectively. The mean ED values in Group 2 were significantly greater than the equivalent values in Group 1 (P less than 0.05). Compared with values in Group 1, ED values in Group 2 represented mean increases of 23, 32, and 32 per cent, respectively. These pharmacodynamic data indicate that the dose of Sch needs to be increased by 32 per cent following a defasciculating dose of dTC 3 mg.70 kg-1 (0.043 mg.kg-1).

Selective antagonism to succinylcholine-induced depolarization by alpha-bungarotoxin with respect to the mode of action of depolarizing agents

1. The interactions of alpha-bungarotoxin or tubocurarine with the neuromuscular block and endplate depolarization induced by succinylcholine (SCh) in the phrenic nerve-diaphragm preparation of mice were studied in order to elucidate the role of depolarization by SCh in the neuromuscular blockade. 2. The SCh concentrations required to depress the indirect twitch response by 20% and the evoked endplate potential in cut muscle preparations by 80% were 10 microm and 6 microM, respectively, while only 2 microM SCh was needed to induce maximal endplate depolarization from -80 mV to about -60 mV. 3. SCh blocked the neuromuscular transmission synergistically with either alpha-bungarotoxin or tubocurarine. There was an initial partial reversal of the neuromuscular inhibition caused by tubocurarine, but not that by alpha-bungarotoxin. 4. alpha-Bungarotoxin (0.025 microM) antagonized SCh (10 microM)-induced depolarization more effectively than it depressed miniature endplate potentials and the antagonism was insurmountable by increasing SCh concentration. By contrast, tubocurarine preferentially depressed miniature endplate potentials and antagonized SCh-depolarization competitively. 5. The above difference was attributed to the irreversible nature of alpha-bungarotoxin binding to acetylcholine receptors, to the slow diffusion of the toxin molecule into the synaptic cleft and thus to the more rapid binding with perijunctional receptors compared with junctional ones. 6. It is concluded that the sustained depolarization of the endplate by SCh results largely from an action on the perijunctional receptor in mice and, unlike cats, the neuromuscular block by SCh is not due to the depolarization per se but rather to a direct attenuation of endplate potential.

[Suppression by pancuronium and tubocurarine of the afferent discharge of the muscle spindle induced by succinylcholine]

Effect of pancuronium on the increased afferent discharge of the muscle spindle induced by succinylcholine (SCC) (Succinylcholine induced discharge, SID) was studied in the decerebrate cat by recording the discharge of the muscle nerve going to the gastrocnemius muscle. This action of pancuronium was compared with that of tubocurarine and the antagonistic action if any by neostigmine of this action of pancuronium and tubocurarine was also studied. Pancuronium 0.025 or 0.05mg.kg-1 reduced the peak values of SID to 25.2% and 6.8% of the control value respectively. Tubocurarine 0.125mg.kg-1 reduced this to 38.2%. Inhibition of the SID by pancuronium or tubocurarine was not reversed by the administration of neostigmine. Thus pancuronium reduced SID depending on its dose. The ability of pancuronium and tubocurarine to suppress SID is related to their neuromuscular blocking effects, but the failure by neostigmine to reverse this action of pancuronium or tubocurarine might suggest a different type of reaction at the acetylcholine receptor of the intrafusal fiber compared with the one at the acetylcholine receptor of the skeletal muscle.

Effect of diltiazem on porcine malignant hyperpyrexia induced by suxamethonium and halothane

We have studied the ability of the calcium channel antagonist diltiazem to inhibit and reverse the porcine malignant hyperpyrexia (MH) syndrome. Pretreatment with diltiazem modified an MH response. Treatment with diltiazem was partially effective against a mild (or early) MH response. Diltiazem should not be considered to be an effective therapeutic agent for MH and should not displace the use of dantrolene.

Sensitivity to dicholines of membranes from vertebrate and invertebrate muscles

1. The depolarizing effectiveness of azelainylcholine (AzCh, a 7-C-chain dicholine) is about 10 times higher than that of succinylcholine (SCh, a 2-C-chain dicholine) in skeletal muscles of chick, frog and fish, and in body muscles of the earthworm. 2. In the chicken anterior latissimus dorsi (ALD) muscle, AzCh is about 100 times more effective than SCh. 3. In contrast to that in mammalian muscles, the AzCh-SCh sensitivity difference is not increased by denervation in frog muscles. 4. d-Tubocurarine is equally effective in the ALD and in other chicken muscles; its effectiveness is not decreased by denervation in frog muscles. 5. Cells containing muscarinic acetylcholine receptors are weakly sensitive to dicholines or not at all.

