SU12.2-3 | Fluid, Electrolyte and Nutritional Support — Summary & Reflection

KEY TAKEAWAYS

Fluid and nutritional support are reasoned prescriptions, not ward habits. Fluids (SU12.2): total body water is ~60% of body weight (ICF two-thirds, ECF one-third; plasma ~a quarter of ECF); normal daily needs are water ~25–30 mL/kg, Na ~1–2 mmol/kg, K ~0.5–1 mmol/kg. Build every prescription from maintenance (Holliday-Segar 4-2-1: 4 mL/kg/h first 10 kg, 2 next 10 kg, 1 each kg thereafter — 110 mL/h for 70 kg) + deficit (estimated from dehydration signs and urine output ≥0.5 mL/kg/h) + ongoing losses (NG, fistula, stoma, drains, third space). Choose the crystalloid by indication: normal saline (Na/Cl 154, no buffer, hyperchloraemic acidosis in large volume), Ringer's lactate (balanced, preferred for resuscitation/replacement), 5% dextrose (free water, not for resuscitation). Nutrition (SU12.3): estimate ~25–30 kcal/kg/day and ~1–1.5 g/kg/day protein; 'if the gut works, use it' — enteral (oral → NG/NJ → PEG/jejunostomy) is preferred over parenteral; reserve TPN for a non-functioning, inaccessible or inadequate gut (prolonged ileus/obstruction, short bowel, high-output proximal fistula, severe malabsorption). Complications: enteral (aspiration, tube malposition/blockage, diarrhoea); parenteral (catheter-related pneumothorax/sepsis/thrombosis, hyperglycaemia, deranged LFTs, gut atrophy); and refeeding syndrome in the previously starved — hypophosphataemia (hallmark) with hypokalaemia, hypomagnesaemia and thiamine deficiency — prevented by feeding slowly, giving thiamine, and monitoring electrolytes.

REFLECT

Think back to a fluid chart you have seen — perhaps the ubiquitous 'three bags of normal saline'. For a patient you remember, could you now reconstruct their prescription properly from maintenance, deficit and ongoing losses, and would you have chosen the same fluid? Recall a malnourished or post-operative patient who was fed: was the enteral route used whenever the gut worked, or was TPN reached for too quickly, and was refeeding syndrome considered before the first feed? How will thinking in terms of compartments, the 4-2-1 rule, 'if the gut works use it', and 'thiamine and go slow' change the very next fluid and nutrition order you write?