Succinylcholine, cholinoceptors and catecholamines: proposed mechanism of early adverse haemodynamic reactions

Succinylcholine: adverse effects and alternatives in emergency medicine

Succinylcholine has long been the favored neuromuscular blocking agent for emergent airway management because of its rapid onset, dependable effect, and short duration. However, it has a plethora of undesirable side effects, ranging from the inconsequential to the catastrophic. When patients requiring tracheal intubation present with potential contraindications to succinylcholine use, the emergency physician will need to substitute a rapid-onset nondepolarizing neuromuscular blocking agent, such as rocuronium or mivacurium. An understanding of the pharmacology of these agents is essential.

Succinylcholine induced hyperkalemia and cardiac arrest death related to an EEG study

Changes in EEGs during cardiac arrest have been described in detail by many authors; however, mortality because of an EEG has never been reported. The authors report the case of a patient who developed cardiac arrest causally related to administration of succinylcholine for reduction of excessive amounts of myogenic artifact during an EEG. This case indicates the need for caution when doing an EEG study in an intensive care unit setting.

Lower oesophageal sphincter tone increases after induction of anaesthesia in pigs with full stomach

PURPOSE

The lower oesophageal sphincter (LOS) is the man mechanism that prevents gastro-oesophageal regurgitation during anaesthesia. The aim of this study was to assess the effect on lower oesophageal sphincter pressure (LOSP) of rapid sequence induction in pigs with full stomachs.

METHODS

Lower oesophageal sphincter pressure and oesophageal barrier pressure (BrP = LOSP minus gastric pressure) were measured using a water-perfused manometric catheter method in 12 pigs after gastric filling with 500 ml of liquid nutrient mixture. Six pigs were randomly allocated to receive 5 mg.kg-1 propofol and 3 mg.kg-1 succinylcholine i.v. and six pigs received 8 mg.kg-1 thiopentone and 3 mg.kg-1 succinylcholine i.v.

RESULTS

After induction, mean LOSP increased during the period with fasciculations from 19 +/- 4 mmHg to 28 +/- 5 mmHg in the propofol-succinylcholine group and from 23 +/- 6 mmHg to 36 +/- 7 mmHg in the thiopentone-succinylcholine group. The LOSP remained elevated after the fasciculations. LOSP and BrP were not different between the groups.

CONCLUSIONS

Induction of anaesthesia with propofol-succinylcholine or thiopentone-succinylcholine increases LOSP and, consequently, BrP in pigs with a full stomach. This increase begins before fasciculations and remains elevated for the period when intubation would occur.

Evaluation of the effects of mivacurium chloride on hemodynamics and left ventricular function in patients with coronary artery disease undergoing abdominal aortic surgery

OBJECTIVE

To determine the effects of two doses of mivacurium chloride on hemodynamics and left ventricular function in patients with documented coronary artery disease undergoing aortic surgery.

DESIGN

A prospective study with the dose of mivacurium determined by randomization.

SETTING

Induction area at a university hospital.

PARTICIPANTS

Twenty consecutive patients undergoing aortic surgery with clinically and/or angiographically documented coronary artery disease.

INTERVENTIONS

Intravenous administration of mivacurium chloride.

MEASUREMENTS AND MAIN RESULTS

Induction of anesthesia was performed with midazolam and fentanyl. Two different doses of mivacurium chloride, 0.15 mg/kg (n = 10) and 0.2 mg/kg (n = 10; 2 and 2.5 ED95; respectively), were administered as a single bolus injection over a 60-second period in the absence of any surgical stimulation. In addition to standard hemodynamic monitoring, pulmonary artery catheterization and transesophageal echocardiography were used. The occurrence of myocardial ischemia was monitored using both a computerized three-lead ST-segment analysis system and the echocardiographic assessment of regional wall motion. No change in heart rate, mean arterial pressure, pulmonary capillary wedge pressure, cardiac output, and global left ventricular function was noted after administration of mivacurium with the two doses studied. No ST-segment change or new segmental wall motion abnormality was noted in either group.