Failure of lidocaine to modify suxamethonium induced biochemical changes

Twenty patients were studied in a prospective double-blind randomized trial to determine the effects of intravenous lidocaine pretreatment on suxamethonium induced biochemical changes. Lidocaine 1 mg. kg-1 failed to attenuate changes in serum potassium, significantly decreased serum calcium, and prolonged duration of suxamethonium blockade. There were no significant changes in plasmacholinesterase activity or other biochemical parameters. It is concluded that pretreatment with 1 mg. kg-1 lidocaine failed to attenuate suxamethonium induced biochemical changes.

Pharmacologic evaluation and structure activity relationships of a series of hemicholinium-3 (HC-3) analogs

Piperidine derivatives of hemicholinium-3 were synthesized, which included the following spacing groups between cationic heads: trans-trans-bicyclohexyl, phenanthrene, naphthalene, and biphenyl. Relatively minor structural alterations in these series of compounds resulted in several different types of pharmacological actions related to cholinergic transmission. Structural requirements of the compounds are discussed and include internitrogen distance, structural planarity, spacing groups, and positional isomerism of the quaternary cationic heads. Selected quaternary piperidine derivatives with 14 A inter-atomic distance between the cationic heads exhibit potent HC-3 like activity which is enhanced if a molecule has a nonpolar space filling group (4-methyl piperidine) approximately 3.7 A from the corresponding quaternary cationic head. With selected piperidine ring substitutions, active tertiary amines were also identified. Compounds containing C = O in the spacing moiety were active inhibitors of cholinesterase with some derivatives being nearly as active as physostigmine. When the C = O moiety was reduced to -CH2 and a 2 or 3-CH3 piperidine ring was present, potent non-depolarizing, short acting neuromuscular blocking agents were obtained.

Prolonged infusion of suxamethonium in infants and children

The neuromuscular blockade produced by a prolonged (greater than 90 min) continuous infusion of suxamethonium and measured with train-of-four stimulation was studied in 20 infants and 20 children during nitrous oxide and halothane in oxygen anaesthesia. The results were compared with a previous study in adults. Suxamethonium requirement was increased in infants and children. Mean peak infusion rates were 297 and 284 micrograms kg-1 min-1 in infants and children, compared with 134 micrograms kg-1 min-1 in adults. An initial tachyphylaxis was followed by bradyphylaxis, and the peak requirement occurred earlier in infants than in children and adults (40 v. 80-100 min). Phase II block developed during the tachyphylaxis. Recovery of neuromuscular activity commenced after stopping the infusion and was accelerated with neostigmine.

Succinylcholine, fasciculations and myoglobinaemia

The prophylactic effectiveness of a small "self-taming" dose of succinylcholine (0.1 mg X kg-1), of d-tubocurarine (0.05 mg X kg-1), and of pancuronium (0.02 mg X kg-1) on succinylcholine-induced fasciculations and myoglobinaemia was studied in 64 healthy children (ages two to nine years), anaesthetized with halothane, nitrous oxide and oxygen. Serum myoglobin was analyzed by radioimmunoassay and taken as a tracer of muscle damage. No correlation was found between the serum levels of myoglobin and the incidence of muscle fasciculations. Self-taming with succinylcholine decreased the incidence of fasciculations (p = 0.001) but did not decrease the succinylcholine-induced myoglobinaemia (p = 0.224). D-tubocurarine (0.05 mg X kg-1) and pancuronium (0.02 mg X kg-1) both significantly reduced the myoglobinaemia and the fasciculations produced by succinylcholine. The pancuronium pretreated group presented less variable values of serum myoglobin which, when compared to the control group, had a more significant p value (p less than 0.001) than for d-tubocurarine pretreated group (p = 0.003). Muscle fasciculations and increased myoglobin levels were observed in children less than four years old who received succinylcholine. The prophylaxis of acute rhabdomyolytic renal failure due to succinylcholine (seven cases reported in the medical literature) is considered.

Antagonism of phase II succinylcholine block by neostigmine

The neuromuscular effect of neostigmine, 1.25 mg/70 kg, was assessed in 40 adult patients 10 min after cessation of a succinylcholine infusion. The patients had received a thiopental-nitrous oxide anesthetic supplemented by halothane or fentanyl during which they were given at least 5 mg/kg succinylcholine over more than 90 min. Train-of-four monitoring was used. Neostigmine accelerated recovery of neuromuscular function in all patients. The degree of recovery was directly related to the train-of-four ratio, and the results in patients who had received halothane were no different from those who had received fentanyl. The findings are compatible with the hypothesis that phase I block depends upon the presence of circulating succinylcholine and decreases as the latter is cleared, whereas phase II block decreases more slowly. Thus succinylcholine block can be antagonized by neostigmine if enough time is allowed for phase I block to disappear and for a pure phase II block to be present.

