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shock is characterized by ________; it can be caused by ________ or by __________. The consequences are _________ and _________.
- systemic hypoperfusion of tissues
- diminished cardiac output
- reduced effective circulating blood volume
- impaired tissue perfusion
- cellular hypoxia
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Types of Shock
- Cardiogenic shock results from low cardiac output due to myocardial pump failure, caused by eg. myocardial damage (infarction), ventricular arrhythmias, extrinsic compression (cardiac tamponade), or outflow obstruction (e.g., pulmonary embolism)
- Hypovolemic shock results from low cardiac output due to loss of blood or plasma volume (e.g., due to hemorrhage or fluid loss from severe burns)
- Septic shock results from arterial vasodilation and venous blood pooling that stems from the systemic immune response to microbial infection.
- Neurogenic shock results from loss of vascular
- tone associated with anesthesia or secondary to a spinal cord injury.
- Anaphylactic shock results from systemic vasodilation and increased vascular permeability that is triggered by an immunoglobulin E–mediated hypersensitivity reaction
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Stages of shock
- initial nonprogressive stage - reflex compensatory mechanisms activated, vital organ perfusion maintained. neurohumoral mechanisms -> tachycardia, peripheral vasoconstriction (septic
- shock initially causes cutaneous vasodilation), renal fluid conservation
- progressive stage - tissue hypoperfusion, onset of worsening circulatory and metabolic derangement, including acidosis. widespread tissue hypoxia -> lactic acidosis -> blunts vasomotor response -> arterioles dilate -> Peripheral pooling
- irreversible stage - severe cellular and tissue injury, survival impossible
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Shock of any form can lead to hypoxic tissue injury if not corrected.
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Septic shock is caused by the host response to bacterial or fungal infections; it is characterized by endothelial cell activation, vasodilation, edema, disseminated intravascular coagulation, and metabolic derangements.
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causes of edema
- Increased Hydrostatic Pressure
- Reduced Plasma Osmotic Pressure - albumin lost (nephrotic syndrome) or synthesized in inadequate (severe liver disease, protein malnutrition)
- Lymphatic Obstruction - result of inflammatory or neoplastic condition
- Sodium and Water Retention
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Edema is the result of the movement of fluid from the vasculature into the interstitial spaces; the fluid may be protein-poor (______) or protein-rich (_______).
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Petechiae
hemorrhage 1 to 2 mm in diameter
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Purpura
3 to 5 mm hemorrhages
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Ecchymoses
1 to 2 cm subcutaneous hematomas (colloquially called bruises)
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Thrombus development usually is related to one or more components of Virchow’s triad:
- endothelial injury - e.g., by toxins, hypertension, inflammation, or metabolic products
- abnormal blood flow, stasis or turbulence - e.g., aneurysms, atherosclerotic plaque
- hypercoagulability: either primary (e.g., factor V Leiden, increased prothrombin synthesis, antithrombin III defciency) or secondary (e.g., bed rest, tissue damage, malignancy)
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Thrombi may propagate, resolve, become organized, or embolize; Thrombosis causes tissue injury by local vascular occlusion or by distal embolization
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Fat Embolism
- Soft tissue crush injury or rupture of marrow vascular sinusoids (long bone fracture) releases microscopic fat globules into the circulation and cause embolism. a small portion of which is fatal.
- Fat microemboli occlude pulmonary and cerebral microvasculature, both directly and by triggering platelet aggregation. exacerbated by fatty acid release from lipid globules -> local toxic endothelial injury. Platelet activation and granulocyte recruitment (with free radical, protease, and eicosanoid release) complete the vascular assault.
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Air Embolism
- Serious if trapped in coronary artery or cerebral arterial circulation
- Small venous gas emboli generally fine
- decompression sickness - also causes Grecian bend (muscle) and choke (respiratory), caisson disease (bone)
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Pulmonary emboli derive primarily from lower-extremity deep vein thrombi; their effects depend mainly on the size of the embolus and the location in which it lodges.
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Systemic emboli derive primarily from cardiac mural or valvular thrombi, aortic aneurysms, or atherosclerotic plaques.
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Pulmonary infarction is a common clinical complication, bowel infarction often is fatal, and ischemic necrosis of distal extremities (gangrene) causes substantial morbidity in the diabetic population.
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Arterial thrombosis or embolism underlies the vast majority of infarctions.
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