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Circulatory Disturbances (Hemostasis (Normal (Process (Coagulation -->…

- - - - Arteries/arterioles: distribution
      - Capillaries: exchange
      - Venules/veins: collection
- - - - Increased metabolic activity or inflammation --> vasodilation and increased flow
      - Tissues are bright and warm
    - - Tissues are dark red, swollen and cool
      - Acute or chronic
      - Usually due to decreased venous outflow (heart failure, venous obstruction)
    - - Congestive heart failure: accumulation of blood behind the failing chamber
        
        Right heart failure: chronic hepatic congestion
        
        Left heart failure: pulmonary congestion
    - - Due to local vascular obstruction, local congestion, or decreased output
      - Metabolic needs of the tissue are not met:
        
        Decreased oxygen delivery (hypoxia)
        
        Decreased nutrient delivery (glucose)
        
        Decreased waste removal (CO2, lactic acid)
      - Clinical Significance
        
        Depends on:
        
        Local vascular anatomy (anastomoses and collateral circulation)
        
        Extent of the decreased perfusion
        
        Rate at which occlusion occured
        
        Metabolic needs of the tissue
        
        Brain and heart: most susceptible due to high need for O2 and nutrients, poor collateral circulation
        
        Lungs, GI tract, kidneys, skin: more tolerant because they already receive more blood than they need
        
        Skeletal muscle: receives blood based on immediate needs (activity)
      - Outcomes
        
        Reperfusion after brief ischemia --> complete recovery possible
        
        Reperfusion after prolonged ischemia/infarct --> inflammation and oxidative damage "reperfusion injury"
        
        Infarct: local area of tissue necrosis due to ischemia
        
        Renal infarcts: discrete triangular wedge shaped foci
        
        Acute to subacute: swollen, dark red (hemorrhagic) to tan
        
        Chronic: depressed firm and tan (fibrotic)
        
        Splenic infarcts: discrete swollen tan foci with hemorrhagic rims
    - - Clinical features
        
        Hypotension, weak pulse, tachycardia, hypervenilation, decreased urine output, hypothermia
        
        Organ system failure occurs in later stages
      - Types of shock
        
        Distributive: decreased peripheral vascular resistance and pooling of blood in peripheral tissues
        
        Hypovolemic: decreased circulating blood volume due to blood loss or fluid loss
        
        Cardiogenic: failure of heart to adequately pump blood
      - Clinical Significance
        
        Tissue perfusion leads to:
        
        Cell injury (reversible --> irreversible
        
        Cell death
        
        Cellular hypoxia, shift to anaerobic metabolism
- - - - Water ~60% of body weight
        
        ~2/3 intracellular
        
        ~1/3 extracellular
        
        ~80% in interstitium
        
        ~20% in plasma
  - - - Gross appearance
        
        Clear to light yellow watery (serous) fluid that expands the interstitium/accumulates in body cavities
      - Terms
        
        Pulmonary edema: serous fluid in the lungs (alveoli/interstitium)
        
        Hydrothorax: serous fluid in thoracic cavity
        
        Hydropericardium serious fluid in pericardial sac
        
        Hyrdoperitoneum: serous fluid in peritoneal cavity also known as ascites
      - Microscopic appearance
        
        Amporphous pale pink fluid or clear space between cells or filling spaces
      - Causes of edema
        
        Increase microvascular permeability
        
        Due to inflammatory/immunologic stimuli
        
        Localized release of inflammatory mediators
        
        Histamine
        
        Bradykinin
        
        Leukotrienes
        
        Increase intravascular hydrostatic pressure
        
        Due to increased blood volume in the microvasculature
        
        Often passive
        
        Localized or generalized
        
        Examples
        
        venous obstruction
        
        increase hydrostatic pressure
        
        fluid movement into extravascular space
        
        edema
        
        Accumulation of blood behind the venous obstruction
        
        heart failure
        
        accumulation of blood in veins and capillaries behind the failing chambers
        
        increase hydrostatic pressure
        
        fluid movement into extravascular space
        
        edema
        
        Right heart failure
        
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        Pooling of blood in pulmonary venous system pulmonary edema
        
        Decrease oncotic (plasma colloid osmotic) pressure
        
        Due to decreased plasma protein concentration
        
        Hypoalbuminemia
        
        Hypoproteinemia
        
        Decrease oncotic pressure
        
        Decrease fluid resoprtion
        
        Extravacular fluid accumulation
        
        Edema
        
        Excessive loss (kidney/GI) or decreased production (liver)
        
        Usually generalized
        
        Decrease lymphatic drainage
        
        Due to lymphatic vessel compression/obstruction
        
        Congential (rare) or due to neoplasia, inflammation, fibrosis
        
        Usually localized
      - Clinical Signficance
        
        Minimal
        
        Subcutatenous edema, ascites: minimal significance but indicator of circulatory dysfunction
        
