Potential adverse effects of replacing high volume hemofiltration exchanges on electrolyte balance and acid-base status using the current commercially available replacement solutions in patients with acute renal failure.

The original substitution and/or dialysates used for continuous hemofiltration and/or dialysis were either based on peritoneal dialysis fluids, or peritoneal dialysates themselves. Although these fluids have been refined over the years, by changing the anionic base from acetate or racemic d+ l-lactate, to bicarbonate or l-lactate, the fluids remain designed for low volume hourly exchanges. Even at relatively low volume exchanges, the composition of these fluids can affect systemic acidbase balance. Those fluids which contain a higher concentration of lactate with a corresponding lower chloride, predispose to a hypochloremic alkalosis, whereas those with a lower concentration of lactate with a corresponding higher chloride potentially lead to a hyperchloremic acidosis. In addition, cation balance, differs when using the same fluid as a replacement solution, compared to dialysate. In particular, sodium balance is greater for post-dilutional fluid replacement, due to the lower sieving coefficient. More recently, citrate has been introduced as an extracorporeal anticoagulant, and a variety of dialysates/replacement fluids have been developed, due to the difference in citrate clearance between dialysis and convection based extracorporeal circuits. Over the last decade, there has been a general increase in the standard hourly dialysate and exchange volumes used in the management of patients with acute kidney injury, from 1 to 2.5-3 l/h. Indeed, even larger volume exchanges, some 6-8 l/h have been advocated to improve patient outcomes. However, before embarking on such continuous high volume exchanges, a new generation of fluids may need to be developed to prevent acid-base and electrolyte imbalances.