Prescribing IV fluids
Decide why the patient needs fluid: resuscitation, maintenance or replacement. Then use the weight and the electrolytes to prescribe, and review every day.
A 70 kg man is nil by mouth after bowel surgery. He is not drinking and his NG tube drained 800 mL today. Sodium 136, potassium 3.4 mmol/L (mEq/L). The night nurse asks you to "write up fluids".
What do you prescribe for the next 24 hours?
- Decide why fluid is neededResuscitation, maintenance, or replacement of losses.
- Resuscitation first if shocked500 mL crystalloid over 15 minutes, then reassess.
- Assess fluid statusPulse, BP, capillary refill, JVP, chest, oedema, urine output, fluid chart, weight.
- Check today's electrolytesSodium, potassium, creatinine, sugar.
- Calculate maintenance by weightWater 25–30 mL/kg/day, sodium and potassium about 1 mmol/kg/day, glucose 50–100 g/day.
- Add ongoing losses separatelyNG, drains, stoma, diarrhoea, fever.
- Write it clearlyFluid, volume, additives, rate, start time.
- Review dailyStop IV fluids as soon as the patient can drink.
- Abnormal sodium or potassium
- Heart failure or already overloaded
- Large ongoing losses (high-output stoma, NG, fistula)
- Children (different calculation)
- Low sodium from too much dextrose
- Overload in the frail
- Low potassium when none is added
- Ongoing losses not replaced
| Maintenance water | 25–30 mL/kg/day. Frail, elderly, heart or kidney failure: 20–25 mL/kg/day |
| Sodium and potassium | About 1 mmol/kg/day each |
| Glucose | 50–100 g/day |
| Resuscitation | 500 mL crystalloid over 15 minutes, reassess |
| Potassium rate | No faster than 10 mmol/hour through a peripheral cannula |
Check every dose against a current drug reference and your hospital protocol.
On this page
The 5 Rs (NICE)
- Shocked or very dry
- 500 mL crystalloid bolus over 15 minutes, reassess
- Cannot drink enough, otherwise stable
- Calculated by weight
- Ongoing losses: NG, vomiting, diarrhoea, drains, stoma, fever
- Replace on top of maintenance
- Fluid in the wrong place: sepsis, oedema, pancreatitis
- Senior advice
Every day, and after every bolus
Fluids available in Pakistan
| Fluid | Sodium (mmol/L) | Potassium | Glucose | Notes |
|---|---|---|---|---|
| 0.9% sodium chloride ("normal saline") | 154 | 0 | 0 | Resuscitation and NG replacement. Large volumes cause high chloride and acidosis |
| Ringer's lactate (Hartmann's) | about 130 | about 4–5 | 0 | Balanced crystalloid for resuscitation. Small amount of potassium |
| 5% dextrose | 0 | 0 | 50 g/L | Water and some sugar. Alone, it causes low sodium |
| Dextrose saline (5% dextrose with 0.9% sodium chloride, "DNS") | 154 | 0 | 50 g/L | Common in Pakistan. High sodium and sugar for maintenance |
| 0.18% sodium chloride with 4% dextrose | 30 | 0 | 40 g/L | Maintenance in adults if available. Not for children or post-operative patients without monitoring |
| Colloids (gelatin, starch) | varies | Not recommended for routine resuscitation. Starches harm kidneys |
Maintenance: a worked example
- Water: 25–30 mL/kg/day = about 2 litres.
- Sodium: about 1 mmol/kg/day = about 70 mmol.
- Potassium: about 1 mmol/kg/day = about 70 mmol.
- Glucose: 50–100 g/day.
One way to prescribe it:
- Bag 1: 500 mL 0.9% sodium chloride + 20 mmol potassium chloride, over 6 hours.
- Bag 2: 500 mL 5% dextrose + 20 mmol potassium chloride, over 6 hours.
- Bag 3: 500 mL 5% dextrose + 20 mmol potassium chloride, over 6 hours.
- Bag 4: 500 mL 5% dextrose, over 6 hours.
