Epinephrine, anaphylaxis, and when to use your Epipen

Epinephrine is a hormone and a neurotransmitter.  This means that it is a molecule that allows tissues and organs to coordinate their behavior.  It belongs to a family of compounds called catecholamines.  It is made by some nerve cells and the adrenal gland.  Fun fact:  epinephrine and adrenalin are the same thing.  Epinephrine is the Greek name, while adrenalin is the Latin.

In order to understand how epinephrine works, we have to first understand what anaphylaxis does to the body.  Anaphylaxis increases the contraction of bronchial smooth muscles, making it harder to breathe; causes vasodilation, allowing fluids to pass easily into tissues and out of the blood stream, which decreases blood pressure; and affects the heart muscle, leading to arrhythmia.  Anaphylaxis can be biphasic, meaning a second reaction can occur, sometimes hours later. 

Death from anaphylaxis is generally from low blood oxygenation due to respiratory distress, or shock due to low blood pressure.  Anaphylaxis causes 500-1000 deaths per year in the US; 20 in the UK; and 15 in Australia.  These deaths are usually triggered by reactions to medication.

Epinephrine counteracts anaphylaxis by being a vasoconstrictor, which allows your body to retain fluid in its blood vessels, increasing blood pressure and reducing swelling in the skin; and relaxing smooth muscle, such as in the respiratory tract, making it easier to breathe.  Early use of epinephrine can also inhibit release of platelet activating factor (PAF), which is often active in life-threatening anaphylaxis.  Use of epinephrine can cause a decrease in plasma potassium levels, an increase in plasma glucose, and tremors. 

There is a lot of mythology surrounding when to use epinephrine.  I wanted to find an iron clad plan for determining when to use epinephrine.  What I found was that the clinical criteria for when to administer epinephrine were actually less stringent than a lot of guidelines floating around the allergic/mast cell affected public. 

The following are the clinical criteria used for diagnosing anaphylaxis.  Anaphylaxis is likely when any one of the following three criteria is met:

Criterion 1: Acute onset of illness with skin and mucosal issue involvement (hives, itching, flushing, swelling of lips/tongue/uvula) with at least one of the following: compromised airway (difficulty breathing, wheezing, low blood oxygenation); or reduced blood pressure or symptoms thereof (fainting, incontinence.)  This is the most common presentation of anaphylaxis.

Criterion 2: Two or more of the following occurring after exposure to a likely allergen: skin or mucosal tissue involvement (hives, itching, flushing, swollen lips/tongue/uvula), compromised airway (difficulty breathing, wheezing, low blood oxygenation); reduced blood pressure or symptoms thereof (fainting, incontinence); or persistent GI symptoms (cramping, abdominal pain, vomiting.) 

Criterion 3: Reduced blood pressure after exposure to known allergen.  For adults, this is <90 mm Hg systolic, or at least 30% decrease from baseline.  For children under 1 year of age, this is <70 mm Hg systolic; ages 11-17, <90 mm Hg systolic.  For children 1-10 years of age, this is <(70 mm Hg + (2x age)).  So for a child who is 8 years old, this would be <(70 + (2 x 8)) = <86 mm Hg.  This is the least common presentation of anaphylaxis.

Reference : Sampson et al, J Allergy Clin Immunol, 2006.

Please note: If you fall outside of these guidelines, and know when you are anaphylaxing, please use your epinephrine.  There will always be outliers; the criteria above encompass about 95% of cases.

So now that we know when to administer epi, let’s go over how to administer it.

Adult epipens come in 0.3 mg doses; child epipens (Epipen Jr.) comes in 0.15 mg doses.  The Mastocytosis Society protocol for patients with mastocytosis is to use one epipen every 5 minutes for up to 3 doses to stabilize blood pressure to >90 mm Hg.  Clinical protocols indicate that for adults, up to 0.5 mg of epinephrine can be administered subcutaneously or intramuscularly (like the Epipen) every 10-20 minutes as necessary for up to four doses.  After the fourth dose, any further epinephrine should be administered under medical supervision.

As you can see from comparing the clinical protocol to the standard dose Epipen, you are well within the safe dosing range by giving yourself one or two doses.  It is also important to remember that your body metabolizes epinephrine VERY quickly. 

To administer your epinephrine using an Epipen, remove the blue cap and firmly press the tip against the outside of your thigh.  Epipens are designed to inject through a single layer of clothing, but not through pockets or seams.  Injecting into the thigh makes it less likely to cause nerve or tendon damage, or accidental injection into a blood vessel.  You will hear the injector click.  Hold it in place for about fifteen seconds, then pull the Epipen away and massage the area where you injected.  Call emergency services. 

Keep two epipens on you at all times.  Store them at room temperature, and away from light.

An expired Epipen is better than no Epipen, and an adult Epipen is better for a child than no Epipen.  (http://www.allergy.org.au/health-professionals/anaphylaxis-resources/adrenaline-autoinjectors-faqs)

Anaphylaxis is a medical emergency.  It can be fatal.  There are stories floating around the internet about people dying from anaphylaxis because they were afraid to use their Epipen.  While I wasn’t able to find any statistics, I believe it.  People think if they inject themselves when they’re not anaphylaxing, it will cause a heart attack.  It will not.  People think it is really painful.  It isn’t.  This medication can save your life but only if you use it.  The risk of not using it when you are anaphylaxing is FAR GREATER than the risk of using it when you’re not anaphylaxing.

If you have any questions about when you should use epinephrine, please contact your prescribing provider.

Additional sources:

http://www.aaaai.org/ask-the-expert/epinephrine-in-anaphylaxis.aspx