CONCLUSION

Mivacurium chloride, when injected over a 60-second period, preserves global and regional myocardial function in patients with documented coronary artery disease undergoing noncardiac surgery.

Should the routine use of atropine before succinylcholine in children be reconsidered?

It is common practice to administer atropine before a first dose of succinylcholine in infants and children. However, the administration of succinylcholine without atropine has not been investigated in children. This study was designed to compare cardiovascular changes after the administration of either atropine with succinylcholine or succinylcholine alone. In 41 ASA I or II patients aged from 1 to 12 yr anaesthesia was induced with thiopentone 5 mg.kg-1. Patients were randomly allocated to receive either atropine 20 micrograms.kg-1 and succinylcholine 1.5 mg.kg-1 (n = 20) or succinylcholine 1.5 mg.kg-1 alone (n = 21). Heart rate and rhythm were recorded continuously from two minutes before induction until two minutes after tracheal intubation. Blood pressure was measured non-invasively before and after induction of anaesthesia and both immediately and two minutes after laryngoscopy. One self-limiting episode of bradycardia was recorded during laryngoscopy in a child who received atropine. Heart rate increased in both groups compared with baseline values (108 +/- 25), with a greater increase in patients who had received atropine (150 +/- 13) than in those who had not (128 +/- 18) (P < 0.05). There was no difference in mean arterial pressure or incidence of arrythmias between the two groups. No recorded arrythmias were judged to be clinically important by a cardiologist. The incidence of bradycardia after succinylcholine in the absence of atropine in children aged from 1 to 12 yr appears to be lower than previously estimated. The use of atropine before a single dose of succinylcholine in children deserves to be reconsidered.

It is not necessary to administer more than 10 micrograms.kg-1 of atropine to older children before succinylcholine

It is common practice at the Hospital for Sick Children, Toronto, to administer atropine 20 micrograms.kg-1 prior to succinylcholine in infants and children. It is unclear whether "prophylactic" administration of this dose of atropine to older children (6-16 yr) is necessary. This study was designed to compare the changes in heart rate, rhythm and mean arterial pressure after administration of either atropine 10 or 20 micrograms.kg-1 with succinylcholine or vecuronium (control group) to older children anaesthetized with thiopentone. Thirty-six ASA I or II patients (6-16 yr) were studied. Anaesthesia was induced with thiopentone 5 mg.kg-1. Patients were randomly assigned to receive: (a) atropine 10 micrograms.kg-1 and succinylcholine 1.5 mg.kg-1 (n = 12), (b) atropine 20 micrograms.kg-1 and succinylcholine 1.5 mg.kg-1 (n = 13) or (c) vecuronium 0.1 mg.kg-1 (n = 11) to facilitate tracheal intubation. Heart rate and rhythm were recorded continuously using a computerised analogue interface whereas blood pressure was monitored non-invasively before induction of anaesthesia, immediately before and at one and three minutes after laryngoscopy. No difference was observed between patients who received atropine 10 or 20 micrograms.kg-1 prior to succinylcholine. No episode of sinus bradycardia occurred. Premature atrial contractions were observed in two patients (one succinylcholine/atropine 20 micrograms.kg-1, one vecuronium). Administration of atropine 20 micrograms.kg-1 prior to succinylcholine provides no advantage over atropine 10 micrograms.kg-1 in older children in terms of cardiovascular stability.

Adverse effects of depolarising neuromuscular blocking agents. Incidence, prevention and management

Muscle relaxants block neuromuscular transmission, acting at nicotinic acetylcholine receptors of the neuromuscular junction. Suxamethonium (succinylcholine) is a depolarising agent, whereas all other relaxants in clinical use are nondepolarising. The desired neuromuscular block results from the structural similarity of muscle relaxants to acetylcholine, enabling the interaction with receptors at the neuromuscular junction. Adverse effects of suxamethonium are generally related to its agonist mode of action. Autonomic cardiovascular effects may result. Other adverse effects include anaphylactic or anaphylactoid reactions, and histamine release. Various disease states may present specific considerations in the use of muscle relaxants. Although many complications of muscle relaxants (such as prolonged block or resistance) are easily treated, others may require immediate intervention and vigorous therapy. Careful selection of appropriate relaxants for particular patients will usually prevent the occurrence of complications.

