A previously healthy 15-year-old girl is brought to the emergency department due to respiratory distress and continuous cough after eating at a buffet in a local restaurant. Blood pressure is 80/40 mm Hg, pulse is 130/min, and respirations are 32/min. She is in marked respiratory distress but is able to speak. Diffuse wheezing and erythematous skin rash are present. Which of the following hemodynamic changes are most likely present in this patient?

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11ec160b_3a77_7015_9249_b7ff67b79f36_MD0001_00 This patient with respiratory distress, wheezing, and erythematous skin rash following food exposure likely has anaphylaxis; her severe hypotension and tachycardia indicate anaphylactic shock. The primary disturbance in distributive shock (eg, septic shock, anaphylactic shock) is profound peripheral vasodilation which, in anaphylactic shock, results from widespread IgE-mediated release of inflammatory mediators (eg, histamine). This has the following effects: Arteriolar vasodilation causes decreased systemic vascular resistance (SVR) and consequent hypotension. Venular vasodilation causes decreased central venous pressure (CVP) and reduces venous return to the right atrium (Choice D). The vasculature becomes leaky, resulting in loss of intravascular volume that further contributes to both hypotension and decreased CVP. With reduced venous return to the right atrium, there is reduced right ventricular output and reduced blood delivery to the left atrium and left ventricle. This leads to decreased pulmonary capillary wedge pressure (PCWP), a reflection of left atrial pressure. Despite the reduced left ventricular preload, cardiac output is commonly normal or increased in early distributive shock due to both the large decrease in SVR and a baroreceptor reflex-mediated increase in heart rate (ie, tachycardia). The increased cardiac output leads to increased mixed venous oxygen saturation due to rapid blood transit through the peripheral capillaries and incomplete oxygen uptake by the tissues. (Choice B) Hypovolemic shock involves massive intravascular volume depletion, leading to decreased CVP and PCWP. SVR is reflexively increased in response to reduced cardiac output and hypotension. (Choice C) Obstructive shock most commonly involves an obstruction to blood flow between the right atrium and the pulmonary capillaries (eg, pulmonary embolism). CVP is increased, PCWP is decreased, and there is a reflexive increase in SVR. (Choice E) Cardiogenic shock results from left ventricular failure. PCWP and CVP are increased due to backward transmission of increased pressure, and there is a reflexive increase in SVR. Educational objective: Anaphylaxis can cause distributive shock due to widespread release of inflammatory mediators (eg, histamine) that leads to massive peripheral vasodilation. Arteriolar vasodilation decreases systemic vascular resistance to cause hypotension, and venular vasodilation decreases central venous pressure and pulmonary capillary wedge pressure. Cardiac output is often increased in early distributive shock due to reduced SVR and a baroreceptor reflex-mediated increase in heart rate. __________ References: Distributive shock. (http://www.ncbi.nlm.nih.gov/pubmed/29261964)

A Previously Healthy 15-Year-Old Girl Is Brought to the Emergency