Pulmonary hypertension

Introduction

• Normally high-flow, low pressure system
• Mean pulmonary arterial pressure 15-20% of MAP
• Normal pulmonary arterial systolic pressure 15-30mmHg
• Normal pulmonary arterial diastolic pressure 4-12mmHg
• Pulmonary hypertension = 
  • Mean pulmonary arterial pressure > 25mmHg at rest or >30mmHg with exertion
  • Pulmonary vascular resistance > 240dynes/s/cm
  • PCWP <15mmHg
• Pulmonary HTN due to left heart disease have PCWP >15
  • This is the most common cause
• Definitive diagnosis requires right heart cath (but can be estimated with echo)
• Accurate diagnosis of type drives treatment

WHO Classification

• Group 1
  • Pulmonary arterial hypertension
    • Idiopathic/genetic/drug/toxin/HIV/liver disease/collagen vascular
    • Least common but 5-year mortality of 30%
• Group 2
  • Pulmonary venous hypertension (left heart) (most common)
• Group 3
  • Chronic hypoxaemic lung disease
    • COAD/intestitial/OSA/chronic high altitude
• Group 4
  • Embolic disease (seen in 4% of patients with chronic thromboembolic disease)
• Group 5
  • Miscellaneous
    • Lymphatic obstruction, myeloproliferative disorders, sarcoidosis, neurofibromatosis, glycogen storage disease, thyroid disorders

Pathophysiology

• Pulmonary arterial hypertension
  • Endothelial dysfunction with imbalance between endogenous vasodilators (prostacyclin) and vasoconstrictors (endothelin-1)
  • Get subsequent vasoconstriction and formation of in situ thrombi
  • Enhanced microvascular permeability, hypoxic vasoconstriction, microvascular thrombosis and vascular remodelling all contribute
  • RV dilates to maintain adequate cardiac output. This increased RV wall tension, oxygen consumption and eventually decreases contractility
  • IV septum eventually displaces to the left, inhibiting LV filling and cardiac output
  • Right coronary artery perfusion depends on pressure gradient between aorta and RV wall tension and normally occurs in systole and diastole
    • In advanced pulmonary HTN, RV wall tension is so high that right coronary flow only occurs in diastole leading to impaired perfusion, impaired contractility and ultimately RV failure and cardiovascular collapse

Clinical features

• Dyspnoea in >50%
• Fatigue, chest pain, near syncope, syncope, exertional lightheadedness
• Often 2 years before diagnosis made
• Early satiety, anorexia, orthopnoea, PND and peripheral oedema as RV failure develops
• Clinical signs arise with disease progression including holosystolic murmur of TR, JVP elevation, hepatomegaly, peripheral oedema and ascites
• Loud P2, parasternal heave

ECG

• Right axis deviation is most common
• R/S ratio >1 in V1
• R/S ratio <1 in V5/6
• qR complex in V1
• S1Q3T3
• Right atrial enlargement on inferior leads
• Incomplete or complete RBBB
• None of these findings are sensitive or specific
• Most common dysrhythmias are atrial fibrillation, flutter, AVNRT

Investigations

• BNP elevation is often seen in pulmonary hypertension and correlates with outcomes
• Elevations in troponin can be due to ischaemia or strain-induced leak – poor prognostic factor
• CXR
  • Enlarged right atrium/RV and hilar pulmonary arteries
  • Might also see signs of underlying cause e.g. interstitial lung disease
  • Rules out other causes of symptoms

Investigations

• Echo
  • Can approximate pulmonary artery pressure, reduced RV function, RA dilatation, RV dilatation, left ward deviation of IV septum and RV:LV end-diastolic diameter >1
  • May detect precipitants such as pericardial effusion, regional wall motion abnormalities and acute valvular pathology

Treatment

• Supplemental oxygen to >90%
• Intubation and ventilation
  • Increased intrathoracic pressures can cause cardiovascular collapse in these patients
  • Sedatives can impair RV function and drop systemic vascular resistance, impairing preload and CO
  • Set to 6mL/kg IBW Vt, Pplat <30, lowest PEEP possible
  • Avoid hypercapnoea by altering RR as this can increase pulmonary vascular resistance, pulmonary artery pressure and RV strain
• Optimise intravascular volume
  • Overload can displace IV septum further to the left
  • Serial boluses of crystalloid 250-500mL
  • Cannot use IVC /CVP due to right heart failure
• RV function
  • Noradrenaline often used to improve coronary perfusion through increasing aortic root pressure and to some degree RV contractility (perhaps indirectly)
  • Dobutamine alternative agent 2-10mcg/kg/min
  • Larger doses risk raising pulmonary pressures and tachydysrhythmias and hypotension
• Right coronary artery perfusion
  • Aortic pressure must be greater than pulmonary artery pressure
  • For the hypotensive patient, use noradrenaline to raise aortic pressure enough to ensure this
  • Very high doses risks increasing pulmonary vascular resistance

Treatment

• RV afterload
  • Pulmonary vasodilators
    • Prostanoids (epoprostenol, iloprost)
      • Potent vasodilators and are first-line
      • Also antiplatelet and anti-proliferative properties
      • Epoprostenol is the only therapy proven to improve survival
      • Can be delivered by continuous pump. First-step is to check that this is working if present acutely unwell and if not -> Must transfer to peripheral IV line and liaise with Respiratory Physician ASAP
    • Endothelin receptor antagonists (bosentan)
      • Oral agents
      • Not been tested for acutely decompensating patients
    • PDE-5 inhibitors (Sildenafil, tadalafil)
      • Oral agents also and not tested for acute deterioration
    • Rapid cessation of pulmonary vasodilators can imminently lead to rapid cardiovascular decline through pulmonary hypertensive crisis
    • Conversely, introduction of pulmonary vasodilators can worsen VQ matching in some patients and lead to deterioration

Last Updated on October 13, 2021 by Andrew Crofton