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A6998 - Which Shunt Is the Culprit? A Case of Hepatopulmonary Syndrome
Author Block: C. Prohaska, A. Shah, C. J. King; Internal Medicine, University of Colorado, Aurora, CO, United States.
Case Information:
A 49-year-old woman with a history of chronic hypoxemia requiring 3 liters supplemental oxygen at baseline, cirrhosis due to alcohol abuse and untreated hepatitis C, and recent intraatrial shunt repair presented for worsening hypoxia. She required 15 liters via non-rebreather and had digital clubbing with orthodeoxia. A transthoracic echocardiogram showed a significant right to left communication during agitated saline test at the level of the interatrial septum suspicious for failure of her atrial septal defect closure device. A cardiac CT showed appropriate positioning of the device without evidence of shunt. Cardiology was consulted and suggested that hepatopulmonary syndrome was more likely than shunt closure device failure, as the bubbles were seen were after several cardiac cycles. A ventilation-perfusion scan showed a shunt fraction of 35%, confirming a diagnosis of grade 4 hepatopulmonary syndrome. She was not a candidate for liver transplantation given her history of recent alcohol abuse. She was discharged on 10 liters of supplemental oxygen with recommendations to follow up with outpatient palliative care.
Discussion:
Shunts are a common cause of hypoxemia, and this patient had two shunts that could have contributed. Intracardiac shunts, including atrial septal defects, result in shunt flow in both directions across the defect which depends upon the pressure gradient and vary during different phases of the cardiac cycle. Blood flow from the left to the right side of the heart causes right-sided cardiac and pulmonary artery dilatation and increased pulmonary vascularity. The increase in blood flow through the pulmonary vasculature also causes increased pulmonary vascular resistance and pulmonary arteriolar hypertension. As the pressure in pulmonary vasculature increases, net flow through the shunt reverses and results in overall right-to-left shunting causing cyanosis that is not amenable to treatment with supplementary oxygen.
Hepatopulmonary syndrome (HPS) occurs in up to 30% of patients with underlying cirrhosis or portal hypertension. HPS is caused by increased pulmonary angiogenesis, dilation of the capillary and precapillary vessels and impaired hypoxia-induced pulmonary vascular vasoconstriction. Mixed venous blood passes rapidly through the pulmonary vasculature despite unchanged alveolar ventilation, leading to ventilation-perfusion mismatch. Impaired oxygen diffusion also plays a role in hypoxia, as the room air concentration of oxygen in the alveolus is unable to oxygenate blood near the center of dilated alveolar capillaries. This can only be overcome by increasing the amount of inspired oxygen, which differentiates HPS, a physiologic shunt, from an anatomic, or right to left, shunt.