- Describe the distribution of Total Body Water intracellularly and extracellularly
- Demonstrate awareness of the composition of the most common Crystalloids and how these distribute into the various body compartments
- Classify Colloids by chemical structure and describe their clinical uses and drawbacks
- Use this knowledge and understanding to select an IV fluid for use in various clinical scenarios
Crystalloids are water-based solutions with added solutes (electrolytes or glucose). They differ in their composition, which determines their distribution throughout the body.
Click through the tabs to compare different crystalloids by content, pH and compartment distribution. It is important to note that glucose effectively becomes free body water (i.e. not limited to the extracellular space) and so is not suitable for fluid resuscitation. ‘Normal’ Saline and ‘Balanced’ Crystalloids (such as Plasmalyte) are retained in the extracellular spaces (in plasma and the interstitium) and so are much more suitable for fluid resuscitation.
4% Glucose with 0.18% NaCl
Colloids have been popular for their use as plasma volume expanders. This is because they are 100% retained within the intravascular space (at least initially). They are a crystalloid base with added colloid substance that does not freely diffuse across cell membranes.
For various reasons, their use has fallen out of favour. However, you should be aware of their chemical classification and the pros and cons associated with each.