Gastric Ultrasound Made Easy: Step-By-Step Guide

Primary Authors: Madeline Carritte, Henry Hongo, Kate Leon, ShengYing (Angela) Chen, Nicole Evangelista, Vi Dinh.

Gastric Ultrasound (GUS) is a Point of Care Ultrasound (POCUS) application that is used to examine gastric and stomach contents and determine a patient’s pulmonary aspiration risk. This is a non-invasive, quick, and effective tool that can be used at the bedside during an emergent intubation or in the perioperative setting prior to anesthesia.

Gastric ultrasound may also be referred to as Gastric Point-of-Care Ultrasound (POCUS), Point-of-Care Gastric Ultrasound, and is commonly abbreviated as GUS for “Gastric Ultrasound”. 

After reading this tutorial, you will be able to use bedside Gastric Ultrasound (GUS) to:

• Obtain the parasagittal view of the gastric antrum
• Perform proper Gastric Ultrasound (GUS) technique
• Evaluate and differentiate gastric contents (empty, clear liquid, thick fluid/solid)
• Qualitatively and quantitatively estimate gastric volume using antrum grading and a predictive model, respectively to assess aspiration risk
• Recognize and troubleshoot common pitfalls while performing Gastric Ultrasound

Gastric Ultrasound Indications

Gastric Ultrasound can be used to evaluate gastric contents in the following clinical presentations:

• Elective, urgent, and emergency procedures

• Unknown patient NPO status
  • Altered mental status
  • Neurocognitive dysfunction
  • Language barrier
  • Limited patient history
  • Pediatric population

• Delayed gastric emptying
  • Diabetes
  • Medications – GLP-1 receptor agonists, opioids, calcium channel blockers, anticholinergics, dopamine agonists, etc.
  • Pregnancy/labor
  • Severe kidney or liver dysfunction
  • Neuromuscular disorders
  • Autoimmune disorders
  • Severe obesity
  • Prior gastric surgery

Gastric Ultrasound Contraindications

There are few contraindications to Gastric Ultrasound however, clinical situations that may not make it feasible include the inability to position the patient in right lateral decubitus (RLD) position due to uncontrolled pain or immobilization, high surgical urgency, polytrauma to the area, or a confirmed full stomach on recent imaging (CT, MRI).

Gastric Ultrasound Preparation

Patient Preparation/Positioning

• Start with the patient supine with the head of the bed flat.
  • This will be the first patient position to begin scanning.

• Transition to right lateral decubitus (RLD).
  • Patient’s right arm rests above the head to prevent obstruction of the ultrasound scanning area. This positioning helps move gastric contents to the antrum to improve assessment and is the most sensitive to measure gastric volume.
  • This will be the second patient position to continue scanning.

Gastric Ultrasound Machine Preparation

• Transducer:
  • Curvilinear or Phased Array for children > 30 kg and adults 
  • Linear for children < 30 kg and leaner adults
• Preset: Abdomen
• Machine Placement: Place the machine on the patient’s right side to scan with your right hand and maneuver the ultrasound machine with your left hand.

Gastric Ultrasound Anatomy

Understanding gastric ultrasound starts with recognizing key anatomical structures and their sonographic appearances. While the stomach has several parts (fundus, body, antrum), the gastric antrum is the main region evaluated in POCUS due to its consistent location and visibility.

Location of the Gastric Antrum

The gastric antrum is located in the epigastric area, typically:

• Between the liver anteriorly and the pancreas posteriorly
• Slightly to the right of the patient’s midline, especially in the right lateral decubitus (RLD) position
• Located superficially 3-4 cm below skin

Gastric Ultrasound Sonographic Landmarks

On ultrasound, you’ll use the following landmarks to identify the gastric antrum:

• Left lobe of the liver (bright and anterior)
• Aorta (pulsatile, thick-walled, left of IVC) or inferior vena cava (compressible, thin-walled, right of aorta)
• Superior mesenteric artery (anterior and parallel to aorta)
• Pancreas (posterior to the stomach, hyperechoic)

In the sagittal plane, the antrum appears between the liver and aorta/IVC as a round or oval target-like structure. The Superior mesenteric artery (SMA) sits between aorta and gastric antrum and can be used as a depth guide.

