Pulmonary Complications



Pulmonary Complications





HEPATOPULMONARY SYNDROME (HPS)


Definition:



  • HPS triad:



    • History of chronic liver disease; Arterial hypoxemia on room air; Presence of intrapulmonary vascular dilation


  • Types of HPS:



    • Type 1: Diffuse pulmonary vascular dilation; Microscopic; Common


    • Type 2: Discrete arteriovenous communications; Macroscopic; Uncommon


Epidemiology:



  • Reported incidence between 4-29%


Etiologies:



  • Develops independent of the cause of liver disease


Pathophysiology:



  • Primary problem with intrapulmonary vascular dilation (as apposed to Portopulmonary hypertension) leading to AV shunting and hypoxemia; Two types of dilation:



    • Type 1: diffusion-perfusion defect


    • Type 2: anatomic shunt


  • Why intrapulmonary vascular dilation: Not definitively known; Nitric oxide (NO) likely plays a role:



    • Exhaled NO levels are increased in those with HPS and normalize after transplant


    • Methylene blue (NO inhibitor) transiently improves HPS


Clinical Manifestations/Physical Exam:



  • Varied symptoms: may complain of symptoms of chronic liver disease and/or have several pulmonary complaints (dyspnea, platypnea)


  • Signs: dyspnea, telangiectasias, cyanosis, clubbing, pulmonary dysfunction that improves with O2 (hypoxia, orthodeoxia)



    • Heart and lung exam is generally normal


Laboratory Studies:



  • ABG (PaO2 < 80 mmHg)


Diagnostic Studies:



  • Blood gas on room air is first diagnostic test (PaO2 < 80 mmHg) – hypoxia


  • CXR: usually normal, unless concomitant disease present; may show increased bibasilar interstitial markings


  • Pulmonary function testing (PFTs): restriction is common in liver disease; may show low diffusion capacity for carbon monoxide


  • Contrast-enhanced echocardiography (“bubble-echo”): preferred modality for demonstrating intrapulmonary vascular dilation



    • Can also evaluate cardiac function and pulmonary artery pressures; Transesophageal more specific than transthoracic


    • Positive in up to 40% of cirrhotic patients with a normal ABG (Qualitative)


    • Concept: contrast (indocyanine green dye or agitated saline) injected with one of three scenarios:



      • Normal: contrast seen in right heart, but not in left heart (filtered by pulmonary capillaries)


      • Intracardiac shunt: contrast seen almost immediately in left heart


      • HPS: contrast seen in left heart after 3-6 heart cycles (dilation of pulmonary vasculature doesn’t allow for filtering)


  • Technetium-labeled macroaggregated albumin scan (Tc-MAA): less sensitive than contrast echo for detecting intrapulmonary vascular dilation



    • Can’t evaluate cardiac function or pulmonary artery pressures; Positive scan is specific for HPS even with concomitant lung disease


    • Concept: 99mTechnitium-labeled albumin is injected and then a body perfusion scan is done with one of two scenarios:



      • Normal: technetium detected almost exclusively in lungs


      • HPS: technetium is detected in other organs as well (brain, spleen) due to limited lung filtering



        • Use Tc-MAA to calculate shunt index (% of uptake in brain compared to lungs): >6% is abnormal (Quantitative)



  • Pulmonary angiography: most invasive; not a standard diagnostic tool in HPS

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Aug 24, 2016 | Posted by in GASTROENTEROLOGY | Comments Off on Pulmonary Complications

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