Anaphylaxis, allergic reactions

Allergic reactions can range from mild urticaria (hives) and angioedema (swelling of the face, eyelids, lips, and tongue) to severe cardiorespiratory disturbances. At the extreme end of this spectrum is anaphylaxis, which can affect the cardiovascular, pulmonary, cutaneous, and digestive systems. It is an acute and life-threatening response in patients previously sensitized to an allergen. In general, the longer the development of anaphylactic symptoms, the less severe the reaction is.

Anaphylaxis caused by food is the most common trigger, particularly peanuts, tree nuts (e.g., hazelnuts, Brazilian nuts, walnuts), fish, and shellfish. Swelling of the face and throat and breathing difficulties are typically predominant.

Anaphylaxis caused by insect stings is the second most common cause. Bee stings can leave behind a venom sac that should be scraped off (not squeezed). Allergens injected this way often lead to cardiovascular disturbances, with hypotension and shock predominating.

Medications are responsible for a high percentage of anaphylactic reactions. Slow-release medications prolong allergen absorption and exposure.

Other causes include latex, seed fluids, and more.


  • Ensure the safety of the scene and apply personal protective measures.
  • Notify the medical team
  • Evaluate ABCDE.

Check the skin for:

  • Urticaria (hives)
  • Edema around the mouth and/or inside the mouth

In the presence of a positive medical history, meaning exposure to a possible trigger, consider an ACUTE ALLERGIC REACTION when the patient has:

  • An acute onset of illness (minutes to hours) and
  • Significant skin changes (e.g., urticaria and/or angioedema)

An ANAPHYLACTIC REACTION should be suspected if, in addition to the above, the patient’s condition worsens, including:

  • Airway disturbances (e.g., dyspnea, hoarseness, stridor, wheezing, throat or chest tightness) and/or
  • Signs of cardiovascular instability (e.g., hypotension, syncope, marked tachycardia)

NOTE: Urticaria and/or angioedema are absent in 10%-15% of anaphylactic reactions, but this diagnosis should be considered when other otherwise typical manifestations are present. An anaphylactic reaction can result in edema or excessive digestive system dynamics. Patients may experience severe abdominal pain, diarrhea, nausea, and vomiting, and may describe a feeling “like it’s the end.”

If signs of anaphylaxis are present, immediately address ABC issues.

In some patients, recurrences occur hours after apparent recovery (biphasic reaction). Therefore, patients who have experienced an anaphylactic reaction should be transferred to the hospital for further evaluation and treatment.

Special attention should be paid to:

  • Airway patency – auscultation, pulse oximetry, if possible, peak expiratory flow rate (PEF)
  • Cardiovascular status (ECG and blood pressure). Systolic blood pressure <90 mmHg indicates hypotension.
  • Does the patient have a history of allergic/anaphylactic reactions?
  • Has the patient used their personal auto-injector (EpiPen)?


Allergic Reaction:

  • Initiate ABCDE care.
  • Notify the medical team
  • Determine if the history and physical findings are consistent with an allergic reaction.
  • Quickly remove the triggering source (if possible).


  • Initiate ABCDE care.
  • Notify the medical team
  • Determine if the history and physical findings are consistent with anaphylaxis (early diagnosis and treatment significantly improve outcomes).
  • Quickly remove the triggering source (if possible).
  • Administer oxygen to all patients (15 L via a mask with a reservoir bag).
  • Establish 2 large IV lines (14G or 16G).
  • Document all observations, measurements, and actions.
  • Transfer the patient to the hospital and notify the hospital if necessary.


  • Anaphylaxis can occur despite a long history of safe exposure to a potential trigger.
  • Anaphylaxis should be considered in the presence of acute skin symptoms and airway or cardiovascular disturbances.
  • Anaphylaxis can be rapid, slow, or biphasic.
  • Oxygen and adrenaline are key medications for treating anaphylaxis.


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