Intravenous epinephrine is an option for patients with severe hypotension or cardiac arrest unresponsive to intramuscular doses of epinephrine and fluid resuscitation. Although dosages are not firmly established, 5 to 10 mcg (0.2 mcg/kg) for hypotension and 0.1 to 0.5 mg intravenously for cardiovascular collapse have been suggested.²¹ Epinephrine infusions have also been successful in treatment of anaphylaxis with hypotension.²¹

Other treatment considerations include high-flow oxygen for respiratory symptoms or hypoxemia and albuterol for bronchospasm refractory to epinephrine. Fluid resuscitation should be guided by initial response to epinephrine. Large volumes of crystalloid can be needed in the first 5 to 10 minutes, because up to 35% of blood volume can extravasate in the first 10 minutes, along with vasodilation that results in pooling, which can decrease circulating blood volume even further.²¹ A combination of both H1- and H2-antagonists has been reported to be more effective in improving the cutaneous reactions in anaphylaxis than H1-antagonists alone.²¹

CRITICAL DECISION

For how long should patients with an anaphylactic reaction be observed?

From 1% to 20% of anaphylactic reactions from all causes will be biphasic, with onset of the second phase anywhere from 1 to 72 hours after the initial onset of anaphylaxis.²¹ Unfortunately, no reliable clinical predictors enable clinicians to identify those who are more at risk for a biphasic reaction, although some studies have suggested that patients requiring higher doses of epinephrine and those who receive delayed administration of epinephrine may be at higher risk.²¹ Given these risks, a reasonable length of time to observe patients is 4 to 6 hours with consideration of a longer period of observation or hospital admission for those with particularly severe reactions or those with refractory symptoms.²¹

Case Resolution

Anaphylactic shock was suspected in this patient who reported a bee sting; epinephrine was given intramuscularly while intravenous access was obtained. He was given a 20-mL/kg fluid bolus. Diphenhydramine, ranitidine, and methylprednisolone were given intravenously. Despite these treatments, his blood pressure remained 84/46, and another fluid bolus and intramuscular dose of epinephrine were administered, after which his blood pressure and clinical condition improved. He was admitted to the emergency department’s observation unit and monitored overnight without return of his symptoms. He was discharged home with a prescription for an auto-injection epinephrine kit and a referral to an allergist.

Summary

Although most spider bites are harmless, several spiders can cause serious morbidity with rare reports of mortality. Incorrectly attributing a skin lesion to a spider bite could delay proper diagnosis and treatment; clinicians should consider the differential carefully. Insect bites are common, and most cause little more than minor irritation. Anaphylaxis, although rare, is a potentially life-threatening condition that clinicians should be able to recognize and treat rapidly.

Pearls

• Most spider bites in the United States are harmless and require only local wound care.
• Widow spider bites are characterized by both localized and generalized pain and autonomic, neurologic, and other nonspecific complaints.
• Recluse spiders are found only in certain locations in the United States and can cause severe skin lesions and systemic effects.
• Anaphylaxis is a rare but potentially lethal condition that can be caused by an insect sting; epinephrine is the treatment of choice.
• When epinephrine is required for treatment of anaphylaxis, intramuscular injection of the anterolateral thigh has faster absorption than subcutaneous or intramuscular injection in the deltoid muscle.

Pitfalls

• Attributing a skin lesion to a spider bite without consideration of other possibilities and failing to obtain an adequate history and physical examination.
• Failing to adequately observe a patient with an anaphylactic reaction for an appropriate amount of time.
• Failing to educate an anaphylactic patient on allergen avoidance and to ensure these patients have an auto-injection epinephrine kit on discharge.

Contributor Disclosures

Contributors

Nathanael J. McKeown, D.O., wrote “Spider and Insect Envenomation.” He is an assistant professor in emergency medicine at Oregon Health & Science University, a medical toxicologist with the Oregon Poison Center, and a staff physician at the Portland Veterans’ Affairs Medical Center and Oregon Health & Science University, Portland, Oregon. Robert C. Solomon, MD, is Medical Editor of ACEP News and editor of the “Focus On … Critical Decisions” series, core faculty in the emergency medicine residency at Allegheny General Hospital, Pittsburgh, Pennsylvania, and assistant professor in the Department of Emergency Medicine at Temple University School of Medicine, Philadelphia. Mary Anne Mitchell is an ACEP staff member who reviews and manages the ACEP “Focus On … Critical Decisions” series.

Disclosures

In accordance with the Accreditation Council for Continuing Medical Education (ACCME) Standards and American College of Emergency Physicians policy, all individuals in control of content must disclose to the program audience the existence of significant financial interests in or relationships with manufacturers of commercial products that might have a direct interest in the subject matter.