Suxamethonium-induced fasciculation or increased muscle tone can be dangerous in patients with fractures or dislocations (especially vertebral, when the drug is relatively con-traindicated), in patients with open-eye injuries or after the eyeball is opened surgically, when an increase in abdominal pressure must be avoided (pheochromocytoma, aortic aneurysm, full stomach, ileus), and in patients in whom a rise in arterial pressure may be catastrophic (cerebral aneurysm, raised intracranial pressure). Prolonged paralysis, occasionally lasting hours, is a risk if the patient is, or has been, taking certain drugs.
In pregnancy the risk of regurgitation has to be weighed against the advantage of rapid intubation. The use of "precurarization'' with small doses of non-depolarizing drugs may reduce the intensity of the fasciculation, but is by no means reliable. If possible, relaxation is better achieved by using a non-depolarizing agent alone.
Patients with muscle disorders (dystrophia myotonica, myotonia congenita, myasthenia gravis, and hyperkalemic periodic paralysis) tend to react unpredictably to suxa-methonium. In myasthenia gravis, small doses of suxamethonium may be tried and the resulting effect monitored. In the other diseases listed non-depolarizers, cautiously used, are preferable. Cardiac arrest has been reported in patients with pseudohypertrophic muscular dystrophy (Duchenne type) and excessive muscle damage may be produced by suxamethonium in this condition.
In myasthenia gravis responses to suxamethonium are unpredictable (265-268). Resistance has been reported and the development of a phase II block can occur more readily, occasionally leading to prolonged paralysis. The measures used to treat the condition, for example plasmapheresis or anticholinesterases, further complicate the picture. Patients with the Eaton-Lambert syndrome are very sensitive to all relaxants.
In patients with asthma or a history of previous allergy, suxamethonium should be used with caution, in view of its potential for causing allergic reactions and bronchospasm. When a patient or a relative has had a previous adverse reaction to an anesthetic, the possibilities of an atypical cholinesterase genotype or malignant hyperthermia should also be considered. Patients with certain muscu-loskeletal and developmental abnormalities, such as a tendency to joint dislocations, squint, ptosis, hernias, some forms of cryptorchidism, pectus excavatum, kypho-sis, foot deformities, and myopathic features, and also those who have reacted to a previous injection of suxamethonium with generalized muscle rigidity or masseter spasm, may be more prone to malignant hyperthermia. Dantrolene should be available to every area where anesthetic agents are used.
The choice of muscle relaxants for rapid sequence induction of anesthesia in patients at risk of aspiration has been controversial for many years. Suxamethonium has been used for decades, because it has a fast onset and a short duration of action, although it can have severe adverse effects. Alternatives have been suggested, all of which have their own pros and cons, but suxamethonium has withstood the test of time and is still widely used. On this background, the use of rocuronium versus suxametho-nium has been subjected to a Cochrane review, in which 40 studies addressing the issue were identified, 26 of which were combined for analysis (269). For rocuronium, the relative risk of excellent intubating conditions was 0.87 (95% CI = 0.81, 0.94) compared with suxametho-nium. In a subgroup of patients who had been given propofol as an induction agent, there was no difference between rocuronium and suxamethonium. The reviewers concluded that overall suxamethonium creates excellent intubation conditions more reliably than rocuronium and should still be used as a first-line muscle relaxant for rapid sequence intubation. Rocuronium, when used with propofol, reliably created excellent intubation conditions and was consequently suggested as a second-line alternative to suxamethonium. In addition, some have suggested that intubating under deep anesthesia without a neuro-muscular blocker is an acceptable third-line alternative if neither suxamethonium nor rocuronium is considered appropriate. To allow rapid-sequence intubation of the trachea without a muscle relaxant, adequate doses of propofol (2.0-2.5 mg/kg) or etomidate (0.3 mg/kg) and a fast-onset opioid, such as alfentanil (50 micrograms/kg) or remifentanil (4 micrograms/kg) are required (270-275).
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