Anaphylaxis or anaphylactic shock is the most severe allergic reaction. It is a massive allergic response affecting the whole body. Anaphylactic shock occurs when a large number of the bodys mast cells (part of the bodys defense system) discharge their mediators e.g. histamine, at once. This reaction may involve any body system; however the skin, nose, throat, lungs, stomach, intestinal tract, heart, and blood vessels are primarily affected. The first sign of anaphylaxis may be a red, itchy rash and a feeling of warmth. These may be followed or accompanied by light-headedness, shortness of breath, or sneezing; a feeling of anxiety; stomach or uterine cramps; and/or vomiting and diarrhea. In most cases of anaphylaxis the symptoms are reversed by adrenaline if given early. In other rare cases, the symptoms are prolonged and may lead to death.
Definition of Anaphylaxis
No universally accepted definition exists because anaphylaxis comprises a constellation of features. A good working definition is that it involves one or both of two severe features: respiratory difficulty (which may be due to laryngeal oedema or asthma) and hypotension (which may present as fainting, collapse, or loss of consciousness).
The confusion arises because systemic allergic reactions can be mild, moderate or severe. For example, generalized urticaria, angioedema, and rhinitis would not be described as anaphylaxis, as neither respiratory difficulty nor hypotension the potentially life threatening features is present.
How does it happen?
One of the effects of mast cell mediators such as histamine is to make blood vessels wider and more leaky. This effect is beneficial during local infections, when it occurs in a restricted area of the body, but during anaphylactic shock it occurs throughout the body. With the same amount of blood coursing through a greatly enlarged set of channels, there is far less blood available to fill the vessels and the blood pressure falls to a dangerously low level. This is the cause of the light-headedness. Often the patient pulse becomes very weak.
Anyone suffering from anaphylactic shock is seriously ill and needs immediate hospital treatment. There is a very real danger of death if treatment is delayed, especially if the person is asthmatic, since the airways also become severely narrowed during the attack.
Is anaphylaxis always life threatening?
Some anaphylaxis is mild and will go away without treatment. However, since it is not possible to predict how a reaction will progress, each episode must be taken seriously.
Do reactions get worse with successive episodes?
Subsequent reactions could be the same, better or worse. The reason this is so unpredictable is that the nature of any reaction depends on two main factors: how allergic you are and the dose of the allergen you are exposed to. While a persons level of allergy may vary in either direction over time, the dose of allergen is an even bigger variable.
For example, with one reaction you may have eaten 1/100th of a peanut and with another the equivalent of 3 peanuts. With the 300-fold higher dose your reaction will almost certainly be much more severe.
The only good research in this area was done with bee sting allergy, in which it was shown that with subsequent stings (which deliver an approximately equal dose), reactions were almost always either the same or less severe.
What are the common causes of anaphylaxis?
The most common agents leading to anaphylaxis are drugs, especially antibiotics like penicillin, foods and insect stings (bees and wasps). Foodsthat frequently cause anaphylaxis in allergic persons include - peanuts, nuts, shellfish, eggs, and seeds. Anaphylactic reactions have also been reported in persons who have eaten milk, chocolate, barley, wheat, rice, citrus fruits, melons, bananas, tomatoes, spinach, mustard, corn, potatoes and soybeans.
More recently, cases of food-related exercise-induced anaphylaxis have occurred in patients who perform aerobic exercises within several hours of a meal. It appears that these reactions can be avoided if the meal and exercise are separated by at least four hours.
Other rare causes of anaphylaxis include: latex products, blood products, semen and hormones (oestrogen and progesterone).
TREATMENT OF ANAPHYLAXIS
Adrenaline needs to be injected immediately to counteract the effects of massive histamine release. Anyone at risk of anaphylaxis should carry a syringe that is pre-loaded with adrenaline. These are made available to anyone with a strong reaction to bee or wasp stings, or to those with severe food allergy. Even a relatively mild reaction, such as localized hives in response to contact with a food, can be the foretaste of something much more serious, and it is vital that such warnings are heeded.
For those who have had a severe anaphylactic reaction to food in the past, it is advisable to carry an adrenaline syringe, in case the food is inadvertently eaten again. There are two adrenaline injection devices on the market in New Zealand, at present. The Epi-Pen autoinjector comes in an adult and paediatric dose. Its main advantage is its spring-activated, concealed needle, which is useful for people who are fearful of needles. The Ana-kit comes in a pre-loaded syringe with two adult doses per syringe.
