Doxacurium and mivacurium do not trigger malignant hyperthermia in susceptible swine

Anesthesia for patients with a history of malignant hyperthermia

PURPOSE OF REVIEW

Malignant hyperthermia-susceptible patients have an increased risk during anaesthesia. The aim of this review is to present current knowledge about pathophysiology and triggers of malignant hyperthermia as well as concepts for safe anaesthesiological management of these patients.

RECENT FINDINGS

Trigger substances and mechanisms have been well defined to date. Anaesthesia can be safely performed with i.v. anaesthetics, nitrous oxide, nondepolarizing muscle relaxants, local anaesthetics as well as xenon. Attention must be directed to the preparation of the anaesthetic machine because modern workstations need longer cleansing times than their predecessors. Alternatively, activated charcoal might be beneficial for elimination of volatile anaesthetics. Day case surgery can be performed in malignant hyperthermia-susceptible patients, if all safety aspects are regarded. Whether there is an association between malignant hyperthermia susceptibility and other disorders is still a matter of debate.

SUMMARY

The incidence of malignant hyperthermia is low, but the prevalence can be estimated as up to 1: 3000. Because malignant hyperthermia is potentially lethal, it is relevant to establish management concepts for perioperative care in susceptible patients. This includes preoperative genetic and in-vitro contracture testing, preparation of the anaesthetic workstation, use of nontriggering anaesthetics, adequate monitoring, availability of sufficient quantities of dantrolene and appropriate postoperative care. Taking these items into account, anaesthesia can be safely performed in susceptible patients.

New neuromuscular blocking drugs

The new nondepolarizing neuromuscular blocking drugs have specific advantages over succinylcholine. Rocuronium has an onset of action that is almost as rapid as that of succinylcholine and may be useful in patients with residual gastric contents. This drug may replace vecuronium, since the two agents are otherwise similar. The onset of action of mivacurium is similar to that of atracurium, but recovery from the blockade is more rapid (if the plasma cholinesterase level is normal), making mivacurium useful for short procedures. Although pipecuronium and doxacurium have minimal effects on the cardiovascular system, their long and variable onset and duration of action limit their usefulness. The need for either drug is questionable. There is still a need, however, for a nondepolarizing drug that has an onset of action as rapid as that of succinylcholine but a duration of action similar to that of mivacurium, with no adverse cardiovascular effects and clearance from the body that is independent of organ function.

Neuroleptic malignant syndrome and mivacurium: a safe alternative to succinylcholine?

Neuroleptic malignant syndrome (NMS) and malignant hyperthermia (MH) may have a common pathogenic mechanism; therefore, it has been suggested that known triggering agents for MH (such as succinylcholine) should be avoided in patients with NMS. Electroconvulsive therapy (ECT) continues to play a major therapeutic role in contemporary psychiatry, and succinylcholine has been the muscle relaxant of choice in attenuating violent muscle contractions induced by ECT. Mivacurium is a non-depolarizing muscle relaxant with a relatively rapid onset and a short duration of action, and to date it has been proved safe in MH-susceptible patients. In this case report, following succinylcholine use during ECT, a patient with NMS developed an increase in temperature and serum creatine kinase (CK) level, possibly due to an MH reaction. Since the patient's mental status necessitated further ECT, mivacurium was administered during subsequent treatment and resulted in effective attenuation of muscle contractions without elevation of patient temperature or CK levels. In addition, there was no marked prolongation of the anaesthetic. Mivacurium is a suitable agent for patients with NMS undergoing ECT, as it has not been associated with precipitation of an MH response.

Neuromuscular Blocking Agents

Neuromuscular blocking (NMB) agents are frequently used in the operating room (OR) as well as the intensive care units. The number of NMB agents available for use in these areas continues to increase. The clinician currently has 10 agents from which to choose, with another (rocuronium) soon to be available. NMB agents are classified as either depolarizing or nondepolarizing. Succinylcholine is the only depolarizing agent in clinical use today. It has the fastest onset of action of all NMB agents, but also the most adverse effects. The nondepolarizing agents as a group can be further differentiated by several characteristics: duration of action, cardiovascular effects, routes of metabolism/excretion, and cost. This allows an agent to be chosen based on patient parameters. Acetylcholinesterase inhibitors can be used to reverse residual neuromuscular blockade. The introduction of agents such as mivacurium, with a short duration of action, may reduce the need for acetylcholinesterase inhibitors; instead, neuromuscular function can be allowed to recover spontaneously. Finally, several factors must be considered when determining whether to add an agent to formulary: surgical case mix, patient acuity, agents currently on formulary, and cost of the new agent compared with those already on formulary.