The effect of diazepam pretreatment on the succinylcholine-induced rise in intraocular pressure

The influence of diazepam on some adverse effects of succinylcholine was studied double-blind. Thirty patients (ASA I-II) were allocated to groups receiving either diazepam 0.08 mg/kg or d-tubocurarine 0.05 mg/kg 5 min before a bolus of succinylcholine, 1 mg/kg and 1.5 mg/kg, respectively. Fasciculations were more frequent in the diazepam group (80%) than in the d-tubocurarine group (13%). Relaxation, onset and duration of neuromuscular blockade were comparable in the two groups. The rise in intraocular pressure after succinylcholine and endotracheal intubation was small (0.27 kPa = 2 mmHg) but significant (P less than 0.01) after diazepam pretreatment. In this group the rise in intraocular pressure was 50% lower than the rise seen in the d-tubocurarine group (P less than 0.01). We conclude that pretreatment with diazepam 0.08 mg/kg will reduce but not prevent a rise in the intraocular pressure after succinylcholine in a rapid sequence induction. In the management of patients with penetrating eye injuries the use of succinylcholine still carries some risk even after diazepam pretreatment.

Effects of suxamethonium on CO2-production

Eighteen patients undergoing alloplastic surgery of the hip were divided into three groups, each consisting of six patients. All operations were performed under endotracheal intubation using halothane N2O-O2 anaesthesia. After a steady state as to CO2-production had been obtained, suxamethonium 1 mg kg-1 was given intravenously to the patients in Group I. A maximum rise in CO2-production of 14.8% (range: 12.9-16.8) was observed after 5 min. In Group II, patients were pretreated with pancuronium 0.01 mg kg-1: no increase in CO2-production was observed. The third group received a continuous infusion of suxamethonium. In this group there was an increase in CO2-production of 17.6% (range: 6.7-22.0) 5 min after start of infusion. The CO2-production then fell to the preinfusion level over the next 10 min.

Pattern of CNS recovery following reversal of neuromuscular blockade. Comparison of atropine and glycopyrrolate

Recovery from anaesthesia was compared, in a group of patients (n = 25) receiving a mixture of glycopyrrolate and neostigmine (to reverse non-depolarizing neuromuscular blockade), with recovery in a group of patients (n = 25) receiving an atropine-neostigmine mixture. Recovery following anaesthesia was more rapid in the patients receiving the glycopyrrolate-neostigmine mixture.

Cardiovascular effects of nondepolarizing relaxants employed for pretreatment prior to succinylcholine

A pregnant woman with severe pre-eclampsia experienced a hypertensive crisis following a pretreatment dose (20 mg) of gallamine. That episode initiated a study to determine the cardiovascular effects of non-depolarizing muscle relaxants in 58 nonobese, ASA physical status I and II adults. Subjects were assigned randomly to one of five treatment groups as follows: gallamine (0.29 mg X kg-1), d-tubocurarine (0.04 mg X kg-1), metocurine (0.014 mg X kg-1), pancuronium (0.007 mg X kg-1), or normal saline (control). Baseline measurements of systolic, diastolic, mean arterial pressure, heart rate (HR) and rate pressure product (calculated RPP) were recorded at one-minute intervals while electrocardiogram, lead II, was recorded continuously. Statistically significant increases occurred in HR at minutes 2, 3 and 4; RPP at minutes 3 and 4; and per cent change in HR at minutes 2, 3 and 4 following gallamine pretreatment. The rise in RPP was predominantly due to the elevation in HR. These results suggest that even modest doses of gallamine should be avoided in clinical situations where lability of cardiovascular dynamics can be anticipated.

Five non-depolarizing muscle relaxants in precurarization

Five different non-depolarizing muscle relaxants and a control solution of saline were studied as precurarization agents. Two hundred and twenty-two surgical patients (ASA I-II) were allocated in a double-blind fashion to one of the following groups: d-tubocurarine 0.05 mg/kg, alcuronium 0.03 mg/kg, pancuronium 0.01 mg/kg, gallamine 0.25 mg/kg, ORG NC-45 (vecuronium) 0.01 mg/kg and saline solution 0.005 ml/kg. Pretreatment was performed 4 min before administering a 1.5 mg/kg bolus of succinylcholine (SCh). Fasciculations, intubation conditions, duration of neuromuscular blockade after SCh, serum potassium changes and postoperative myalgias (in 60 patients) were recorded. All the drugs studied prevented fasciculations significantly (P less than 0.05) more than in the control group. d-Tubocurarine and alcuronium were superior to the others in this respect. Intubation conditions were best in the control and pancuronium groups, but there was no significant difference between the pancuronium and d-tubocurarine or between the d-tubocurarine and alcuronium groups. Pancuronium pretreatment prolonged the SCh block significantly, whereas other agents shortened the duration of the SCh block. The antagonism of the SCh block apparently also affected intubation conditions, although intubation remained satisfactory. A statistically significant rise in serum potassium level was measured only in the control and pancuronium groups. In the control and pancuronium groups, four patients out of 10 had postoperative myalgias, whereas in the other groups only one or none out of 10 had them (0/10 vs. 4/10; 0.10 greater than P greater than 0.05). In conclusion, d-tubocurarine and alcuronium seem to have advantages over pancuronium, ORG NC-45 and gallamine for precurarization.

