Shock caused by a large tension pneumothorax is categorized as:
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.
What is true about baroreceptors?
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 aortic arch and carotid bodies respond to alterations in pressure or stretch of the arterial wall, responding to larger reductions in intravascular volume or pressure. These receptors normally inhibit induction of the autonomic nervous system (ANS). When activated, these baroreceptors diminish their output, thus disinhibiting the effect of the ANS. The ANS then increases its output, principally via sympathetic activation at the vasomotor centers of the brain stem, producing centrally mediated constriction of peripheral vessels.
Chemoreceptors in the aorta and carotid bodies do NOT sense which of the following?
Chemoreceptors in the aorta and carotid bodies are sensitive to changes in O2 tension, H+ ion concentration, and carbon dioxide (CO2) levels. Stimulation of the chemoreceptors results in vasodilation of the coronary arteries, slowing of the heart rate, and vasoconstriction of the splanchnic and skeletal circulation. In addition, a variety of protein and nonprotein mediators are produced at the site of injury as part of the inflammatory response, and they act as afferent impulses to induce a host response.
Neurogenic shock is characterized by the presence of:
Neurogenic shock is caused by loss of arteriolar and venular tone in response to paralysis (such as occurs with high spinal anesthesia), acute gastric dilatation, or sudden pain, or unpleasant sights; as such, it is characterized by a decrease in peripheral vascular resistance. Affected patients usually present with warm, dry skin, a pulse rate that is slower than normal, and hypotension. A normovolemic state usually exists, and urine output is generally well maintained. Although blood volume measurements indicate a normal intravascular volume, because of the greatly increased reservoir capacity of the arterioles and venules, there is a decrease in cardiac output secondary to decreased venous return to the right side of the heart.
When a patient with hemorrhagic shock is resuscitated using an intravenous colloid solution rather than lactated Ringer solution, all of the following statements are true EXCEPT:
Because of higher osmotic pressure, colloid solutions draw extracellular fluid into the vascular space, increasing the extracellular fluid deficit. In addition, the ionized fraction of serum calcium is decreased, circulating levels of immunoglobulin drop, and reaction to tetanus toxoid given to the patient suffering from major trauma is decreased. Endogenous production of albumin also decreases. Colloid resuscitation is no more effective than crystalloid resuscitation, and it is more expensive.
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