Expansion
Crystalloids distribute by tonicity; colloids stay longer in the plasma
Expansion
| Fluid | Sodium | Chloride | Distribution | Notes |
|---|---|---|---|---|
| 0.9% saline | 154 | 154 | Extracellular | Hyperchloraemic acidosis in volume |
| Hartmann’s / Ringer’s lactate | 131 | 111 | Extracellular | Balanced; lactate is metabolised to bicarbonate |
| 5% dextrose | 0 | 0 | Total body water | Effectively free water once glucose is metabolised |
| Plasma | 135 to 145 | 95 to 105 |
Distribution of one litre
- 5 per cent dextrose: about 80 ml stays intravascular
- 0.9 per cent saline: about 250 ml stays intravascular
- Colloid: most stays intravascular initially
Practical consequences:
- Dextrose is for free water replacement, not resuscitation
- Balanced crystalloid is preferred for resuscitation and large volumes
- Hartmann’s contains potassium and is traditionally avoided in hyperkalaemia, although in practice it raises potassium less than saline does, because the acidosis caused by saline shifts potassium out of cells
- Starch colloids are no longer used, having been shown to increase renal failure and mortality