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• W1567258608 abstract "Portopulmonary hypertension (PPHTN) has the distinction of being an orphan disease under the umbrella of another orphan disease. PPHTN is sub-classified under WHO Group I pulmonary arterial hypertension (PAH) because the limited data available indicate that patients with PPHTN appear to share the pathology, clinical course and response to treatment seen in other forms of PAH. PPHTN is a rare disease and little progress has been made into the delineation of its pathologic mechanisms and treatment since its initial description in 1951. Because the paucity of large cohorts, evolving clinical experience has been the principal driver of change in the management of these patients. PPHTN is defined as pulmonary hypertension with coexisting portal hypertension. It is defined haemodynamically as an elevated mean pulmonary artery pressure (mPAP > 25 mmHg), an increased pulmonary vascular resistance (PVR) (> 3 wood units) and a normal pulmonary artery occluding pressure (PAOP) <15 mm Hg or elevated transpulmonary gradient (TPG-mPAP-PAOP, normal 12). This lengthy definition is particularly important in PPHTN because of the variety of haemodynamic derangements identified in patients with liver disease. Many patients with liver disease and portal hypertension will exhibit a high cardiac output state and a low systemic vascular resistance, which are thought to be caused by overproduction of nitric oxide. These patients may exhibit a high mean pulmonary artery pressure (mPAP) on right heart catheterisation, but they will have a normal PVR. In addition, patients with liver disease are often volume overloaded and exhibit elevated mean PA pressures and PAOPs, but normal transpulmonary gradients and PVRs. True PPHTN is characterised by both an elevated mPAP and PVR, but because this disease may coexist with volume overload in liver disease, an elevated transpulmonary gradient may be used rather than the PAOP for diagnosis (1). Nearly all of the descriptive data about PPHTN arises from liver transplant. Within the liver transplant population, prevalence ranges from 2 to 20% (2). The severity of the PPHTN does not correlate with the severity of the liver disease or the portal hypertension. Yet, the presence of PPHTN in the patient with liver disease markedly affects prognosis. A retrospective analysis published in 1991 revealed that patients with PPHTN who are neither treated nor transplanted have a mean survival of 15 months (median 6 months) from the time of diagnosis with half of the deaths attributed to PPHTN (3). Because of these sobering survival statistics, liver transplantation as an option for treatment was pursued. Despite reported cures of PPHTN after liver transplantation, early mortality data were disappointing. In 1997, Ramsay et al., demonstrated that PPHTN patients had a 3-year postliver transplant survival of only 21% (4). In addition, a more recent multi-centre database analysis indicated that perioperative mortality was 36% in those with a mPAP > 35 mmHg. Interestingly, this database revealed that the majority of the diagnoses of PPHTN were made in the operating room and thus patients were not treated for their PPHTN prior to transplantation (5). In response to these statistics, for a few years many liver transplantation centres avoided liver transplantation in PPHTN patients. Subsequently, few centres began to report case series of successful liver transplantation in PPHTN patients, and reinforced that the PPHTN is often cured in the weeks to months after liver transplant. It was in this climate that, the European Respiratory Society’s Task force on Pulmonary-Hepatic Vascular Disorders met and created diagnostic treatment recommendations for PPHTN. These included liver transplantation for those with mild (< 35 mmHg mPAP) PPHTN and consideration for treatment with pulmonary vasodilators for those with moderate (mPAP 35–45 mmHg) PPHTN prior to transplantation (1). As experience mounted with liver transplantation, a disparity between the poor survival of these patients without liver transplant and their low model for end-stage liver disease (MELD) score was noted. The severity of the PPHTN appears to be unrelated to the severity of liver disease in these patients, and thus the MELD underestimates their risk of mortality on the wait-list. The MELD Exception Points Study Group and Conference attempted to account for this disparity with exception recommendations published in 2006 (6). MELD exception is a process by which additional MELD points may be granted through the regional review board, thereby increasing the patient’s chances for liver transplantation regardless of their baseline synthetic liver function. The committee’s recommendations suggest that MELD exception should be based on standardised data, which can then be collected and analysed through the NIH-supported study group for pulmonary vascular complications of liver disease. Many, but not all, regional review boards