POCUS 101 Tip

Gastric Wall Layers

The antrum has a distinctive, multilayered wall appearance (from outer to inner):

1. Mucosal-air surface – Thin, hyperechoic
2. Muscularis mucosae – Hypoechoic
3. Submucosa – Hyperechoic
4. Muscularis mucosae – Hypoechoic
5. Serosa – Thin, hyperechoic

These layers help differentiate the antrum from the surrounding bowel and assess for content.

Gastric Ultrasound Protocol

We will now review a simple, step-by-step protocol for performing gastric ultrasound.

Step 1: Obtain Gastric Ultrasound View

The main objective of GUS is to identify the gastric antrum to determine the presence of stomach contents and the likelihood of aspiration risk. The antrum is preferred as the most accurate location for assessing gastric content due to easy visualization on ultrasound and proportional dilation with stomach contents (Putte & Perlas, 2014). 

Supine View

• Point the probe with the indicator pointing towards the patient’s head. Place the probe beneath the sternum using a pencil grip, beginning at the midline and sliding slightly right if needed to visualize the tip and edge of the liver. The gastric antrum is adjacent to the tip of the liver and can be identified by its characteristic circular appearance.

Right Lateral Decubitus (RLD) View:

• We recommend beginning with the patient in supine position, then transitioning to RLD if possible, for the patient. Place the probe beneath the sternum using an underhand grip to better manipulate the probe. These two positions may yield different findings described below, and the RLD additionally brings the stomach closer to the anterior abdominal wall for greater visualization (Nguyen et al, 2023)

The structures you will want to identify on ultrasound will be:

• Liver
• Stomach
• Pancreas
• SMA (Superior Mesenteric Artery)
• Inferior Vena Cava or Aorta

Step 2: Gastric Content Assessment

The presence of fluid or food intake is assessed by distinct qualitative findings of the gastric antrum, notably disruption to the uniformity and echogenicity of the gastric antrum. Along with the following qualitative assessments of gastric content, imaging findings can be graded by the Perlas antral grading system, a three-point system (0-2) that correlates with predicted gastric volume that is described in detail under the “Gastric Volume Assessment” section below. 

Editor’s Note: Remember to do BOTH the Supine and Right Lateral Decubitus views to assess for gastric content.

Empty Stomach

An empty stomach will appear on the ultrasound as a “target” or “bull’s eye” pattern as shown in the images below. The contracted and empty antrum is uniformly hyperechoic and encircled by the muscularis propria which appears hypoechoic. An empty stomach indicates low aspiration risk.

Fluid-Filled Stomach

A uniformly hypoechoic or anechoic image of the antrum is due to the presence of fluid within the stomach. Visualization of fluid may reflect some risk of aspiration, and we recommend obtaining both supine and RLD views for further assessment. Low fluid volumes may be visualized in the supine position only, whereas increased fluid volumes may be apparent in both RLD and supine positions.

Food in Stomach

Food intake produces a “frosted-glass” or “ground glass” appearance in the antrum with heterogeneity visualized due to the mix of food, air, and fluid. With the presence of solid food and/or an expanded lumen, patients with this gastric ultrasound exam finding are considered high risk of aspiration. 

Step 3: Gastric Volume Assessment

Qualitative Assessment – Antral Grading System

The most commonly used qualitative sonographic evaluation is the Perlas antral grading system, a three-point system (0-2) that correlates with predicted gastric volume. This system predicts aspiration risk through assessment of the gastric antrum in both the supine and RLD positions. Due to the poor prognosis with aspiration of any particulate content, patients with thick fluid or solid gastric content are considered high risk and excluded from this grading system (Perlas and Kruisselbrink).

