库存血之迷‘——BecauSe they lack aR essential component，blood transfusions may be killing some of the people they are intended to save．由于缺少一种必需的成分，输进体内的血液可能会杀死它本来要挽救的人。SciencePhotoLibrary闫传海译If there were any sure bets in medicine，you might think that“blood transfusions save lives” would be one of them．But there aren’t．Even though deaths caused in the1980s by accidentalHIV infection mean that donated blood is now screened meticulously to keep it free of infectious agents， there is still a nagging feeling that something is wrong．In2004，for instance，SunilRao ofDukeUniversityMedicalCentre。 inNorthCarolina，carried out a study of people suffering from acute coronary syndrome(a specitic type of heart attack)．One conclusion that could be drawn from his research was that unnecessary blood transfusions might be causing tens of thousands of deaths inAmerica alone．DrRao found that patients who had had a transfusion because of a low red blood-cell count had an8％chance of dying within30 days．Without a transfusion，only3％died．Those numbers need to be treated with caution．AsDrRao points out，the patients who underwent transfusion were，on average，sicker and older如若医学上有任何能够稳操胜券的赌注的话，你或许会认为“输血能够挽救生命”就是其中之一。但其实不存在这种胜算。即使20世纪80年代因意外感染艾滋病病毒所导致的死亡意味着捐献的血现在须经过极其细致的检查，以使其不含感染性物质，人们依然对输血有一种挑剔看法，认为其中必定有什么差错。例如，2004年，美国北卡罗来纳州杜克大学医学中心的苏尼尔·拉奥对急性冠状动脉综合症(心脏病的一种类型)患者开展了一项研究，他的研究得出的一条结论便是：单是在美国，不必要的输血就可能导致成千上万人死亡。拉奥博士发现，因血红细胞含量低而接受过输血的病人在30天内死亡的机率为8％。如果不输血，仅有3％的病人死亡。这些数字需谨慎对待。拉奥博士指出，接受过输血的病人的病情一般都比那些没有输过血的病人严重，而且更趋衰老。然而，他的研究并非输血中某种差错的唯一可能。2007年第12期总第324期隰蒸 than those who did not．Nevertheless， his study iS not the only indication of something amiss．In recent years，research has suggested that transfusion is not necessarily a good thing for patients suffering from serious inj uries，for those who have undergone surgery and even for those who are anaemic．And a study carried out earlier this year found that critically ilI children whose red bloo小cell counts had dropped by half fared no better after a transfusion than those who did not receive one．As a result of all this．questions are being asked about whether some- thing happens to blood when it is banked that causes it to stop working properly．What that might be has remained a mystery．But it may be one no10nger．A group ofDrRao’S colleagues，led byJonathanStamler， think the answer iS a gas called nitric oxide—or，rather，a lack of it．The main reason for giving a patient blood is that it carries oxygen．It carries lots of other things，too， such as glucose．But it is a lack of oxygen that will kill you quickest．However，asDrStamler points out， what determines whether transfused blood works as a treatment iS not merely hoW much oxygen it is carry- ing，but whether that oxygen can reach the tissues that need it．This i8 where nitric oxide comes in．Nitric oxide increases the flow硎舞骟近年来的研究表明，输血对那些遭受重伤的病人，对那些进行过手术的人，甚至对那些贫血症患者来说并不见得一定是什么好事。今年年初开展的一项研究发现，血红细胞数量下降一半的病危儿童在输血后，其病情好转的情况与那些没有接受输血的儿童相比，并没有出现明显变化。其结果便是，人们不禁要问，血液在库存期间是否发生了什么变化，致使它不能真正发挥作用。到底发生了什么变化目前依然是个迷。但这个迷可能不久将被解开。由乔纳森·斯戴姆勒领衔的拉奥博士的一组同事认为，答案在于一种名叫一氧化氮的气体——或者不如说是这种气体的缺失。给病人输血的主要原因是血液携带有氧。血液也携带有其他多种物质，如葡萄糖等。但缺氧是迅速致人于死地的原因。然而，正如斯戴姆勒博士所指出的，决定所输的血能否发挥治疗效用的不仅仅是看它携带多少氧，还要看这些氧气能否到达缺氧的组织。而一氧化氮的作用就在于此。一氧化氮可以舒张穿过组of blood to tissues by dilating the arteries that penetrate those tissues．However，it is not iust blood vessels that nitric oxide relaxes．