Volume of clear liquids for NPO status

[Ronin786]

Here's a scenario for you guys.

Healthy ASA 1, 26 year old presenting for a knee scope. No comorbidities. When asking about NPO status, patient had a meal last night and drank a 2L bottle of water at a little before 6 AM. Surgery is scheduled for 8. What do you do? Cancel/delay? RSI? ETT? LMA? And if you're going to delay, how long are you going to wait? Also if you don't care about the 2L, what would your cutoff be?

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[vector2]

Here's a scenario for you guys.

Healthy ASA 1, 26 year old presenting for a knee scope. No comorbidities. When asking about NPO status, patient had a meal last night and drank a 2L bottle of water at a little before 6 AM. Surgery is scheduled for 8. What do you do? Cancel/delay? RSI? ETT? LMA? And if you're going to delay, how long are you going to wait? Also if you don't care about the 2L, what would your cutoff be?

WTF, 2L?? I'd probably wait at least two more hours and proceed. On a related note, this may be the wave of the future for assessing NPO:

"Our results suggest that the gastric antrum and body have a distinct sonographic appearance when empty, after fluid intake, after effervescent fluid intake, and after a solid meal. Furthermore, our data suggest that the gastric antrum expands from a baseliune empty state as fluid enters the stomach, and that antral CSA as measured by ultrasonography correlates well with gastric volume in a close-to-linear manner, particularly when measured in the right lateral decubitus position. This close-to-linear relationship is limited to relatively small volumes (up to 300 ml). This is expected because the gastric antrum can only expand up to a certain limit. Volumes in excess of 300 ml result in only modest further increases in antral size, with excess volumes being accommodated by more proximal areas of the stomach. According to our model, measured CSA can be used to predict gastric content volume. For example, according to our inverse regression model curve, we can be 95% confident that an adult patient with a measured CSA-lateral of 4 cm2has an empty stomach, whereas a CSA-lateral of 10 cm2corresponds to a gastric volume of between 100 and 240 ml. Similarly, a patient with a CSA-lat of 24 cm2has a gastric volume of at least 300 ml (fig. 10). These findings support the use of antral CSA as a surrogate marker of intragastric volume and the use of two-dimensional ultrasonography as the first tool to assess gastric volume in a noninvasive manner. We believe that gastric ultrasonography can have significant future clinical and research applications. As an accurate, noninvasive tool, it can help better define aspiration risk both on a given individual as well as in different patient populations.20 "

http://anesthesiology.pubs.asahq.org/article.aspx?articleid=1923819

 

[Iso4ane]

2L is a crap ton of fluid. But, if they also decent amount of urine output in the interim, I would be inclined to continue to the case under RSI.

Anecdotally, I have my morning caffeine bolus (~600ccs) when I wake up, it's mostly out before I start my first case less than 2hours later.

 

[partydoc]

ha, I wouldn't postpone the case, our pre op instructions say clears are OK 2 hours before surgery

but just given that large amount of volume, it makes me uncomfortable and i would RSI

this paper shows stomach emptying related to the number of calories, but their volume is 500cc
http://bja.oxfordjournals.org/content/early/2014/09/25/bja.aeu338.full.pdf

 

[Ezekiel2517]

awake NGT, awake foley, awake fiberoptic. or just do a spinal. or prop/sux/tube. all equally terrific options.

 

[caligas]

ha, I wouldn't postpone the case, our pre op instructions say clears are OK 2 hours before surgery

but just given that large amount of volume, it makes me uncomfortable and i would RSI

this paper shows stomach emptying related to the number of calories, but their volume is 500cc
http://bja.oxfordjournals.org/content/early/2014/09/25/bja.aeu338.full.pdf

Just to play devils advocate:

If you are concerned enough about the risk of aspiration, a catastrophic complication, to do an RSI, shouldn't you delay this totally elective case until it is safer? Does doing an RSI eliminate the risk of aspiration?

 

[partydoc]

You're absolutely right, it does not, but how can I postpone a case when the patient clearly followed pre op directions?

 

[deleted59964]

You're absolutely right, it does not, but how can I postpone a case when the patient clearly followed pre op directions?

Because he's an idiot, maybe he followed the instructions to the letter - but certainly not the spirit of them.

