Emergency Treatment

The patient having an anaphylactic reaction, as defined by airway compromise or hypotension, is a true medical emergency and must be rapidly assessed and treated. Exposure to the causative agent, if identified, must be terminated if ongoing. Vital signs, intravenous (IV) access, oxygen, cardiac monitoring, and pulse oximetry measurements should be ordered immediately. Securing the airway is the first priority. The airway should be examined for angioedema. If angioedema is producing respiratory distress, the patient should be intubated immediately, since delay may result in complete airway obstruction secondary to progression of angioedema. An endotracheal tube one or more sizes smaller than normal may be needed.10 The patient should be given sufficient oxygen to maintain a pulse oximetry value greater than 92%. Intubation is indicated if hypoxemia is refractory to 100% oxygen therapy.

Epinephrine is the cornerstone of treatment for anaphylactic reactions. If the patient has severe bronchospasm, laryngeal edema, signs of upper airway obstruction, respiratory arrest, or signs of shock, IV epinephrine is indicated.10 Initially, 100 ^g of IV epinephrine should be given in a 1:100,000 dilution. This can be done by placing 0.1 mL of 1:1000 epinephrine in 10 mL of normal saline solution (NS) and infusing it over 5 to 10 min (a rate of 1 to 2 mL/min). 21! If the patient is refractory to the initial bolus, then an epinephrine infusion can be started, according to the 1997 Advanced Cardiac Life Support (ACLS) guidelines, by placing 1 mg of 1:1000 epinephrine in 500 mL of dextrose in water (D5W) or NS and running at a rate of 1 to 4 ^g/min (0.5 to 2 mL/min), titrating to effect. The pediatric epinephrine infusion rate starts at 0.1 ^g/kg/min and can be increased up to 1.5 ^g/kg/min.11 If hypotension is present, the patient should receive a NS bolus of 1 to 2 L concurrently with the epinephrine infusion. For hypotension refractory to 2 L NS infusion and epinephrine, colloid infusion should be considered. Physicians are often hesitant to give IV epinephrine due to its side effects. It should be stressed that the initial adult dose is 100 ^g (0.1 mg) IV of 1:100,000 dilution given over 5 to 10 min and that the dose can be stopped immediately if arrhythmias or chest pain occurs.

For less severe signs, such as decreasing blood pressure without hypotension [systolic blood pressure (SBP) > 90 mmHg], symptomatic dyspnea, abdominal cramps, and urticaria, subcutaneous (SC) epinephrine can be given.10 The dose is 0.3 to 0.5 mL of 1:000 epinephrine (pediatric dose 0.01 mL/kg 1:1000) SC, repeated every 5 to 10 min according to response. If the patient is refractory to treatment despite repeated SC epinephrine, then IV epinephrine infusion should be instituted.

The first-line therapies for anaphylaxis are epinephrine, IV fluids, and oxygen, which have immediate effect during the acute stage of anaphylaxis. The second-line drugs are antihistamines, corticosteroids, glucagon, albuterol, and aminophylline. These drugs are used to prevent recurrences and treat anaphylaxis refractory to the first-line treatments. All patients with anaphylaxis should receive corticosteroids and antihistamines. Methylprednisolone 125 mg IV and a histamine 1 (HJ blocker, such as diphenhydramine 25 to 50 mg IV, should be given.2 Since the histamine2 (H2) blockers have been shown to be effective in shock refractory to epinephrine, fluids, steroids, and H blockers, it is recommended that H2 antihistamines be given as well.27 It is the authors' opinion that an H2 blocker other than cimetidine should be used in anaphylaxis. Cimetidine prolongs metabolism of b blockers, resulting in a possible prolongation of the anaphylactic state in patients who take b blockers. Cimetidine likewise interferes with the metabolism of many other drugs, including aminophylline, which may be used in refractory bronchospasm. After the initial IV dose of steroids and antihistamines, the patient may be switched to oral medication (T.aMe...,3.0.-2.).

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