Kidneys play a crucial role in the regulation of electrolytes and acid-base homeostasis. Impaired renal function is associated with greater urinary strong ion difference (SIDu) in patients with metabolic acidosis . In critically ill patients, several factors, such as infused fluids and acid endogenous production, would lead to changes in plasma SID and acid-base homeostasis without renal regulation of urinary electrolytes and SIDu . Hence, AKI can be highlighted as an inability to address acid-base metabolic disturbances, which may be detected before major increases in creatinine or decreases in urine output. We evaluated the effects of renal function on urinary strong ion excretion using the Stewart approach to acid-base in critically ill patients with AKI.