have adopted these recommendations. The study group suggested that exception points be given to patients who meet the haemodynamic definition of PPHTN and who are acceptable liver transplant candidates. To achieve extra points, PPHTN patients must initially have moderate to severe PPHTN (mPAP> 35 mmHg) and have been treated with an FDA-approved pulmonary hypertension therapy with a good response. That response is defined as an improvement in mPAP (< 35), PVR (< 5 wood units), and satisfactory right ventricular function. If patients demonstrate this haemodynamic response to treatment, their MELD score for transplantation would automatically be increased to 26. They also recommended consideration for an additional MELD upgrade after 6 months on the wait-list. These criteria aim to reserve liver transplantation for those who would benefit from and are more likely to survive the transplant process according to available data. This standardisation not only makes liver transplantation more accessible to PPHTN patients but also allows more reliable collection and analysis of data across various centres. In addition, it will provide a framework for a description of the appropriate in PPHTN patients. As more PPHTN patients undergo liver transplantation, the data will continue to evolve and will likely provoke further change in clinical practice. Subsequent to the MELD exception points study group findings, the Mayo group published a retrospective screening-RHC analysis of its PPHTN database and analysed their survival according to treatment for PPHTN and transplant status (7). Although the database spanned a 14-year time period, during which the treatments and clinical practice varied, they noted a marked change in survival between different treatment approaches. Patients who received neither a liver transplant nor PH therapy did worst, with a 14% 5-year survival. The patients who were transplanted without PH therapy also did rather poorly with a 25% 5-year survival. The patients who were treated for PH but not transplanted had a 45% 5-year survival. The group with the best outcome were those who were treated for PH before liver transplantation, who exhibited a 67% 5-year survival. Mortality did not correlate with initial haemodynamics, type of liver disease, or the severity of their liver disease. This study underscored the importance of screening for PPHTN in the liver transplant population and prioritising PH therapy. Meticulous, collaborative collection of outcome data for PPHTN patients is essential to evolve our clinical pratice and ensure appropriate organ allocation. Yet, as screening for PPHTN becomes more aggressive, it is possible that the one-size-fits-all approach to transplant evaluation is doing a disservice to some. PH specialists are sometimes faced with patients who have both minimal liver dysfunction and PPHTN that was initially severe, but responded dramatically to medication. In this case, under the current MELD exception guidelines one could list this very functional patient for liver transplantation and have an organ match within months. The long term-prognosis of some of these ‘responders’ to PPHTN may be quite good, and the perioperative risks of transplant may be unacceptable. On the other hand, if we wait, do we risk the development of ‘fixed’ pulmonary arteriopathy and decrease the chance that it will ‘regress’ after liver transplantation? It is very likely that there are disparate practices with regards to these patients between transplant centres with some favouring an aggressive early transplant approach and others favouring a more conservative approach. This nuance is unlikely to be detectable in the current data collection. PPHTN is a rare disease which affects not only each patient’s individual survival but also the availability and allocation of donor organs. Continued description of the characteristics, pathology and prognosis of PPHTN will require cooperation between multiple centres, strict adherence to guidelines for the standardisation of data, and diligent documentation and sharing of information. The study of PPHTN may also have broader implications for PAH in general. PPHTN has the unique position of being pathologically identical to PAH, yet curable with liver transplantation while leaving the heart and lungs intact. This is an unmatched opportunity for studying the development and resolution of pulmonary arteriopathy in vivo. As data emerges from the study group for pulmonary vascular complications of liver disease, we will need to continually alter our collection of information to target emerging clinical questions. As no single centre will be able to harness enough timely data for analysis in this rare condition, we must work together to maximise treatment and outcomes for our patients." @default.
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• W1567258608 title "Portopulmonary hypertension: a disease in search of multi-centre cooperation" @default.
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