Removal characteristics and total dialysate content of glutamine and other amino acids in critically ill patients with acute kidney injury undergoing extended dialysis.

Background: Acute kidney injury in critically ill patients is associated with the activation of protein catabolism and a negative nitrogen balance. Renal replacement therapy (RRT) aggravates this problem by eliminating a substantial amount of amino acids. However, there is scarce data on the removal characteristics of modern dialysis membranes in extended dialysis. Methods: This is a prospective study in 10 extended dialysis sessions using a 1.8-m2 polysulfone membrane (EMiC2 dialyzer or AV 1000S; FMC, Germany). Blood samples for 19 amino acids were drawn before, during, and after 10 h of extended dialysis (blood/dialysate flow 150 ml/min). In addition, samples for the calculation of dialyzer clearance and samples from the total spent dialysate were measured using a Biochrom 30 amino acid analyzer. Results: Despite no significant difference in pre- and postdialysis plasma amino acid levels, we found an impressive amount of amino acids in collected spent dialysate, i.e. 10.5 g/10 h of treatment. The dialyzer clearance ranged from 67.6 ml/min for phenylalanine to 140.0 ml/min for valine. The total eliminated masses of the measured amino acids had equal values for both membranes. There was a significant difference between the dialyzer clearance of the investigated membranes for glutamine (AV 1000S: 83.3 ml/min vs. EMiC2: 92.0 ml/min, p = 0.02) and serine (88.8 ml/min vs. 91.8 ml/min, p = 0.005). Discussion: Our data indicate that the modern forms of RRT eliminate amino acids to an extent that has not been met by our nutritional support standards. Especially the removal of glutamine, important for immune function and cell regeneration, might have detrimental effects on the recovery of critically ill patients.