Received: 10 June 2002 Accepted: 17 April 2003 Published online: 29 May 2003 © Springer-Verlag 2003 This study was supported by the Austin Hospital Anaesthesia and Intensive Care Trust Fund (Melbourne, Australia), the Laerdal Foundation (Stavanger, Norway) and Hospal Pty. Ltd. (Lyon, France). Abstract Objective: To evaluate the effect of high-volume hemofiltra- tion (HVHF) with lactate-buffered replacement fluids on acid-base balance. Design: Randomized cross- over study. Setting: Intensive Care Unit of Tertiary Medical Center. Participants: Ten patients with sep- tic shock and acute renal failure. Interventions: Random allocation to 8 h of isovolemic high-volume hemofiltration (ultrafiltration rate: 6 l/h) or 8 h of isovolemic continu- ous venovenous hemofiltration (ultrafiltration rate: 1 l/h) with lac- tate-buffered replacement fluid with subsequent crossover. Measurements and results: We measured blood gas- es, electrolytes, albumin, and lactate concentrations and completed quan- titative biophysical analysis of acid- base balance changes. Before high- volume hemofiltration, patients had a slight metabolic alkalosis [pH: 7.42; base excess (BE) 2.4 mEq/l] despite hyperlactatemia (lactate: 2.51 mmol/l). After 2 h of high-volume hemofiltra- tion, the mean lactate concentration increased to 7.30 mmol/l (p=0.0001). However, a decrease in chloride, strong ion difference effective, and strong ion gap (SIG) compensated for the effect of iatrogenic hyper- lactatemia so that the pH only de- creased to 7.39 (p=0.05) and the BE to -0.15 (p=0.001). After 6 h, despite persistent hyperlactatemia (7 mmol/l), the pH had returned to 7.42 and the BE to 2.45 mEq/l. These changes remained essentially stable at 8 h. Similar but less in- tense changes occurred during con- tinuous venovenous hemofiltration. Conclusions: HVHF with lactate- buffered replacement fluids induces iatrogenic hyperlactatemia. How- ever, such hyperlactatemia only has a mild and transient acidifying effect. A decrease in chloride and strong ion difference effective and the removal of unmeasured anions all rapidly compensate for this effect. Keywords Hemofiltration · Lactate · Lactic acidosis · Chloride · Acid-base physiology · Continuous renal replacement therapy Intensive Care Med (2003) 29:1113–1120 DOI 10.1007/s00134-003-1812-1 ORIGINAL Louise Cole Rinaldo Bellomo Ian Baldwin Matthew Hayhoe Claudio Ronco The impact of lactate-buffered high-volume hemofiltration on acid-base balance Introduction Hemofiltration appears to have a significant and variable impact on acid-base balance [1, 2, 3, 4, 5, 6]. It has been reported to either correct [5, 7] or induce metabolic aci- dosis [4] according to circumstances. The pathogenesis of these acid-base effects remains poorly understood. These effects may be much greater with the use of higher ultrafiltration (UF) rates [so-called high-volume hemofil- tration (HVHF)]. Experimental work has suggested that increasing the rate of UF production during continuous renal replace- ment therapy (CRRT) might achieve a clinically impor- tant beneficial hemodynamic effect in septic shock [8, 9]. Such HVHF has now been applied to the treatment of septic shock patients with promising early results [10]. L. Cole · R. Bellomo ( ✉ ) · I. Baldwin M. Hayhoe Department of Intensive Care, Austin and Repatriation Medical Centre, Studley Road, 3084 Heidelberg, Victoria, Australia e-mail: rinaldo.bellomo@armc.org.au Tel.: +61-3-94965992 Fax: +61-3-94963932 C. Ronco Divisione di Nefrologia, Ospedale San Bortolo, Vicenza, Italy