Hahn Robert G, Lyons Gordon
From the Research Unit, Södertälje Hospital, Södertälje, and Section for Anaesthesia, Linköping University, Linköping, Sweden.
Eur J Anaesthesiol. 2016 Jul;33(7):475-82. doi: 10.1097/EJA.0000000000000436.
An understanding of the half-life (T1/2) of infused fluids can help prevent iatrogenic problems such as volume overload and postoperative interstitial oedema. Simulations show that a prolongation of the T1/2 for crystalloid fluid increases the plasma volume and promotes accumulation of fluid in the interstitial fluid space. The T1/2 for crystalloids is usually 20 to 40 min in conscious humans but might extend to 80 min or longer in the presence of preoperative stress, dehydration, blood loss of <1 l or pregnancy.The longest T1/2 measured amounts to between 3 and 8 h and occurs during surgery and general anaesthesia with mechanical ventilation. This situation lasts as long as the anaesthesia. The mechanisms for the long T1/2 are only partly understood, but involve adrenergic receptors and increased renin and aldosterone release. In contrast, the T1/2 during the postoperative period is usually short, about 15 to 20 min, at least in response to new fluid.The commonly used colloid fluids have an intravascular persistence T1/2 of 2 to 3 h, which is shortened by inflammation. The fact that the elimination T1/2 of the infused macromolecules is 2 to 6 times longer shows that they also reside outside the bloodstream. With a colloid, fluid volume is eliminated in line with its intravascular persistence, but there is insufficient data to know if this is the same in the clinical setting.
了解输注液体的半衰期（T1/2）有助于预防医源性问题，如容量超负荷和术后间质水肿。模拟显示，晶体液半衰期的延长会增加血浆容量，并促进液体在间质液空间的积聚。在清醒的人体中，晶体液的半衰期通常为20至40分钟，但在术前应激、脱水、失血<1升或怀孕的情况下，可能会延长至80分钟或更长。测量到的最长半衰期为3至8小时，发生在手术及机械通气的全身麻醉期间。这种情况会持续到麻醉结束。半衰期延长的机制仅部分为人所知，但涉及肾上腺素能受体以及肾素和醛固酮释放增加。相比之下，术后的半衰期通常较短，至少在对新输入液体的反应中约为15至20分钟。常用的胶体液血管内持续半衰期为2至3小时，炎症会使其缩短。输注的大分子清除半衰期长2至6倍，这表明它们也存在于血管外。对于胶体液，液体量会根据其血管内持续时间而消除，但尚无足够数据了解在临床环境中是否也是如此。
