Ott P, Keiding S, Bass L
Medical Department A. Rigshospitalet, Copenhagen, Denmark.
Eur J Clin Invest. 1992 May;22(5):347-57. doi: 10.1111/j.1365-2362.1992.tb01473.x.
Intrinsic hepatic clearance (K) of indocyanine green (ICG) is used as a quantitative measure of liver function. ICG is tightly bound to plasma proteins. The purpose of this study was to examine the effect of changes of plasma protein concentration on K in anaesthetized pigs with intact hepatic circulation. In addition, an attempt was made to evaluate the corresponding changes of the unbound intrinsic clearance of ICG. The plasma protein concentration was changed by exchange of plasma with either dextran-70 or donor pig plasma. Plasma albumin concentration was measured in a peripheral artery and changes of the concentrations of other plasma proteins were assumed to parallel those of albumin. ICG was given as a constant infusion and K was calculated from peripheral artery and hepatic vein concentrations of ICG according to the sinusoidal perfusion model. One experimental series comprised 3 measurement periods: From Period 1 to Period 2 (eight animals) albumin concentration was decreased by 36.6 +/- 6.5% (Mean +/- SD). This was associated with an increase of K of 32.8 +/- 28.8% (P = 0.004). From Period 2 to 3 (five animals) albumin was increased by 13.2 +/- 3.2% and K decreased by 18.5 +/- 8.3% (P = 0.03). In the second experimental series (eight animals), albumin concentration was increased by 21.6 +/- 10.3% and K decreased by 20.3 +/- 8.1% (P = 0.001). For both series, changes in albumin concentration were associated with oppositely directed changes of K in 20 out of 21 comparisons (P less than 0.001). Thus K depends not only on hepatocyte function but also on plasma protein concentration. This finding should affect interpretation of K when used as a liver function test. Changes of the unbound intrinsic clearance of ICG were examined indirectly by means of the K.a product (a: albumin concentration). According to the overall evaluation of the data the unbound intrinsic clearance of ICG was not affected by the changes in plasma protein concentration, but the results were internally inconsistent, apparently due to a time-dependency of the K.a product. We suggest this to be due to a slow but steady decrease of the 'background' K. After correction for the average decrease of K of 0.102% per min our data were in accordance with the hypothesis that the unbound clearance of K was enhanced by the binding protein(s) of ICG.
吲哚菁绿（ICG）的肝内固有清除率（K）被用作肝功能的定量指标。ICG与血浆蛋白紧密结合。本研究的目的是在肝循环完整的麻醉猪中，研究血浆蛋白浓度变化对K的影响。此外，还尝试评估ICG未结合固有清除率的相应变化。通过用右旋糖酐-70或供体猪血浆置换血浆来改变血浆蛋白浓度。在周围动脉中测量血浆白蛋白浓度，并假定其他血浆蛋白浓度的变化与白蛋白的变化平行。以恒定输注方式给予ICG，并根据正弦灌注模型从周围动脉和肝静脉中ICG的浓度计算K。一个实验系列包括3个测量期：从第1期到第2期（8只动物），白蛋白浓度降低了36.6±6.5%（平均值±标准差）。这与K增加32.8±28.8%相关（P = 0.004）。从第2期到第3期（5只动物），白蛋白增加了13.2±3.2%，K降低了18.5±8.3%（P = 0.03）。在第二个实验系列（8只动物）中，白蛋白浓度增加了21.6±10.3%，K降低了20.3±8.1%（P = 0.001）。对于两个系列，在21次比较中的20次中，白蛋白浓度的变化与K的相反方向变化相关（P＜0.001）。因此，K不仅取决于肝细胞功能，还取决于血浆蛋白浓度。这一发现应会影响将K用作肝功能测试时的解读。通过K.a乘积（a：白蛋白浓度）间接检测ICG未结合固有清除率的变化。根据数据的总体评估，ICG未结合固有清除率不受血浆蛋白浓度变化的影响，但结果在内部不一致，显然是由于K.a乘积的时间依赖性。我们认为这是由于“背景”K缓慢但稳定地下降。在对K每分钟平均下降0.102%进行校正后，我们的数据符合以下假设：ICG的结合蛋白增强了K的未结合清除率。
