Hemorrhage, Emboli, and Shock

Lecture 10

Failure of hemostasis often results in what?

hemorrhage or thrombosis or in certain disease states a combination of both

What are the four major factors that influence hemostasis and damage or loss of/abnormal function of these factors may result in hemorrhage?

• endothelium

• blood vessel

• platelets

• coagulation factors

What are some causes of hemorrhage?

• trauma

• infectious agents

• collagen disorders

• thrombocytopenia or decreased platelet function

• dissmeinated intravascular coagulation (DIC)

• neoplasia

• severe liver disease

Define hemarthrosis.

articular hemorrhage

Hemarthrosis in guinea pigs is most often a result of what?

Vitamin C deficiency

Guinea pigs cannot synthesize what from glucose like most mammalian species?

ascorbic acid (vitamin C)

Other than guinea pigs, what is another mammalian species that cannot synthesize ascorbic acid (vitamin C) from glucose?

primates

The disease of vitamin C deficiency is known as?

scurvy

What is required by fibroblasts, odontoblasts, and osteoblasts to form collagen, dentin, and osteoid?

vitamin C

Why does hemorrhage occur as a result of vitamin C deficiency?

because the collagen is weaker resulting in increased vessel fragility

Anticoagulant rodenticides inhibit what?

vitamin K dependent coagulation factors (II, VII, IX, and X)

Define hemoperricardium.

extensive hemorrhage into the pericardial sac

Hemoparricardium can result in what?

inability of the heart to expand and contract properly which is known as cardiac tamponade

What is cardiac tamponade?

inability of the heart to expand and contract properly

What are some general causes that an animal cannot produce enough platelets?

• estrogen toxicity

• radiation / drugs

• viral infection

• liver failure

What is a cause for increased platelet destruction in an animal?

autoimmune disease

What is a cause for increased use of platelets in the body?

disseminated intravascular coagulation (DIC)

What are general causes of thrombocytopenia?

• can’t produce enough platelets

• increased platelet destruction

• increased use of platelets

Melena is indicative of what?

upper gastrointestinal bleeding

What are causes of decreased platelet function?

• inherited

• von Willebrand’s disease

• uremia

• NSAIDs like aspirin

What is thrombosis?

the mechanism involved in formation of an excessive or inappropriate thrombus (blood clot) within an injured blood vessel

Thrombi are a mixture of what?

• platelets

• fibrin

• erythrocytes

• inflammatory cells

What are the major determinants of thrombosis as explained by Virchow’s triad?

• abnormal blood flow

• hypercoaguability (coagulation factors and platelet activity)

• endothelial injury (vascular injury)

Of the three major determinants for thrombosis as explained by Virchow’s triad, which is the most important?

endothelial injury

Why is endothelial injury the most important determinant of thrombosis?

it is a potent stimulus for platelet aggregation and coagulation

Reduced blood flow is most important in which vessels?

veins since they already have a slow rate of flow anyways

Why is reduced blood flow a problem?

it can accumulate activated coagulation factors and increase their contact with platelets and the endothelium

Dilated heart chambers and dilated vessels are sites of reduced blood flow which can predispose an animal to what?

thromboses

Turbulent blood flow disrupts what?

lamina flow

Turbulent blood flow can directly damage what?

endothelium

Hypercoaguability is generally due to what?

an increase or decrease in the concentration of activated hemostatic proteins (coag factors, coag or fibrinolytic inhibitors) either from enhanced activation or decreased degradation of these proteins

What is the most common cause of hypercoaguability?

inflammation

What is the appearance of an artieral thrombi?

• tapering tail

• pale red to tan

• dull

• friable

• loosely adherent to the vessel wall or endocardium

Why are arterial thrombi palers than venous thrombi?

they tend to not have a lot of red blood cells embedded within them due to them being formed under higher pressure and higher flow states

What is the appearance of a venous thrombi?

• dull

• mottled dark red with regions of pale tan to red

• molded to vessel wall

• not as apparent of a tail

• occlude the entire lumen

Small thrombi are removed via?

thrombolysis

Larger thrombi are often unable to be completely cleared, so what happens?

phagocytes come in and clear what they can but invasion by fibroblasts occurs and formation of a new vascular lumen called recanalization occurs

What are the two types of postmortem clots?

• current jelly clots

• chicken fat clots

What is an embolus or emboli?

piece of free floating foreign amtieral within a vessel

What are examples of embolus/emboli?

• thromboemboli

• bacterial

• parasitic

• fat

• fibrocartilagenous

• neoplastic

• air

What is a saddle thrombus?

thromboemboli (NOT a thrombus)

Shock is also known as?

cardiovascular collapse

What is shock/cardiovascular collapse?

circulatory dyshomeostasis

Shock causes what?

hypotension

Hypotension due to shock results in what?

• impaired tissue perfusion

• cellular hypoxia

• a shift to anaerobic metabolism

followed by cellular degeneration and death

Persistent shock results in what?

irreversible cell injury and death

What are the three types of shock?

• cardiogenic

• hypovolemic

• blood maldistribution

What is cardiogenic shock?

failure of heart to adequately pump blood (decreased stroke volume and cardiac output)

What are causes of cardiogenic shock?

• myocardial infarction

• ventricular tachycardia

• fibrillation or other arrythmias

• advanced dilated ot hypertrophic cardiomyopathy

• obstruction of blood flow (pulmonary thromboembolism, pulmonary or aortic stenosis, caval syndrome)

What is hypovolemic shock?

reduced circulating blood volume causes tissue hypoperfusion then peripheral vasoconstriction which results in an increase in blood flow to vital organs such as heart, brain, and kidney

What are causes of hypovolemic shock?

• hemorrhage (35-45% blood loss)

• fluid losses (vomiting, diarrhea, burns)

What amount of blood loss results in a dramatic drop in blood pressure and cardiac output?

35-45%

What is blood maldistribution?

decreased peripheral vascular resistance resulting in pooling of blood in peripheral tissues

What is a type I hypersensitivity (IgE induced) reaction which results in release of histamine resulting in peripheral vasodilation amongst other signs like pulmonary bronchoconstriction?

anaphylactic shock

What occurs when vasodilation results from autonomic discharges followed by venous pooling and hypoperfusion?

neurogenic shock

What are the three causes of blood maldistribution?

• anaphylactic shock

• neurogenic shock

• septic

Of the three causes of blood maldistribution, which is the most common?

septic

What is the condition where peripheral vasodilation is caused yb an infectious agent (bacteria or fungus) whcih induces excessive release of inflammatory mediators?

septic

What is the most common reason for the body to be septic?

endotoxic shock due to endotoxin

What is an endotoxin?

a lipopolysaccharide (LPS) which is in the cell wall of gram negative organisms

What are clinical and morphological features of shock?

• hypotension

• weak pulse

• tachycardia

• hyperventilation with pulmonary rales

• reduced urine output

• hypothermia

• late stage decompensated (organ and system failure)