Enteral Feedings:  Free Water

The term “free water” may also be seen as “feed water”, depending on the source.  Free water is the amount of liquid an enteral formula (aka tube feeding formula) is actual water as an ingredient.  If you look at the ingredients list of any liquid enteral nutrition formula, you will see ingredients that are sources of carbohydrates, proteins, and fats, and you will also see “water”.  Water is a component of a liquid formula, and this water is what gets counted towards a patient’s fluid needs.

 

Free water should not be confused with water flushes, which is additional water provided to a patient in their daily regimen to:

  • Clear the feeding tube periodically throughout the day (may be 25 to 50 ml per flush)
  • Mixed with medications and infused into the tube (also may be around 25 to 50 ml per flush)
  • Provide additional water to help meet the patient’s daily fluid needs (wide range from 25 to 200 ml, depending on the patient’s needs and volume tolerance)

 

Tube feeding formulas come in a variety of caloric strengths with the most common being 1.0 cals/ml, 1.2 cals/ml, 1.5 cals/ml, and 2.0 cals/ml.  The chart below provides the ranges of free water percentages per liter.

Caloric Strength
Free Water Range
  • 1.0 cals/ml
  • 1.2 cals/ml
  • 1.5 cals/ml
  • 2.0 cals/ml
  • 83% – 85% per liter
  • 81% – 82% per liter
  • 76% – 78% per liter
  • 69% – 72% per liter

 

The percentages in the above chart may also be expressed in ml.  For example, the 1.0 calorie per ml formula can contain between 830 ml and 850 ml of free water.  It is always best to refer to the formula manufacturer’s website or product guide for the exact amounts of free water in a tube feeding formula.  The images below show an example of a manufacturer’s 1.5 calorie per ml formula expressed as both a percentage and a volume.

 

Sample Calculation

We have a patient receiving a 1.0 calorie per ml formula.  The formula runs from 7am to 10pm at 125 ml per hour.  After reviewing the manufacturer’s product guide, we see that this formula provides 844 ml free water per liter of formula.  How much fluid from this tube feeding regimen is counted towards this patient’s daily fluids needs?

 

The first step is to determine how much total volume of formula this patient is receiving.  The formula runs from 7am to 10pm, so this is 15 hours of total time the formula runs.  The other variable we use for this first calculation is the infusion rate of 125 ml per hour:

125 ml per hour infusion rate X 15 hours = 1,875 total ml of formula provided daily between 7am and 10pm

 

Next, we will utilize the information regarding the free water in the formula from the manufacturer’s product guide of 844 ml free water per liter of formula.  This patient received a total of 1,875 ml of the formula, not just one liter (1,000 ml).  If we convert the volume of formula provided from ml to liter, we get a useful factor to calculate the total amount of free water given to this patient.  We can actually utilize this factor for calculating the total amounts for any nutrient in the formula, but we’re only concerned with the fluid for this question:

1,875 ml / 1,000 ml per liter = 1.875 liters

 

Finally, multiply the volume of formula in liters by the amount of free water in the formula in one liter:

1.875 liters of formula X 844 ml free water per liter = 1,582.5 ml

 

In 1,875 ml of this tube feeding formula, 1,582.5 ml is considered free water that gets counted towards this patient’s daily fluid needs.

 

Some final thoughts on this example:

  • 100% of the amount of free water in a formula is counted towards a patient’s fluid needs, meaning the entire 1,582.5 ml gets counted, not just a smaller portion of the amount
  • This 1,582.5 ml of water from the formula may not be enough to meet this patient’s daily fluid goals.  He may need additional water flushes to reach his daily goals