新的MELD肝臟移植規範減少等待名單的死亡率


  November 20, 2007 — 根據11月Archives of Surgery期刊中的一篇研究,等待移植名單者的死亡率居高不下,新的末期肝病模式(MELD)分配移植肝臟規範減少了等待名單的死亡率,也減少了病患等待新肝臟的時間。
  
  Vanderbilt大學醫學中心的Mary T. Austin醫師和同事表示,1999年時,醫學研究中心[Institute of Medicine; IOM] 認為等待時間是移植的不利因素,也會惡化病症,因此等待名單的死亡率就相當有意義;IOM建議可以藉由設立一種機制改善分配屍肝,改善病症和減少病患等候時間,MELD認為這些需求有潛在意義。
  
  這項研究的目標是評估MELD對等待名單死亡率的影響,使用間段時間序列設計,介入開始時為2002年2月27日(MELD 政策制定之日);使用1999年3月1日到2004年7月30日的器官分享標準移植分析與研究聯合網路(United Network for Organ Sharing Standard Transplant Analysis and Research)資料庫,研究者探索等待名單中的所有的等候捐肝的美國籍成人,初級終點是等待時死亡、等待移植的時間、新註冊者人數,以及移植後存活率。
  
  MELD制定之前,並不知道趨勢,不過,介入之後,馬上有明顯效果,等待名單的死亡率從每月每1000位註冊者11-13人死亡降至2.2人死亡(95% 信心區間[CI], 1.1 – 3.4; P = .001);之後,等待名單死亡率經時減少(每月每1000位註冊者減少0.09人死亡;95% CI, -0.16到 -0.03; P <.001);減少等待時間也立即有效果(從將近294天減少到250天;減少44.4天;95% CI, -77.1到 -11.7 天;P < .001),穩定到一個較低的介入後穩定狀態。
  
  註冊者人數每月列表,MELD政策改變後,並未影響移植後3和6個月的存活率。
  
  研究作者表示,等待名單的死亡率以前是增加的,開始MELD為基礎的政策之後,整體的等待名單死亡率和等待時間減少;隨著分配政策的改變,強調等待時間是疾病惡化的重要原因,若不強調等待時間,許多較不嚴重的註冊者會因為累計時間而被移除,而導致剩餘註冊者的整體移植時間被低估。
  
  研究限制包括生態研究設計;政策改變只是諸多可能影響等待名單死亡率的因素之一;使用國家資料庫;單一選擇方式;都會限制分析結果的衍譯。
  
  研究作者結論表示,實質器官移植中,肝臟移植是最先適用此器官分配政策的目標;仔細評估此一分配改變,捐肝者減少是重要因素之一,因為會直接影響後續的分配政策,由於明顯的資源被擴展到分配器官的公平性,本研究提供了對此政策改變的經驗評價。
  
  健康來源及服務管理局(Health Resources and Services Administration)贊助本研究的一部分,作者宣稱沒有相關財經關係 。
  
  Maryland大學的Benjamin Philosophe醫師和Stephen T. Bartlett醫師在受邀評論時指出,MELD對存活率的效果仍是有爭議的。
  
  Philosophe醫師和Bartlett醫師指出,此研究無法對MELD評分制度對整體末期肝病的衝擊有完整評估,在執行MELD評分制度之前,需要長期的輿論;因此,肝臟移植中心須有長時間對政策改變因應;這些資料無法完整評估的是,政策改變是否影響移植中心的實務、是否影響死亡率和對所有末期肝病患者的結果,包括那些不在移植等待名單上者。
  
  Philosophe 醫師和Bartlett醫師宣稱沒有相關財經關係。

New MELD Liver Transplant Crit

By Laurie Barclay, MD
Medscape Medical News

November 20, 2007 — After a temporary increase in death rate among those on the waiting list, the new Model for End-Stage Liver Disease (MELD) criteria for allocating livers for transplant have decreased the waiting list mortality rate as well as the amount of time patients spend waiting for a new liver, according to a study reported in the November issue of the Archives of Surgery.

"In 1999, the [Institute of Medicine; IOM] deemed that waiting time was a poor indicator of medical urgency and that rates of transplantation, illness severity, and waiting list mortality were much more meaningful," write Mary T. Austin, MD, MPH, from Vanderbilt University Medical Center in Nashville, Tennessee, and colleagues. "The IOM recommended that allocation of deceased donor livers could be improved by instituting a mechanism that favored disease severity and deemphasized patient waiting time.... The [MELD] was identified as potentially meeting these requirements."

The objective of this study was to assess the effect of MELD on waiting list mortality, using an interrupted time series design with a nominal inception point of the intervention (implementation of the MELD policy) on February 27, 2002.

Using the United Network for Organ Sharing Standard Transplant Analysis and Research database from March 1, 1999, to July 30, 2004, the investigators studied all adult candidates on the waiting list for liver transplantation in the United States. The primary endpoints were mortality while on the waiting list, waiting time to transplantation, number of new registrants, and survival after transplantation.

Before implementation of MELD, no trend was identified. However, after the intervention, there was an immediate effect of increasing waiting list mortality by 2.2 deaths per 1000 registrants per month (from approximately 11 to 13 deaths per 1000 registrants per month; 95% confidence

interval [CI], 1.1 – 3.4; P = .001). Subsequently, waiting list mortality decreased over time (−0.09 death per 1000 registrants per month; 95% CI, −0.16 to −0.03; P < .001). There was also an immediate effect of decreased waiting time (from approximately 294 to 250 days; −44.4 days; 95% CI, −77.1 to −11.7 days; P < .001), which stabilized to a lower postintervention steady state.

The number of new registrants listed per month and 3- and 6-month posttransplantation survival were not affected by the MELD policy change.

"After an initial increase in waiting list mortality, the implementation of the MELD-based allocation policy was associated with an overall decline in waiting list mortality and time to transplantation," the study authors write. "With the transition in allocation policy from a system that emphasized waiting time to one that favored disease severity with a de-emphasis on patient waiting time, many less-ill registrants placed on the list for the sole purpose of 'banking time' may have been removed, leading to an overall decrease in the time to transplantation for the remaining registrants."

Study limitations include ecologic study design; policy change of only one of many possible variables that may affect waiting list mortality; use of a national database; and simple selection, which may limit the interpretation of the analyses.

"In solid-organ transplantation, the liver transplantation community was the first to adopt an objective score as the basis of organ allocation policy," the study authors conclude. "Careful evaluation of this major change in the allocation of deceased donor livers is essential because it may direct future allocation policies.... Because significant resources are expended in efforts to equitably allocate organs, this work provides empiric justification of this policy change."

The Health Resources and Services Administration supported this work in part. The authors have disclosed no relevant financial relationships.

In an invited critique, Benjamin Philosophe, MD, PhD, and Stephen T. Bartlett, MD, from the University of Maryland in Baltimore, note that the effect of MELD on survival remains controversial.

"The impact of the MELD scoring system on total burden of end-stage liver disease cannot be fully assessed by the study," Dr. Philosophe and Dr. Bartlett write. "A long period of public comment preceded the implementation of the MELD scoring system; therefore, liver transplantation centers had a long lead time to react to the policy change. What cannot be fully assessed by these data are whether the policy change affected listing practices of transplantation centers and the effect on mortality and outcome for all patients with end-stage liver disease, including those who were not on transplantation waiting lists."

Dr. Philosophe and Dr. Bartlett have disclosed no relevant financial relationships.

Arch Surg. 2007;142(11):1079–1085.

    
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