• What is a general anaesthetic?

    A general anaesthetic is the use of drugs that cause you to become unconscious. It is often the most suitable way of keeping you safe and comfortable for an operation. You are unaware of what is happening during your operation. The general anaesthetic may be given in two ways. Medications can be given through a drip, usually in your arm or hand. Alternatively you can breathe gases through a mask.

    How common is allergy to anesthesia?

    Severe allergic reactions during anesthesia are fortunately rare, occurring only once in every 5,000 to 25,000 anesthetics. Unfortunately, these reactions can sometimes be fatal, with 3% mortality.

    What is the manifestation of such allergy?

    The most severe form of allergic reaction is known as `anaphylaxis`. During an anaphylactic reaction the patient may experience difficulty breathing, as air passages close up. Swelling of the face and mouth can occur, and a reddish skin rash is also sometimes seen. The heart and blood vessels are severely affected, and this is the hallmark of the condition: the heart rate increases and blood pressure can drop to dangerously low levels.

    What are the agents responsible for such allergy?

    Among the cases of anaphylaxis attributed to neuromuscular blocker agents in the literature, the following substances have been incriminated, in decreasing order of importance: suxamethonium, vecuronium, atracurium, pancuronium, rocuronium, mivacurium and cisatracurium.

     

    What are the risk factors to develop this condition?

    • A significant female predominance has been reported.
    • Perioperative allergic reactions rarely occur in children, and most that do occur are caused by latex.
    • It has been generally agreed that atopy is a risk factor for allergic reactions because case reports of perioperative allergic reactions have reported a high prevalence of atopy.
    • There is no evidence that multiple anaesthesias promote sensitization to a given anaesthetic. However, if an allergy has developed during a previous anaesthesia, anaphylaxis is bound to occur if a subsequent anaesthesia is performed using the same product.

     

    What are the major groups of these agents?

    There are 2 major groups:

    (1) Esters

    They contain such drugs as Cocaine, Procaine, Tetracaine, Chloroprocaine and Benzocaine.  Today, only benzocaine is routinely used in dentistry, and its use is limited to topical application.  The others are used today mostly in obstetrics and for producing spinal anesthesia. In general, a patient known to be allergic to one ester anesthetic is likely to be allergic to all ester anesthetics. The use of ester based anesthetics can be avoided entirely since 5% lidocaine gel works quite well as a topical anesthetic to numb the gums before the shot is given.

    (2) Amines

    They include Lidocaine, mepivicaine, bupivicaine, articaine, prilocaine and bupivicaine. Since dentists now use amine based anesthetics, and no longer use ester based anesthetics, we see almost no allergic reactions to the injectable local anesthetics.   If you have suffered allergic reactions at the dentist’s office, it is most likely that the reaction was to the topical anesthetic applied with a swab before the shot, or to the preservative used in anesthetics containing vasoconstrictors.

     

    What about the preservative in these agents?

    Upon occasion, a patient may have a legitimate allergic reaction to an injected dental local anesthetic.  It is likely that he or she may in fact be allergic only to the bisulfite preservative used to stabilize the vasoconstrictor.

     

    How do we diagnose allergy to anaesthesia?

    One of the most commonly used skin tests used by physicians to test for general allergy is called the T.R.U.E. Test.  This is a patch test that applies 23 allergens to the skin contained in 12 polyester patches.  One of the patches contains a mixture of several anesthetics and is used to test for allergy to local anesthetics in general. A clinical history consistent with a delayed cutaneous reaction to local agents, combined with a positive patch test result, is sufficient for diagnosis.

     

    How do we manage allergy to anaesthesia?

    Management consists of identifying other agents that the patient tolerates. When evaluating patients for tolerance to other agents, usually we recommend choosing an agent from the other chemical group. Information about cross-reactivity among local agents is limited, although there is evidence for cross-reactivity within each group of agents and minimal evidence for cross-reactivity between the two groups. Thus, we suggest choosing one or more drugs from the other local agents group as an alternative agent for patch testing.

     

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