When a red blood cell reaches any tissue in need of oxygen it releases nitric oxide in order to dilate the capillaries．only then can it deliver its cargo．And that is doubly true of the cells in stored blood since red blood ceils become1ess flexible with age，and thus less able to squish into capillar— ies．DrStamler thus wondered if a lack of nitric oxide was causing the problelTlS associated with transfusions．F‰it he and his colleagues dis— covered，and published this week in theProceedings o厂theNationalAcademy o厂Sciences，was that the amount of nitric oxide in stored blood does indeed decrease--and does so rapidly．Within a day of storage，blood loses70％of its nitric oxide．After a few days，uD to90％has been lost．A second paper in the same journal，byDrStamler’s colleagueTimothyMcMahon，confirmed this result(in fact，it showed that the initial drop of around70％happens within three hours of collection) and showed that it was not caused by the way blood is processed，but merely by the passage of time．DrMcMahon also established that stored blood does indeed lose its ability to dilate blood vessels．DrStamler is in little doubt织的动脉血管，从而使流入这些组织的血液量增加。然而，一氧化氮舒张的不仅仅是血管。当血红细胞到达任意一个缺氧的组织时，就会释放出一氧化氮，以使毛细血管扩张。只有到那时，它才能释放出所携带的物质。库存过的血液中的血红细胞更是如此，因为随着时间的流逝，血红细胞柔韧性降低，因此就更不容易挤进毛细血管。斯戴姆勒博士因此怀疑是否是一氧化氮的缺失导致了与输血相关的问题。斯戴姆勒博士及其同事的发现刊登在本周的美国《国家科学院学报》上，即库存血液中一氧化氮的含量确实会下降——并且下降得很快。库存一天，血液中的一氧化氮含量就会下降70％。几天以后，多达90％的一氧化氮将会消失。在《学报》同一期的另一篇论文中，斯戴姆勒博士的同事蒂莫西·麦克马洪证实了这一结果(事实上，70％的一氧化氮含量下降最开始发生于血液采集后的三小时之内)。他指出，这是由时间的流逝本身，而非血液采制过程造成的。他明确指出，库存血液舒张血管的能力确实会下降。斯戴姆勒博士对这些发现2007年第12期总第324期纛 about the significance of these find- ings．Furthermore，he warns that putting blood lacking nitric oxide into the body does not merely dilute what gas is already present in the bloodstream．Blood that iS poor in nitric oxide will scavenge the gas from other tissues，causing the vessels in those tissues to constrict．If the tissue in question is heart muscle， the result will be a heart attack．These papers，therefore，make a strong case that a lack of nitric oxide iS creating the problems with transfusions--though asMichaelStrong，the president of theAmericanAssociation ofBloodBanks，points out，they do not settle the issue once and for a11．That would require a proper，randomised clinical trial．And therein lies the rub．Because blood transfusion iS such an old practice(it dates back to1818)it has never been subjected to modern clinical standards．Nobody iS ques— tioning whether car-crash victims， say，should have transfusions after massive blood lOSS．Without it they would undoubtedly die．But for those not threatened with exsanguination it iS far less clear whether a transfusion iS3 good idea．There are no rules about when to transfuse and who to do it to．These are matters of j udgment，and knowledge is typically passed from doctor to doctor．乃e good news from this study iS that the problem should be easy的重大意义确信不疑。而且，他还警告说，将缺少一氧化氮的血液输入体内的结果不仅仅是稀释了血流中已有的气体。一氧化氮含量低的血液还将会从其他组织中寻找该气体，致使这些组织中的血管收缩。如果涉及的组织是心肌，其结果将是心脏病发作。因此，这些论文为证实是缺少一氧化碳使输血产生了问题这一观点提供了强有力的论据——尽管如美国血库协会主席迈克尔·斯特朗所指出的那样，这些论文并没有一劳永逸地解决问题。要解决问题，还需要进行适当的随机临床试验。而难就难在这里。因为输血是一种相当古老的做法(可以追溯到1818年)，它从来不受现代临床医学标准的规范。没人会质疑撞车的受害者在大量失血后应该接受输血。毫无疑问，不接受输血，他们就会死去。但对于那些没有受到失血过多威胁的人来说，输血是否是个好主意就远没那么清晰了。至于何时输，给谁输，并无规则可循。这全依赖于人的判断，而且这方面知识仅由医生们通过口口相传的方式传播。这项研究所带来的一个好消息是，这个问题应该不难纠