Fluid management during Surgery

Anesthesiologists have a lot of control in how much fluid a patient will be given during a procedure. I remember coming across the equation for maintenance fluid (4-2-1 rule) for my surgery shelf exam but have long since forgotten it. I wanted to remind myself here about the process of figuring out the amount of fluid a patient should be given during a procedure. 

1. Take the patient's weight in kg

2. Multiple the 1st 10 kg by 4

3. Multiple the 2nd 10 kg by 2

4. Multiple the leftover kg by 1

5. Add them all up and you will get the maintenance fluid in mL/hr

Example

1. Pt weighs 88 kg 

2. 4 x 10kg = 40

3. 2 x 10kg = 20

4. 1 x 68kg = 68

5. 40 +20 + 68 = 128 mL/hr

When your patient is going to have surgery, they usually have been NPO for 7-12 hours. Once you have the maintenance fluid amount, you can figure out what the patient's deficit is. So, if my patient in the example has been NPO for 10 hours, then I would multiple 128 mL x 10 and say that they have a 1.28 L deficit. 

Another factor that you need to think about is fluid loss during the procedure which includes blood and evaporation. This is called insensible loss. Loss due to evaporation is case dependent (3-15 cc/hour). You will have more evaporation loss in an open case versus a laparoscopic case. Blood loss to crystalloid ratio should be replaced in a 1:3 ratio. So, if my patient lost 300 cc of blood during the procedure then I would add on 900 cc of NS to the fluid total to be given.