Grade 0: Empty gastric antrum with no content visible in both supine and RLD positions, suggesting baseline gastric secretions with low aspiration risk

Grade 1: Fluid found only in RLD suggesting low gastric volume. Correlates with negligible fluid volumes that are common in fasted individuals with baseline gastric secretions and low aspiration risk (Perlas et al., 2011)

Grade 2: Visible fluid in the gastric antrum in both supine and RLD, suggesting higher than baseline gastric secretions and high aspiration risk (Perlas et al., 2011)

Quantitative Assessment – Gastric Volume Calculation

When the gastric antrum contains clear fluids, a quantitative assessment can estimate volumes to predict risk of aspiration and differentiate between clinically insignificant volumes (<1.5 ml/kg) from volumes greater than baseline secretions (>1.5 ml/kg) (Perlas et al., 2016). Due to their linear relationship, the cross-sectional area (CSA) of the gastric antrum can predict gastric volume (Perlas et al., 2013). 

The predictive mathematical model can estimate gastric volumes from 0 to 500 ml and is reliable in nonpregnant adults of normal to severely obese BMIs (Perlas et al., 2016, Kruisselbrink et al., 2017). While there is no explicit gastric volume threshold above which aspiration risk increases, a volume less than 1.5 ml/kg is common in fasted individuals and associated with low risk of aspiration (Perlas et al., 2013). 

To calculate gastric volume:

1. Identify the gastric antrum at the level of the abdominal aorta in the RLD.

2. Obtain a still image when the antrum is at rest (between peristaltic contractions). This may require viewing the antrum for 10-15 seconds prior to capturing an image (Perlas and Kruisselbrink).

3. Use the tracing tool to measure the antral CSA (cm²) including the full thickness of the gastric wall (from serosa to serosa) (Perlas et al., 2016).

4. Use the following equation to estimate total gastric volume (Perlas et al., 2013):

Gastric volume (ml) = 27.0 + (14.6 × RLD CSA) − (1.28 × age)

5. To assess risk of aspiration from gastric volume use the following ratio of the gastric volume to the patient’s weight:

Gastric volume (ml) ÷ Patient weight (kg)

Gastric Volume Ratio Interpretation:

• <1.5 ml/kg = low risk
• >1.5 ml/kg = high risk

Gastric Ultrasound Algorithm

Here is a proposed algorithm that consolidates the steps described above:

Both qualitative and quantitative volume assessments can accurately predict aspiration risk (Kruisselbrink et al., 2019). While quantitative assessment can only be used in patients with clear fluid content, qualitative assessment includes patients with an empty gastric antrum. With clear fluids present, quantitative assessment can further assist in risk stratification.

With high aspiration risk, consideration should be taken to delay or cancel the procedure particularly for elective surgical procedures. For urgent or emergent surgical procedures or for patients with conditions where gastric emptying may not occur with time such as gastroparesis, proceeding with surgery with full aspiration precautions may be warranted (Perlas et al., 2013). Aspiration precautions may include considering alternatives to general anesthesia, gastric decompression with an NG tube preinduction, avoiding an unprotected airway with deep sedation, securing the airway with endotracheal intubation, and RSI when general anesthesia is required (Perlas and Kruisselbrink). 

GLP-1 Agonists and Gastric Ultrasound

The increased use of GLP-1 agonists in the management of various medical conditions such as diabetes, obesity, and overall weight management can pose increased challenges in the setting of intubation and surgery. The mechanism of GLP-1 agonists results in increased satiety, delayed gastric emptying, and subsequent residual gastric contents despite following proper fasting protocols in the perioperative period. This increases patient safety concerns. The greatest concern is the increased risk of pulmonary aspiration of residual gastric contents during procedures, which can result in aspiration pneumonia, a condition associated with increased morbidity and mortality.

