MDCalc

Body Fluid Balance Calculator by Inputs and Outputs

Calculates fluid balance from sodium concentrations which indicate net 0.9% saline, and free water losses (GI, urine, etc) and gains (IV fluids, PO, etc).

All entries for fluids and solutions should be entered as positive numbers.

Body fluid LOST (enter as positive numbers, e.g. 100 mL, not -100 mL)

mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL

Parenteral (IV) solutions administered

mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL

Enteral solutions administered

mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL
mL

Result:

Please fill out required fields.
Advice

  • Volume replacement may include sodium-containing solutions like 0.9% saline, sodium bicarbonate, buffered solutions like Ringer’s lactate, Plasmalyte, and blood products including albumin, fresh frozen plasma, platelets, and packed red blood cells.

  • Free water replacement may include oral or nasogastric solutions which contain primarily water, or IV 5% dextrose in water.

  • Remember, packed RBCs remain in the intravascular compartment, while all other inputs and losses equilibrate between the intravascular and extravascular compartment.

Management

Principles for treatment of concurrent sodium and water disorders:

 

Hyponatremia

Normal plasma [Na+]

Hypernatremia

Hypovolemia*

Give isonatremic solution for volume expansion.

Replace ongoing sodium losses.

Restrict free water.

Do not replace water losses (unless plasma [Na+] rises too rapidly).

Give isonatremic solution for volume expansion.

Replace ongoing sodium and free water losses.

Give isonatremic solution for volume expansion.

Replace ongoing sodium losses.

Replace ½ free water deficit (decrease [Na+] <8-10 mEq/L per day).

Replace ongoing water losses.

Euvolemia*

Replace ongoing sodium losses with isonatremic solution.

Loop diuretic to impair urine concentrating ability.

Restrict free water. Do not replace water losses.

Replace ongoing sodium and free water losses.

Replace ongoing sodium losses with isonatremic solution.

Replace ½ free water deficit and all ongoing free water losses.

Hypervolemia*

Restrict sodium.

Loop diuretic for volume and impaired urine concentrating.

Restrict free water.

Do not replace ongoing free water losses.

Restrict sodium.

Loop diuretic for volume overload.

Replace ongoing free water losses.

Restrict sodium

Loop diuretic for volume overload.

Replace ½ free water deficit and all ongoing free water losses.

*The patient’s volume status requires assessment based on the clinical findings.

Table and figure adapted from Kaptein Clinical Nephrology 2016.

 

Examples:

  • A patient with heart failure and anemia with hypernatremia is being treated with oral “fluid” restriction and diuretics.  

    • Q: What is the most likely consequence? A: Most oral liquids are primarily free water. So you have restricted free water which will worsen hypernatremia, but not improve the heart failure.

    • The patient has 2 liters of urine output. Q: What is the free water loss? A: Approximately 1 liter.

    • The patient has 1 liter of ultrafiltrate removed by hemodialysis. Q: What is the free water loss? A: Minimal.

  • A patient with heart failure and anemia with hypernatremia receives 1 unit of pRBCs (350 mL).

    • Q: How much urine output with a diuretic is necessary to be volume even? A: Saline equivalent volume of pRBCs is 2.8 times the volume of pRBCs, and urine output with a diuretic is ½ of 0.9% saline, so urine output must be approximately 5 to 6 times the volume of pRBCs given to be volume even.

    • Q: How much ultrafiltrate is necessary to be volume even? A: Saline equivalent volume of pRBCs is 2.8 times the pRBC volume given so approximately 1 liter of ultrafiltration is required since ultrafiltrate is approximately 0.9% saline.

Have feedback about this calculator?