Example

What is the NPO deficit for a patient who weighs 50 kg who has been NPO for 10 hours prior to surgery?  The answer is 1 liter (500 mL 1st hour, 250 mL 2nd hour, and 250 mL 3rd hour).  See how the numbers were used on the calculator below.

Formula

IV fluid replacement for NPO  deficit = 2mL/kg for each hour NPO prior to surgery. 

50% of this deficit is replaced within the first hour of surgery with the remaining 50% being replaced over the next 2 hours.  If the patient stayed in the hospital overnight with an IV infusing while NPO, subtract this amount from the NPO deficit.

In the example above:

2 mL/kg/hr = 2 x 50 x 10 = 1000
@1st hr, 500 mL will be replaced
2nd hr, 250 mL will be replaced
3rd hr, 2hr 250 mL will be replaced

If in this example, the patient stayed in the hospital overnight with an IV infusion at 100 mL/hr while NPO, all their NPO deficit (1 liter) would already be replaced.