Management of metabolic acidosis in the critically ill

Metabolic acidosis (MA) commonly complicates critical illness, usually manifesting as a fall in arterial pH (<7.4) accompanied by a concomitant fall in serum bicarbonate concentration. Acidosis caused by unmeasured anions (UMA), can be distinguished from Hyperchloraemic acidosis by demonstrating a widening of the anion gap (AG). AG should be corrected for albumin and lactate. The base deficit (BD) calculates degree of metabolic acidosis and represents the amount of strong cation required to restore the pH to 7.4. Neither the AG nor the BD specify the cause of acidosis, and are unhelpful in the setting of mixed disorders. The base deficit gap (BDG) is used to calculate the effect of free water, sodium, chloride and albumin on the BD. It is the difference between BDcalc and BDmeasured (on a blood gas) and represents UMA. The strong ion gap more robustly calculates the amount of UMA than AG or BDG, and may be more accurate at predicting outcomes in the emergency room. Lactic acidosis is due to hypovolaemia until otherwise proven. In the majority of cases aggressive fluid resuscitation is warranted. In the presence of normal tissue blood flow regional hypoperfusion, poisoning or exogenous catecholamines should be considered. Ketoacidosis is due to intracellular glucose deficiency, caused by hypoinsulinaemia or starvation. The former is treated with isotonic crystalloid and insulin. Renal acidosis is treated with renal replacement therapy or recovery of renal function.