        Critical
        
        Pulmonary edema, hydrothorax, hydropericardium: can significantly impact lung/heart function
        
        Cerebral edema: increased pressure in confined space of cranial cavity can significantly impact brain function
- - - - Coagulation --> fibrin meshwork (secondary hemostasis)
      - Fibrinolysis --> removal of platelet/fibrin plug (thrombus retraction)
      - Vasoconstriction and platelet aggregation --> platelet plug formation (primary hemostasis)
      - Tissue repair
  - - - Blood vessels
      - Platelets
      - Coagulation factors
      - Terms
        
        Hematoma: in a focal confined space
        
        Hemothorax: blood in thoracic cavity
        
        Suffusive: even larger (>3cm)
        
        Hemopericardium: blood in pericardial sac
        
        Ecchymosis: larger (up to 2-3cm)
        
        Hemoabdomen or meoperitoneum: blood in abdominal/peritoneal cavity
        
        Petechia: pinpoint (1 to 2mm)
        
        Hemarthrosis blood in joint
      - Causes
        
        Blood vessel injury
        
        Endotoxemia
        
        Uremic toxins
        
        Infectious agents
        
        Immune complexes (type III hypersensitivity)
        
        Invasive neoplams
        
        Collagen disorders (inherited or nutritional)
        
        Inflammation
        
        Trauma
        
        Examples
        
        Guttural pouch mycosis --> carotid artery injury and hemorrhage
        
        Vitamin C deficiency predisposing to blood vessel injury and hemorrhage
        
        decreased collagen cross linking --> fragile blood vessels
        
        due to dietary deficiency in species that cannot synthesize vitamin C
        
        humans and most human primates
        
        guinea pigs
        
        bats
        
        Decrease platelets
        
        Increase destruction/use (immune-mediated thrombocytopenia, DIC)
        
        Decreased function (inherited or acquired)
        
        Decreased production (megakaryocyte injury/destruction, bone marrow suppression)
        
        Examples
        
        Thrombocytopenia --> cutaneous hemorrhage (petechiae/ecchymoses)
        
        Disseminated intravascular coagulation (DIC)
        
        Due to diffuse endothelial damage or generalized platelet activation --> microthrombi and ischemia
        
        Continuous activation of coagulation and fibrinolytic pathways --> consumption of platelets and coagulation factors (consumptive coagulopathy) --> widespread hemorrhage
        
        Many possible causes infectious agents, neoplasia, inflammation/necrosis, intravascular hemolysis, envenomation
        
        Decrease clotting factors
        
        Decreased production
        
        Inherited deficiencies
        
        Increased use
        
        Examples
        
        Anticoagulant rodenticide poisoning
        
        Vitamin K antagonists: found in prescription medications (warfarin, Coumadin), anticoagulant rodenticides (warfarin, brodifacoum), moldy sweet clover (dicumarol)
        
        Inhibit vitamin K epoxide reductase decrease active reduced vitamin K, decreased production of vitamin K dependent coagulation factors (II, VII, IX, X)
        
        Hookworm Infection
        
        Mucosal damage and anticoagulant secretion by worms --> intestinal blood loss and anemia
      - Clinical Significance: depends on amount, rate, and location
        
        Slow/persistant blood loss: compensation possible
        
        Pressure from hemorrhage can interfere with tissue function (most significant in vital organs or tissues with little room to expand, such as brain or heart)
        
        Hypovolemic shock: rapid loss of large volume
    - - Thrombus: aggregate of platelets, fibrin, and other blood elements (erythrocytes, neutrophils) formed on a vessel or heart wall
      - May be physiologic (part of normal hemostasis; usually rapidly resolved after vascular healing) or persistent/inappropriate
      - Terms
        
        Mural thrombus: is attached to the vessel or heart wall at its site of origin
        
        If a thrombus or fragment breaks loose and enters the circulation, it becomes a thromboembolus
        
        Embolus: any intravascular solid, liquid, or gaseous mass carried in the circulation to a site away from its origin
      - Causes of thrombosis: Virchow's Triad:
        
        Endothelial injury
        
        Hypercoagulability
        
        Alterations in blood flow (stasis or turbulence)
      - Appearance
        
        Dull, rough, red to tan, +/- laminated (alternating layers of platelets, fibrin, and other blood cells)
        
        Occlusive or non-occlusive
        
        Must distinguish from postmortem clots, which are shiny and gelatinous
      - Examples
        
        Cardiomyopathies in cats --> static/turbulent blood flow--> thrombosis and aortic "saddle" thromboembolism
        
        Strongylus vulgaris migration --> cranial mesenteric arteris and thrombosis
      - Clinical significance
        
        Ischemia: inadequate tissue perfusion (due to vascular obstruction by thromboembolus)
        
        Infarct: local area of tissue necrosis due to ischemia
        
        Depends on location and ability to inhibit blood flow