Acid-base changes caused by 5% albumin versus 6% hydroxyethyl starch solution in patients undergoing acute normovolemic hemodilution - A randomized prospective study

Background Preoperative acute normovolemic hemodilution (ANH) is an excelle nt model for evaluating the effects of different colloid solutions that are free of bicarbonate but have large chloride concentrations on acid-base eq uilibrium., Methods: In 20 patients undergoing gynecologic surgery, ANH to a hematocrit of 22% was performed. Two groups Of 10 patients each were randomly assigne d to receive either 5% albumin or 6% hydroxyethyl starch solutions containi ng chloride concentrations of 150 and 154 mm, respectively, during ANH, Blo od volume (double label measurement of plasma and red cell cell volumes), p H, Pace,, and serum concentrations of sodium, potassium, chloride, lactate, ionized calcium, phosphate, albumin, and total protein were measured befor e and 20 min after completion of ANH. Strong ion difference was calculated as serum sodium plus serum potassium minus serum chloride minus serum lacta te. The amount of weak plasma acid was calculated using a computer program. Results: After ANH, blood volume was well maintained in both groups. ANH ca used slight metabolic acidosis with hyper-chloremia and a concomitant decre ase in strong ion difference. Plasma albumin concentration decreased after hemodilution with 6% hydroxyethyl starch solution and increased after hemod ilution with 5% albumin solution. Despite a three-times larger decrease in strong ion difference after ANH with 6% hydroxyethyl starch solution, the d ecrease in pH was nearly the same in both groups. Conclusions: ANH with 5% albumin or 6% hydroxyethyl starch solutions led to metabolic acidosis. A dilution of extracellular bicarbonate or changes in strong ion difference and albumin concentration offer explanations for this type of acidosis.