Map which Chapter 8 bases apply, then show the need is daily and can be met only in a SNF (the practical-matter test). This is what a coverage reviewer looks for on a Part A day.
Covered skilled procedure
Administration and monitoring of intravenous fluids is a direct skilled service under Chapter 8 when required.
Observation & assessment of an unstable condition; management & evaluation
Dehydration or a fluid-electrolyte disturbance carries a reasonable potential for a rapid, dangerous change; recognizing and managing the daily fluid balance requires nursing judgment.