Pseudocholinesterase deficiency and anaesthesia

Plasma cholinesterase is an enzyme found in the blood. Gloucestershire Hospitals NHS Foundation Trust describes it as essential for breaking down acetylcholine, a chemical involved in sending nerve signals. Its other names are pseudocholinesterase and butyrylcholinesterase (BChE).

The enzyme also breaks down two muscle relaxants used in anaesthesia: suxamethonium, also called succinylcholine or scoline, and mivacurium. Newcastle Hospitals laboratory notes that the enzyme shows a great deal of genetic variation, and some variants lead to an effective deficiency.

If your enzyme is deficient or works poorly, these drugs stay active for longer than planned. That is why the condition is also known as suxamethonium apnoea. Apnoea simply means a pause in breathing.

Suxamethonium is a fast, short-acting muscle relaxant used to help an anaesthetist place a breathing tube. Sheffield Children's describes it as normally wearing off within a few minutes. Under general anaesthesia you are already asleep and your breathing is supported by the team, so a longer effect does not mean pain or awareness.

In someone with reduced enzyme activity, the muscles stay relaxed for longer, including the muscles used for breathing. The anaesthetist will notice that the usual signs of recovery are slow and will keep supporting your breathing.

Most people only discover they have the condition because of an unexpectedly slow recovery. Others learn of it because a relative was affected.

Severity varies with the type of change in the enzyme. Sheffield Children's says about 1 in 25 people (4%) have a mildly reduced amount. In these people the drug takes a little longer than usual to break down, and the apnoea is usually short-lived.

In rare cases, fewer than 1 in 2000 people according to the same Trust, it can take up to 4 hours for the medicine to wear off.

Gloucestershire Hospitals NHS Foundation Trust says the deficiency is inherited in an autosomal recessive way. In simple terms, a person with a significant deficiency has typically inherited a changed copy of the gene from each parent, while carriers with one changed copy are usually less affected.

Sheffield Children's notes that low activity can also come from "other medical factors", not only inheritance. The pathology notes do not list them, so ask your anaesthetist if this applies to you.

The same Trust page adds that people who work with organic phosphorus insecticides may have cholinesterase studies, ideally with a baseline sample taken before exposure. This is a separate occupational use of the same test.

Sheffield Children's describes the management as supportive. The anaesthetic team continues to support breathing while the body clears the drug. That may mean the person stays asleep a little longer than usual. In some cases there is an extra stay of a few hours in the theatre recovery area or an overnight stay in intensive care for close monitoring.

Once the medicine wears off, the Trust says recovery is complete and there should be no long-lasting effects.

Afterwards, the anaesthetist or surgical team should explain what happened, why it happened and what to do next. Do not be shy about asking for this in writing.

If you feel unwell after any anaesthetic once at home, such as breathing difficulty or severe weakness, call 999.

Patients are not routinely tested before an operation, unless a family member is known to have had suxamethonium apnoea. After a suspected episode, a blood test is arranged, but not straight away. Timing is important so that the result is accurate.

Sheffield Children's says the sample is taken 12 to 24 hours after the anaesthetic. Gloucestershire Hospitals says samples should be collected 24 hours after the suxamethonium dose, when the patient has recovered and is breathing unaided. Local laboratories differ, so follow the instructions you are given.

The Newcastle laboratory directory lists a turnaround of 3 to 4 weeks, with samples sent to a specialist laboratory. Sheffield Children's says the test shows enzyme levels, how the body processes certain medicines and whether you carry an inherited form of low activity. If the first result is abnormal, a second test is done on the sample already taken.

Genetic testing may also be done if clinically indicated, according to Gloucestershire Hospitals.

If a significant abnormality is found, Sheffield Children's says a warning card is given to show to doctors in future. Your anaesthetist and GP discuss what the results mean and whether any relatives need testing.

Because the condition is inherited, Gloucestershire Hospitals advises testing for individuals whose first-degree relative has had suxamethonium apnoea, and notes this normally requires referral to a clinical geneticist. Sheffield Children's says birth parents and siblings may need testing if there is a definite inherited problem, and that testing is usually done in adults and older children rather than under 12s unless needed before surgery.

Sharing the result with family members is worthwhile, as it lets them tell their own anaesthetist before any operation.

Sheffield Children's says anaesthetists can easily plan safe alternatives for future anaesthetics. That usually means choosing a different muscle relaxant or technique. Always tell every healthcare provider, including dentists and day surgery units, that there is a history of suxamethonium apnoea, and carry your warning card.

Having the deficiency does not generally limit which operations you can have. It simply changes which drugs the team chooses.

The same applies whether surgery is on the NHS or private: tell the pre-assessment team and the anaesthetist in advance.