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Perioperative fluid therapy
Fluids are a drug: give the right type (most of the time a balanced crystalloid), in a goal-directed amount, and avoid both hypovolaemia and overload.
Why it matters in the exam
Questions test the distribution of body water and how much of each solution stays in the circulation, why large volumes of 0.9% saline cause hyperchloraemic acidosis, why starches (HES) are no longer given to the critically ill, and the daily need for fluid and electrolytes. They also ask how to tell whether the patient will respond to fluid (leg raising, pulse-pressure variation under controlled ventilation).
Water makes up about 60% of body weight: two thirds inside the cells and one third outside, of which only a quarter is plasma. So of one litre of isotonic crystalloid roughly a quarter stays in the circulation, and of one litre of 5% glucose almost nothing, because it spreads through all body water. In the 2018 RELIEF trial an overly restrictive approach in major abdominal surgery increased kidney injury — so the goal is balance, not drying out.
In exam questions ask three questions about every fluid request: does the patient need resuscitation, replacement of losses or only maintenance. Resuscitation is given in small boluses with reassessment, replacement matches the type of loss (for example vomiting or drains), and maintenance is calculated from the daily need. In enhanced recovery programmes (ERAS) clear drinks are allowed until two hours before surgery and drinking and eating resume early, to limit intravenous fluid.
Key points
- Water: 60% of body weight; two thirds in the cells; a quarter of extracellular fluid in plasma.
- A balanced crystalloid is the default choice.
- Large volumes of NaCl 0.9% → hyperchloraemic acidosis.
- Maintenance: 25–30 mL/kg per day, sodium and potassium about 1 mmol/kg per day.
- Give fluid to those who respond to it; not responsive → vasopressor.
Summary table
| Solution | Main content | Advantage | Drawback |
|---|---|---|---|
| NaCl 0.9% | Na 154 and Cl 154 mmol/L | Simple; preferred in head injury | Hyperchloraemic acidosis and kidney injury in large volumes |
| Balanced (Ringer lactate, Plasma-Lyte) | Na about 130–140, with a buffer (lactate or acetate) | The usual choice in most patients | Slightly hypotonic (Ringer lactate) |
| Glucose 5% | Free water | Water without sodium | Does not expand volume; hyponatraemia |
| Albumin | Natural colloid | Small volume for a similar effect | Expensive; harmful in head injury |
| Starches (HES) | Synthetic colloid | — | Kidney injury and higher mortality in sepsis; withdrawn from most uses |
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Sources
- NICE guideline CG174: Intravenous fluid therapy in adults in hospital, 2013, updated 2017 — Maintenance and replacement
- Miller's Anesthesia, 9th edition (2020) — Perioperative Fluid and Electrolyte Therapy
- Restrictive versus Liberal Fluid Therapy for Major Abdominal Surgery (RELIEF trial), 2018 — Main results
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.