Academe Learn
CBME Curriculum Preview

Page 11 of 11

SU12.1-3 | Nutrition, Fluids and Electrolytes — PBL Case

CLINICAL SETTING

Mrs S is a 62-year-old woman admitted with a high-output small-bowel enterocutaneous fistula that developed after surgery for Crohn's disease at another hospital. She is thin and exhausted, her clothes hang off her, and the fistula is losing more than a litre and a half of fluid each day. The surgical team must stabilise her fluids and electrolytes, work out how to feed her, and do so without harming her — a situation that brings together everything in this module about malnutrition, fluid balance and nutritional support. You are the firm caring for her over the coming days.

Trigger 1: The thin, depleted patient

On admission Mrs S has clearly lost a great deal of weight, has wasted temporal muscles and loose skin folds, and reports eating very little for weeks. The covering doctor checks an albumin, finds it low, and writes 'severely malnourished — albumin 21 g/L' in the notes.

DISCUSSION POINTS

  • What is malnutrition, what are its types, and which mechanistic causes are operating in Mrs S given her fistula and Crohn's disease?
  • Why is it wrong to base the diagnosis of malnutrition on the low albumin, and what should the team have used instead to assess her?
  • Map the likely consequences of her malnutrition onto the specific surgical risks she now faces (wound and fistula healing, infection, muscle weakness).
Click to reveal Trigger 2: Fluids draining away (discuss previous trigger first!)

Trigger 2: Fluids draining away

Over the first 24 hours Mrs S loses about 1.6 litres from the fistula on top of her normal losses; her urine output falls, her mouth is dry and her heart rate is up. The intern has been replacing her with 'maintenance fluids only' and is puzzled that she is getting more dehydrated.

DISCUSSION POINTS

  • How would you build a rational 24-hour fluid prescription for her, separately estimating maintenance, deficit and the ongoing fistula losses?
  • Which crystalloid would you choose to replace small-bowel fistula fluid, and how do normal saline and Ringer's lactate differ in composition and acid-base effect?
  • Why does prescribing 'maintenance only' fail this patient, and what monitoring would tell you whether your replacement is adequate?
Click to reveal Trigger 3: Feeding her safely (discuss previous trigger first!)

Trigger 3: Feeding her safely

Once her fluids are corrected, the team plans nutritional support. The fistula is high and the proximal bowel is short, so enteral feeding is likely to be inadequate. A junior suggests simply starting full-rate parenteral feeding straight away to 'catch her up quickly'.

DISCUSSION POINTS

  • How would you estimate her energy and protein requirements, and how do you decide between enteral and parenteral nutrition here using the 'if the gut works, use it' principle?
  • Why is it dangerous to start full-rate feeding immediately in a patient this depleted, and what is refeeding syndrome?
  • Set out the specific steps to prevent refeeding syndrome — thiamine, feed rate, and which electrolytes to monitor and replace — and the complications of parenteral nutrition you would watch for.

Group Task Assignments

  • Group A: Prepare a structured malnutrition assessment proforma for Mrs S using only clinical and anthropometric evidence (weight loss, BMI, intake history, examination), and present a one-paragraph critique of why albumin should not appear as a diagnostic criterion.
  • Group B: Produce a worked 24-hour fluid and electrolyte prescription that explicitly separates maintenance, deficit and ongoing fistula losses, choosing and justifying the crystalloid, and list the bedside and biochemical parameters used to titrate it.
  • Group C: Draft a safe refeeding protocol for a high-risk patient (thiamine, starting feed rate, escalation plan, electrolyte monitoring and replacement schedule) and a checklist of enteral versus parenteral complications to monitor.

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [SU12.1] What are the causes and consequences of malnutrition in the surgical patient, and how is malnutrition correctly assessed when biochemical markers such as albumin are unreliable?
  2. [SU12.2] How are fluid and electrolyte requirements estimated and replaced in the surgical patient, including maintenance, deficit and ongoing losses, and how do the common crystalloids differ?
  3. [SU12.3] What are the nutritional requirements of surgical patients, how do you choose between enteral and parenteral support, and what are the complications including refeeding syndrome?