Acid-base disturbances may cause a variety of symptoms, multi-organ failure and compromised immune defense. The aim of this paper is to provide an overview of acid-base disturbances in intensive-care patients.The article is based on a non-systematic search in Pub Med, a textbook on intensive care and the authors' clinical experience.The Henderson-Hasselbalch equation describes acid-base status by changes in pCO2 and bicarbonate. Changes in pCO2 reflect the respiratory and bicarbonate the metabolic status. Standard base excess describes the metabolic part more exactly. Anion gap is calculated as a supplement. The Stewart method, describes acid-base status through three independent variables (pCO2, weak acids and strong ion difference [SID]) that regulate the dependent variables pH and bicarbonate concentration.The Henderson-Hasselbalch equation and standard base excess do not consider which acids or bases that are involved, The anion gap may disclose unmeasured anions and distinguish hyperchloremic acidosis from other types of metabolic acidosis, but the calculation is associated with uncertainty. The Stewart method describes the involved ions, but complicated equations makes it unsuitable in clinical practice. A combination of standard base excess and anion gap corrected for albumin levels provide a good description of acid-base status.