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Normal acid-base homeostasis is severely challenged in the intensive care setting. In this review, we address acid-base disturbances, with a special focus on the use of continuous (rather than intermittent) extracorporeal technologies in critical ill patients with acute kidney injury. We consider hypercapnic acidosis and lactic acidosis as examples in which continuous modalities may have different roles and indications than the traditional intermittent approaches to renal replacement therapy. Hypercapnic acidosis develops as a consequence of alveolar hypoventilation. In this condition, correction of pH above 7.2 is not currently recommended, and may even abrogate the beneficial effects of hypercapnic acidosis on overall outcomes. Extracorporeal technologies support lung protection while maintaining overall patient homeostasis. Similarly, in lactic acidosis, current evidence does not support bicarbonate infusions to correct acidosis. The management of lactic acidosis should correct the underlying causative disturbances. Most often, lactic acidosis is a biomarker denoting unfavorable outcomes, rather than an intrinsic pathogenetic mechanism. Extracorporeal procedures may assist in the removal of pathogenic drugs or toxins, as well as partially correcting acidemia. Whether or not these approaches will permit normalization of systemic pH, and the impact of these approaches on patient outcomes, needs to be addressed with prospective controlled trials.

Background: Regional anticoagulation with trisodium citrate is an effective form of anticoagulation for continuous renal replacement therapy (CRRT) for patients with contraindications to heparin. However, because of the metabolic complications of trisodium citrate, it is a complicated technique requiring specialized dialysis solutions. We have designed a simplified protocol for citrate regional anticoagulation for CRRT., Methods: Two percent trisodium citrate was delivered at 250 mL/h via the prefilter port of a COBE PRISMA device, with the rate adjusted to maintain a postfilter ionized calcium (iCa++) <0.5 mmol/L. A central calcium gluconate infusion was used to maintain a systemic iCa++ at 1.1 mmol/L. A standard dialysate solution consisting of 0.9% saline, KCl 3 mmol/L, and MgSO4 1 mmol/L was delivered at 1000 mL/h. We retrospectively reviewed the outcomes and complications associated with this protoco1 in 29 patients treated from July 1999 to October 1999, evaluating the frequency of clotting of the dialyzer, bleeding complications, citrate toxicity, and patient mortality., Results: The Kaplan-Meier curve for dialyzer survival demonstrated a 61% survival rate at 48 hours. There were no episodes of significant bleeding or citrate toxicity. Seventy-two percent of patients died for reasons unrelated to CRRT., Conclusions: A CRRT protocol using regional 2% trisodium citrate anticoagulation is not associated with significant bleeding complications or citrate toxicity, and represents a simplified approach compared with previous applications using 4% trisodium citrate.