Pulmonary thromboembolism

Etiology

• Hepatic abscess is the most common primary cause in cattle, this leads to thrombus formation in the vena cava Thrombosis of the vena cava.
• Phlebitis Phlebitis (Most commonly of the jugular vein and most often iatrogenic).
• Cardiac disease: 
  • Dilated Cardiomyopathy Cardiomyopathy.
  • Endocarditis Endocarditis 
• Neoplasia Neoplasia.
• Disseminated Intravascular Coagulation (DIC)
• Sepsis.
• Hyperviscosity syndromes (i.e.polycythemia vera).
• Secondary to other disease, such as mastitis Mastitis acute Mastitis chronic, Metritis, Traumatic reticulitis Traumatic reticulitis, Foot abscess etc.

Predisposing factors

General

• Hepatic abscess due to hematogenous spread from infection elsewhere in body.
• Hepatic abscess secondary to rumenitis (Excess carbohydrate -> ruminal acidosis-> rumenitis).

Pathophysiology

• Occlusion of pulmonary vasculature by clot or embolus.
• Clot formation requires one or more of the following: hypercoagulable state, vascular stasis or damage to the vascular endothelium.
• Clot usually forms as a result of disease in organs other than lungs.
• Various mechanisms of clot formation, eg: 
  • Hepatic abscess -> Infiltration of vena cava-> thrombophlebitis -> thrombus formation -> embolism to pulmonary vasculature. (often -> pneumonia and multiple pulmonary abscess formation).
  • IV catheters IV catheters.
  • Cardiac disease, such as cardiomyopathy Cardiomyopathy → vascular stasis within the heart.
  • Neoplasms often have abnormal vascular endothelial surfaces which can cause vascular stasis or activate the coagulation cascade.
• Clot/embolus formation → occlusion of pulmonary vessels → ventilation perfusion mismatch → hypoxemia.
• Arterial hypertension may result due to obstruction or reflex vasoconstriction. Vasoactive substances and/or vagal reflexes may cause bronchoconstriction and increased airway resistance.
•  Pulmonary arterial aneurysms  -> rupture  -> extensive hemorrhage.
•  Pulmonary abscess -> erosion into airways -> rupture -> hemorrhage.