Porth's Essentials of Pathophysiology, 4e

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Heart Failure and Circulatory Shock

C h a p t e r 2 0

In a number of clinical trials, the occurrence of DIC appeared to be associated with an unfavorable outcome and was an independent predictor of mortality. The mortality rates for persons admitted to the intensive care unit who developed DIC were 45% to 78%. 76 However, it remains uncertain whether DIC was a predictor of unfavorable outcome or merely a marker of the serious- ness of the underlying condition causing the DIC. The management of sepsis-induced DIC focuses on treatment of the underlying disorder and measures to interrupt the coagulation process. Anticoagulation therapy and administration of platelets and plasma may be used. Clinical trials have shown modest to marked reductions in mortality based on the dose of antithrombin III used. Multiple Organ Dysfunction Syndrome Multiple organ dysfunction syndrome (MODS) repre- sents the presence of altered organ function in an acutely ill patient such that homeostasis cannot be maintained without intervention. 77,78 As the name implies, MODS commonly affects multiple organ systems, including the kidneys, lungs, liver, brain, and heart. Multiple organ dysfunction syndrome is a particularly life-threatening complication of shock, especially septic shock. It has been reported as the most frequent cause of death in the noncoronary intensive care unit. Mortality rates vary from 30% to 100%, depending on the number of organs involved. 77 A high mortality rate is associated with failure of the brain, liver, kidneys, and lungs. The pathogenesis of MODS is not clearly understood, and current manage- ment therefore is primarily supportive. Major risk factors for the development of MODS are severe trauma, sep- sis, prolonged periods of hypotension, hepatic dysfunc- tion, infarcted bowel, advanced age, and alcohol abuse. Interventions for multiple organ failure are focused on support of the affected organs. ■■ Circulatory shock is a life-threatening condition in which body tissues are deprived of oxygen and cellular nutrients or are unable to use these materials in their metabolic processes.The clinical presentation varies and is dependent upon the length of time tissue perfusion has been compromised. ■■ The manifestations of circulatory shock reflect both the impaired perfusion of body tissues and the body’s attempt to maintain tissue perfusion through conservation of water by the kidney, translocation of fluid from the extracellular to the intravascular compartment, and activation of sympathetic nervous system mechanisms that increase heart rate and divert blood from less essential to more essential body tissues. SUMMARY CONCEPTS

■■ Circulatory shock can result from insufficient volume within the vascular compartment (i.e., hypovolemic shock), failure of the heart as a pump (cardiogenic shock), obstruction of blood flow or venous return to the heart (i.e., obstructive shock), or a maldistribution of blood due to expanded vascular space as a result of excessive vasodilation (i.e., distributive shock). ■■ Hypovolemic shock, which serves as a prototype for circulatory shock, is characterized as low peripheral blood flow and excessive compensatory sympathetic stimulation. Decreased intravascular volume produces thirst, changes in skin temperature, decreased blood pressure, increased heart rate, decreased venous pressure, decreased urine output, and changes in the sensorium. The intense vasoconstriction that serves to maintain blood flow to the heart and brain causes a decrease in tissue perfusion, impaired cellular metabolism, excessive production of lactic acid, and, eventually, cell death. Whether the shock is irreversible or the patient will survive is determined largely by changes that occur at the cellular level. ■■ Cardiogenic shock occurs when the heart suddenly fails to pump blood sufficiently to meet the body’s demands. It most commonly occurs from an acute myocardial infarction, but may occur with other types of shock because of inadequate coronary blood flow. ■■ Obstructive shock results from mechanical obstruction of the flow of blood through the central circulation (great veins, heart, or lungs) that can be caused by a number of conditions, including dissecting aortic aneurysm, cardiac tamponade, pneumothorax, atrial myxoma, and evisceration of abdominal contents into the thoracic cavity because of a ruptured hemidiaphragm. ■■ There are three types of distributive shock that share the same basic circulatory pattern: neurogenic shock, anaphylactic shock, and septic shock. Septic shock, which is the most common of the three types, is a complex process that is associated with impaired tissue perfusion and an imbalance in the inflammatory response. Sepsis and septic shock have a high mortality rate. ■■ The complications of shock result from the continued deprivation of blood flow to vital organs or systems. Acute lung injury/acute

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