Refeeding Syndrome

Know who is at risk - The NICE criteria are low BMI, unintentional weight loss, starvation, a history of alcohol abuse, and low initial electrolyte concentrations. Eating disorders, malabsorptive disease such as inflammatory bowel disease, prior bariatric surgery, hemodialysis, poorly controlled diabetes, oncologic disease, and the postoperative patient who has not eaten all sit in this group.

Get the numbers before calories start - Check phosphate, potassium, and magnesium at baseline, then every 12 hours for the first three days in a high-risk patient. Hypophosphatemia was reported in 34% of ICU patients starved at least 48 hours, on average 1.9 days after feeding restarted. The derangement arrives after the decision to feed, not with it, so a normal panel on the day feeding began proves nothing.

Phosphate is the one to chase - Hypophosphatemia is defined as phosphate below 2.5 mg/dL; below 1.0 mg/dL it brings hemolytic anemia, heart failure, tachypnea, CNS effects including seizures, and death. Replete phosphate, potassium, and magnesium before an elective case rather than during it.

Hypophosphatemia is a ventilator problem - Low phosphate weakens the diaphragm and respiratory muscle and can produce frank respiratory failure. A refeeding patient who will not hold a tidal volume on emergence or who fails a weaning attempt needs a phosphate level, not more pressure support.

Left-shifted oxyhemoglobin curve - Depleted 2,3-DPG raises hemoglobin's affinity for oxygen and reduces release to tissue, starving metabolically active tissue even when the saturation reads well. Do not judge adequacy of oxygen delivery from the pulse oximeter alone in these patients.

Potassium and magnesium drive the arrhythmia risk - Both hypokalemia and hypomagnesemia prolong the QT and contribute to torsades de pointes. Correct magnesium whenever you replace potassium, since low magnesium increases renal potassium wasting and will defeat the repletion. For torsades, magnesium stabilizes the cardiac membrane and 2 g IV is the recommended initial dose; an unstable patient with a pulse may need synchronized cardioversion.

Thiamine before dextrose - Give 100 mg of thiamine at least 30 minutes before any dextrose-containing solution, continued twice daily for 7 to 10 days. Deficiency presents as Wernicke encephalopathy (ophthalmoplegia, ataxia, memory impairment) progressing to Korsakoff amnesia and confabulation, and as cardiac dysfunction from failed ATP production. Lactate accumulates because the conversion of lactate to pyruvate stalls without it - an unexplained lactate in a malnourished patient may be thiamine, not perfusion.

Feed slowly - ASPEN starts at 100 to 150 g of dextrose or 10 to 20 kcal/kg in the first 24 hours, advancing by about a third of the replenishment goal every 1 to 2 days. In a high-risk patient with severe deficits, hold nutrition until potassium, phosphate, and magnesium are corrected. Enteral feeding is preferred over parenteral where the gut will tolerate it.

Expect hemodynamic fragility - Reported cardiovascular manifestations include hypotension, bradycardia, tachycardia, arrhythmias, cardiomyopathy, shock, and cardiac arrest. Nausea in these patients has been described as a precursor to hypotension; treat a new complaint of nausea as a warning rather than a symptom.

Muscle findings change the emergence plan - Rhabdomyolysis, weakness, myalgias, muscle twitching, and diaphragm weakness are all described. Titrate neuromuscular blockade against a monitored twitch and confirm return of strength before extubation rather than assuming a normal recovery.

Gut findings change the induction plan - Paralytic ileus, nausea, vomiting, diarrhea, and constipation follow the hypokalemia and hypomagnesemia. A patient with an ileus who is also being tube fed is a full stomach.

It is not confined to electrolytes - Acute tubular necrosis, renal failure, and metabolic acidosis have been reported from the sodium and phosphate shifts, and pulmonary edema and hypoventilation from the fluid shift. A patient who looked stable when feeding started can be a different patient 48 hours later, which is the window that usually contains your case.

Do not trust albumin as a nutrition marker - Albumin and prealbumin are acute phase reactants; albumin's half-life is about 20 days and prealbumin's 2 to 3 days. Clinical examination and the electrolyte panel tell you more about where this patient is than either number.

Refeeding syndrome is the fluid and electrolyte collapse that follows reintroducing calories after prolonged starvation. Starvation drives gluconeogenesis and proteolysis and quietly depletes intracellular phosphate, potassium, magnesium, and thiamine while serum values often still read normal. Carbohydrate arriving in the bloodstream triggers insulin, which drives phosphate and potassium into cells - phosphate to phosphorylate glucose in glycolysis, potassium through direct stimulation of the sodium-potassium ATPase. Serum levels fall abruptly on an already empty reserve.

Hypophosphatemia is the hallmark. Phosphate is required for ATP and for 2,3-DPG, so its loss cuts myocardial contractility, weakens respiratory muscle, and shifts the oxyhemoglobin curve left. Thiamine, the cofactor for glucose metabolism, is consumed as feeding resumes.