Anaphylaxis medical therapy
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Medical Therapy
Emergency treatment
Anaphylaxis is a life-threatening medical emergency because of rapid constriction of the airway, often within minutes of onset, which can lead to respiratory failure and respiratory arrest. Brain and organ damage rapidly occurs if the patient cannot breathe. Due to the severe nature of the emergency, patients experiencing or about to experience anaphylaxis require the help of advanced medical personnel. First aid measures for anaphylaxis include rescue breathing (part of CPR). Rescue breathing may be hindered by the constricted airways, but if the victim stops breathing on his or her own, it is the only way to get oxygen to him or her until professional help is available.
Another treatment for anaphylaxis is administration of epinephrine (adrenaline). Epinephrine prevents worsening of the airway constriction, stimulates the heart to continue beating, and may be life-saving. Epinephrine acts on Beta-2 adrenergic receptors in the lung as a powerful bronchodilator (i.e. it opens the airways), relieving allergic or histamine-induced acute asthmatic attack or anaphylaxis. If the patient has previously been diagnosed with anaphylaxis, they may be carrying an EpiPen (or TWINJECT TM) for immediate administration of epinephrine. However, use of an EpiPen or similar device only provides temporary and limited relief of symptoms.
Tachycardia (rapid heartbeat) results from stimulation of Beta-1 adrenergic receptors of the heart increasing contractility (positive inotropic effect) and frequency (chronotropic effect) and thus cardiac output.[1] Repetitive administration of epinephrine can cause tachycardia and occasionally ventricular tachycardia with heart rates potentially reaching 240 beats per minute, which itself can be fatal. Extra doses of epinephrine can sometimes cause cardiac arrest. This is why some protocols advise intramuscular injection of only 0.3–0.5mL of a 1:1,000 dilution.
Some patients with severe allergies routinely carry preloaded syringes containing epinephrine, diphenhydramine (Benadryl), and dexamethasone (Decadron) whenever they go to an unknown or uncontrolled environment.These three injections, taken at the beginning of anaphylaxis, can often bring it under control and avoid a trip to the Emergency Room.
Clinical care
Paramedic treatment in the field includes administration of epinephrine IM (or IV infusion in severe cases), Benadryl IM, steroids such as Decadron, IV Fluid administration and in severe cases, pressor agents (which cause the heart to increase its contraction strength) such as Dopamine for hypotension, administration of oxygen, and intubation during transport to advanced medical care.
In severe situations with profuse laryngeal edema (swelling of the airway), cricothyrotomy or tracheotomy may be required to maintain oxygenation. In these procedures, an incision is made through the anterior portion of the neck, over the cricoid membrane, and an endotracheal tube is inserted to allow mechanical ventilation of the victim.
The clinical treatment of anaphylaxis by a doctor and in the hospital setting aims to treat the cellular hypersensitivity reaction as well as the symptoms. Antihistamine drugs such as Benadryl (which inhibit the effects of histamine at histamine receptors) are continued but are usually not sufficient in anaphylaxis, and high doses of intravenous corticosteroids such as Decadron or Solu-Medrol are often required. Hypotension is treated with intravenous fluids and sometimes vasopressor drugs. For bronchospasm, bronchodilator drugs (e.g. Salbutamol, known as Albuterol in the United States) are used. In severe cases, immediate treatment with epinephrine can be lifesaving. Supportive care with mechanical ventilation may be required.
It is also possible to undergo a second reaction prior to medical attention or using an epipen. It is suggested to seek one to two days of medical care.
The possibility of biphasic reactions (recurrence of anaphylaxis) requires that patients be monitored for four hours after being transported to medical care for anaphylaxis.[2]