Wasp Stings Treatment & Management

The "ABCs" (airway, breathing, circulation) of patient resuscitation and care take precedent. Airway patency and security is the prime concern, especially if there is any evidence of potential airway obstruction from angioedema manifested by stridor, hoarseness of voice, difficulty swallowing, or pooling of secretions. Breathing should be assessed for the rate, depth and adequacy of ventilation with pulse oximetry and auscultation of the chest to determine air movement, and the presence of wheezing from bronchial constriction and spasm. The patient's circulatory status should be evaluated for presence of distributive shock, assessing the blood pressure, nail bed capillary refill, and the patient's mental status.

Local wound care

Apply ice to keep the area comfortably cool and to reduce swelling. Unlike honeybee stings, members of the wasp family (including hornets and yellow jackets) generally do not lose their stinging apparatus in the wound. Consider a secondary bacterial infection at the site in patients who present several days after the sting with fever or continued redness, warmth, swelling, and tenderness over the site or progression of the redness—red streaks that progress proximally.

Urticaria

Antihistamines remain the mainstay of therapy. H1 blockers such as oral diphenhydramine (Benadryl) or hydroxyzine (Atarax) have proven useful in reducing the severity of the itching and rash. Oral steroids (eg, prednisone, methylprednisolone [Medrol]) can be added to the regimen if needed, depending on the extent and severity of the patient's symptoms. Epinephrine, 0.3-0.5 mL subcutaneously in a 1:1000 solution, can also be used. Although it reverses the extent and itching of the urticaria, its benefit-to-risk ratio must be considered. The alpha effect of epinephrine increases the systemic vascular resistance, while its beta effect has a positive inotropic and chronotropic effect on the heart. This produces an increase in the heart's work and increases the myocardial oxygen demand. This may have a deleterious effect in patients with preexisting heart disease or coronary artery disease.

Anaphylaxis

The patient may present with airway obstruction due to angioedema, respiratory compromise due to bronchospasm, or circulatory collapse or with a combination of these three conditions. Follow the ABCs of emergency medicine as expediently as possible. The airway must be secured. Intubate the patient with rapid sequence technique upon evidence of impending airway obstruction due to swelling or evidence of respiratory failure due to bronchospasm. It is easier to extubate a patient than to wait too long and try to pass a tube through an edematous larynx. Establish two large-bore intravenous lines to provide a route for medication administration and for fluid bolus in the event of circulatory collapse. Place the patient on both pulse oximetry and a cardiac monitor.

Angioedema

If intubation is impossible because of the degree of swelling, obtain a surgical airway through cricothyrotomy. Surgical cricothyrotomy is contraindicated in patients younger than 8 years. In these cases, perform needle cricothyrotomy using the largest-bore needle practical as a temporizing measure. Obtain an emergency consultation with an anesthesiologist and an otorhinolaryngologist (ENT) to prepare the child for the operating room for definitive angioedema/airway management if parenteral beta agonists, histamine 1 (H1) blockers, and glucocorticoids do not relieve the obstruction.

Bronchospasm

Treatment of bronchospasm without obstruction depends on the acuity of the patient's presentation. Treat mild-to-moderate distress with a combination of nebulized beta agonist (eg, albuterol 0.5 mL of 0.5% solution in 2.5 mL of normal saline nebulized q15min) and parenteral glucocorticoids (eg, methylprednisolone 125 mg IV). As the severity of the respiratory distress increases, weigh the benefit-to-risk ratio of using a parenteral beta agonist (eg, epinephrine). As bronchospasm worsens, a point of peaked expiratory flow and forced expiratory volume decrease occurs and the only area being ventilated with the nebulized beta agonist is the appropriately named dead space.

Epinephrine, 0.3-0.5 mL of a 1:1000 solution, may be administered intramuscularly. Its onset of action should be 3-5 minutes; however, impending circulatory collapse with peripheral vasoconstriction due to anaphylaxis may make this route ineffective. Intravenous epinephrine using 3-5 mL (0.3-0.5 mg) of the 1:10,000 solution (0.1 mg/mL) diluted in 10 mL of normal saline or distilled water should be administered slowly over a 1- to 2-minute period, depending on the patient's condition. ^[28] The primary cause of death in anaphylaxis is failure to administer epinephrine in a timely manner. Less than a quarter of patients with cardiac arrest from anaphylaxis receive epinephrine before the cardiac arrest. ^[23] Epinephrine is given in less than half of cases of true anaphylaxis. ^[8]

As an alternative, 3-5 mL of 1:10,000 solution can also be administered via the endotracheal tube. Administer this solution via a catheter with the tip placed below the end of the endotracheal tube and then flushed through with several milliliters of saline or distilled water. Several positive ventilations follow to force the epinephrine into the terminal bronchioles and alveoli.

