# Intravenous Fluid Therapy

> Intravenous fluid therapy for NEET-PG Medicine: crystalloid versus colloid, maintenance and resuscitation volumes, balanced solutions and overload risks.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/intravenous-fluid-therapy
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: Harrison's Principles of Internal Medicine; Oxford Handbook of Critical Care; Surviving Sepsis Campaign guidelines
- How to cite: "Intravenous Fluid Therapy", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/intravenous-fluid-therapy

## Direct answer

Intravenous fluid therapy replaces water, electrolyte and volume losses, and the central choice is between crystalloids and colloids. Balanced crystalloids such as Ringer's lactate are preferred for most resuscitation, since large volumes of 0.9 per cent saline can cause hyperchloraemic acidosis. Sepsis resuscitation commonly begins with about 30 mL per kg of crystalloid within three hours, while adult maintenance needs about 25 to 30 mL per kg per day.

## What you must remember

- **Crystalloids:** Saline and balanced solutions distribute mostly into extracellular fluid, so only a fraction, roughly a quarter to a third, stays intravascular after an hour.
- **Colloids:** Albumin and synthetic starches stay intravascular longer; hydroxyethyl starch is restricted because it is linked to kidney injury, coagulopathy and mortality in critical illness.
- **Normal saline:** Contains 154 mmol/L each of sodium and chloride, so large volumes produce hyperchloraemic metabolic acidosis; balanced solutions are preferred in resuscitation.
- **Maintenance:** About 25 to 30 mL per kg of water per day in adults, with roughly 1 mmol per kg each of sodium and potassium.
- **Hypotonic fluids:** Five per cent dextrose and half-normal saline carry a risk of hyponatraemia in premenopausal women, children and neurologically injured patients.
- **Fluid responsiveness:** Passive leg raise, pulse pressure variation or stroke volume variation predict benefit better than central venous pressure.
- **Fluid overload:** Pulmonary oedema threatens patients with heart failure, renal failure and ARDS, so each bolus should be small and reassessed.

## Resuscitating a septic adult and an overloaded heart

Two patients with different circulatory states need different fluid strategies, and the table sets out how each is managed.

| Feature | 70-kg man with sepsis | 74-year-old woman with heart failure |
|---|---|---|
| Picture | Pneumonia, lactate of 4 mmol/L, mean arterial pressure of 58 mmHg, cold and mottled extremities | Decompensated heart failure with an ejection fraction of 25 per cent, breathless, with crackles and raised jugular venous pressure |
| Fluid | About 30 mL per kg (about 2.1 litres) of balanced crystalloid, given as boluses of 500 mL to 1 litre over the first three hours | Boluses cut to 250 to 500 mL |
| Reassessment | Capillary refill, urine output, mentation, lactate clearance and pulse pressure variation if ventilated | A clinical check after every bolus, because overload is the risk |
| Next step | A vasopressor such as noradrenaline if mean arterial pressure stays below 65 mmHg despite adequate fluid | Diuretics considered once overload is established |

In major haemorrhage the strategy changes again, since large volumes of crystalloid dilute clotting factors and platelets, and blood products guided by the clinical picture take priority.

## Where the exam tries to catch you

Fluid questions turn on a few predictable traps.

- **Trap:** assuming saline is physiological and safe in any volume — **Correct:** its chloride load is higher than that of plasma, so large saline volumes produce the acidosis the exam tests.
- **Trap:** prescribing hypotonic dextrose maintenance after surgery — **Correct:** it drives hyponatraemia when antidiuretic hormone is raised after surgery or pain, a classic cause of seizures in postoperative patients.
- **Trap:** expecting colloids to reduce mortality — **Correct:** large critical care trials have not shown that colloids reduce mortality compared with crystalloids, so colloid use is driven by specific circumstances.
- **Trap:** guiding fluid therapy by central venous pressure — **Correct:** central venous pressure is a poor guide to volume status, so passive leg raise or dynamic indices are the answer.

## Frequently asked questions

### What volume of crystalloid is recommended in early sepsis?

Current sepsis guidance suggests at least 30 mL per kg of intravenous crystalloid within the first three hours for sepsis-induced hypoperfusion. Reassessment after each bolus guides further fluid, because many patients need less volume or a vasopressor instead.

### Why are hydroxyethyl starches avoided in critical illness?

Hydroxyethyl starch has been associated with acute kidney injury, coagulopathy and higher mortality in critically ill patients, so guidance restricts its use. Albumin or balanced crystalloids are generally preferred when a colloid is considered necessary.

### What is the maintenance fluid requirement in an adult?

An average adult needs about 25 to 30 mL of water per kg per day, with sodium and potassium added at roughly 1 mmol per kg per day each. Requirements rise with fever and losses, so the prescription should be reviewed daily against clinical and biochemical findings.

### Why does hypotonic maintenance fluid cause hyponatraemia?

Hypotonic maintenance fluids such as five per cent dextrose or half-normal saline provide free water, and when antidiuretic hormone is raised this lowers serum sodium dangerously. Premenopausal women, children and postoperative patients are most at risk, so isotonic fluids are preferred in these groups.

### How is fluid responsiveness assessed at the bedside?

A passive leg raise that produces a rise in stroke volume or cardiac output predicts whether a further fluid bolus will help. In ventilated patients, pulse pressure variation serves a similar purpose, whereas central venous pressure is not a reliable marker of fluid responsiveness.