Anesthetics

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Anesthetics

by Dr. P.J. Halsall and Professor F.R. Ellis

People with neuromuscular disorders must take great care if they are to

have a local or general anesthetic. Even someone with very mild, or

non-existent symptoms, or someone who has a family history of a

disorder, needs to let the anesthetist know well in advance so that

tests can be carried out and proper care after the operation can be

arranged.

Many people are afraid of having an anesthetic, mainly through

ignorance, but when we look at the rate of complications and even deaths

arising from anesthesia 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 such as High Dependency

Units (HDU) and Intensive Care Units (ICU).

Patients with neuromuscular disorders (NMDs) deserve special attention

when it comes to anesthesia 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 anesthetic 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 anesthesia so it

is important to consider that too.

Anesthetics 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

anesthetic vapors, 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 vapors are

all slightly different from each other, some having more effect on the

heart than others. So it is important that the anesthetist 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.

Anesthetics 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 anesthetic 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.

Muscle Relaxants;

Muscle relaxant drugs should only be used if essential because they tend

to have a more profound and prolonged effect in NMD patients 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. In patients with NMD 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 preoperative blood

test to check K+ levels is therefore important.

Local anesthetics:

A local anesthetic works by preventing the normal electrical activity in

the nerve around which the anesthetic agents are placed. For minor

procedures, such as stitches for cuts, they are probably the first

choice for patients with NMD because they have few if any side-effects.

However for major local anesthetic techniques, e.g. spinal or epidiural,

careful assessment of the patient is needed and the type of NMD

considered well before the operation.

Changes in body temperature and preoperative 'starvation':

Patients with NMD do not tolerate changes in body temperature or the

starvation often associated with anesthesia or surgery as well as normal

patients, so steps need to be taken to minimize these problems by

keeping the patient warm and well hydrated using drips.

Malignant hyperthermia (MH) and Central Core Disease:

Malignant hyperthermia (MH) is an inherited disorder which causes an

unexpected, sometimes fatal, reaction in the patient to certain

anesthetic drugs. Because some patients with NMD have sometimes

experienced similar problems during anesthesia there have been claims

that patients with NMD may also have MH. However, it is generally

accepted that the only neuromuscular condition truly related to MH is

Central Core Disease (CCD), although this is not always the case.

Patients with CCD 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 anesthesia in NMD is not to be undertaken lightly. Such patients

should expect the anesthetist 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 preoperative investigations, and enough time and recovery

facilities should be available after the operation. It is absolutely

essential that the person affected by NMD should inform the anesthetist

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 anesthesia,

particularly in young children.

The anesthetist should also be warned if there is an inherited NMD in

the family.

If possible ask for the anesthetist 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 Fact Sheets about your condition, and if you are going to have

an anesthetic you could show your anesthetist this article.

The authors, Dr. Halsall and Professor Ellis, work at the Academic Unit

of Anesthesia, St. University Hospital, Leeds.

Reprinted with permission from The Search magazine, Winter, 1996 issue,

published by the MDA-UK, and the April-May, 1997 issue of Living Smart.