Maintenance Fluids Calculations. Determining IV fluid rates for patients who are not taking oral fluids (either from vomiting or being NPO). Determining IV fluid requirements for patients who are dehydrated or have insensible losses or third spacing.Ideal Body Weight · Disclaimer · Scientific Advisory Board · Pediatric Ins and Outs. May 6, - ALLOW PATIENTS TO EAT AND DRINK IF POSSIBLE. So WHY does the patient need IV fluid? Maintenance fluid only – patient does not have.