New multi-society clinical practice guidance, including from the American Gastroenterological Association, American Society for Metabolic and Bariatric Surgery, American Society of Anesthesiologists, International Society of Perioperative Care of Patients with Obesity, and the Society of Gastrointestinal and Endoscopic Surgeons all aim to minimize the aspiration risks due to delayed stomach emptying from GLP-1 agonist use in patients undergoing sedation and procedures all of which are summarized below.

First, a shared-decision making approach with the patient and care teams should be incorporated that weighs the risks and benefits of GLP-1 agonist use in the perioperative period. This includes assessing: 

• Frequency and dosage of GLP-1 agonist
• Medication phase (escalation versus maintenance)
• Presence of GI symptoms that may be indicative of delayed gastric emptying or intestinal transit duration (nausea, vomiting, abdominal pain, dyspepsia, constipation) in the patient
• Comorbid conditions that exacerbate GI symptoms or increase delayed gastric emptying

After assessment, the decision to withhold or continue GLP-1 agonists should be balanced with risks of inducing perioperative hyperglycemia or hypoglycemia during bridging therapy. If the decision to withhold GLP-1 agonist is made due to a perceived elevated risk, current guidelines suggest following the American Society of Anesthesiologists (ASA) guidance of holding medication the day of surgery for daily formulations and one week prior for weekly formulations. Regardless, all patients should be assessed the day of surgery for GI symptoms that may suggest delayed gastric emptying.  

Second, care teams should aim to minimize risks of pulmonary aspiration by optimizing the patient’s perioperative diet, modifying the anesthesia plan when appropriate, and utilizing gastric ultrasound to assess for retained gastric contents on the day of a procedure when there is a continued concern for retained gastric contents.

Incorporating routine gastric ultrasound during the perioperative period can provide an individualized assessment of aspiration risk. This tool may aid anesthesia professionals in airway management, anesthetic planning, and overall, patient care. Point-of-care gastric ultrasound utilization has the potential to avoid unnecessary surgical case cancellations, leading to more cost- and time-effective perioperative care. 

Gastric Ultrasound Pathology

While evaluating aspiration risk for pre-operative patients, you may encounter incidental findings on GUS. It is important to know that ultrasound is not the gold standard modality for diagnosis of these findings, and clinical judgement should guide further management.

Simple gastric cysts

Gastric cysts are seen on ultrasound as well-defined anechoic structures; however, empty stomachs may obscure their exact location. A distended stomach with liquids by mouth may help to distinguish the cyst’s location. Simple gastric cysts are generally considered benign but do have potential for malignant transformation. Ultrasound is not the gold standard for diagnosing simple gastric cysts, and upper GI endoscopy with biopsy would be preferred to rule out malignant potential (Deslandes et al).

Hiatal Hernia

Hiatal hernias typically present as a funneling of the distal esophagus in the left upper quadrant. A sliding hiatal hernia is suggested when the gastroesophageal junction is not visualized, and there is a widening of the gastrointestinal tract greater than 16 mm at the esophageal hiatus of the diaphragm (Aliotta et al). Diagnosis is most often made via endoscopy, with additional evaluation guided by the type of hernia and severity of symptoms.

Menétriér’s Disease

This may be seen on ultrasound as multiple echogenic, polypoid lesions in the stomach. Menétriér’s disease may be confirmed when a gastric polyp remains adherent to the stomach wall despite changes in the patient’s position from supine to upright.

The presence of Menétriér’s disease may not change your clinical decision making for pre-operative aspiration risk as the condition is considered benign, however these patients are at increased risk for gastric carcinoma (Deslandes et al). If this is seen on gastric ultrasound, further management should include gastroscopy and regular monitoring.

