Anaphylaxis: Clinical sciences

Anaphylaxis refers to an acute, potentially life-threatening allergic reaction that occurs in response to antigens that don’t cause problems for most people. Common anaphylactic triggers include foods like nuts, milk, shellfish, and eggs, as well as certain medications like penicillin, IV contrast agents; and insect stings.

The first exposure to a specific antigen is called sensitization and typically occurs with minimal or no signs or symptoms. But, on second exposure, IgE-mediated activation of basophils and mast cells leads to the release of pro-inflammatory mediators, such as histamine, prostaglandins, and cytokines. These mediators reach the bloodstream and spread throughout the body, causing an overwhelming systemic inflammatory reaction that can ultimately result in anaphylactic shock or even death.

Now, if you suspect anaphylaxis, you should first perform an ABCDE assessment to determine if your patient is unstable or stable. If the patient is unstable, stabilize the airway, breathing, and circulation. This means that you might need to intubate the patient. Do this as soon as possible, since airway edema can progress quite quickly and become more severe, making intubation very difficult. However, if you are unable to intubate, immediately call the surgery team to evaluate for possible surgical airway management, such as cricothyrotomy.

Next, obtain IV access and, if your patient is hypotensive, start IV fluids for volume resuscitation. In severe cases, you may need to administer immediate intramuscular epinephrine, even before obtaining very focused history and physical examination. Finally, put your patient on continuous vital sign monitoring, such as pulse oximetry, blood pressure, and heart rate.

Let’s go back to the ABCDE assessment. Now, if the patient is instead stable, obtain IV access and put them on continuous vital sign monitoring. Now that you’ve initiated the acute management, in both, stable and unstable individuals, it’s important to quickly obtain focused history and physical examination. Also order labs, primarily tryptase, which is a good indicator of mast cell degranulation. History often reveals definite or at least suspected recent allergen exposure, but in some cases, the trigger can remain unknown.

Next, physical examination typically reveals mucocutaneous, respiratory, cardiovascular, and gastrointestinal findings. Common mucocutaneous findings include urticaria, intense itching, and edema of the mucous membranes. In severe cases, edema of the larynx can result in laryngeal edema, which can be associated with voice hoarseness and stridor. On the other hand, common respiratory findings include labored breathing and wheezing, while cardiovascular manifestations include hypotension and syncope. In addition, if the gastrointestinal system is affected, the patient might present with crampy abdominal pain and vomiting. Finally, labs might reveal an elevated tryptase level, which helps confirm the diagnosis. However, keep in mind that tryptase won’t peak until 1 to 1.5 hours after the onset of symptoms.

Now that you have identified anaphylaxis, there are a few measures you'll want to take immediately. First, administer intramuscular epinephrine into the lateral thigh at the midpoint. This should not be delayed for any reason! Epinephrine is generally well tolerated, and there are no absolute contraindications to its administration. Epinephrine raises blood pressure, reduces bronchospasm, and counteracts the effect of circulating inflammatory mediators. In children weighing less than 25 kg, administer 0.15 mg of epinephrine; while in children weighing more than 25 kg and adults, administer 0.30 mg.

Next, put your patient in an appropriate position based on their clinical presentation. If your patient presents with cardiovascular manifestations, such as hypotension, lay them in a supine position with the legs elevated to maximize central perfusion. Alternatively, if they are vomiting or unconscious, position them in a recovery position. Moreover, pregnant patients should always be positioned on the left side to avoid compression of the inferior vena cava, which can lead to further cardiovascular complications. If they present with respiratory manifestations, put them in a sitting position with their legs outstretched to maximize lung expansion. Finally, if the patient is a baby or child, hold them flat, not upright.

Once your patient is appropriately positioned, look for the trigger. If you identify the potential trigger, remove it! For example, you can stop the infusion of a causative medication or remove an insect stinger stuck in the skin. However, keep in mind that this is often not possible, because triggers like nuts or shellfish might have been ingested.