Neostigmine antagonism of succinylcholine phase II block: a comparison with pancuronium

To assess the efficacy of neostigmine antagonism of succinylcholine phase II block, succinylcholine infusions were given to 17 patients for durations varying from 44 to 192 minutes. A control group (17 patients) received a pancuronium infusion for similar times. Ninety per cent neuromuscular block was maintained in these two groups by adjustment of the infusion rates and, in a third group, with intermittent doses of pancuronium. Neuromuscular transmission was monitored with train-of-four stimulation every 12 seconds and anaesthesia was maintained with N2O-O2-enflurane. Ten minutes after the infusion was stopped, atropine and neostigmine were given to all patients who received pancuronium and to 11 patients in the succinylcholine group whose train-of-four ratio (T4/T1) was less than 0.7. During the subsequent 15 minutes, recovery was more rapid in the succinylcholine group than in either the pancuronium-infusion or pancuronium-bolus groups. It is concluded that succinylcholine-induced phase II block can be safely and rapidly antagonized with neostigmine.

The heart rate response to succinylcholine in children: a comparison of atropine and glycopyrrolate

To determine whether intravenous atropine and glycopyrrolate are equally effective in preventing succinylcholine-induced heart rate changes, we studied the heart rate during the first 78 seconds of anaesthesia in 40 children anaesthetized with either thiopentone, atropine (0.02 mg X kg-1) and succinylcholine (2 mg X kg-1), or thiopentone, glycopyrrolate (0.01 mg X kg-1) and succinylcholine (2 mg X kg-1). Each treatment group was divided into four subgroups which differed only in the interval (6, 10, 15, 20 seconds) between injection of atropine or glycopyrrolate and succinylcholine. During the 54 seconds after succinylcholine, the mean heart rate of each subgroup decreased transiently and then returned to the pre-induction heart rate or higher. There was no difference in either the magnitude or the duration of the decrease in heart rate or the subsequent increase in heart rate between respective subgroups. Bradycardia occurred in only two patients, both of whom received glycopyrrolate. We conclude that atropine (0.02 mg X kg-1) and glycopyrrolate (0.01 mg X kg-1) are equally effective in attenuating succinylcholine-induced changes in heart rate in children.

Failure of diazepam to prevent the suxamethonium-induced rise in intra-ocular pressure

The effects of intravenous suxamethonium chloride (1 mg/kg) on intra-ocular pressure (IOP) were studied following pretreatment with diazepam 0.05 mg/kg, tubocurarine 0.05 mg/kg, and in a control group, at induction of anaesthesia. In all three groups, a significant increase in IOP was seen during the induction sequence. In a further study, the effects of intravenous suxamethonium chloride (1 mg/kg) on IOP were studied following a period of stable general anaesthesia and pretreatment with diazepam 0.05 mg/kg. A significant rise in IOP was again seen following the administration of suxamethonium. The authors conclude that neither of the techniques described herein will reliably and predictably prevent the rise in IOP seen following the use of suxamethonium.

Chronotropic effects of succinylcholine and succinylmonocholine on the sinoatrial node

The mechanism of bradycardia caused by the administration of succinylcholine has not been fully elucidated. Accordingly, the effects of succinylcholine and succinylmonocholine on the sinoatrial node were studied in 35 mongrel dogs. The sinus node artery was selectively perfused with autologous blood from a femoral artery at a constant pressure of 100 mmHg, and 30 to 1,000 micrograms of succinylcholine or succinylmonocholine was administered directly into the artery. Succinylcholine caused a transient (63-600 s) dose-related positive chronotropic effect. The heart rate was increased to 14.4 +/- 2.1% (mean +/- SE) above the control value after the administration of 1,000 micrograms of succinylcholine. This positive chronotropic effect was inhibited by pretreatment with pindolol or reserpine. By contrast, succinylmonocholine produced a transient (30-248 s) dose-related negative chronotropic effect. The heart rate was decreased to 17.5 +/- 1.4% below the control value after administration of 1,000 micrograms of succinylmonocholine. The negative chronotropic effect was blocked partially by atropine. It was concluded that the positive chronotropic effect of succinylcholine may be mediated through beta-adrenergic receptor stimulation by catecholamine released from the adrenergic nerve endings in the sinoatrial node, and that the negative chronotropic effect of succinylmonocholine may be the result of excitation of cholinergic receptors in the sinus node. However, a direct effect of succinylmonocholine on the sinus node could not be ruled out.