Gastric Adenocarcinoma

Gastric adenocarcinoma is the second most common malignancy worldwide. Clinical diagnosis is difficult in early stages and is typically made in later stages and metastasis. The gold standard diagnosis of gastric adenocarcinoma is endoscopy. On ultrasound, thickening of the stomach wall with antrum thickness between 11.5 mm and 20.3 mm was seen in patients with gastric adenocarcinoma while antral thickness between 3 mm and 6.2 mm was seen in patients without gastric adenocarcinoma. Abdominal ultrasound can also be used to screen for secondary spread (local lymph nodes and liver metastases) at the time of initial assessment, however abdominal ultrasound should not be the primary modality for diagnosis of gastric adenocarcinoma (Rappacinni, et al.).

Gastric Ultrasound Pitfalls

Patient positioning 

• Always assess your patient in both the supine and right lateral decubitus (RLD) positions. 
• RLD helps move gastric contents to the antrum to improve assessment and visibility. 

Incorrectly identifying the gastric antrum and adjacent structures 

• Use anatomical landmarks. For example, the antrum is located between the left lobe of the liver anteriorly and both the pancreas and aorta posteriorly. 
• The gastric antrum characteristically has a “bull’s-eye” or “target” sign when empty but can also appear flattened depending on patient’s PO status. 
• Color Doppler can be used to differentiate vascular structures from the gastric antrum. 

Air artifacts can mimic an empty stomach  

• Gas is characterized as “dirty shadowing” or “starry night appearance” instead of the typical “bull’s eye” appearance. 
• Repositioning the patient to the RLD can move the gas and enhance the view. 

Abnormal gastric anatomy can limit the utility and findings of Gastric Ultrasound. 

Examples include:

• Previous Gastric Surgery – Gastric bypass (Roux-en-Y), sleeve gastrectomy, or Billroth I/II
• Hiatal Hernia
• Gastric Outlet Obstruction – Pyloric stenosis, gastric tumors or polyps
• Gastric Dilatation and Volvulus
• Congenital Anomalies – Gastric duplication cysts, malrotation

