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Refeeding Syndrome

(For MD Anaesthesiology Examination)

Definition

Refeeding syndrome is a potentially life-threatening constellation of metabolic and electrolyte disturbances that occurs when nutrition - oral, enteral, or parenteral - is reinstituted after a period of prolonged starvation or severe malnutrition. The hallmark is hypophosphatemia, accompanied by hypokalemia, hypomagnesemia, thiamine deficiency, fluid shifts, and sodium retention.

(Sources: Yamada's Textbook of Gastroenterology 7e; Sabiston Textbook of Surgery; Schwartz's Principles of Surgery 11e)

Historical Background

First described after World War II when severely malnourished Japanese prisoners of war were refed and subsequently developed electrolyte abnormalities and sudden death.

Pathophysiology

During Starvation (Catabolic State):

Fat and amino acids become the primary fuel sources
Intracellular phosphate, potassium, and magnesium are progressively depleted
Serum electrolyte levels may paradoxically remain normal (maintained by bone storage pools and extracellular buffering)
Insulin secretion is low; gluconeogenesis dominates

On Refeeding (Anabolic Switch):

Reintroduction of carbohydrates triggers a surge in insulin secretion
Insulin activates Na-K ATPase → drives potassium, phosphate, and magnesium into cells
Phosphate is additionally consumed for ATP synthesis and glycolysis (phosphorylation of glucose)
Thiamine (vitamin B1) is a cofactor for pyruvate dehydrogenase; it is rapidly consumed - pyruvate cannot enter the Krebs cycle, leading to lactic acidosis
Sodium and water retention occur → fluid overload

(Figure: Yamada's Textbook of Gastroenterology 7e - Pathogenesis of Refeeding Syndrome)

Electrolyte Abnormalities

Electrolyte	Direction	Consequence
Phosphate	↓↓ (Hallmark)	Cardiac arrhythmia, respiratory failure, rhabdomyolysis, cardiac arrest
Potassium	↓	Arrhythmias, muscle weakness, paralysis
Magnesium	↓	Worsens hypokalemia, seizures, arrhythmias
Calcium	↓	Tetany, seizures
Thiamine	Depleted	Wernicke's encephalopathy, lactic acidosis

Clinical Features

Cardiac: Arrhythmias (life-threatening), heart failure, oedema
Respiratory: Respiratory failure (diaphragmatic weakness from hypophosphatemia)
Neurological: Confusion, seizures, Wernicke syndrome
Muscular: Profound weakness, rhabdomyolysis
Metabolic: Lactic acidosis (thiamine deficiency), severe hyperglycaemia (blunted basal insulin secretion)
Haematological: Haemolytic anaemia, impaired leucocyte function (ATP-dependent)

Patients at Risk (NICE Criteria - Bailey & Love 28e / Tietz 7e)

High Risk - ONE of the following:

BMI < 16 kg/m²
Unintentional weight loss > 15% within the last 3-6 months
Little or no nutritional intake for > 10 days
Low potassium, phosphate, or magnesium before refeeding

Moderate Risk - TWO or more of the following:

BMI 16-18.5 kg/m²
Unintentional weight loss > 10% within 3-6 months
No/negligible nutrition for > 5 days
History of alcohol abuse, or drugs including insulin, chemotherapy, antacids, or diuretics

Clinical conditions commonly associated: anorexia nervosa, chronic alcoholism, prolonged starvation, cancer, kwashiorkor, inflammatory bowel disease, post-bariatric surgery, ICU patients on delayed nutritional support.

Diagnosis

Recent consensus criteria (Tietz Laboratory Medicine 7e):

Severity	Criterion
Mild	Decrease in phosphate / potassium / magnesium of 10-20%
Moderate	Decrease of 20-30%
Severe	Decrease of > 30%

Prevention and Management

Step 1 - Identify At-Risk Patients

Screen all patients before initiating nutritional support.

Step 2 - Correct Deficits Before Refeeding

Correct electrolyte (phosphate, potassium, magnesium, calcium) and fluid deficits before starting nutrition
Thiamine 100 mg IV/oral must be given before the first feed or any glucose-containing fluids (especially in alcoholism, prolonged starvation)
Continue thiamine 100 mg/day for 5-7 days in high-risk patients

Step 3 - Start Nutrition Slowly

Begin at 10 kcal/kg/day (or 50% of estimated energy requirements on Day 1)
Gradually increase over 4-7 days to meet full requirements
For PN: start with only 50% dextrose on Day 1
Supplement potassium (20-30 mmol/L), phosphate (20-30 mmol/day), magnesium, and multivitamins routinely

Step 4 - Monitor Closely

Vital signs and fluid balance daily
Serum electrolytes (phosphate, potassium, magnesium, calcium, glucose) at baseline, then daily for the first week
Correct deficits aggressively as they evolve
Strict glycaemic control (insulin infusion if hyperglycaemia on PN)

Anaesthesia Relevance

Preoperative assessment - recognize malnourished patients at risk; postpone elective surgery if possible to optimize nutrition
Perioperative glucose-containing fluids (e.g. dextrose saline, TPN) can trigger refeeding syndrome in fasted, malnourished ICU patients - always give thiamine first
Respiratory failure from hypophosphatemia can cause failure to wean from mechanical ventilation - check phosphate in all difficult weaning cases
Cardiac arrhythmias - ECG changes, VF risk in hypokalemia + hypomagnesemia; treat before induction
Post-op ICU patients - initiate early enteral nutrition cautiously at low caloric targets; monitor electrolytes daily

Key Points to Remember for the Exam

Hallmark electrolyte = Hypophosphatemia
Mechanism = Insulin surge → intracellular shift of phosphate, potassium, magnesium
Always give thiamine before glucose/feeds in at-risk patients
Start feeds at 10 kcal/kg/day, increase over 4-7 days
Wernicke's encephalopathy is a direct complication of thiamine depletion in refeeding
Can occur with oral, enteral, or parenteral nutrition equally

References (Standard Textbooks):

Bailey & Love's Short Practice of Surgery, 28e - Ch. 25, Summary Box 25.5
Schwartz's Principles of Surgery, 11e - Ch. 3 (Malnourished Patients)
Sabiston Textbook of Surgery (latest ed.) - Ch. Nutritional Support
Yamada's Textbook of Gastroenterology, 7e - Ch. 23
Tietz Textbook of Laboratory Medicine, 7e - Box 46.7
Barash: Clinical Anesthesia, 9e (hypophosphatemia/electrolytes chapter)

Recent Evidence: A 2025 systematic review (PMID: 39187889) identified the strongest risk factors in adults as low BMI, prolonged fasting, and pre-existing electrolyte deficits - consistent with NICE criteria above. A 2026 systematic review (PMID: 41793849) specifically addresses risk prediction models in critically ill adults, relevant to ICU anaesthesia practice.

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