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# Plasma volume expanders (colloids)

Solutions with large molecules, such as human albumin, that stay in the vessels and draw fluid into the circulation to restore blood volume.

Updated 2026-11-01

## What they are

Colloids restore circulating volume in hypovolaemia and support it after large-volume paracentesis in cirrhosis. Albumin is derived from human plasma; synthetic colloids (dextrans, gelatins such as polygeline) are alternatives on some lists. Fluid overload is the main risk.

## Mechanism of action

Large molecules that do not cross the capillary wall easily raise plasma oncotic pressure, which draws interstitial fluid into the vessels and keeps infused volume in the circulation.

Target: Plasma oncotic pressure

## Key points

- Albumin draws interstitial fluid into the circulation
- Main risk: circulatory overload and pulmonary oedema
- Albumin is never diluted with sterile water for injection: it causes haemolysis
- Used after large-volume paracentesis in cirrhotic ascites

## Drugs in this class

- [**Human albumin** A plasma-derived protein solution that restores blood volume in hypovolaemia, burns and after large-volume… Plasma oncotic pressure (albumin itself)](https://durgical.com/en/pharmacology/human-albumin/)

## Others in the class

- dextran 70
- polygeline

## Test yourself

Think of the answer, then tap the question to see it.

## How do colloids expand plasma volume?

They raise oncotic pressure and draw fluid into the vessels.

## What is the main risk of albumin infusion?

Circulatory overload (pulmonary oedema).

## Which diluent must never be used for albumin?

Sterile water for injection (haemolysis).

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Albumin (Human) Injection: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a626061.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [DailyMed - ALBUMIN (HUMAN)- albumin human solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=07734008-9dd3-b006-0825-65147c58e1ac) (DailyMed (U.S. National Library of Medicine), 2026); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025).

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Representative model, for educational purposes only.

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