Nowadays, the myasthenias should not cause problems for the anaesthetist thanks to better awareness, understanding and treatment. Also, patients are usually much better prepared in advance for their operations. The one exception, of course, is when the myasthenia is not suspected. However, myasthenia is such a well-known pitfall for anaesthetists that it is a very common question in their final exams.

It helps both sides if patients can discuss all the options in advance with the anaesthetist who can then also assess the severity of the myasthenia and the overall fitness for anaesthesia and surgery. An intensive care bed can also be arranged for recovery afterwards if necessary. Importantly, it gives patients confidence and courage, and that helps everyone.

Very often, so as not to depress breathing, doctors prefer local or regional to general anaesthetics (e.g. with lignocaine, bupivacaine; also mepivacaine which is shorter-acting and has fewer side effects). These drugs are injected around nerves and block their electrical conduction completely for several hours. They work identically whether they are injected near the nerve endings or around the nerve roots (as for spinal and epidural anaesthetics). They are often chosen to avoid the depression of breathing that is caused by some general anaesthetics and to allow other treatments to continue normally. Local anaesthesia combined with light sedation is suitable for most operations below the waist, e.g. hip/knee surgery, varicose veins, hernias, and some gynecological operations. Local anaesthetics are preferable to general for people with myasthenia.

Before any general anaesthetic, the myasthenia should be under the best possible control, which may mean ‘tuning up’ with plasma exchange or IVIG about two weeks beforehand. Then it should be just as safe in patients with myasthenia as in anyone else, as long as care is taken over:

(a) muscle relaxants* and competitive blockers of nerve → muscle triggering (like curare), which now include atracurium, rocuronium and vecuronium. They are given nowadays for easier access for ‘deep’ operations, to relax all the voluntary muscles. Because these drugs also paralyse the breathing muscles, mechanical ventilation is obviously also essential.

Competitive blockers are another group of ‘depolarising’ drugs (like suxamethonium) which paralyse muscles after first stimulating them; myasthenic patients are 2-fold less sensitive to them, because they have fewer receptors.

Many operations need neither muscle relaxants nor ventilation. When they did, in the old days, we used deeper anaesthesia instead, which meant more depression of blood pressure and breathing and longer recovery times, often with much nausea and vomiting.

With their lower reserve of muscle-triggering power, patients with myasthenia are much more sensitive to muscle relaxants so the dose has to be reduced by 5 or even 10 times. The degree of muscle paralysis can be monitored throughout the operation by a peripheral nerve stimulator. These cheap and simple instruments are in routine use in all operating theatres. Neostigmine, a short-acting pyridostigmine cousin, is routinely used to stop the effects of muscle relaxants at the end of operations.

It still occasionally happens that patients with unsuspected myasthenia (including LEMS) are given standard doses of relaxants and then need more neostigmine than expected to perk them up after the operation – one roundabout way in which myasthenia can be diagnosed, even today.

(b) pyridostigmine. It should not be stopped before local or general anaesthetics. But, because it counteracts the muscle relaxants, they may need to be given at slightly higher doses if pyridostigmine has just been taken (adjusted according to the nerve stimulation results). This should not be a problem, and may even help, because so many myasthenia patients find it reassuring to take it regularly. After the operation, it is often given into a stomach tube if the patient has trouble with swallowing.

(c) steroids. The dosage will need to change because the natural steroid response to stress that tides us over operations is shut off by prior steroid treatment. So we usually supplement with extra steroids by injection before, during and after the operation.