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Chapter 5: Shock

Shock caused by a large tension pneumothorax is categorized as

A. Trauma shock

B. Vasodilatory shock

C. Cardiogenic shock

D. Obstructive shock

Answer: D

In 1934, Blalock proposed four categories of shock: hypovolemic, vasogenic, cardiogenic, and neurogenic. Hypovolemic shock, the most common type, results from loss of circulating blood volume. This may result from loss of whole blood (hemorrhagic shock), plasma, interstitial fluid (bowel obstruction), or a combination. Vasogenic shock results from decreased resistance within capacitance vessels, usually seen in sepsis. Neurogenic shock is a form of vasogenic shock in which spinal cord injury or spinal anesthesia causes vasodilation due to acute loss of sympathetic vascular tone. Cardiogenic shock results from failure of the heart as a pump, as in arrhythmias or acute myocardial infarction (MI).

In recent clinical practice, further classification has described six types of shock: hypovolemic, septic (vasodilatory), neurogenic, cardiogenic, obstructive, and traumatic shock. Obstructive shock is a form of cardiogenic shock that results from mechanical impediment to circulation leading to depressed cardiac output rather than primary cardiac failure. This includes etiologies such as pulmonary embolism or tension pneumothorax. In traumatic shock, soft tissue and bony injury lead to the activation of inflammatory cells and the release of circulating factors, such as cytokines and intracellular molecules that modulate the immune response. Recent investigations have revealed that the inflammatory mediators released in response to tissue injury (damage-associated molecular patterns [DAMPs]) are recognized by many of the same cellular receptors (pattern recognition receptors [PRRs]) and activate similar signaling pathways as do bacterial products elaborated in sepsis (pathogen-associated molecular patterns [PAMPs]), such as lipopolysaccharide. These effects of tissue injury are combined with the effects of hemorrhage, creating a more complex and amplified deviation from homeostasis. (See Schwartz 10th ed., p. 109.)

What is true about baroreceptors?

A. Volume receptors can be activated in hemorrhage with reduction in left atrial pressure.

B. Receptors in the aortic arch and carotid bodies inhibit the autonomic nervous system (ANS) when stretched.

C. When baroreceptors are stretched, they induced increased ANS output and produce constriction of peripheral vessels.

D. None of the above.

Answer: B

Baroreceptors also are an important afferent pathway in initiation of adaptive responses to shock. Volume receptors, sensitive to changes in both chamber pressure and wall stretch, are present within the atria of the heart. They become activated with low volume hemorrhage or mild reductions in right atrial pressure. Receptors in the ...

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