Introduction: Re-feeding Syndrome (RS) is a deadly complication, which can be encountered during “re-
feeding” of malnourished patients. In these patients, thiamin deficiency may develop and “risk awareness” is the
most significant factor in the management of these patients. In this case report, the treatment is presented of an
elderly patient who was diagnosed with RS and followed-up in the intensive care unit (ICU) due to resistant fluid-
electrolyte imbalance. Case: An 87-year-old elderly woman was admitted to the hospital due to aspiration pneu-
monia. On day 4, during parenteral nutrition (30 kcal/kg/day), severe electrolyte imbalance developed. Total par-
enteral nutrition (TPN) was stopped, and enteral feeding together with potassium (90 mmol/day, i.v.) were started.
During follow-up, plasma potassium values remained less than 3 mmol/L. Despite replacement therapy, hypoal-
buminemia, hypomagnesemia, hypocalcemia, and hypophosphatemia persisted. Considering the parenteral nutri-
tion (30 kcal/kg/day) during the hospitalization period, a diagnosis of RS was made. On day 10, thiamin (200
mg/day, i.v.) and folic acid (5 mg/day) were added, and the patient subsequently responded to electrolyte re-
placement treatment. The patient was discharged on day26 with a home-care plan. Conclusion: In patients with malnutrition, thiamin replacement should be given before starting nutrition to prevent RS. Energy intake should
be 10kcal/kg/day at the start, and be gradually increased between days 4-10. Hemodynamic-laboratory parameters
should be closely monitored. All these measures may be life-saving for patients at high risk.