IV Fluid Therapy Basics
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Direct answer
Intravenous fluid therapy restores or maintains fluid, electrolyte and acid-base balance and delivers drugs directly into the circulation. Fluids are classified by tonicity — isotonic (0.9 per cent saline, Ringer lactate, 5 per cent dextrose), hypotonic (0.45 per cent saline) and hypertonic (3 per cent saline) — each suited to a different problem. Nursing covers checking the order, regulating the rate, maintaining the line and detecting complications.
What you must remember
- Isotonic fluids expand circulating volume — the choice for shock and dehydration; Ringer lactate approximates plasma electrolytes, its lactate converting to bicarbonate in the liver (caution in severe liver disease and alkalosis).
- Hypotonic fluids (0.45 per cent saline) hydrate cells in hypernatraemic dehydration but can worsen cerebral oedema; hypertonic fluids shift water out of cells for symptomatic hyponatraemia and cerebral oedema under close monitoring.
- 5 per cent dextrose is isotonic on infusion but acts as free water once glucose is metabolised — it supplies water and calories, not resuscitation volume.
- Drip rate: drops per minute equals total volume times the drop factor divided by minutes; macro sets deliver 10, 15 or 20 drops per mL and micro (burette) sets 60, the paediatric standard.
- Cannula sizes: higher gauge means smaller lumen — 16 to 18 gauge for rapid resuscitation or blood, 20 to 22 for routine therapy, 24 for small veins.
- Complications: phlebitis (pain, redness, tender venous cord), infiltration (cool, pale, swollen site), extravasation of vesicants, circulatory overload (dyspnoea, crackles, raised jugular veins) and site infection.
- Monitor vitals, intake-output, urine output of at least 0.5 mL per kg per hour and the site each shift; verify fluid, additives, rate and duration before every bottle change.
Common confusion
Normal saline and Ringer lactate are treated as interchangeable, but saline carries 154 mEq each of sodium and chloride and can cause hyperchloraemic acidosis in large volumes, while Ringer lactate buffers via its lactate and holds a small potassium load. Infiltration and phlebitis are swapped: infiltration leaks fluid into tissue (cool, pale swelling); phlebitis inflames the vein (warm, red, tender cord). And micro and macro sets at the same drip count deliver very different volumes — always read the drop factor.
Exam-focused takeaway
The drip-rate formula is guaranteed numerical material — practise hour-to-minute conversions and remember the 60 drops per mL micro set rule. Learn each fluid's tonicity, compartment of action and classic indication, with the contraindication logic: no dextrose for resuscitation, caution with hypertonic fluids, Ringer lactate in liver disease. Complication stems describe a swollen cool site (stop, elevate, resite), sudden dyspnoea during a fast infusion (slow or stop, sit up and inform) and fever with a tender site (culture and resite).
Frequently asked questions
How is the drip rate calculated?
Drops per minute equals volume times the drop factor divided by minutes — 1000 mL over 8 hours with a 20 drops per mL set gives about 42 drops per minute.
What is the difference between isotonic, hypotonic and hypertonic fluids?
Isotonic fluids expand blood volume, hypotonic fluids shift water into cells, and hypertonic fluids pull water out of cells to correct severe electrolyte problems.
When is Ringer lactate preferred?
For dehydration, burns and shock when a balanced electrolyte solution is desired — used cautiously in severe liver disease and alkalosis.
What are the signs of phlebitis and infiltration?
Phlebitis causes warmth, redness, tenderness and a cord-like vein; infiltration a cool, pale, swollen site — both need the infusion stopped and the cannula resited.
What urine output indicates adequate perfusion in an adult?
About 0.5 mL per kg per hour — roughly 30 mL hourly in an average adult — tracked on the intake-output chart.