Final answer:
Metabolic acidosis occurs in the oliguric phase of AKI as a result of impairment of bicarbonate excretion.
Step-by-step explanation:
Metabolic acidosis occurs in the oliguric phase of AKI as a result of impairment of excretion of bicarbonate. In the kidney, tubular cells are not permeable to bicarbonate, so it is conserved rather than reabsorbed. Impairment of bicarbonate excretion leads to an increase in acid levels in the blood, resulting in metabolic acidosis.