That gives 2 litres of water, 77 mmol sodium, 60 mmol potassium and 75 g glucose. Use pre-mixed potassium bags wherever available.
- 08:00Bag 1: 0.9% saline + 20 mmol KCl
- 14:00Bag 2: 5% dextrose + 20 mmol KCl
- 20:00Bag 3: 5% dextrose + 20 mmol KCl
- 02:00Bag 4: 5% dextrose
- Elderly, frail, heart or kidney failure, malnourished: 20–25 mL/kg/day, and check electrolytes more often.
- Obese patients: use ideal body weight for the calculation.
- Children: different rules and fluids (isotonic fluids, Holliday-Segar volumes). See your paediatric protocol.
Replacing losses
- NG or vomit losses: replace mL for mL with 0.9% sodium chloride plus potassium (gastric fluid is rich in sodium, chloride and potassium).
- Diarrhoea or stoma: Ringer's lactate or 0.9% sodium chloride plus potassium, mL for mL.
- Fever: roughly an extra 10% of maintenance for each degree above 37 °C, adjusted to the patient.
- Drains: depends on the fluid: senior advice for large volumes.
In the case: 2 litres maintenance + 800 mL NG replacement as 0.9% sodium chloride with potassium. Potassium is 3.4, so he needs his potassium replaced as well.
Potassium in fluids
Never inject potassium chloride directly. Undiluted or concentrated potassium given IV stops the heart. Always in a bag, mixed well, on a pump, labelled.
Resuscitation fluid
Daily review
- Is the patient still unable to drink? Stop IV fluids as soon as possible.
- Fluid balance chart, weight, urine output.
- Sodium, potassium, creatinine at least daily while on IV fluids.
- Signs of overload: crackles, raised JVP, swelling, falling SpO₂.
- Signs of low sodium: confusion, headache, vomiting.
Common mistakes
- Running 5% dextrose alone for days (low sodium and fits).
- "3 litres a day, 1 salty 2 sweet" for every patient, regardless of weight, age or heart.
- Forgetting potassium in a patient who is nil by mouth for days.
- Giving potassium to a patient with AKI and no urine.
- Not replacing NG or stoma losses.
- Leaving fluids running after the patient is drinking well.
Frequently asked questions
How do you calculate maintenance fluid for an adult?
Water 25–30 mL/kg/day, sodium and potassium about 1 mmol/kg/day each, and 50–100 g of glucose per day. Use 20–25 mL/kg/day in the elderly, frail, and those with heart or kidney failure.
Which fluid is used for resuscitation?
A crystalloid such as Ringer's lactate or 0.9% sodium chloride, given as 500 mL boluses over 15 minutes with reassessment after each.
What is the maximum rate of potassium through a peripheral cannula?
Usually no faster than 10 mmol per hour, from a pre-mixed bag, on a pump.
Why is 5% dextrose alone dangerous?
Once the sugar is used, it is just water. Given for long periods without sodium, it lowers the blood sodium and can cause brain swelling and fits.
What are the main types of IV fluids?
Crystalloids such as 0.9% sodium chloride, Ringer's lactate (Hartmann's) and dextrose solutions, and colloids. Crystalloids are used for almost all resuscitation and maintenance.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A 60 kg woman is nil by mouth with normal electrolytes and kidneys. What is her daily maintenance water requirement?
Answer: 1.5–1.8 litres. Adults need about 25–30 mL/kg/day of water, about 1 mmol/kg/day each of sodium and potassium, and 50–100 g glucose.
- Varies so much that no estimate is possible: 25–30 mL/kg/day is the estimate.
- 3 litres: Too much for 60 kg.
- 0.5 litres: Too little.
- 2.5 litres plus 1 litre insensible: Too much.
2. A patient lost 1 litre via NG tube today. What is the most appropriate replacement?
Answer: 0.9% saline with potassium. Replace ongoing GI losses with a sodium- and potassium-containing crystalloid, on top of maintenance fluids.
- Colloid: Not indicated.
- 1 litre of 5% dextrose: NG losses contain sodium, potassium and chloride.
- Oral water: NG drainage means not absorbed.