References

• Kruisselbrink R, Gharapetian A, Chaparro LE, Ami N, Richler D, Chan VWS, Perlas A. Diagnostic Accuracy of Point-of-Care Gastric Ultrasound. Anesth Analg. 2019 Jan;128(1):89-95. doi: 10.1213/ANE.0000000000003372. PMID: 29624530.
• Tankul R, Halilamien P, Tangwiwat S, Dejarkom S, Pangthipampai P. Qualitative and quantitative gastric ultrasound assessment in highly skilled regional anesthesiologists. BMC Anesthesiol. 2022 Jan 3;22(1):5. doi: 10.1186/s12871-021-01550-z. PMID: 34979932; PMCID: PMC8722139.
• Perlas A, Mitsakakis N, Liu L, Cino M, Haldipur N, Davis L, Cubillos J, Chan V. Validation of a mathematical model for ultrasound assessment of gastric volume by gastroscopic examination. Anesth Analg. 2013 Feb;116(2):357-63
• Perlas A, Kruisselbrink R. POCUS spotlight: gastric ultrasound. ASRA News 2021;46. doi: 10.52211/asra110121.065
• Van de Putte P, Perlas A. Ultrasound assessment of gastric content and volume. Br J
• Anaesth. 2014;113(1):12-22. doi:10.1093/bja/aeu151
• Nguyen H, Paluska MR, Falcon R, Petersen TR, Soneru C. Rapid Evaluation of Gastric Content With Ultrasound: An Educational Tool. Cureus. 2023;15(11):e49031. doi:10.7759/cureus.49031
• Perlas A, Kruisselbrink R. POCUS spotlight: gastric ultrasound. ASRA News 2021;46. doi: 10.52211/asra110121.065
• Perlas A, Davis L, Khan M, Mitsakakis N, & Chan VW. Gastric sonography in the fasted surgical patient: a prospective descriptive study. Anesthesia and analgesia. 2011;113(1), 93–97. doi:10.1213/ANE.0b013e31821b98c0
• Perlas A, Van de Putte P, Van Houwe P, Chan VW. I-AIM framework for point-of-care gastric ultrasound. Br J Anaesth. 2016 Jan;116(1):7-11. doi: 10.1093/bja/aev113. Epub 2015 May 7. PMID: 25951832.
• Perlas A, Mitsakakis N, Liu L, Cino M, Haldipur N, Davis L, Cubillos J, Chan V. Validation of a mathematical model for ultrasound assessment of gastric volume by gastroscopic examination. Anesth Analg. 2013 Feb;116(2):357-63. doi: 10.1213/ANE.0b013e318274fc19. Epub 2013 Jan 9. PMID: 23302981.
• Kruisselbrink R, Arzola C, Jackson T, Okrainec A, Chan V, Perlas A. Ultrasound assessment of gastric volume in severely obese individuals: a validation study. Br J Anaesth. 2017 Jan;118(1):77-82. doi: 10.1093/bja/aew400. PMID: 28039244.
• Kruisselbrink R, Gharapetian A, Chaparro LE, Ami N, Richler D, Chan VWS, Perlas A. Diagnostic Accuracy of Point-of-Care Gastric Ultrasound. Anesth Analg. 2019 Jan;128(1):89-95. doi: 10.1213/ANE.0000000000003372. PMID: 29624530.
• Perlas A, Chan VWS, Lupu CM, Mitsakakis N, Hanbidge A. Ultrasound assessment of gastric content and volume. Anesthesiology. 2009 Jul;111(1):82-9. doi:10.1097/ALN.0b013e3181a97250.
• Kar Man Chan L. Gastric ultrasound: Enhancing preoperative risk assessment and patient safety. J of Perioper Pract. 2024;0(0). doi:10.1177/17504589241302220
• Kindel TL, Wang AY, Wadhwa A, Schulman AR, Sharaiha RZ, Kroh M, Ghanem OM, Levy S, Joshi GP, LaMasters T; Representing the American Gastroenterological Association, American Society for Metabolic and Bariatric Surgery, American Society of Anesthesiologists, International Society of Perioperative Care of Patients with Obesity, and the Society of American Gastrointestinal and Endoscopic Surgeons. Multi-society clinical practice guidance for the safe use of glucagon-like peptide-1 receptor agonists in the perioperative period. Surg Endosc. 2025 Jan;39(1):180-183. doi: 10.1007/s00464-024-11263-2. Epub 2024 Oct 29. PMID: 39370500; PMCID: PMC11666732.
• Kozlow JH, Berenholtz SM, Garrett E, Dorman T, Pronovost PJ. Epidemiology and impact of aspiration pneumonia in patients undergoing surgery in Maryland, 1999-2000. Crit Care Med. 2003 Jul;31(7):1930-7. doi: 10.1097/01.CCM.0000069738.73602.5F. PMID: 12847385.
• Sen S, Potnuru PP, Hernandez N, Goehl C, Praestholm C, Sridhar S, Nwokolo OO. Glucagon-Like Peptide-1 Receptor Agonist Use and Residual Gastric Content Before Anesthesia. JAMA Surg. 2024 Jun 1;159(6):660-667. doi: 10.1001/jamasurg.2024.0111. PMID: 38446466; PMCID: PMC10918573.
• Aliotta A, Rapaccini GL, Pompili M, Grattagliano A, Cedrone A, Trombino C, De Luca F, De Vitis I. Ultrasonographic signs of sliding, gastric, and hiatal hernia: their prospective evaluation. American Institute of Ultrasound in Medicine [Internet].
• Deslandes A. Sonographic demonstration of stomach pathology: Reviewing the cases. Australas J Ultrasound Med [Internet].
• Rapaccini GL, Aliotta A, Pompili M, Grattagliano A, Anti M, Merlino B, Gambassi G. Gastric wall thickness in normal and neoplastic subjects: a prospective study performed by abdominal ultrasound. Gastrointest Radiol [Internet].