Anaesthetics

You can download this factsheet as a PDF document: Anaesthetics.pdf (106 kb) [pdf]

People with neuromuscular disorders must take great care if they are to have a local or general anaesthetic. Even people with very mild symptoms or those with a family history of a disorder need to let the anaesthetist know well in advance so that tests can be carried out and proper care after the operation can be arranged.

Written by Dr.P.J.Halsall and Professor F.R.Ellis for the Muscular Dystrophy Campaign

Contents:


Who should read this?

  • Everyone who has a neuromuscular disorder, even if their symptoms are very mild
  • Everyone who has, or had a relative, with a neuromuscular disorder
  • Professionals involved with the care of people with neuromuscular disorders around operations or treatment under local anaesthetic


A list of neuromuscular disorders

Neuromuscular disorders include:

  • all the muscular dystrophies
  • myotonic disorders
  • congenital myopathies including minicore, central-core and multi-core disease plus nemaline and myotubular myopathies
  • mitochondrial myopathies
  • lipid storage myopathies
  • inherited metabolic myopathies including glycogen storage disease
  • familial periodic paralysis
  • inflammatory myopathies, including infective myositis
  • autoimmune myositides including polymyositis and dermatomyositis
  • spinal muscular atrophies
    • hereditary and idiopathic peripheral neuropathy which is also known as Charcot-Marie-Tooth disease
  • inflammatory, autoimmune and toxic neuropathies including Guillain Barre syndrome and CIDP
  • disorders of the neuromuscular junction, including Myasthenia Gravis


Anaesthetics and medical conditions/neuromuscular conditions

Many people are afraid of having an anaesthetic, mainly through ignorance, but when we look at the rate of complications and even deaths arising from anaesthesia we see that it is in fact very safe. This safety is the result of a thorough understanding of the patient’s medical condition, with a careful assessment before the operation, marked technical improvements in monitoring facilities during the operation, and the provision of good recovery facilities such as High Dependency Units (HDU) and Intensive Care Units (ICU).

Patients with neuromuscular disorders deserve special attention when it comes to anaesthesia because many of the agents (gases and chemicals) used have effects on both muscle and nervous tissue. The main areas of concern are how the anaesthetic agents will affect the muscle and how they will affect the heart that is itself a muscle.

A skeletal deformity such as scoliosis, or curvature of the spine, can also affect the way the patient responds to anaesthesia so it is important to consider that too.

Anaesthetics and the heart

People with neuromuscular disorders can sometimes have associated heart disease. This can occur as a cardiomyopathy, when the heart muscle doesn’t work effectively, or as a defect in the way the electrical activity of the heart is transmitted - a conduction defect.

The anaesthetic vapours – the smelly agents such as ether and halothane which are inhaled – can reduce the effectiveness of the heart’s muscle contractions and also aggravate any condition defect. The vapours are all slightly different from each other, some having more effect on the heart than others. So it is important that the anaesthetist makes a good assessment of the heart’s condition before the operation. The assessment should include the level of physical activity that the patient can manage and an ECG. Occasionally a more extensive assessment is needed.

Anaesthetics and breathing

Doctors need to measure how weak the patient’s muscles are, usually by:

  • assessing the amount of physical activity that the patient can perform
  • taking a blood test to measure levels of a muscle enzyme, creatine kinase (CK)

Any anaesthetic agent that affects the muscles will also affect the muscles we use to breathe. Strong analgesic or sedative agents will affect these muscles indirectly and muscle relaxants will have a direct effect on them.

As breathing (or respiration) may already be difficult for patients with neuromuscular disorders these drugs should be used cautiously. Monitoring of breathing after the operation is absolutely essential. As a result, the patient is usually best cared for in a High Dependency Unit (HDU) or Intensive Care Unit (ICU) immediately after the operation. The muscles used for swallowing can also be affected which is another reason why good post-operative care is important.

Muscle relaxants

Muscle relaxant drugs should only be used if essential because they tend to have a more profound and prolonged effect on patients with neuromuscular disorders, compared to other patients.

One type of muscle relaxant, called suxamethonium, should usually be avoided. It causes the release of potassium ions (K+) from the muscle tissue into the blood. In normal patients this is usually of little practical significance. However, in patients with neuromuscular disorders the muscle may normally leak K+ so that a further increase in the levels of K+ in the blood may cause abnormal heart rhythms. A pre-operative blood test to check K+ levels is therefore important.

Local anaesthetics

A local anaesthetic works by preventing the normal electrical activity in the nerve around which the anaesthetic agents are placed. For minor procedures, such as stitches for cuts, they are probably the first choice for patients with neuromuscular disorders because they have few if any side-effects.

However for major local anaesthetic techniques, for example, spinal or epidural, careful assessment of the patient is needed and the type of neuromuscular disorder considered well before the operation.

Changes in body temperature and pre-operative ‘starvation’

Patients with neuromuscular disorders do not tolerate changes in body temperature or the starvation often associated with anaesthesia or surgery as well as normal patients, so steps need to be taken to minimise these problems by keeping the patient warm and well hydrated using drips.

Malignant hyperthermia and central core disease

Malignant hyperthermia (MH) is an inherited disorder that causes an unexpected, sometimes fatal, reaction from the patient to certain anaesthetic drugs. As some patients with neuromuscular disorders have sometimes experienced similar problems during anaesthesia there have been claims that these patients may also have MH.

However, it is generally accepted that the only neuromuscular condition truly related to MH is central core disease, although this is not always the case. Patients with central core disease should be considered potentially susceptible to MH unless proved otherwise by a special type of muscle biopsy, which screens for MH.


To sum up...

  • Clearly anaesthesia in people with neuromuscular disorders is not to be undertaken lightly. Such patients should expect the anaesthetist to make a careful and thorough assessment of their particular condition and their current state of health.
  • They are not suitable to be treated as ‘Day Cases’ because doctors should carry out pre-operative investigations and enough time and recovery facilities should be available after the operation.
  • It is absolutely essential that the person affected by any neuromuscular disorder should inform the anaesthetist, even if there are only minor symptoms or no symptoms at all. Occasionally a neuromuscular disorder in a person who had no symptoms has come to light only because of an unexpected problem with anaesthesia, particularly in young children. The anaesthetist should also be warned if there is an inherited neuromuscular disorder in the family, even if the individual has no symptoms.
  • If possible ask for the anaesthetist to be forewarned before admission to hospital and consider wearing a Medic Alert bracelet or similar in case of accidents.
  • It is always a good idea to make sure hospital staff have copies of factsheets about your condition. If you are going to have an anaesthetic you could show your anaesthetist this factsheet.