Intravenous (IV) fluids are among the most commonly prescribed treatments in hospitals worldwide, yet they are drugs with real risks. Too little and patients develop kidney injury; too much and they drown in fluid; the wrong type and sodium can swing dangerously. Nurses set up, run and monitor almost every bag, so understanding them is essential.
The 5 Rs of IV fluid therapy
The UK’s NICE guidance on IV fluids in adults organises fluid therapy into five Rs:
- Resuscitation: restoring circulation in shock or severe dehydration, usually with a crystalloid bolus.
- Routine maintenance: for patients who cannot drink enough. NICE suggests about 25–30 mL/kg/day of water for adults, with appropriate sodium, potassium and glucose.
- Replacement: of ongoing losses (vomiting, diarrhoea, drains, burns).
- Redistribution: managing fluid shifts in very sick patients.
- Reassessment: checking the patient’s response throughout.
Types of IV fluid
Isotonic crystalloids (same concentration as plasma)
| Fluid | Common uses | Watch for |
|---|---|---|
| 0.9% sodium chloride (normal saline) | Resuscitation, dehydration, giving blood, diluting drugs | Large volumes can cause high chloride and metabolic acidosis; fluid overload |
| Hartmann’s solution / Ringer’s lactate | Resuscitation, surgery, burns; closer to plasma than saline | Contains potassium and calcium; caution in severe hyperkalaemia; do not run with blood in the same line |
| Balanced crystalloids (e.g. Plasma-Lyte) | Resuscitation, critical care | Availability and cost vary by country |
Glucose (dextrose) solutions
- 5% dextrose: isotonic in the bag but, once the glucose is used, acts as free water. Used for maintenance and to give water. Not for resuscitation. Too much can cause hyponatraemia, especially in children and after surgery.
- Dextrose-saline (e.g. 4% dextrose with 0.18% saline, or 5% dextrose with 0.45% saline): used for maintenance in some settings.
- 10% and higher dextrose: for hypoglycaemia and neonatal care. Concentrated solutions can damage veins.
Hypotonic and hypertonic fluids
- Hypotonic (e.g. 0.45% saline): move water into cells. Used for some cases of high sodium. Risk of cerebral oedema if given wrongly.
- Hypertonic (e.g. 3% saline): pull water out of cells. Used in specialist settings for severe symptomatic hyponatraemia or raised intracranial pressure, often via a central line with close monitoring.
Colloids and blood products
Colloids such as albumin contain larger molecules that stay in the blood vessels longer. Starch-based colloids are now restricted in many countries because of harm to the kidneys. Blood products are covered in our separate blood transfusion guide.
Potassium: a high-risk additive
- Never give potassium chloride as a bolus or IV push. It can stop the heart.
- Use pre-mixed bags wherever possible rather than adding concentrated potassium on the ward.
- Follow your policy on maximum rate (commonly no more than 10 mmol/hr via a peripheral line in general wards) and use an infusion pump.
- Check the patient is passing urine and monitor blood potassium.
Monitoring: what nurses check
- Fluid balance chart: record all input (oral, IV, NG) and output (urine, vomit, drains, stool). Total every 24 hours. Aim for urine output of at least 0.5 mL/kg/hr in adults.
- Daily weight: the most accurate way to track fluid status. 1 kg = about 1 litre of fluid.
- Vital signs and early warning score.
- Blood results: sodium, potassium, urea, creatinine, glucose.
- The IV site: at least every shift (often using the VIP score) for phlebitis or infiltration.
Signs of fluid overload vs dehydration
| Fluid overload | Dehydration (hypovolaemia) |
|---|---|
| Breathlessness, rising respiratory rate | Thirst, dry mouth |
| Crackles in the lungs, falling SpO₂ | Rising heart rate, falling blood pressure |
| Swollen ankles or sacrum | Low urine output, dark urine |
| Raised jugular venous pressure | Slow capillary refill, cool peripheries |
| Rapid weight gain | Weight loss, confusion, dizziness on standing |
Patients at highest risk of overload include older adults and those with heart failure, kidney failure or liver disease. Children and older adults are also at higher risk of sodium problems.
Peripheral cannula care
- Use aseptic technique for insertion and every line access. Hand hygiene first.
- Secure with a clear, sterile dressing, and label with the date of insertion.
- Check the site at least every shift; remove at the first sign of phlebitis, or when no longer needed.
- Flush as per policy to keep it patent.
- Never leave a cannula in “just in case”. Unused cannulas are an infection risk.
For calculating pump and gravity drip rates, see our drug calculation formulas with worked examples.
Based on NICE guideline CG174 (Intravenous fluid therapy in adults in hospital) and NICE NG29 for children, plus WHO guidance. Educational content: follow your prescription and local policy.