Vasopressin 40 IU has also been used for refractory hypotension.

Hypotension

The cause of hypotension is multifactorial. Histamine, prostaglandin, and leukotriene can reduce the systemic vascular resistance by vasodilating the peripheral vessels and increase the capillary endothelial permeability, allowing extravasation of fluid into the third space. The net effect of both of these processes increases the vascular bed and decreases the amount of fluid in the vascular compartment. Begin treatment with the establishment of 2 large-bore intravenous lines and crystalloid fluid boluses. Vasopressors then can be added, depending on the patient's clinical appearance. Epinephrine can be administered via continuous infusion by mixing 1 mg in 250 mL of normal saline and infusing at a rate of 0.5-1 mL/min. Norepinephrine (Levophed) can also be used. It has the advantage of having more of an alpha effect and less of a beta effect than epinephrine.

Pregnancy

Envenomations can cause miscarriage, stillbirth, placenta abruptio, and preterm birth. Current literature suggests that the best approach to improve fetal output is to optimize the maternal health by treating hypotension and anaphylaxis in the mother. Observation and fetal monitoring are mandatory in severe envenomations with viable fetuses. ^[29]

All patients who present with a moderate-to-severe reaction to a wasp sting that required treatment should be observed. A rebound or biphasic reaction has been reported in 1-20% of patients as initial treatment wears off.

Airway

Proactively treat patients who experience throat tightness resulting from a wasp sting. A treatment spectrum progresses from the asymptomatic patient to the patient with symptoms of mild throat tightness to the patient in respiratory distress from angioedema.

Assess the airway as soon as possible in the patient who experiences throat tightness. Although cross-lateral neck radiography to assess soft tissue can be helpful to rule out gross swelling, it has several disadvantages. It may not reveal early swelling. If transferred to the radiology department for the radiograph, the patient should be accompanied by both an intubation tray and a physician capable of managing the airway.

The airway is best visualized by either an otorhinolaryngologist or an emergency department (ED) physician using a Machida scope or, if a flexible fiberoptic scope is not available, indirect laryngoscopy. An intubation tray must be available at the bedside.

Supplemental oxygen supplied by a humidified cool mist is often helpful in the patient with minimal inflammation who does not need immediate intubation and is being observed.

Breathing

Continually monitor patients with pulse oximetry. Peak flow measurement may help evaluate the progression of bronchial spasm.

Evidence of poor ventilation with decreasing oxygen saturations, poor air movement, wheezing, poor air exchange, prolongation of the expiratory phase, or increased work of breathing requires aggressive management.

A nebulized beta agonist (eg, albuterol) can reduce bronchial spasm and improve oxygenation.

Use methylprednisolone 125 mg IV to decrease the inflammatory response of the airways.

Circulation

The cardiac rate and rhythm and the intravascular fluid compartment are 2 components of circulation that must be monitored.

Put the patient on a cardiac monitor and observe in an area where the patient can be intubated if necessary.

The BP must be monitored continuously because of the release of multiple factors in anaphylaxis that can reduce capillary integrity, increase capillary permeability, and subsequently decrease the amount of fluid in the vascular compartment and, at the same time, decrease the systemic vascular resistance.

Consider a surgical airway in any patient with evidence of upper airway edema or laryngeal spasm who is experiencing respiratory deterioration. The equipment and expertise to perform a cricothyrotomy should be readily available if orotracheal or nasotracheal intubation cannot be achieved.

Transfer the patient to the nearest facility capable of providing critical care monitoring if critical care monitoring cannot be performed at the facility initially treating the patient (in accordance with the current standards established by the Emergency Medical Treatment and Labor Act [EMTALA]).

A person capable of aggressively managing the patient's airway and monitoring and managing the patient's cardiopulmonary function should accompany the patient.

The transporter should have all the equipment and medication necessary to resuscitate the patient.