It is still necessary to avoid the food, of course the contents of the syringe will only be effective if a very small amount has been eaten. An aerosol spray containing adrenaline (Medihaler-Epi) can be issued to those who have suffered severe swelling of the throat in the past, in case they unintentionally eat the food again. It may also be useful if you feel you could not cope with giving yourself an injection in an emergency. The Medihaler-Epi is no longer available in many countries. Your doctor should be able to prescribe either the injection or the spray. Do not delay in using the syringe or the spray if you begin to experience a severe reaction to food. In this situation a wait-and-see attitude could be disastrous. The sooner you use the adrenaline, the more effective it will be, and you will avoid the possibility of lasting, irreversible damage to the body. Having used the syringe or spray, dial 111 and go to a hospital or emergency clinic, because you will probably need further treatment. The adrenaline injection should be repeated every 10 15 minutes until you are fully recovered. Tell the doctor if you have been taking steroids (e.g. prednisone) as these may suppress your body's normal ability to produce its own corticosteroids, which are needed in this crisis situation.
Not all anaphylactic reactions come on immediately. They can sometimes take an hour or even two hours to develop. There are usually some initial signs that things are amiss, such as itching or swelling in the mouth, nausea and stomach pains. If the food is affecting the throat, hoarseness or a lump in the throat sensation may be the first signs. Should these be followed by more generalized feelings, such as itching all over, sneezing, runny nose, diarrhea and weakness, a serious anaphylactic reaction may be developing. Other kinds of sensation that may accompany this stage are a feeling of warmth, and a peculiar sense of dread or apprehension. Incontinence, disorientation and abdominal pains may also be experienced. If there are any signs such as these, do not delay in getting medical help. Go to the accident and emergency department if you can, and make sure you are seen quickly – dont sit quietly waiting your turn.
What should be done after the first anaphylactic reaction?
Blood might need to be taken within 1 – 5 hours to measure Mast cell Tryptase, if diagnosis is in doubt.
Refer to an allergy clinic to determine the cause – to prevent future attacks
Organize self treatment of future reactions (by Allergist or Aware Physician)
Anyone who has had a severe reaction in the past should consider wearing a Medic Alert bracelet with the relevant information on it. (You can find out how to obtain these bracelets from your doctor). If you were to eat your culprit food by mistake, or were stung by the insect you are allergic to, while away from home, and were found unconscious, it could save your life. Without it, you might not get the correct medical help.
Frequently Asked Questions About Anaphylaxis Treatment
(Adapted & modified from FAN, Robert Wood, MD)
Can any medication be used to prevent Anaphylaxis?
Unfortunately, no medication will reliably prevent anaphylaxis. Some patients take antihistamines before going out to a restaurant, but this should not be recommended, as it will not prevent a severe episode.
Do I always need Adrenaline?
This has to be decided on an individual basis in conjunction with your doctor. Patients with a history of severe reactions should certainly take adrenaline as soon as they suspect they have eaten a problem food or feel a reaction starting.
In patients with asthma adrenaline should be used more routinely because these patients are at higher risk for more dangerous reactions.
For patients with a history of milder reactions, such as isolated hives, just giving an antihistamine and observing them for evidence of more severe reaction may be appropriate.
Which medicine should be given first?
If you belong to the group of those who have severe reactions, adrenaline should be given first. If you dont fit into that group, start with antihistamine and be ready with the adrenaline in case the reaction progresses.
The effects of steroids are not seen for several hours, so immediate administration is less critical.
Are steroids always needed?
Steroids are usually recommended for any severe reaction, as they might prevent symptoms from persisting or recurring (biphasic reactions).
Which patients should carry Adrenaline?
This should always be decided on an individual basis after discussion with your doctor.
All patients with peanut and nut allergy should carry adrenaline. Many patients with eggs and milk allergy do not need to carry adrenaline because their reactions have always been mild.
Once adrenaline is prescribed, it must be carried all the time.
At what age should a child be switched from EpiPen Jr to a full strength EpiPen?
The answer depends on size and not age. The regular strength EpiPen is appropriate for children over 30Kg. A study published in JACI, Feb 2001 concluded "In young children at risk for anaphylaxis who weigh 15-30 Kg, adrenaline injected using the EpiPen Jr appears to have a better benefit-to-risk ratio than the EpiPen.
At what age can a child carry his/her EpiPen?
Probably after the age of 12 might be reasonable. The problem is not knowing how to inject, but when to inject.
How many doses of adrenaline can be given during an anaphylactic reaction?
Although a single dose is enough in most cases, some cases require multiple doses. This is the reason why all patients should be taken to an emergency clinic after administering their first dose of adrenaline.
It is normally recommended that additional doses be given every 10 to 15 minutes if symptoms persists or worsen
Is Adrenaline harmful or dangerous?
The majority of people who die from anaphylaxis, die because adrenaline was not given early enough or not enough given. Therefore, we recommend when in doubt give the adrenaline. The autoinjectors given to patients usually give intramuscular injections which is adequate for treating anaphylaxis outside the hospital setting, and avoid the possibility of adrenaline overdose which can occur with giving intravascular adrenaline.