Certified Registered Nurse Infusion (CRNI) Practice Exam

Which substance is unable to be filtered through a 0.2 micron filter?

1. Normal saline

2. Lipid emulsion

3. Glucose solutions

4. Protein solutions

The correct answer is: Lipid emulsion

A 0.2 micron filter is utilized to remove bacteria and other pathogens from solutions, but it is not capable of filtering larger molecules. Lipid emulsions, which are composed of fat globules suspended in water, contain lipid particles that are generally larger than 0.2 microns in diameter. This means that when trying to filter lipid emulsions through a 0.2 micron filter, the fat globules will not pass through and will remain in the original container, making it ineffective for this type of solution. In contrast, normal saline, glucose solutions, and protein solutions can generally pass through a 0.2 micron filter. Normal saline, being a simple electrolyte solution, does not contain particulate matter significant enough to be retained by the filter. Glucose solutions, primarily composed of dissolved glucose, do not have particles larger than the filter's pore size. While protein solutions can contain various sized proteins, many proteins are also small enough to be filtered successfully. However, the size of the lipid particles in emulsions makes them unsuitable for filtration with this size filter.