A 72-year-old male with past medical history significant for pulmonary hypertension and congestive heart failure presents to the ICU in cardiogenic shock with hypotension. Despite initiation of vasopressor therapy, the patient remains hemodynamically unstable and develops worsening hypoxemia. Bedside transthoracic echocardiography shows bowing of the intra-atrial septum toward the left atrium with positive Doppler color flow across the intraatrial septum and a hypokinetic right ventricle.
What is the most likely cause of the patient’s hypoxemia?
A. V/Q mismatchCorrect Answer: B
In this scenario, based on the patient’s echocardiography results, the patient is showing signs of right-sided heart failure with increase in right atrial pressure leading to right to left shunt through an atrial septal defect. In patients with pulmonary hypertension, it is crucial to avoid hypoxemia, hypercarbia, and acidosis as this can increase pulmonary vascular resistance and if severe enough lead to right heart failure. When the right-sided heart fails to eject blood against the high pulmonary vascular resistance, significant tricuspid regurgitation can develop and rise in right atrial pressure higher than the left atrial pressure can result. Bowing of the intra-atrial septum toward the left atrium indicates increased right atrial pressure, which in presence of an atrial septal defect (seen as color Doppler flow across the septum) causes flow of unoxygenated blood from the right side of the heart to mix with oxygenated blood in the left atrium causing systemic hypoxemia. The resulting hypoxemia can further worsen the patient’s pulmonary hypertension and lead to cardiopulmonary decompensation. Measures to decrease pulmonary hypertension may reduce the right to left shunting.
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