Anaesthetics

This is from an article that appeared in the Winter 1996 Edition of Target MD and is recreated with permission If you wish to subscribe to Target MD please contact them by Email at targetmd@muscular-dystrophy.org

ANAESTHETICS Dr P ) Halsall and Professor F R Ellis

People with neuromuscular disorders must take great care if they are to have a local or general anaesthetic. Even someone with very mild, or non-existent symptoms, or someone who has a family history of a disorder; needs to let the anaesthetist know well in advance so that tests can be carried out and proper care after the operation can be arranged.

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 NMD around operations or treatment under local anaesthetic.

Which are the neuromuscular disorders (NMDs)?

Neuromuscular disorders include all the muscular dystrophies plus: myotonic disorders; congenital myopathies including mini-core, central-core and multi-core disease plus nemaline and myotubular myopathies; mitochondria! 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 (HMSN 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.

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 (NMDs) deserve special attention when it comes to anaesthesia because many of the agents used (gases and chemicals) 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 which 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

An article printed in the Winter 1995 No. 20 edition of The Search, showed how people with NMDs 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 conduction 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 which would 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, and by taking a blood test to measure levels of a muscle enzyme, creatine kinase (CK). Any anaesthetic agent which 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 NMDs, these drugs should be used cautiously, and monitoring of breathing after the operation is absolutely essential. As a result, the patient is usually best cared for in a High Dependency Unit or Intensive Care Unit immediately after the operation. The muscles used for swallowing can also be affected which is another reason why good post-operative care is important.