inpatient / Pulmonology and critical Care

Pulmonary Hypertension

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If You Remember Nothing Else

Pulmonary hypertension, while simple in principle, is challenging to properly diagnose and manage. It can also be rapidly fatal if pressures begin to cause the RV to fail. Pulmonary hypertension is most commonly Group 2 (cardiac etiology), or Group 3 (chronic hypoxia as etiology); in these cases, the treatments will be centered on losing weight, using home O2 and CPAP, treating HTN, and trialing diuretics to achieve euvolemia. The rarer and more heterogeneous Group 1 (PAH) can be treated with endothelin receptor antagonists (macitentan, bosentan), PDE5i (sildenafil, tadalafil), and prostacyclin antagonists (epoprostenol). Do not stop these medications when patients are admitted even if they are hypotensive - the meds are usually selective for the pulmonary vasculature and their removal can cause rebound pulmonary hypertension and lead to rapid RV failure.

When patients are hypoxic or decompensating, prioritize HFNC over NIPPV - positive pressure leads to less venous return, lower preload, and can lead to lower CO. For the same reasons, such patients can also rapidly decompensate and arrest when intubated. You should always be mindful of volume status and shoot for euvolemia. Be careful with boluses and aggressive diuresis. Too much volume overloads the system leading to heart failure whereas too little volume leads to poor forward flow and cardiogenic shock (i.e. the patient is "pre-load dependent"). These patients should almost always be co-managed with a pulmonary hypertension specialist given their precarity.
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Clinical Pearls

• Pulmonary Hypertension diagnosed with mPAP >20; note that it was previously 25
• WHO Classification Group - PAH, Left Heart, chronic hypoxia, chronic obstruction, miscellaneous; all except group 2 are considered pre-capillary and will have low PCWP on cath
• Functional Class - I asx, II sx with ordinary activity, III sx with minimal activity, IV sxs at rest
• 90% are due to LHD, chronic lung disease, or a combo of the two
• Common to miss/delay diagnosis >2 years, especially type III since symptoms similar to chronic lung disease
• Often asx early in the disease course, later see DOE, fatigue, syncope
• Life expectancy is 3-5 years w/o treatment, eventually, RV fails; group 3 has the worst prognosis - over time, RV pressure leads to structural changes (dilation or hypertrophy) and eventually impaired function (cor pulmonale), then leads to arrhythmia and death
• Decompensations often caused by arrhythmia, PE, sepsis, missed treatments
• Hypoxia leads to vasoconstriction with airway smooth muscle hypertrophy and vascular bed destruction, leading to increased PVR
• Remember before doing a RHC, need to be euvolemic otherwise all pressures will be high and not interpretable for pHTN - pulmonary venous pressure can also be increased by more volume or pressure overload from left heart failure
• Pulmonary flow is increased by shunt and anemia (increased CO)
• Loud S2 is caused by the closure of the pulmonic valve (often split, caused by delayed closure)
• Be very careful with volume status - too much volume overloads the system, and too little leads to poor forward flow and cardiogenic shock (preload dependent)
• EKG evidence of RV hypertrophy includes RAD, P Pulmonale (narrow peaked P wave in inferior leads suggesting RA enlargement), R/S >1 in V1, RBBB
• TTE - TR peak velocity >3.4 high likelihood of pHTN, PA diameter >25mm, acceleration time <105, RV dilation, RV>LV, IVC >21mm
• Loud S2 is caused by the closure of the pulmonic valve (often split, caused by delayed closure)
• Only 33-75% of those diagnosed with CTEPH had known prior VTE; occurs after ~4% of PEs; V/Q scan is the gold standard - has nearly 100% negative predictive value
• DO NOT stop PAH-specific therapy if BP is low - the drugs lower pulmonary pressure NOT systemic pressure, and do not cause postural hypotension 
• BMPR2 loss of function mutation can lead to PAH - no inhibition of fibroblast activity in pulm vasculature and leads to fibrosis and narrowing
• Amiodarone can cause ILD which in turn can cause pHTN
• The most common rheum associations with PAH are lupus, scleroderma, MCTD
• DO NOT stop PAH-specific therapy if BP is low - the drugs lower pulmonary pressure NOT systemic pressure, and do not cause postural hypotension 
• Pulmonary vasodilators work well and help with hypoxia because you are dilating at the best ventilated portions of the lung (i.e the part that the inhaled medicine is actually getting to!); if you were to give IV epoprostenol in the same situation, you would be dilating all of the vasculature regardless of how well ventilated the areas are, and you would not be doing anything to help with V/Q mismatch - this can be help with the pulm pressure, but would not help with oxygenation
• Pulmonary veno-occlusive disease (PVOD) is due to obstruction at the end of the capillaries in the pulmonary vasculature - it is one of the rare examples when giving pulmonary vasodilators may actually make a patient's hypoxia worse because more blood will enter the capillaries with nowhere to go but into the interstitium leading to pulmonary edema and interlobular septal thickening; it can be caused by a mutation in the EIF2AK4 gene

Trials and Literature

• Algorithm for Diagnosing pHTN - ERJ 2019
• Most Up-to-Date Clinical Classifications for pHTN - (ERJ 2019)
• Treatment Guidelines for pHTN from 2015 - ERJ 2015
• Review of CTEPH - ERJ 2019
• Macitentan Reduced Morbidity and Mortality in Group 1 - NEJM 2013 - and bosentan was previously known to decrease symptoms and increase 6MWT - NEJM 2002
• PDE5 Inhibitors decrease symptoms and increase 6MWT in group 1 - NEJM Review 2009
• Continuous IV Epoprostenol increases QOL in sickest patients - NEJM 2013
• STELLAR Trial - sotatercept on top of background therapy improved 6MWT - NEJM 2023

Other Resources

• Curbsiders Podcast - Curbsiders Pulmonary HTN 2018; Curbsiders pHTN update 2021
• Clinical Problem Solvers - CPS Pulm HTN