Either he's fasted and he gets an lma or he's not and he waits for his elective procedure. RSI s what we do to minimise, not eliminate risk of not being fasted. If he aspirates despite your rsi you are fckd

Just put him last on your scope list

 

[Sonny Crocket]

Is this a joke? Don't do an unnecessary RSI. This is an ELECTIVE case. Delay it.

 

[Ronin786]

What volume of liquids would you be comfortable with? 1L? 500CC?

 

[deleted171991]

If in doubt, just do a gastric ultrasound in right lateral decubitus. If the antrum is distended, you'll see it.

Theoretically, all that fluid should have left the stomach in an ASA 1 patient, but I would use an ETT just for peace of mind. Delaying for a few hours is also very defendable.

From what I recall, as long as the stomach was already empty, fluids should just flow through (in a healthy patient). The question is how full is the small bowel, and at what point will the stomach evacuation stop until the bowel catches up.

(The small bowel absorbs water at a rate of about 0.035 ml/min/cm, per summary Google search. For 7 meters of small bowel, that's about 25 ml/min, assuming it's all empty, which is not true. Assuming 1/3 of the small bowel is initially empty, there should be about 1000 ml of water left after 2 hours, but probably not in the stomach and duodenum.)

For how long after eating 2 kg of watermelon (92% water) does one have polyuria? I would guess it's much more than 2 hours.

P.S. In the end, @Sonny Crocket is right. It's an elective case so, if the patient is not optimized (e.g. NPO), the case should be postponed. The problem with anesthesiology is how many textbook cases like this can one postpone before getting fired (especially if lucrative).

 

[Mman]

2L of water? Nighty, night. No delay. WTF would I delay for? Water is gone through his stomach in probably <30 minutes. NPO guidelines don't mention volume because it doesn't matter. I don't delay a case for 6 donuts any longer than I delay for 1/2 donut.

If I'm feeling like an a-hole, I'll make him chug some bicitra as punishment for the large volume of water.

 

[partydoc]

2L of water? Nighty, night. No delay. WTF would I delay for? Water is gone through his stomach in probably <30 minutes. NPO guidelines don't mention volume because it doesn't matter. I don't delay a case for 6 donuts any longer than I delay for 1/2 donut.

If I'm feeling like an a-hole, I'll make him chug some bicitra as punishment for the large volume of water.

LMA? or tube?

 

[Mman]

LMA? or tube?

whatever is appropriate and the water > 2 hours pre induction isn't going to change my anesthetic technique

 

[Planktonmd]

Do a femoral + sciatic nerve block and little sedation. But LMA is not a problem either!

 

[AdmiralChz]

LMA? or tube?

Some of the newer LMAs allow for an OG to be placed down (honestly, never used them), although if you are that worried about it there are few contraindications to RSI tube...

 

[Ronin786]

I'd been wondering about this for a while and could never find an answer as far as what an acceptable volume of clear liquids would be prior to surgery. After further research I came up with the following:

1) The point of being NPO is minimizing the amount of gastric fluids and the risk of pneumonitis in the chance of aspiration. The maximum amount of remaining fluids has been classically taught to be 0.8 ml/kg (although this is mainly based on animal studies).

2) The half life for clear liquids in your stomach is 15 min. At 2 hours (or 8 half lives), .4% of whatever was ingested remains.

3) Based on the above, assuming a 70kg male has a 56ml maximum acceptance of gastric contents at 2 hours, that would be .4% of the maximum amount you could drink two hours prior to induction. With some simple math, that comes out to 14,336 mls. (You can also plug those numbers into this fancy calculator: http://www.calculator.net/half-life-calculator.html?type=1&nt=56&n0=&t=120&t12=15&x=68&y=7 T1/2= 15 minutes and final volume = 56)



As such, you would have to drink over 14L 2 hours prior to surgery in order to have a residual gastric amount significant enough to cause pneumonitis in the case of aspiration. Which ultimately makes you realize why the volume of liquids is never really mentioned.



Unfortunately, after all that, I came across this article (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1365873/pdf/jphysiol01404-0052.pdf) which actually showed that there was a certain delay in gastric emptying related to ingestion of greater than 750ml of volume. However, even with meals sized at 1250ml, there was almost complete emptying before 120 minutes.