Effects of high-volume plasmapheresis on ammonia, urea, and amino acids inpatients with acute liver failure

OBJECTIVE: In acute liver failure (ALF), urea production is severely impair ed, and detoxification of ammonia by glutamine synthesis plays an important protective role. The aim of this study was to examine the effects of thera peutic high-volume plasmapheresis (HVP) on arterial concentrations and spla nchnic exchange rates of ammonia, urea, and amino acids-in particular, glut amine. METHODS: A quantity of 8 L of plasma was exchanged over the course of 7 h i n 11 patients with ALF after development of hepatic encephalopathy grade II I-IV. Splanchnic exchange rates of ammonia, urea, and amino acids were meas ured by use of liver vein catheterization. RESULTS: HVP removed ammonia and glutamine at a rate of 1 mu mol/min and 27 mu mol/min. respectively. Arterial ammonia decreased from 160 +/- 65 to 11 4 +/- 50 mu mol/L (p < 0.001). In contrast, arterial glutamine was only min imally changed from 1791 +/- 1655 to 1764 +/- 1875 <mu>mol/L (NS). This imp lied that the rate of systemic glutamine synthesis was increased by 27 mu m ol/min. Splanchnic exchange rates (before vs after HVP) were as follows: fo r ammonia. -93 +/- 101 versus -70 +/- 80 mu mol/min (NS); urea-nitrogen, 0. 08 +/- 1.64 versus -0.31 +/- 0.45 mmol/min (NS); alanine, -73 +/- 151 versu s 12 +/- 83 mu mol/min (p < 0.05), and glutamine: 132 +/- 246 versus 186 +/ - 285 <mu>mol/min (NS), with negative values denoting release. CONCLUSIONS: Arterial ammonia decreased during HVP in patients with ALF. Th e data suggest that this effect of HVP could be explained by increased hepa tic urea synthesis and possibly by increased glutamine synthesis in muscle tissue. (Am J Gastroenterol 2001;96:1217-1223. (C) 2001 by Am. Coll. of Gas troenterology).