While fluid intake and output can be performed during routine checking of vitals by nursing, it is often not part of an encounter or a predictable workflow; rather, recorded as fluids are given (oral, IV fluids, blood transfusions) and collected/cleaned (urine, diarrhea, vomitus). Each can be recorded as a number of mL (milliliters) and reported as the total ins minus the total outs over the past 24 hours. Patients with large deficits (e.g., -3000 mL) are in trouble for dehydration; patients with large excess (e.g., +3000 mL) are at risk for fluid overload.
I'd approach these with a targeted form for quickly recording counts, expecting that they would be entered ad hoc as they are given or collected. Allowing entry of negative numbers allows for quick corrections for mistaken entries.
Anyway, not worth building if they aren't crying out for it. Given what I know of EVD combined with some of the I&O's I've seen reported (10-12 liters/24 hours for some, which is massive), I'm just guessing that managing fluid balance and prioritizing fluid resuscitation would be far more critical & lifesaving compared to recording hiccups or coughs throughout the day. And, a system that made I&O recording & monitoring incredibly simple would be a lifesaver.
But I'm not an Ebola expert and I'm not the one in the field, so treat this is just my 2¢ from the sidelines.