Patients should be taught the use of the EpiPen 0.3 mg auto-injector or the EpiPen Jr 0.15 mg before they leave the ED. The patient should be taught the indications for the use of the EpiPen such as the signs and symptoms of a severe allergic or anaphylactic reaction. They should be taught to inject the EpiPen into the anterolateral aspect of the thigh and that once the auto-injector is triggered to maintain the auto-injector in place for several seconds until all the medication is injected. The patient should be advised to keep one EpiPen in the home and one on his or her person at all times. Epinephrine is light sensitive and should be stored between 15^o -30^o C (59^o -86^o F). ^[30] Placement of an EpiPen in the car where internal summer temperatures can be well over 100^o F is not recommended.

Oral H1 blockers (eg, diphenhydramine, hydroxyzine) and corticosteroids (eg, prednisone, methylprednisolone) also may be helpful.

A consultation with an otorhinolaryngologist may be necessary to visualize the epiglottic and supraglottic regions with a flexible fiberoptic laryngoscope in patients who experience throat tightness or throat closing and who present with little or no objective signs of airway compromise.

In patients with symptoms of throat tightness or throat closing with mild-to-moderate signs of airway compromise or patients who have evidence of early airway obstruction on flexible fiberoptic laryngoscopy, consultation with an anesthesiologist may be necessary to assist in securing the airway.

Patients who have moderate-to-severe signs and symptoms of airway compromise, such as increasing dyspnea, hoarseness, dysphagia, inability to clear secretions, use of accessory muscles, or decreasing oxygen saturation on pulse oximetry, require emergent consultation with both an anesthesiologist and an otorhinolaryngologist to place a surgical airway if intubation is unsuccessful. Rapid sequence intubation in these patients should be used with caution. The airway may be maintained open only by the patient's laryngeal muscles. The use of paralytics may allow the airway to be completely occluded.

Advise patients who have experienced an allergic reaction to prior wasp stings or to any Hymenoptera stings to exercise caution while outdoors during mild-to-warm weather. Advise these patients to avoid wearing any scented material (eg, perfume, hairspray, soaps, deodorants, sunscreen). Brightly colored clothing, especially floral designs, should be avoided. Tell patients who have experienced a severe reaction to a wasp sting to curtail solitary outdoor activities. Advise that the patient should be accompanied when outdoors and away from populated areas (eg, hiking, fishing) in case help is needed.

Because odors tend to attract wasps, tell patients and their families to examine the home environment to decrease risks of attracting insects. Cover garbage pails. Remove rotting fruit on the vine or tree or after having fallen to the ground.

Encourage patients to carry EpiPen auto-injectors when outdoors and to have one device in the home. Advise the patient that auto-injectors left in the car for prolonged periods during hot days may not be effective. They should periodically review the expiration date of the auto-injectors.

Teach the patient how to modify behavior, to dress, and to use toiletries and perfumes appropriately (see Activity).

Refer the patient to an allergist for desensitization to Hymenoptera venom. Desensitization by venom immunotherapy can be accomplished by the injection of depot extracts using a slow and conventional schedule, which minimizes local and systemic side effects, or it can be accomplished rapidly by using a rush protocol with aqueous extracts if protection needs to be achieved rapidly. However, the incidence of severe reactions makes the rush protocol less than ideal for an outpatient procedure and requires hospitalization. ^[31]

Venom immunotherapy can reduce the relative risk of a future severe reaction to 0.1 as well as reduce the severity of the local reaction. Unfortunately, health economic analysis shows that it is not cost effective because of the infrequency that people are stung. In patients who are at risk for frequent stings, such as beekeepers, venom immunotherapy improves the quality of their life and can be cost effective. ^[32]

Up to 25% of patients who are on venom immunotherapy will still develop a severe anaphylactic reaction when re-stung. ^[31]

Prescribe autoinjectors (eg, EpiPen) and oral H1 blockers (eg, diphenhydramine, hydroxyzine). Teach the patient and patient’s family that they need to hold the auto injector on the skin for 10 seconds to let all the medicine enter the muscle.

Delayed biphasic reactions can occur in 4% of severe allergic reactions and up to 72 hours after exposure. Risk factors include prior history of anaphylaxis, unknown trigger, and delay of epinephrine use more than 60 minutes from onset of symptoms. ^{[33, 34]}

Direct outpatient care at preventing any further reaction.

Provide patient education to reduce high-risk activities that may lead to exposure (see Activity).

Prescribe self-administered auto-injectors (eg, EpiPen) to patients who have the potential for a severe reaction or who may be away from readily available medical assistance.

Refer patients to an allergist for desensitization. This follow-up referral should be made expeditiously. The factors to consider are include initial reaction of the patient and the patient's risk of being stung again, such as the patient's occupation and time of year.