Combined effects of succinylcholine and calcium on membrane-bound acetylcholinesterase activity

The effects of succinylcholine and calcium (Ca2+), alone and together, on membrane-bound acetylcholinesterase ("true-type" cholinesterase) were examined using human erythrocyte ghosts to elucidate the combined pharmacological activity of succinylcholine and calcium in in vivo system. Succinylcholine inhibited the acetylcholinesterase by a mixed style. Calcium alone exhibited an inhibitory effect on the enzyme, but a biphasic effect together with succinylcholine: marked restoration of the enzyme activity at calcium concentrations lower than 6 mM and depression at its higher concentrations. It is suggested that calcium induces a conformational change of the enzyme protein leading to the altered binding capacity of succinylcholine. In anesthetic practice, therefore, the use of calcium may not be indicated for the treatment of SCh phase II block.

Clinical pharmacology of muscle relaxants in patients with burns

Pathophysiologic changes accompanying burn trauma can alter the pharmacokinetics and pharmacodynamic responses to neuromuscular relaxants. Pathophysiologic changes that can potentially affect kinetics in the hypermetabolic phase of burn injury include increased hepatic blood flow, increased glomerular filtration, and increased protein binding. Except for D-tubocurarine, the pharmacokinetics of neuromuscular relaxants relative to burn trauma have not been studied. The unbound volume of distribution, clearance, and half-life of D-tubocurarine were not significantly different from controls, but the plasma binding and renal elimination at 24 hours was increased in burn patients. The aberrant pharmacodynamic responses to neuromuscular relaxants in burn patients include the potential for lethal hyperkalemia with the administration of depolarizing relaxant, succinylcholine, and a 2.5- to 5.0-fold increase in the dose or plasma concentration requirement for nondepolarizing relaxant, including D-tubocurarine, metocurine, pancuronium, and atracurium. The altered pharmacodynamic responses are probably related to an increase in nicotinic acetylcholine receptor number. An alternative to succinylcholine to produce rapid-onset neuromuscular paralysis include the administration of 3XED95 doses of pancuronium and metocurine in combination (but recovery from paralysis is prolonged). Vecuronium and atracurium have good cardiovascular stability and faster recovery times even in high dosages in healthy patients, but the pharmacokinetics and pharmacodynamics of these drugs in patients with burns have not been fully characterized.

Contribution of muscle relaxant to the haemodynamic course of high-dose fentanyl anaesthesia: a comparison of pancuronium, vecuronium and atracurium

To define the role of muscle relaxants in haemodynamic responses to high-dose (75 micrograms X kg-1) fentanyl anaesthesia and to noxius stimuli associated with intubation and sternal spread during coronary artery bypass surgery, we compared haemodynamics between three groups of patients given either pancuronium (0.1 mg X kg-1, n = 11), vecuronium (0.086 mg X kg-1, n = 11) or atracurium (0.43 mg X kg-1, n = 12). Additional doses of the relaxants were given to maintain a 90 per cent neuromuscular block. Patients given pancuronium showed no increases in mean values of heart rate, arterial pressure or cardiac output during the induction of anaesthesia or after intubation, whereas a decrease in these variables was observed in the vecuronium group. The haemodynamics in the atracurium group were intermediate compared with the other two study groups. In spite of a decrease in coronary perfusion pressure, no patient given vecuronium developed myocardial ischaemia. An advantage of vecuronium over pancuronium and atracurium was an attenuation of the blood pressure response to sternotomy. Patients given atracurium had a small increase in pulmonary vascular resistance during sternotomy. Our patients continued their beta-adrenergic antagonist medication until the morning of the day of operation and they were pretreated with a small intravenous dose of diazepam (0.1 mg X kg-1) before induction of anaesthesia. These drugs may have prevented the deleterious haemodynamic effects observed by some investigators after the administration of pancuronium during high-dose fentanyl anaesthesia.