45-year-old female presents to the Emergency Department with worsening shortness of breath over the past two days. She has history of pulmonary hypertension secondary to interstitial lung disease requiring 3 liters of supplemental oxygen at baseline. Which WHO category for pulmonary hypertension does this patient fall into? 

1. Class 1

2. Class 2

3. Class 3

4. Class 4

5. Class 5

Answer: Class 3

Normally flow through the pulmonary artery is high flow with low resistance. Pulmonary arterial systolic pressures are 15-30 mmHg with diastolic ranging from 4-12 mmHg. Pulmonary hypertension is defined as mean pulmonary artery pressures >25 mHg. It is classified based on pulmonary capillary wedge pressure (PCWP), which is obtained by measurement of right sided heart pressures. 

Group 1: Pulmonary Arterial Hypertension- idiopathic, genetic abnormalities, drug/toxin induced, HIV, liver disease

Group 2: Left Heart Disease- systolic or diastolic heart failure, mitral valve disease, aortic valve disease

Group 3: Chronic Hypoxemic Lung Disease- COPD, ILD, OSA, chronic high altitude 

Group 4: Embolic Disease

Group 5: Everything else- lymphatic disease, myeloproliferative disorders, sarcoid, thyroid disease, glycogen storage disease 

Patients with severe disease develop significant dilation of the RV which leads to decreased perfusion of the right coronary artery during systole and further ischemia. RV dilation leads to decreased left ventricular cardiac output due to bowing of the septum into the LV cavity. 

Treatment of acute on chronic hypoxia includes increasing supplemental oxygen. It is imperative to avoid intubation if possible as positive pressure during ventilation can lead to cardiovascular collapse in these patients. Fluid administration should be performed slowly as well as volume overload leads to worsening RV dilation and decreased LV output. In acute RV failure dobutamine or milrinone can be considered to help increase contractility. Norepinephrine is the vasopressors of choice to help increase RCA perfusion. Prostanoids such as epoprostenol at strong vasodilators that improve perfusion. Typically they require continuous IV infusions. PDE-5 inhibitors such as sildenafil are given orally and help improve exercise tolerance. Ultimately patients in class 3 may require lung transplants to improve mortality. 

Resources:

M. Winters. (2016). Section 7: Cardiovascular Disease. In Tintinalli's Emergency Medicine: A Comprehensive Study Guide (8th ed., pp. 409-412). New York, NY: McGraw-Hill Education.