Pulmonary Hypertension

Introduction

Pulmonary vascular system is a high-flow, low-resistance circuit. Normal pulmonary arterial systolic pressures range from 15 to 30 mm Hg, whereas diastolic pulmonary arterial pressures range from 4 to 12 mm Hg and Pulmonary hypertension is defined as a mean pulmonary arterial pressure >25 mm Hg at rest or >30 mm Hg during exertion.

Although echocardiography can estimate pulmonary arterial pressure in a patient with suspected pulmonary hypertension, definitive diagnosis requires right heart catheterization. The World Health Organization classifies pulmonary hypertension into five categories based on cause and response to treatment:

Accurate classification of pulmonary hypertension is key to directing treatments. Regardless of the cause, patients with pulmonary hypertension have high morbidity and mortality rates.

Pathophysiology

Endothelial dysfunction results in an imbalance between endogenous vasodilators and vasoconstrictors with net effect leading to vasoconstriction and formation of in situ thrombi. Other pathologic processes include alterations in microvascular permeability, abnormal hypoxic vasoconstriction, microvascular thrombosis, and the formation of plexiform lesions, leading to vascular remodeling. 

Ultimately, these abnormalities result in sustained elevations of pulmonary vascular resistance and impairment of pulmonary blood flow leading to RV dilatation and poor contractility. With progressive RV dilation, the intraventricular septum is displaced toward the left ventricle. This displacement inhibits left ventricular filling and ultimately impairs cardiac output and systemic perfusion.

Clinical Presentation 

• Symptoms can be non-specific which often leads to delayed diagnosis
• Dyspnea, fatigue, chest pain, near syncope, syncope, exertional lightheadedness
• Orthopnea, paroxysmal nocturnal dyspnea, and peripheral edema

The physical examination is often normal in the early stages of pulmonary hypertension.

Late signs include a holosystolic tricuspid regurgitation murmur, jugular venous distention, hepatomegaly, ascites, and lower extremity edema

Diagnosis 

ECG: The most common ECG abnormality seen in pulmonary hypertension patients is right axis deviation. Additional findings associated with pulmonary hypertension include an R/S ratio >1 in lead V1, an R/S ratio<1 in leads V5 and V6, a qR complex in lead V1, an S1Q3T3, right atrial enlargement in the inferior leads, and an incomplete or complete right bundle branch block. The most common dysrhythmias in patients with pulmonary hypertension are atrial fibrillation, atrial flutter, and atrioventricular nodal reentrant tachycardia.

B-type natriuretic peptide and N-terminal B-type natriuretic peptide are often elevated  Elevations in troponin from myocardial ischemia or a strain-induced leak can be seen.

CXR: Common abnormalities associated with pulmonary hypertension include enlargement of the right atrium, RV, and hilar pulmonary arteries. 

TTE: Transthoracic echocardiography is the best initial diagnostic test to assess pulmonary hypertension in the ED. It allows estimation of the pulmonary artery systolic pressure and detection of decreased RV function, right atrial hypertrophy right ventricular hypertrophy and leftward deviation of the intraventricular septum.

Treatment 

No consensus guidelines exist for the management of critically ill patients with pulmonary hypertension in the ED. The mainstays of ED therapy include:

1. Supplemental oxygen (Target SpO2 >90%)

2. Optimizing intravascular volume, augmenting right ventricular function, maintaining coronary artery perfusion, and decreasing right ventricular afterload 

Treatments caveats:

• Intubation: In patients with severe pulmonary hypertension, intubation and venti- lation can cause rapid cardiovascular collapse due to increased intrathoracic pressure from positive-pressure ventilation and effects of sedative medications on right ventricular function and systemic vascular resistance. Adjust the respiratory rate to avoid hypercapnia, which can increase pulmonary vascular resistance, pulmonary artery pres- sure, and RV strain.
• Fluids in RV Failure: Volume overload can cause RV dilation, displacing the intraventricular septum, impairing left ventricular output, and ultimately compromising tissue perfusion.3 For patients who are hypovolemic, give serial boluses of an isotonic crystalloid solution in 250- to 500-mL aliquots with close monitoring.
• RV Dysfunction: Dobutamine is preferred inotrope of choice. Avoid doses>10 micrograms/kg/min, because large doses can increase pulmonary vascular resistance and cause tachydysrhythmias and hypotension. For patients unable to tolerate dobutamine, milrinone is an alternative. Higher doses of milrinone can cause hypotension.
• RCA Perfusion: For the hypotensive pulmonary hypertension patient, use a vasopressor to increase aortic root pressure and maintain RCA perfusion. Norepinephrine is recommended for this purpose. Avoid high doses of nor- epinephrine because it can increase pulmonary vascular resistance and impair right ventricular output.
• RV Afterload reduction: These medications are rarely used in ED setting. Reducing right ventricular afterload with pulmonary vasodilators is a critical component in the management of stable patients with pulmo- nary hypertension. The most commonly used pulmonary vasodilators are prostanoids, endothelin receptor antagonists, and phosphodiesterase-5 (PDE-5) inhibitors. These medications are used primarily in the treatment of patients with pulmonary arterial hypertension. 

Prostanoids (epoprostenol, treprostinil, and iloprost) are potent vasodilators and are the initial treatment of choice in patients with pulmonary arterial hypertension and right ventricular failure. These medications have antiplatelet and antiproliferative properties.

Endothelin receptor antagonists (Currently not used for critically ill ED patients) are administered orally and increase exercise capacity, improve hemodynamics, and can delay the time to clinical worsening in pulmonary hypertension patients. Drugs: bosentan and ambrisentan. 

PDE-5 inhibitors (Currently not used for critically ill ED patients) sildenafil and tadalafil are approved for use in patients with pulmonary hypertension. They are administered orally, seeking to improve hemodynamics and exercise capacity in patients with pulmonary arterial hypertension.

Pulmonary HTN patients presenting to ED are often critically ill and require HDU/ICU level care. Therefore, almost all of them require admission with expert input. 

Posted by:

              

     Lakshay Chanana

     

     ST4 Trainee

     Royal Infirmary of Edinburgh
     Department of Emergency Medicine

     Edinburgh
     Scotland

     @EMDidactic