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Diagnosis of hepatopulmonary syndrome in children

      The United Network for Organ Sharing developed a system for prioritizing candidates waiting for liver transplants based on statistical formulas that predict urgency. The Model for End Stage Liver Disease (MELD) is used for candidates ≥12 years of age, and the Pediatric End Stage Liver Disease Model (PELD) is used for younger patients (http://www.unos.org/docs/MELD_PELD.pdf). However, it has been recognized that the calculated MELD/PELD score may not truly reflect a candidate's need for a liver transplant and that “exceptions” must be made so that additional points can be awarded. One of the complications that would qualify a candidate for automatic MELD/PELD exception points is the diagnosis of hepatopulmonary syndrome (HPS). This decision is based on the documented lower survival rate for affected patients. The burden is on the transplant center to accurately diagnose HPS, which may not be straightforward.
      HPS is characterized by an oxygenation defect induced by intrapulmonary vascular dilatation (IPVD) in the setting of liver cirrhosis or portal hypertension. The resultant ventilation-perfusion mismatch and arteriovenous shunting cause limited diffusion and impaired oxygen exchange. In both adults and children, HPS is defined by abnormal pulse oximetry (SO2 97%) and an increased alveolar arterial oxygen gradient (> 15 mm Hg). Clinically, HPS is associated with the insidious onset of progressive dyspnea. Contrast-enhanced transthoracic echocardiography is the most effective test to demonstrate IPVD. Another method for detecting IPVD is the radionuclide lung perfusion scanning, using technetium-labeled macroaggregated albumin particles. Pulse oximetry has been used as a non invasive screening test for HPS. However, in this issue of The Journal, Hoerning et al report that pulse oximetry is not suitable for preventive screening and early diagnosis in children. In this study, pulse oximetry detected “only late and severe forms of HPS at a stage where liver transplantation is a high-risk associated with severe complications affecting the postoperative survival.” The authors suggest that contrast-enhanced transthoracic echocardiography and capillary blood gas determination be utilitized in the evaluation of HPS in children with cirrhosis.
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