POCUS to Diagnosis Gastric Content

Gastric byte

Diagnostic Accuracy of Point-of-Care Gastric Ultrasound

Anesthesia and Analgesia April 2018 - Pubmed Link


Take Home Points

1. Gastric POCUS appears highly accurate in determining full stomach in healthy volunteers.

2. Unclear how well this translates into determining aspiration risk in other patients.


Background

Ultrasound the stomach?! Why? That is certainly a reasonable question to ask before moving forward. The reason is that sometimes, unlike Las Vegas, what happens in the stomach does not stay in there. It can, on occasion, be regurgitated onto your shoes, your face, or - of most concern to the patient, into the airway. Having a full stomach increases the chance that there is going to be aspiration during anesthesia. Therefore, it has been posited in the past that a gastric ultrasound could help indicate the risk for aspiration during airway control. Why can’t you just count on patient’s being NPO? Three reasons 1) Sometimes its an emergency 2) Sometimes stomachs are full despite fasting and 3) Sometimes patients lie. This has particular relevance to anesthesiologists, but also can apply to anyone who does procedural sedation or intubation procedures.


Question

Can point of care gastric ultrasound accurately identify or rule out a full stomach in healthy volunteers?


Population

Authors from Canada

Healthy volunteers recruited


Inclusion:

  • 18-85 years old

  • ASA physical status I-II (normal or mild systemic disease)

  • Height > 145 cm

  • Ability to understand study protocol


Exclusion:

  • Pregnancy

  • Gastric or lower esophageal surgery

  • Known abnormalities in upper GI tract (hiatal hernias, gastric tumors)

  • Diabetes

  • Renal or hepatic impairment

  • Neurologic disorders


Design

Prospective, randomized, single blinded study


Intervention

Study subjects fasted for at least 8 hours (no solids or liquids)

US performed to confirm empty stomach at baseline


Randomized into 2 groups

      Group 1: remained fasted

      Group 2: ingested either 250 mL apple juice or solid meal (muffin + coffee with cream)


3 minutes after ingestion, index gastric ultrasound performed

Content identified as one of 3 categories:

  • Nothing

  • Clear fluid

  • Solid

After 24 hours, same people randomized a second time into one of the 2 groups

Process repeated


Who did the ultrasounds?

Staff anesthesiologist with >100 gastric examinations, blinded to group allocation


The Scan

Low frequency curvilinear transducer, abdominal settings

Curvi


Standardized protocol in supine and right lateral decubitus

Step 1: Transducer in epigastrium in sagittal plane. Transverse view of antrum identified between liver (anteriorly) and pancreas and aorta (posteriorly). Repeat in right lateral decubitus.

  • Empty = antrum collapsed, no content seen

  • Clear fluid = hypoechoic/anechoic homogenous content

  • Solid = hyperechoic or mixed echogenicity

Step 2: If clear fluid visualized, patient placed in right lateral decubitus and a cross-sectional area of the gastric antrum was measured (at the level of the aorta) to estimate the volume.

  • Volume = 27 + 14.6 x CSA - 1.28 x age (this was validated by endoscopically guided gastric suctioning)

  • Fun idea: Try having a friend drink an unknown quantity of liquid. Measure the stomach to see how accurate this equation is


Key Point:

Considered positive for full stomach if A) Solid content or B) >1.5 mL/kg of clear fluid

Considered inconclusive if could not image gastric antrum in both uspine and RLD positions or if there was uncertainty.


GastricUltrasound.org - Everything you wanted to know and more

Ultrasound Podcast on Gastric ultrasound Part 1 and Part 2


Results

The Patients

Screened 42 but 2 of them found to have full stomach at baseline

N = 40 → 80 sessions

  • 19 males

  • Mean age 37

  • Mean weight 69 kg

  • Mean height 168 cm

  • Mean BMI 24 kg/m2


Primary Outcomes

Accuracy of POCUS for diagnosis full stomach:

Sensitivity 100% (CI 0.925-1)

Specificity 97.5% (CI 0.95-1)

+LR 40

-LR 0


All patients who ingested solids were true positives (14.3% only had high volume of fluid, no solid matter identified)

All patients who ingested juice were true positives (94.7% of patients had high volume of fluid, a single patient was thought to have solid content)

There was only one incorrect exam - this was a false positive (fasting patient called as full stomach).

There were no inconclusive studies.

No adverse events.


Limitations

Healthy, really healthy volunteers - couldn’t even have diabetes or a hiatal hernia. Couldn’t even be short! May not represent your population. We don't know how well this would work in any sick population or a population with potentially impaired gastric motility.

The sonographic appearance may be different with different amounts of food. In this study, just a single muffin with coffee was examined. What if eating a steak doesn't show up as well?

Each individuals used more than once. Really this is still only 40 unique patients, just reproducing it a second time.


Discussion

Authors note some important aspects of gastric ultrasound. Air in the antrum can cause an artifact seen at anterior wall that could resemble solid material. Need to measure the antral area in the right lateral decubitus. Measuring of the antrum should be between peristaltic contractions and include the full thickness of the gastric wall.

So if we accept that ultrasound can accurately predict if the stomach is filled, the next question to ask yourself is if this will change anything. What do you do with the knowledge that the stomach is full? If pre-op, delay case? If emergent, place NG? Authors suggest only changing management if pre-test uncertainty.


Take Home Points

1. Gastric POCUS appears highly accurate in determining full stomach in healthy volunteers.

2. Unclear how well this translates into determining aspiration risk in other patients.


Our score

3 Probes


Published on 05/07/18 06:00 AM
comments (5)
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By Anonymous on 05/07/18 05:29 PM
Great synopsis -many thanks. On reading around, one issue is that no-one quite agrees on what ml/kg number constitutes signficant contents.....1.5ml/kg is only one of the many cutoffs.
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By Anonymous on 05/08/18 02:33 PM
Why was the one fasting patient called a false positive for a full stomach? Doesn’t this actually tell us that for whatever reason they had delayed gastric emptying?
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By Mike Prats on 05/10/18 08:58 AM
Thanks for the comments. Regarding the first comment - I agree that there needs to be a consensus about the correct gastric volume that constitutes a significant risk of aspiration. It would be hard to perform this study because we would need to follow subjects with varying gastric volumes to see if there is difference in aspiration events. It is important to figure this out because there may be different accuracy of ultrasound depending on the volume you choose. However, the alternative, and what this group has done, is to just pick a volume and see how that works when you use it. To the second comment - another great point! The problem is that we don't know if the ultrasound was positive because there was significant content in the stomach or if there was some other reason that made it positive. This study was attempting to determine the accuracy of ultrasound as a diagnostic modality, therefore - we can't assume on the basis of our intuition, that if the ultrasound visualizes content, it represents a full stomach. The reason that this was called a false positive is because the patient had no content visualized at their baseline ultrasound (before the randomization to fasting or ingestion), but afterwards, had some content visualized.
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By Anonymous on 05/14/18 12:34 AM
forget juice......needs to be redone with 1-fasting, 2-beer, 3-pizza and beer...sorry i couldn't resist AND was it really juice?? I imagine the healthy volunteers might have included residents..
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By Mike Prats on 05/14/18 08:20 AM
Good point - probably could redo the study many times to assess for different patient populations and their choice combinations of stomach contents!