Overview
Doctors use anaesthetics during medical procedures to prevent patients from experiencing pain. There are several different types of anaesthesia, with the two main categories being local or generalised anaesthesia. Local anaesthesia temporarily stops you from feeling pain in a specific area of the body. Therefore, it is mostly used in minor medical procedures. In contrast, a general anaesthetic renders you unconscious, ensuring you remain unaware of the procedure and guaranteeing a pain-free experience. Commonly used general anaesthetics include induction medications, which induce unconsciousness, analgesics; which provide pain relief and muscle relaxants, which prevent muscle contractions or spasms that may be triggered by artificial ventilators.¹ As such, general anaesthesia is mainly reserved for major surgeries. The decision as to whether a patient is given local or general anaesthesia is made by an anaesthetist, who will also decide on the type and dosage of anaesthetic given. It is vital that patients are given the correct types and doses of anaesthesia to avoid complications both during and after surgery.
In this article, we will discuss what happens when a patient has an adverse (or allergic) reaction to anaesthesia. Further, we will discuss how these reactions can be treated and how further research could lead to the introduction of routine allergy testing before anaesthetics are given.
What causes anaesthetic allergy?
Reactions to local anaesthetics are typically the result of the body’s response to adrenaline (which is produced when you are scared), the overdose of a specific drug component, or vasovagal syncope (which causes you to faint).² However, there have also been reported cases of adverse reactions to amides, a chemical group found in many anaesthetics.²
Symptoms of anaesthetic allergy
One of the most severe reactions to anaesthetic is anaphylactic shock. This is a potentially life-threatening reaction triggered by our bodies coming into contact with external substances that it is hypersensitive to. This can include food, insect stings (such as bee or wasp stings), and drugs, including anaesthetics. Anaphylactic shock can be recognised by the following symptoms:
- Swelling of the throat and tongue
- Having difficulty breathing and swallowing
- Confusion
- Coughing
- Wheezing
- Feeling faint
- Pale skin
Anaphylactic shock requires immediate medical attention, as it is characterised by rapid progression and can have lethal consequences if left untreated. Adrenaline injections are the first-line treatment for anaphylactic shock and help stop your body’s hypersensitivity reaction. After this, patients should be given drugs to reverse this immune reaction. These drugs are always available during surgery if needed to prevent further complications and keep you safe.
It is important to emphasise that not all allergic reactions involve anaphylactic shock. Some reactions do not involve your entire immune system but are instead caused by the histamine released by your body in response to anaesthetics. In these cases, your body recognises the anaesthetic as foreign and potentially dangerous (like it would a bacterium or fungus), triggering a symptomatic immune response.³ These reactions are known as anaphylactoid reactions. From the outside, anaphylactoid reactions are not massively different from anaphylactic shock; tests are needed to assess your risk of having either type of reaction.³ Specifically, these tests measure the levels of certain immune cell types in your blood, including histamine, tryptase, and IgE antibodies (which are produced by the body during allergic reactions), before and after you are given an anaesthetic and can give important information that helps avoid anaphylactic or anaphylactoid reactions during surgery.
Epidemiology of anaesthetic allergy
Currently, the UK, France, New Zealand, and Australia are leading researchers in epidemiology, as well as in the causes and prevention of anaesthetic allergy.⁴ Anaphylactic shock is reported to occur in between 1 in 10,000 to 20,000 patients and is often triggered by muscle relaxant anaesthetics. Indeed, one French study found that 69.1% of anaesthetic allergy-mediated anaphylactic shocks were triggered by muscle relaxants.⁴ The same study reported that 12% of patients show allergic reactions to latex, which is commonly used in medical gloves and catheter tips.
Pre-surgery testing
Two effective ways to detect anaesthetic allergies before surgery are intradermal injections (which involve injecting a small dose of anaesthetic into the skin) and prick testing (in which a small patch of skin is scratched prior to the application of the anaesthetic being tested).⁵ Intradermal injections are reportedly more accurate than the prick test, but are more invasive and potentially painful. Consequently, doctors will often opt to use the prick test on young children.⁵
Summary
Allergic reactions to anaesthetic substances used during surgery is a life-threatening but avoidable, kind of allergic reaction. During surgery, these reactions can result in anaphylactic shock or anaphylactoid reactions, causing symptoms such as heaviness of breath, a swollen throat, and pale skin. Anaesthetists have crucial jobs in surgeries requiring general anaesthetic. They decide on the type and dosage of anaesthetic a patient is given, and monitor the patient’s heart rate and breathing during surgery to ensure their continued safety.
Whilst the current pre-surgery checklist only requires doctors to take blood tests and discuss any previous allergic reactions you have had, other tests can be very helpful in detecting anaesthetic allergies before surgery. These include intradermal injections and prick tests. Whilst these tests may be briefly uncomfortable, they can significantly reduce your risk of anaphylactic shock during surgery - and make anaesthetics even safer than they are today.
FAQs
What tests are usually done before surgery?
Allergic reactions are not the only threat posed to patients during surgery, and some other physiological values need to be evaluated before surgery. This requires several tests, including:
- Chest x-rays and examination: these are done to study lung and chest function, as you can detect proper heartbeat, lung and breath sounds
- Electrocardiogram: Electrocardiograms evaluate the electrical activity of the heart and help doctors detect any irregularities
- Urinalysis: urine tests are performed to study your kidney and bladder function and identify any potential infections
- Blood tests, including a white blood cell count to check for infections and total blood cell counts
- Glucose tests, to study blood sugar
- Potassium tests, to study levels of electrolytes in your blood - essential for correct heart function
- Coagulation studies to assess your risk of blood clots during and after surgery.
What can I do to prevent an anaphylactic shock?
If you believe you could have allergies to certain anaesthetics, you should talk to your GP and ask them about having a prick test or intradermal injection, as well as a blood test, to test your reaction to different anaesthetics.
References
- Australian Society of Anaesthetists. Anaesthetic medications [Internet]. Cited Sep 2023 via: https://asa.org.au/patient-information/anaesthetic-medications/#:~:text=There%20are%20four%20main%20types,relaxants%20to%20induce%20muscle%20relaxation
- Brown DT, Beamish D, Wildsmith JAW. Allergic reaction to an amide local anaesthetic. Br. J. Anaesth. 1981;53:435–7.
- Lagopoulos V, Gigi E. Anaphylactic and anaphylactoid reactions during the perioperative period. Hippokratia. 2011;15:138–40.
- Mertes PM, Laxenaire MC. Allergic reactions occur during anaesthesia. Eur. J. Anaesthesiol. 2002;19:240–62.
- Fisher MM, Bowey CJ. Intradermal compared with prick testing in the diagnosis of anaesthetic allergy. Br. J. Anaesth. 1997;79:59–63.
