10. Vascular Disorders: Hemorrhage, Emboli, & Shock

What does failure of hemostasis often result in?

hemorrhage or thromboses or in certain disease states, a combination of both

What does damage or loss of/abnormal function to one of the four major factors that influence hemostasis result in?

hemorrhage

What are the 4 major factors that influence hemostasis?

1. E

2. B

3. P

4. C

1. endothelium

2. blood vessel

3. platelets

4. coagulations factors

What are causes of hemorrhage?

T
I
C
T
D
N
S

• trauma

• infectious agents

• collagen disorders

• thrombocytopenia or decreased platelet function

• disseminated intravascular coagulation (DIC)

• neoplasia

• severe liver disease

What infectious agents can lead to hemorrhage?

B
V
F
I
E

• bacteria

• viral

• fungal

• immune complexes

• endotoxemia

Hemarthrosis is most often a result of what type of deficiency in guinea pigs? Why is this typical?

vitamin C; guinea pigs cannot synthesize ascorbic acid (vitamin C) from glucose like most mammalian species

What is vitamin C deficiency known as?

scurvy

What is vitamin C required by and why?

fibroblasts, odontoblasts, and osteoblasts to form collagen, dentin, and osteoid

What happens when you are deficient in vitamin C?

lack of bone deposition as well as hemorrhage

Why does hemorrhage occur with vitamin C deficiency?

the collagen is weaker, resulting in increased vessel fragility

What is this image showing? Why is it probably occurring?

hemarthrosis; vitamin C deficiency

What is this image showing?

extensive hemorrhage of the right hind limb due to anticoagulant rodenticide toxicosis

What do anticoagulant rodenticides do?

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

What is this image showing?

collagen disorder

What do collagen disorders result in? Why?

weakening of the vessels and hemorrhage; vessels have collagen in and surrounding them to support them

What is this image showing?

horse gutteral pouch mycosis

extensive hemorrhage into the pericardial sac that can result in the inability of the heart to expand and contract properly, which is a condition known as cardiac tamponade which often results in sudden arrest

hemopericardium

What is this showing?

hemopericardium

What are the general causes of thrombocytopenia?

C
I
I
I
P
B

• can’t produce enough platelets

• increased platelet destruction

• increased use of platelets

• iatrogenic

• platelet sequestration in sinusoids of the spleen

• blood loss

What are reasons that an animal could not produce enough platelets?

E
R
V
L

• estrogen toxicity

• radiation/drugs

• viral

• liver failure

What is a main reason for increased platelet destruction?

autoimmune

What is the main reason for increased use of platelets? Why?

DIC; intravascular coagulation and consumption of platelets and coagulation factors

What is this an image of?

androgen producing adrenal tumor (decreased production related thrombocytopenia)

What are reasons for decreased platelet function?

I
V
U
N

• inherited along with coagulation factor inherited deficiencies)

• von willebrand’s disease (autoantibodies against vWf leads to decreased platelet aggregation)

• uremia

• NSAIDs (aspirin)

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

thrombosis

mixture of platelets, fibrin, erythrocytes, and inflammatory cells which are adhered to the vascular wall (blood or lymphatic vessel)

thrombi

explains the major determinants of thrombosis

Virchow’s triad

What are the 3 major determinants of thrombosis?

1. A

2. H

3. E

1. abnormal blood flow

2. hyper coagulability

3. endothelial injury

What is the most important factor of thrombosis? Why?

endothelial injury; potent stimulus for platelet aggregation and coagulation

What are examples of abnormal blood flow?

reduced blood flow and turbulent flow

In veins, what is the most important determinant of thrombosis? Why?

reduced blood flow; have a slow rate of flow anyway

What can reduced blood flow cause?

accumulation of activated coagulation factors and increase their contact with platelets and the endothelium

Where are sites of reduced blood flow? What does this mean for that animal?

dilated heart chambers and dilated vessels; predispose an animal to thromboses

What is the effect of turbulent blood flow?

disrupts lamina flow such that the thin layer of plasma which separates the cellular constituents of blood, such as platelets and coagulation factors, now come into contact with the endothelium

What else can turbulent blood flow do?

directly damage the endothelium

What is hyper coagulability generally due to?

increase or decrease in the concentration of activated hemostatic proteins either from enhanced activation or decreased degradation of these proteins

What is the most common cause of hyper coagulability?

