Continuous renal replacement therapies (CRRT) are often used to manage complex acid-base problems in critically ill patients. These techniques allow a constant manipulation of the plasma composition. Several technical factors from CRRT influence the acid-base status; namely, the effluent rate, the operational characteristics of the technique, the content of the solutions and the metabolic rate of the buffer. This article reviews the common acid base disorders occurring in the intensive care unit, using both the anion gap and the strong ion gap approaches, and describes the influence of CRRT on acid-base physiology. The use of CRRT as a customized therapy for acid-base disorders is discussed, allowing an integration of both physiological and technical concepts.