Treatment

Special equipment is necessary to deal with anaphylactic events that occur in the office (Box 20-7). An algorithm for the management of the acute episode is shown in Figure 20-5.

On suspicion that an anaphylactic event has occurred, therapy should be initiated immediately (Box 20-8). The airway, circulation, and level of consciousness should immediately be assessed. Oxygen should be started and the patient placed in the recumbent position with feet elevated. The recumbent position is important because death has been associated with the upright position. The upright position allows decreased venous return to the heart, resulting in pulseless ventricular contractions and arrhythmias.

Simultaneous with assessment, epinephrine should be administered. Intramuscular (IM) injection in the lateral thigh gives a more rapid peak level than subcutaneous or deltoid IM injection; therefore the lateral thigh is the preferred site of injection. For adults, the dose is 0.2 to 0.5 mL of a 1:1000 aqueous epinephrine preparation. For children, the

Table 20-6 Tests Used to Confirm a Diagnosis of Anaphylaxis

Test

Comment

Tests Used to Rule in Anaphylaxis

Serum tryptase

Peaks at 60 to 90 minutes after onset of symptoms. May be elevated up to 6 hours. Ideal time to obtain blood is 1 to 2 hours after symptoms begin.

Plasma histamine

Begins to rise 5 to 10 minutes after onset of symptoms. Remains elevated only up to 60 minutes.

24-hour urinary

May be assayed in urine for up to 24 hours after initiation of histamine metabolite symptoms.

Tests Used to Rule out Other Conditions

Serum serotonin

Rules out carcinoid.

Urinary 5-hidroxyendolicetic acid

Rules out carcinoid.

Serum vasointestinal hormonal polypeptide panel"

Rules out vasoactive polypeptide-secreting gastrointestinal tumor or medullary carcinoma of thyroid.

Plasma-free metanephrine and urinary vanillylmandelic acid

Rules out paradoxical response to pheochromocytoma.

"For example, pancreastatin, pancreatic hormone, vasointestinal polypeptide, and substance P.

dose is 0.01 mg/kg to a maximum of 0.3 mg. A more precise dosage regimen has been recommended by the Resuscitation Council of the United Kingdom (Box 20-9). If symptoms do not improve, this dose can be readministered at 5-minute intervals (or more frequently if the physician deems necessary). After several injections, if there is no response, an intravenous (IV) infusion of epinephrine may be considered. An infusion can be prepared by adding 1 mg (1 mL of 1:1000 dilution of epinephrine) to 250 mL of D5W, yielding a concentration of 4.0 ^/mL. This solution is infused at a rate of 1 to 4 ^/min (15-60 drops/min with microdrop apparatus), increasing to a maximum of 10.0 ^/min for adults and adolescents. For children, the dose is 0.01 mg/kg (0.1 mL/ kg of 1:10,000 solution up to 10 ^/min); maximum recommended dose is 0.3 mg.

Epinephrine is mandated and the drug of choice for anaphylaxis. Other drugs include Hj and H2 antagonists; a combination of both is more effective than an Hj antagonist alone for vascular manifestations. Diphenhydramine, 25 to 50 mg for adults and 1 mg/kg for children, can be given by slow IV infusion. Ranitidine can be administered in a dose of 1 mg/kg in adults and 12.5 to 50 mg in children, infused over 10 to 15 minutes. No controlled studies have demonstrated efficacy of corticosteroids, but they should help in prolonged reactions. Although there is no established dose, the suggested dose equivalent is 1 to 2 mg/kg of methylpred-nisolone every 6 hours.

For persistent hypotension, fluids or other vasopressors (or both) should be administered. For adults with persistent hypotension, 1 to 2 L of normal saline can be administered

Box 20-7 Equipment and Medication for Therapy of Anaphylaxis in the Office

Primary

Supporting

Epinephrine solution (aqueous) 1:1000 (1-mL ampules and multidose

Dopamine

vials)

Suction apparatus

Epinephrine solution (aqueous) 1:10,000 (commercially available

Sodium bicarbonate

preloaded in a syringe)

Aminophylline

Tourniquet

Atropine

1-mL and 5-mL disposable syringes

IV setup with needles, tape, and tubing

Oxygen tank and mask or nasal prongs

Nonlatex gloves

Diphenhydramine injectable

Optional

Ranitidine or cimetidine injectable

Injectable corticosteroids

Defibrillator

Ambubag, oral airway, laryngoscope, endotracheal tube, no. 12 needle

Calcium gluconate

Intravenous setup with large-bore catheter

Neuroleptic agents for seizures

IV fluids: 2000 mL of crystalloid solution, 1000 mL of hydroxyethyl starch

Lidocaine

Aerosol beta-II bronchodilator and compressor nebulizer

Glucagon

Electrocardiogram

Normal saline: 10-mL vial for epinephrine dilution

Observe for a minimum of 2 hours and if severe episode, longer; then discharge.

Good clinical response

Assess airways, state of consciousness; initiate oxygen; place patient in recumbent position with legs elevated. Inject epinephrine.

Consider the following: Intravenous epinephrine Combination of H1 and H2 antagonists Inhaled bronchodilators for asthma Corticosteroids Vasopressors

Begin measures for transportation to tertiary care unit

Resume further therapy in tertiary care unit

Poor clinical response

Figure 20-5 Algorithm for managing an episode of anaphylaxis.

at rates of 5 to 10 mg/kg in the first 5 minutes. After resolution of symptoms, patients should be observed because biphasic reactions can occur in up to 23% of cases (Scranton et al., 2009). The observation period should range from 6 to 24 hours, depending on the severity of the reaction (Tole and Lieberman, 2007).

Patients who have experienced episodes of anaphylaxis and who are at further risk of future events (e.g., insect sting hypersensitivity, food allergy) should have a prescription for an epinephrine autoinjector and should be instructed in its use. In addition, such patients should not take, if at all possible, drugs that might increase the severity of any future event or interfere with the use of epinephrine to treat such an event (Table 20-7).

KEY TREATMENT

Epinephrine should be the first medication used in the treatment of anaphylaxis (SOR: A).

Patients should be placed in supine position and oxygen administered, if needed (SOR: A).

Treatment with IV fluids, antihistamines (both H, and H2), and corticosteroids should be considered after epinephrine administration (SOR: A).

Glucagon or atropine should be considered in anaphylaxis recalcitrant to treatment (SOR: A).

Box 20-8 Therapy for Anaphylaxis

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