inflammation

Arterial thrombi often form a ________ ________. They are ________ ________ to the wall of the vessel or the endocardium. They are ________ than venous thrombi because they tend to not have a lot of ________ embedded within in. This is because they are formed under ________ pressure and ________ flow rates rather than venous thrombi. They are also ________ and ________.

tapering tail; loosely adherent; paler; RBCs; higher; higher; dull; friable

What is this showing?

arterial thrombus

Venous thrombi become ________ to the vessel wall, as they are formed under ________ pressure circumstances with increased ________ ________. They tend to have more ________ within the thrombus. They are ________, mottled ________ ________ with regions of ________ ________ to ________. They are ________ ________ to the wall but will occlude the entire ________ and often do not have an apparent ________ as the arterial thrombi do.

molded; low; blood stasis; erythrocytes; dull; dark red; pale tan; red; loosely adherent; lumen; tail

If you see a dull thrombus, what should this tell you?

it is not a postmortem change

What is this showing?

venous thrombi

How are small thrombi removed? What about larger ones?

via thrombolysis; often unable to be completely cleared

How are larger thrombi cleared?

phagocytes come in and clear as much of the debris as possible but invasion by fibroblasts occurs and formation of a new vascular lumen called recanalization occurs

What is this showing?

recanalization

What are the two types of postmortem clots?

C
C

• current jelly clots

• chicken fat clots

What is the appearance of postmortem clots? What else is unique about them?

smooth and glistening; they are not adhered to the vessel wall at all

What is the appearance of current jelly clots?

dark-red/purple

What is this showing?

postmortem clots

piece of free-floating foreign material within a vessel

embolus or emboli

What are types of emboli?

T
B
P
F
F
N
A

• thromboemboli

• bacterial

• parasitic

• fat

• fibrocartilagenous

• neoplastic

• air

A saddle thrombus is not a _________ but a ________. That is because it is not ________ to the ________, but instead comes from the ________.

thrombus; thromboemboli; adhered; wall; heart

What is this showing?

saddle thrombus

What is significant about these pictures?

showing the emboli that the saddle thrombus came from

What is shock also known as? What is it?

cardiovascular collapse; circulatory dyshomeostasis

True or false: The causes of shock are very diverse but the results are similar.

true

What will persistent shock lead to?

irreversible cell injury and death

Shock causes ________, which results in impaired ________ ________, ________ ________, a shift to ________ ________, followed by ________ ________ and ________.

hypotension; tissue perfusion; cellular hypoxia; anaerobic metabolism; cellular degeneration; death

reduced vascular perfusion due to underlying cause

shock

What are the three types of shock?

C
H
B

• cardiogenic

• hypovolemic

• blood maldistribution

failure of the heart of adequately pump blood due to decreased stroke volume and cardiac output

cardiogenic shock

What are the causes of cardiogenic shock?

M
V
F
A
O

• myocardial infarction

• ventricular tachycardia

• fibrillation or other arrhythmias

• advanced dilated or hypertrophic cardiomyopathy

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

What is this showing?

myocardial infarction (cardiogenic shock)

reduced circulating blood volume leading to tissue hypo perfusion, peripheral vasoconstriction, and an increase in blood flow to vital oprgans such as the heart, brain, and kidney

hypovolemic shock

What are causes of hypovolemic shock?

H
F

• hemorrhage

• fluid losses (vomiting, diarrhea, burns)

Blood loss of up to what percent can be easily compensated for?

10%

Blood loss which approached what percent results in dramatic drops in blood pressure and cardiac output?

35-45%

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

blood maldistribution

What are the types of blood maldistribution?

A
N
S

• anaphylactic

• neurogenic

• septic

type I hypersensitivity (IgE induced) reaction, which results in the release of histamine resulting in peripheral vasodilation among other signs (pulmonary bronchoconstriction)

anaphylactic shock

vasodilation results from autonomic discharges followed by venous pooling and hypoperfusion (trauma, electrocution, fear)

neurogenic shock

What is the most common type of blood maldistribution?

septic shock

peripheral vasodilation caused by the infectious agent (bacteria or fungus) which induces excessive release of inflammatory mediators

septic shock

What is the most common type of septic shock?

endotoxic shock from endotoxin which is an LPS in the cell wall of gram negative organisms

What are the clinical and morphological features of shock?

H
W
T
H
R
H
L

• hypotension

• weak pulse

• tachycardia

• hyperventilation with pulmonary rales

• reduced urine output

• hypothermia

• late stage decompensated leads to organ and system failure

characterized by compensatory mechanisms which counteract hypoperfusion

nonprogressive stage of shock