pulmonary embolism

• write out what you know about the aims of this lecture:

  •Describe the types of pulmonary embolism

  •Basic science

  •Imaging

  •Treatments

  •Sequelae

  •Controversies

  here
• Why do emboli end up in lungs?

  • All blood goes through lungs every 45sec

  • Massive protective filter - catch emboli and allow them to dissolve -> sieve and prevent them from going further -> air embolism can diffuse out

  • Immune organ - lungs act as an immunologic organ -> pulmonary immune responses provide resistance to infectious agents -> both T and B cell circuits present

  • Anti-inflammatory in highly oxidative environment

  •Capacity to cope

  – Pneumonectomy survival complication -> increased risk
• what are the four main types of embolism?

  • mycotic (infective)
  • fat
  • air
  • thrombotic
• thrombotic emboli are normally from deep veins of legs, but consider other sites - e.g. iv lines. Paget Schroetter Syndrome – upper limb DVT, musical intruments are a risk factor
• Paget Schroetter syndrome (PSS) is effort-induced thrombosis of the axillary and subclavian veins associated with compression of the subclavian vein at the thoracic outlet.
• Mycotic -Transfer of infective pathogens to the

  lungs from a distant source, normally due to IV infections, unclean needle practices (injection into the groin veins)
• what is this image of?

  osler's nodes

  
• what is the difference between osler's and Janeway nodes?

   Osler's nodes are thought to be caused by localised immunological-mediated response while Janeway lesions are thought to be caused by septic microemboli.
• what is the image of?

  janeway lesions

  
• what is the image of?

  splinter haemorrhages

  
• what is the image of?

  Roth spots - most commonly associated with infective (bacterial) endocarditis. Also seen in leukaemia, anaemia, hypertensive retinopathy, preeclampsia, diabetic retinopathy, and anoxia.

  micro infarctions of the retina

  
• splinter haemorrhages can be indicative of endocarditis
• osler's nodes normally on finger tips and janeway lesions normally on palm
• Endocarditis is most commonly seen (mycotic) –> infection becomes lodged onto heart valves -> breaks off and either can affect the pulmonary or systemic circulation
• symptoms associated with endocarditis:

  • Osler's nodes
  • Janeway lesions
  • Splinter haemorrhages
  • Roth spots
• what does this CT show?

  lung abscess

  
• what does this image show?

  US of endocardial clot on Right heart valve (left on picture)

  
• fat embolisms:

  • Long bone fractures – needs ample marrow, femur fractures or hip fractures and replacements

  • Fat causes multifocal inflammation in lungs
• Air:

  • Murder mystery classic

  • IRL – 42% cannulations = gas in veins -> may cause airlock in heart -> circulatory collapse and death

  • Lungs act as filters: Except in HHT/Osler-Weber-Rendu

  –Multiple hereditary AVMs, esp in lungs

  –Don’t inject/cannulate these patients  unnecessarily!!
• Osler-Weber-Rendu syndrome / Hereditary haemorrhagic telangiectasia  (HHT) cause blood vessels that have not developed properly and sometimes cause bleeding, known as arteriovenous malformations (AVMs).
• HTT can cause AV malformations which means that air embolis from venous circulation pass through the right heart to the left and bypass pulmonary circulation and get into systemic circulation. This means the air embolis isn't dealt with and can cause stokes
• risk in lung biopies -> air embolism can occur -> bonchial artery -> bonchial vein -> stroke
• lung is less sensitive to air emboli in the pulmonary circulation because it has oxygenated vascular supply from the bronchial arteries (from the left/systemic side)

  1. Alveoli are full of air -> simple diffusion will supply the cells to a degree
  2. There is collateral circulation
  3. The tissues are less sensitive to anoxia

  Furthermore, because of an extensive collateral circulation and the efficiency of gas transfer, there is minimal impact on O2 saturation levels, assuming the emboli are small and not continually arriving.
• Air in a vessel will absorb faster than a thrombotic emboli, but if in a vessel supplying an area sensitive to anoxia (usually the brain as air goes up) will still remain long enough to cause hypoxic injury - e.g. a stroke
• what makes up Virchow Triad (thrombosis)?

  venous stasis

  endothelial disruption / inflammation

  hyper-coagulability / absence of clotting inhibition
• the problem PEs and DVTs cause:

  Untreated DVT causes PE in up to 50%

  Up to 80% pts have calf DVT post pelvic surgery

  2nd cause of adult-sudden death

  Age dependent - increased risk
• PE: lung tissue is ventilated but not perfused leads to intra-pulmonary dead space and impaired gas exchange.

  Reduced cross-sectional area of pulmonary arterial bed -> elevated pulmonary arterial pressure -> reduced cardiac output -> potential circulatory collapse and cardiac arrest due to RVF -> alveolar collapse occurs, worsening hypoxaemia.
• PE: unperfused lung may infarct, but often does not do so because oxygen continues to be supplied by the bronchial circulation and the airways
• Present with breathlessness and hypoxia -> clot blocks pulmonary arterioles -> rise in right atrial pressure increase -> decreased cardiac output as less left filling -> reduction in BP -> circulatory collapse -> normally not pulmonary infarcts due to dual blood supply
• D-dimer is the degradation product of crosslinked fibrin by plasmin
• D-dimer

  • 95% sensitive, 50% specific

  • Use in negative prediction

  • Does not prove PE

  – Shows increased inflammation, infection, cancer

  • Positive above threshold - (age adjusted scores)

  • Over-measured due to fear of clinical criticism
• D-dimer has negative predictor value and checks for thrombosis (PE or DVT)
• Wells scoring for PE (note also well score for DVT) - score above 4 is likely (original score) and equal/above 2 for simplified score

  
• doppler US

  • Standard USS technique – compressibility

  • Doppler allows assessment of the non- visualised venous system

  • Good specificity and sensitivity

  Operator dependent
• compressive US:

  A and B, Ultrasound images of a normal femoral vein without (A) and with (B) compression. The artery (Art) is anterior to the vein. After compression, the vein is completely collapsed, indicating normal compressibility. C and D, Ultrasound images of acute femoral vein thrombus without (C) and with (D) compression After compression (D), the vein does not collapse but has an oval shape indicating an acute DVT based on the noncompressible but deformable vein. DVT indicates deep venous thrombosis.

  A – fem artery and vein

  B – vein has obliterated

  
• doppler US - not diagnostic but can help, shows blood flow, speed and direction
• V/Q matching - Air that reaches your lungs matched by the amount of blood flow in the capillaries in your lungs.
• Dead space - ventilation but inadequate perfusion, oxygen can’t enter the bloodstream.

  • Anatomic - areas in the respiratory tract with oxygen and no blood flow

  • Physiologic - alveoli has oxygen but not enough blood flow to carry this oxygen

  Shunt occurs - adequate blood flow or perfusion, but not enough ventilation.
• Pulmonary artery constriction -> redivert blood to better ventilated areas of lungs -> hunched over lower is less efficient divert to top
• V/Q scan is low dose of a radioactive contrast, two scans first is for ventilation and the second is for perfusion.