Anaphylaxis (Allergic Reactions)

ANAPHYLAXIS (ALLERGIC REACTIONS) AND ANAESTHESIA

INTRODUCTION

Allergic reactions are one of the serious complications that can occur with medical treatment of many different sorts both in hospitals and in the general practice setting. Allergic reactions are particularly important in anaesthesia because many different anaesthetic drugs are used for each anaesthetic and they are administered directly into patients. Many of these drugs carry are recognised risk of causing allergic reactions with a relatively high frequency. For these reasons it is important for patients to be aware of this problem and communicate clearly with their anaesthetist if they are aware of previous allergic reactions. This explanation is designed to provide a better insight into the problem.

ALLERGY/ANAPHYLAXIS

Anaphylaxis is the medical term used to describe a severe allergic reaction. The concept was first described at the beginning of the 20th century and since then our understanding of the immune system has expanded tremendously. However it is still not understood why some people develop an allergy to a particular substance while others do not.

When a substance to which someone is allergic is absorbed into their body, it sets off an immune reaction. The antigen (usually a foreign protein) binds to specific immune globulins and this complex attaches to Mast cells. Following this, the mast cells release substances such as histamine and leukotrienes into the blood stream. These substances mediate the immune reaction.

The clinical response includes urticaria (skin swelling), flushing, nausea and vomiting, abdominal pain, laryngeal oedema (swelling of the throat), bronchospasm (asthma), cardiovascular collapse (severe fall in blood pressure). An allergic reaction can include some or all these features. For example a substance applied to the skin to which someone is allergic will cause urticaria. In the situation where someone is allergic to a drug that is injected into the muscle, under the skin or into a vein, then a more severe reaction will occur. If left untreated, a severe allergic reaction will almost certainly result in death.

Treatment of an allergic reaction involves recognising and stopping the administration of the causative agent, securing the airway, establishing intravenous access, administration of adrenaline and other drugs that counteract the effect of the allergy, intravenous fluids and possible even cardiopulmonary resuscitation (heart massage). This requires the rapid and coordinated response from a number of medical personnel. After the patient is stabilized, a period in the Intensive Care Unit will be necessary to continue the treatment until the full effects of the allergy can be reversed. This may take one to two days.

An allergic reaction can be difficult to diagnose as it can resemble other complications/problems such as a heart attack, vasovagal reaction, cerebrovascular accident, hereditary angioedema and serum sickenss to name but a few.

For this reason, medical staff have to be alert to the possibility that a patient may develop an allergic reaction. This means ensuring that staff have the appropriate training to deal with this emergency and that the equipment needed is readily available in the operating theatres and the hospital environment. Patients will be asked on numerous occasions by nursing and medical staff as to whether they are aware of any allergies they may have.

INVESTIGATION

The investigation of an allergic reaction begins with taking a detailed history from the patient. However this can be difficult as patients may not remember the details of an event that happened many years ago and it is also possible to confuse the side effects of a drug with the symptoms of a true allergy. For example a patient may suffer nausea and vomiting after the administration of morphine. This is a common side effect of the medication and would probably only be part of an allergic reaction if there were other symptoms such as skin swelling, asthma and low blood pressure.

Following a severe reaction to a drug that looks like an anaphylactic reaction, it is possible to do a blood test to confirm whether this has the case. This test will confirm that there has been an allergic reaction but will not identify the specific causative agent. To identify the agent, skin tests, radiosorbent testing or a provocative challenge will have to be conducted. Even with these tests it is not always possible to identify the exact agent that caused a reaction.

The most important agents that cause severe allergic reactions are the penicillin group of antibiotics. Among the anaesthetic drugs there are numerous agents such as neuromuscular blockers, the induction agents such as propofol and thiopentone, local anaesthetics such as lignocaine and bupivicaine and the opiate analgesics such as morphine. It is difficult to establish the exact frequency with which these agents cause an allergic reaction. However as an example it is thought that some of the neuromuscular blocking agents cause an allergic reaction with a frequency of 1 in 5000. Considering the number of anaesthetics administered every year the event is not rare. An anaesthetist practicing full time can expect to see a number of allergic reactions during the course of their career.

LATEX ALLERGY

This is a problem that was first identified in the latter part of the last century with the increased use of latex containing products in the medical world. Latex is a complex mixture of foreign proteins and if someone is exposed to latex repeatedly, they stand the risk of developing latex allergy. Healthcare workers are especially at risk of developing this problem as they are exposed to latex on a daily basis.

If a patient is allergic and they are exposed to latex, they can develop, skin swelling, throat swelling and cardiovascular collapse. The onset of these symptoms can sometimes be over a slightly longer period of time as the latex is brought into contact with the skin or membranes of the body and is not being injected into the blood stream. This can make it more difficult to diagnose the problem.
Patients that are more likely to develop a latex allergy are those that have frequent urological procedures and exposure to latex containing urinary catheters. In fact patients in this group have an estimated incidence of latex allergy in the region of 50%.

The diagnosis of latex allergy can be accurately performed with skin prick testing. However this form of testing can cause an allergic reaction itself and is reserved for patients with a compelling history and inconclusive serological testing.

The approach to the management of a patient with a latex allergy is to treat them in a latex free environment. All hospitals have policy guidelines to facilitate the process. The American Society of Anesthesiologists has developed a set of guidelines on this topic and can be found on the website

http://www.asahq.org/publicationsAndServices/latexallergy.pdf