Читать книгу Emergency Medical Services - Группа авторов - Страница 180

Distributive shock, characterized by a decrease in systemic vascular resistance, is associated with abnormal distribution of microvascular blood flow [38]. Causes of distributive shock include sepsis, anaphylaxis, medication overdose, and acute neurological injury. The treatment of distributive shock involves the combination of vasoactive medications, which constrict the dilated vasculature, and fluids, which fill the expanded vascular tree. Commonly used vasoactive medications for distributive shock in the field include epinephrine, norepinephrine, and dopamine. Although epinephrine is easily administered via several routes (e.g., intramuscular, intravenous bolus, or infusion), the drug has significant adverse effects. Norepinephrine infusions are associated with a lower incidence of cardiac dysrhythmias than either dopamine or epinephrine [39]. In addition, studies of cardiogenic shock suggest increased mortality associated with dopamine [40]. However, continuous infusions may be difficult to maintain without special infusion pumps.

Anaphylaxis is a serious, generalized allergic or hypersensitivity reaction that can be of rapid onset (minutes to hours) and is potentially fatal. Mediators that have been implicated in the pathophysiology of anaphylaxis target the skin, digestive, respiratory, and cardiovascular systems (see Chapter 21) [41]. With respect to the cardiovascular system, these mediators can precipitate hypotension, tachycardia, vasodilatation, and increased vascular permeability. These effects result in a decrease in peripheral vascular resistance and an expanded vascular tree, precipitating distributive shock. In reality, mediators also contribute to decreased cardiac inotropic and chronotropic effects and fluid loss via edema, contributing to components of cardiogenic and hypovolemic shock, respectively [41].

The classic presentation of anaphylaxis – urticaria, shortness of breath, and hypotension precipitated by a bee sting, medication injection, or ingestion of a previously known allergen (e.g., peanut ingestion) – is rarely missed in the field. However, anaphylaxis presenting with hypotension but without a rash or an identifiable precipitant would be difficult to identify.

Epinephrine is a nonselective agonist of all adrenergic receptors. These receptors are present within organ systems affected by anaphylaxis [42, 43]. By increasing peripheral resistance via α‐1 receptors and increasing cardiac output via β‐1 receptors, epinephrine helps to reverse the distributive shock state.

The treatment of anaphylaxis is the administration of epinephrine as soon as the condition is recognized. The initial dose is typically injected intramuscularly in the lateral thigh as additional monitoring and intravenous access are obtained. The administration of antihistamines and steroids should never delay the administration of epinephrine. Prompt prehospital epinephrine injection is associated with a lower risk of hospitalization and fatality [41, 44].