Lec 20 Pulmonary Thromboembolism Flashcards
What is pulmonary thromboembolism?
movement of blood clot from systemic vein through R side of heart to pulmonary circulation
What is common source of thrombi to lung?
usually from lower extremities; rarely from arms, pelvis, R chambers of heart
What is virchow’s triad of risk factors for thrombosis?
- hypercoagulability
- damage to endothelium of vessel wall
- stasis/stagnation of blood flow
What are some hereditary risk factors for hypercoagulability?
- antithrombin deficiency
- protein C deficiency
- protein S deficiency
- factor V leiden
- prothrombin gene mutation
What are acquired risk factors for hypercoagulability?
- advanced age
- previous venous thromboembolus
- cancer
- obesity
- surgery
- immobilization –> long flight
- pregnancy
- estrogens
- having a catheter
What is factor 5 leiden?
- single base substitition –> factor Va resistant to action of protein C
het individuals have 3-5x increase risk of venous thromboembolism
What happens in prothrombin gene mutation?
G20210A mutation in untranslated region of prothrombin
het individuals have 30% increase in prothrombin and 2-3x increase risk of thromboembolism
What are sequalae of pulm embolism?
- have hemodynamic perturbations and impaired gas exchange
b/c mechanical obstruction of vessels + thrombus releases mediators
How does PE cause vasoconstriction?
thrombus releases mediators serotonin and thromboxane A2 causes vasoconstriction
What 3 factors determine the hemodynamic effects of PE?
- degree of cross sectional reduction of pulm vascular bed
- preexisting status of cardiopulm system [worse if high pulm pressure to start]
- physiologic consequences of hypoxic and neurohumorally mediated vasoconstriction
What happens if obstruction < 20%?
normal PAP and PVR b/c of recruitment and distension of pulm vessels
CO maintained
What happens if obstruction 30-40%?
increase PAP and modest increase RAP
What happens if obstruction > 50%?
compensatory mech overcome
CO begins to fall and RAP increases
What is maximum mean PAP right ventricle can generate in patient without prior cardiopulm disease?
40 mmHg
What happens to PaCO2 level in PE?
have increase dead space ventilation but also have increase in total minute ventilation
–> can get low CO2 [hypocapnia]
What are 5 mechanisms that can lead to hypoxemia?
- hypoventilation
- V/Q mismatch
- shunt
- diffusion impairment
- low PIO2
Does dead space ventilation cause hypoxemia?
nope! not on its own
How do you get hypoxemia due to decrease CO in pulm embolism?
have decrease CO –> decrease O2 delivery but your tissues still taking up the O2 and consume it –> lower O2 sat –> decrease CaO2
What are 4 mechs causing hypoxemia in pulm embolism?
- increased PVR
- decreased CO reducing the O2 in venous admixture
- loss of pulm surfactant
- bronchoconstriction
What is mech of increase PVR causing hypoxemia in PE?
- increased PVR –> causes increased perfusion to poorly ventilated areas and get V/Q mismatch + if really high PVR –> can get reverse shunt
What is mech of loss of surfactant causing hypoxemia in PE?
-loss of pulm surfactant after 24 hrs of occlusion –> atelectasis and edema
hypoxemia if partial thrombus resolution of perfusion but now have lack of ventilation = shunt
What is mech of bronchoconstriction in PE?
platelet mediators in thrombus cause vaso/bronchoconstriction
hypocapnia that occurs in PE also causes bronchoconstriction
WHat are the 3 potential sources of O2 for pulmonary parenchyma?
- airways
- pulm arteries
- bronchial arteries
What are symptoms of PE?
- acute onset dyspnea [most common]
- pleuritic chest pain
- hemoptysis
- syncope [rare]
WHat do you see in phyiscal exam with PE?
- tachycardia, hypotension, tachypnea, hypoxemia
- lung exam may be normal or may have rales, wheezing, findings of pleural effusion
- cardiac: RV heave, split S2, loud P2, systolic TR murmur
- extremities: tender, edema, palpable cord in vessel
What is hampton’s hump?
shallow wedge-shaped opacity in periphery of lung with its base against pleural surface
represents lung infarction
What is westmark’s sign?
localized area of decreased lung vascular markings
What are advantages/ disadvantages of CT pulmonary angiography?
advantages: high quality visualization; quick
disadvantages: radiation exposure, requires IV contrast
What is a ventilation perfusion scan?
perfusion: use radiolabeled macroaggregated albumin particle injected into peripheral vein; lodges in small vessels that are perfused
ventilation: inhale xenon radioisotope; asses which parts of lung ventilated
What is use of lower extremity ultrasound in pulmonary thromboembolism?
- if have DVT the vein will be non-compressible
if no thrombus –> will be able to compress easily
What is D dimer test?
tests if you have any forming clots –> will have positive D dimers of fibrin that break down when you give plasmin
What does positive D Dimer test tell you? negative?
positive = doesn’t tell you much = poor specificity
negative = very sensitive and tells you that its probably not a thrombus
What is natural history of thromboembolism?
- thrombus grows, propagates; have fibrinolysis or roganization/recanalization
resolves a lot in first week; gradual over next 4-8 wks
most pts able to restore normal pulm hemodynamics + gas exchange
What is treatment for thromboembolism?
- anticoagulation
- thrombolysis or surgery in big thromboembolus
What are some examples of anti-coagulants?
- heparin
- warfarin
- coumadin
What are some examples of thrombolytics?
- tPA
- streptokinase
- urokinase
What is IVC filter? side effect?
- traps thrombi from lower extremities en route to pulm circulation
increases risk of deep vein thrombosis
What are indications for IVC filter?
- if contraindicated to anticoagulant therapy
- if thromboembolism recurs despite anticoagulation
- if limited pulm vascular reserve [already have pulm HTN]
