Regarding patients diagnosed with dehydration and diarrhea. We know fluid intake must be considered in this condition. Many of the patients in post operative wards and those getting IV fluids want to know their fluid requirement. In these cases how can I calculate their requirement of fluids? What should I do if the patient provided with IV fluid and can drink fluids too?
The short answer to your question is that fluid requirements differ by age and physiological need (see table 7.2 below). There are several ways of calculating requirements. In my experience the method of calculating fluid requirements will depend more on the preference of the unit/hospital you work in. Some may use weight based calculations, some are based on energy intake and some on body surface area. I personally either use Kcal based or weight based (see below)
Weight related for average adult maintenance fluid requirements
Method 1 : 1ml/kcal x 2200 kcal
Method 2: 30- 35 ml/kg (I personally use this one)
Method 3: 30 - 40 ml/kg
All the above formula's are used to calculate maintenance fluids, which are total fluid requirements from all sources (oral intake and IV). We generally negotiate with the doctors and share the fluid between IV and enteral (both oral and tube feeds). The general practice is that if a patient is able to meet their full fluid requirements via the enteral route then we discontinue IV fluids. We taper down IV fluids as enteral input goes up.
Fluid req.= 100ml/kgBW for 1st 10kg Body wt. + 50ml/kgBW for 2nd 10kgBW (+15ml/kgBW)
We use the requirement that you gave more for the pediatric patients. I have never seen the addition of 15 ml/kg/BW (highlighted in yellow) after the first 20kgs in weight. I cannot speak too much on that. I would use the requirements provided below. This is from the Nutrition Therapy and pathophysiology book by Marcia Nelms.
So to answer your questions:
Can I use this formula if patient is asking how much fluid should he drink in a day?
Technically IV fluid requirements are maintenance fluid requirements. So its the same thing, and yes you can advice patients using the above formulas on how much fluid to drink.
What should I do if the patient provided with IV fluid and can drink fluids too?
If the patient is on IV fluids subtract the total volume of what is provided from the IV fluids from their maintenance fluid requirements and make sure they are meeting the difference via the oral route.
Naturally, we give additional fluids for patients with losses of fluids (e.g. diarrhea, vomiting and stoma losses). The most accurate way is to try and replace the volume of fluid lost, which means you must be measuring losses on your input/output chart. In such patients we give maintenance fluids + ongoing losses