- No replacement needed: Losses must be replaced.
3. A post-operative patient on only 5% dextrose for 3 days becomes confused. Which test is most important first?
Answer: Serum sodium. Large volumes of hypotonic fluid after surgery cause hyponatraemia, which presents with confusion and fits.
- CT head: Check sodium first.
- Thyroid function: Not first.
- Blood cultures: Possible, but sodium first.
- Urine dipstick: Not first.
4. What is the daily maintenance fluid requirement for a healthy 25 kg child?
Answer: 1600 mL/day. Holliday–Segar: 100 mL/kg/day for the first 10 kg, 50 mL/kg/day for the next 10 kg, 20 mL/kg/day for each kg above 20. For 25 kg: 1000 + 500 + 100 = 1600 mL/day (~65 mL/h with the 4-2-1 rule: 40 + 20 + 5). Use isotonic fluids (0.9% saline + 5% dextrose) to avoid hyponatraemia; restrict in SIADH-risk conditions.
- 2500 mL/day: 2,500 mL overestimates; 1,000 + 500 + 100 = 1,600 mL.
- 1000 mL/day: 1,000 mL covers only the first 10 kg.
- 1250 mL/day: 1,250 mL underestimates.
5. A well-hydrated 25-kg child is nil by mouth after surgery. Using the Holliday–Segar formula, what is the daily maintenance fluid requirement?
Answer: 1,600 mL/day. Holliday–Segar: 100 mL/kg/day for the first 10 kg, 50 mL/kg/day for the next 10 kg, and 20 mL/kg/day for each kg above 20 kg. For 25 kg: 1,000 + 500 + 100 = 1,600 mL/day (~67 mL/h). Use isotonic fluid (0.9% saline with 5% glucose, or Plasma-Lyte with glucose) to avoid hyponatraemia; monitor electrolytes and glucose daily. Restrict to ~70% in conditions with high ADH (meningitis, post-op, pneumonia).
- 2,500 mL/day: 100 mL/kg — too much.
- 1,250 mL/day: 50 mL/kg — too little.
- 1,900 mL/day: 1,900 is a calculation error: 100 × 10 + 50 × 10 + 20 × 5 = 1,600 mL/day.
6. A man with chronic liver disease has ascites and ankle oedema. What is the main reason fluid leaves his capillaries?
Answer: Low oncotic pressure (low albumin). The liver makes albumin, the main contributor to plasma oncotic pressure. With less albumin, less fluid is pulled back into capillaries, so it collects in the tissues. In cirrhosis, portal hypertension and sodium retention (secondary hyperaldosteronism) add to ascites.
- Raised plasma oncotic pressure: High oncotic pressure keeps fluid in.
- Increased capillary permeability: The main cause in burns and sepsis.
- High interstitial oncotic pressure: Not the main mechanism.
- Low capillary hydrostatic pressure: Low hydrostatic pressure would reduce oedema.
7. Which statement describes the Frank–Starling law of the heart?
Answer: SV rises with end-diastolic volume. Greater ventricular filling stretches the fibres toward optimal sarcomere overlap and increases troponin's calcium sensitivity, so the heart pumps more strongly. This matches the output of the two ventricles. Cardiac output = stroke volume × heart rate.
- HR rises with temperature: Not the Starling law.
- Afterload increases stroke volume: Afterload reduces stroke volume.
- Contractility depends on sympathetic tone: Starling is intrinsic, independent of nerves.
- CO equals SV divided by HR: CO = SV × HR.
References and dose sources
- NICE CG174: Intravenous fluid therapy in adults in hospital
- NICE NG29: IV fluid therapy in children and young people
- Potassium chloride dosing: Drugs.com: Potassium chloride dosage (see also our potassium chloride dose page)
- Ringer's lactate (Hartmann's solution) dosing: Drugs.com: Lactated Ringer's dosage (see also our ringer's lactate (hartmann's solution) dose page)
- Sodium chloride (normal saline, 3% saline) dosing: Drugs.com: Sodium chloride dosage (see also our sodium chloride (normal saline, 3% saline) dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.