title: Acid-base status of critically ill patients with acute renal failure: analysis based on Stewart-Figge methodology.
abstract: BACKGROUND
  The aim of the present study is to understand the nature of acid-base disorders in critically ill patients with acute renal failure (ARF) using the biophysical principles described by Stewart and Figge. A retrospective controlled study was carried out in the intensive care unit of a tertiary hospital.
  
  
  METHODS
  Forty patients with ARF, 40 patients matched for Acute Physiology and Chronic Health Evaluation II score (matched control group), and 60 consecutive critically ill patients without ARF (intensive care unit control group) participated. The study involved the retrieval of biochemical data from computerized records, quantitative biophysical analysis using the Stewart-Figge methodology, and statistical comparison between the three groups. We measured serum sodium, potassium, magnesium, chloride, bicarbonate, phosphate, ionized calcium, albumin, lactate and arterial blood gases.
  
  
  RESULTS
  Intensive care unit patients with ARF had a mild acidemia (mean pH 7.30 +/- 0.13) secondary to metabolic acidosis with a mean base excess of -7.5 +/- 7.2 mEq/l. However, one-half of these patients had a normal anion gap. Quantitative acid-base assessment (Stewart-Figge methodology) revealed unique multiple metabolic acid-base processes compared with controls, which contributed to the overall acidosis. The processes included the acidifying effect of high levels of unmeasured anions (13.4 +/- 5.5 mEq/l) and hyperphosphatemia (2.08 +/- 0.92 mEq/l), and the alkalinizing effect of hypoalbuminemia (22.6 +/- 6.3 g/l).
  
  
  CONCLUSIONS
  The typical acid-base picture of ARF of critical illness is metabolic acidosis. This acidosis is the result of the balance between the acidifying effect of increased unmeasured anions and hyperphosphatemia and the lesser alkalinizing effect of hypoalbuminemia.
authors.affiliation: Department of Intensive Care and Department of Medicine, University of Melbourne, Australia.
authors.forename: Jens
authors.initials: J
authors.lastname: Rocktaeschel
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Morimatsu
authors.forename: Shigehiko
authors.initials: S
authors.lastname: Uchino
authors.forename: Donna
authors.initials: D
authors.lastname: Goldsmith
authors.forename: Stephanie
authors.initials: S
authors.lastname: Poustie
authors.forename: David
authors.initials: D
authors.lastname: Story
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Gutteridge
authors.forename: Rinaldo
authors.initials: R
authors.lastname: Bellomo
mesh_terms: D000136:Acid-Base Equilibrium; D058186:Acute Kidney Injury / Q000503:physiopathology*; D001315:Australia; D016022:Case-Control Studies; D016638:Critical Illness; D006801:Humans