How to calculate NG tube replacement.

For some reason, this isn't very clear to me. Can someone please help me understand how to calculate?

A patient's IV fluid is D51/2 NS with 20 mEq of potassium at 70 ml/hr. Her NG output must be replaced with Lactated Ringer's ml/ml every 4 hours.

This means the NG drainage is to be emptied and measured every 4 hours, and that volume will be replaced with LR over the next 4 hours. For example, if the drainage were 60 ml at 10:00, the client would get 15 ml/hr of LR over the next 4 hours.)

Thank you!

11 Answers

Specializes in Critical Care.

Let's get some basics down.

1) An NG tube is a Nasogastric Tube inserted via the nose and terminates in the stomach.

2) The Nasogastric Tube is often abbreviated NGT.

3) The NGT tube can be used for

A) Giving medications

B) Giving nutrition/feeds

C) Suctioning and decompressing

4) You always need an order before you can administer meds, and placement is confirmed with a chest X-ray. Once the X-ray is taken, the provider must place a nursing other order stating that the tube is clear for use. You also check placement as part of your assessment by inserting a small amount of air via a catheter tip syringe. You will auscultate with your stethoscope and review for the sound of air or gurgling.

5) NGTs are often set to low intermittent wall suction, which means it will intermittently (every few seconds) suction as opposed to continuous suction (which can harm the folds of the stomach).

6) Patients that have small bowel obstructions are often on NGT. Patients that are on a ventilator have NGT as well to prevent aspiration.

The catheter of the NGT is sitting in the stomach. Our stomachs have digestive gastric juices, and these will be suctioned out. Over time, you will see an accumulation of these gastric contents on the NGT output canister.

You walk into your patient's room, and it is 8 AM. You notice the canister has 400 mL in the canister. Remember your order says to replace every milliliter of NG tube output with 1 mL lactated ringers - over FOUR hours. Thus you will divide 400 by 4, which equals 100. So every hour, you will infuse 100 mL of LR.

Specializes in Burn, ICU.

Maybe you're confused by the idea of NG output. When I was in school, I had patients getting tube feeds--NG input, but I don't recall having one with the NG tube hooked up to a suction canister on the wall.

When we're resting someone's bowel after a major surgery, or if they have an obstruction and nothing is moving through the bowel, and fluid has nowhere to go but up & out, this is what we do.

Depending on the circumstances, NG output can be a lot of volumes, including some critical electrolytes (see your maintenance IV fluid for a hint!). I've had a patient fill multiple suction canisters in a shift (~1L per canister)!

So, for this setup, your patient will have an IV pole with two channels and two bags of fluid. One channel is your maintenance IV fluid of D51/2NS+20KCl running at 70mL/hour as the doctor ordered. You won't change this rate unless the doctor changes the order. You'll hang a new bag when needed. The other channel is LR, and at 0800, you'll look at how much NG drainage there has been since 0400, divide that amount by 4 (so if it were 200mL, you would divide by four and get 50mL/hour), and program your LR channel to run at 50mL/hour for the next 4 hours. Then at 1200, you'll come back and recheck it and reprogram it.

Your I&O flowsheet will have 3 lines (ignoring other possible lines like urine, wound vacs, or whatever).

  1. One line is your maintenance IV; the pt gets 70mL IN each hour.
  2. One line is your LR replacement; each pt gets 50mL IN (in my example).
  3. The 3rd is your NG; every 4 hours, the pt has an amount of output you measure. So, what would you come up with if I asked you what the patient's fluid balance between these three lines was over 4 hours? (Again, this patient should also be making some urine, but we'll ignore that now!)

Hopefully, that helps.

Specializes in Pediatric Hematology/Oncology.

I'm unsure what's confusing you because you seem to have it down. This has an illustration of that problem, so maybe that will help.

Nasogastric Tube Insertion | ALFA

Whatever is draining out of the NG over a fixed time period (here, q4h) needs replacement with LR over the same specified period. So, from 0400-0800, the NG drained 120 ml to the suction canister. How many ml per hour did the NG drain? 30 ml/hr (4 hours X 30 ml = 120 ml per 4 hours). So, the replacement volume is 120 ml from 0800-1200 (or 30 ml/hr for 4 hours = 120 ml LR volume). Does that help?

Specializes in Pedi.
mancor_123 said:
The example was part of the question; I wasn't sure how they got that.

But your explanation does help; thank you!

The NG drained 60 mL. It would be best to replace it 1:1 with LR over 4 hours. 60 mL/4 hrs = 15 mL/hr.

Specializes in ICU Registered Nurse.

A nasogastric (NG) tube is a thin, soft tube made of plastic or rubber placed into the stomach through the nose and throat. It provides food or medicine to the gut for people with difficulty eating or swallowing, and it can also be used to remove liquids or air from the stomach.
Since the question is about fluid replacement, it is indicated that the patient is placed in NG suction, and the gastric fluid is being suctioned out in the suction jar or canister.
According to the question, the drain must be monitored every 4 hours, and the order says to replace every milliliter of NG tube output with 1 milliliter of lactated ringers - over 4 hours. Thus, you will divide the amount of drain by 4. For example, if the drain is 200ml in 4 hours, then the fluid to be replaced is 200ml divided by four which equals 50 ml. So, you will infuse LR at the rate of 50ml/hrs. You will continue to do it every 4 hours.

The example was part of the question; I wasn't sure how they got that.

But your explanation does help; thank you!

Specializes in Burn, ICU.
marienm said:
One line is your LR replacement; each pt gets 50mL IN (in my example).

Sorry, "each HOUR the pt gets 50mL IN" I'm not very good at typing on the tablet!

Specializes in Critical Care.

I wish I could help the OP, but I don't understand what they are not understanding. Isn't it a pretty straightforward 3rd-grade math word problem? OP, please be more direct.

Specializes in Critical Care.

You have a nursing other order that states to infuse half mL of LR for every ONE mL of NG tube output over 4 hours.

You walk to your patient's room at noon and notice that they have put out 100 milliliters since 8 AM.

Have you provided this information? What total amount of lactated ringers will you have to infuse?

Secondly, at what rate are you going (remember you're running over four hours) to run your LR to achieve that total?

A further question, If the MD ordered "replace urine output 1â�"2 mL per mL every 4 hours with the maintenance IV fluid," and instead of the 1:1, it's now 1:2 MI reading this straight through like "replace half the urine output per mL." For example, the 120mL loss is only replaced with 60mL of LR?

lysser said:

A further question, If the MD ordered "replace urine output 1â�"2 mL per mL every 4 hours with the maintenance IV fluid," and instead of the 1:1, it's now 1:2 MI reading this straight through like "replace half the urine output per mL." For example, the 120mL loss is only replaced with 60mL of LR?

Yes, this is correct.

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