Ultrasonographic Evaluation of Gastric Content in Fasting Volunteers and in Tirzepatide Users: an Observational and Cross-sectional Study
Conditions: Full Stomach Status
Sponsor: Hospital Israelita Albert Einstein

 
 
 
Ultrasonographic evaluation of gastric content in fasting volunteers and in 
tirzepatide users: an observational and cross-sectional study 
 
 
Date: February 4, 2026 
      

Ultrasonographic evaluation of gastric content in fasting volunteers and in 
tirzepatide users: an observational and cross-sectional study 
 
 
 
 
1. INTRODUCTION 
 
Obesity and type 2 diabetes mellitus constitute a global public health problem. 
Medications with glucagon-like peptide-1 (GLP-1) receptor agonist activity are a 
modern therapeutic option for both diseases (1,2,3). Liraglutide, semaglutide, 
dulaglutide and tirzepatide are representatives of this drug class (1), whose mechanism 
of action results in delayed gastric emptying, reduced gastric motility and increased 
gastric volume (4). These effects are implicated both in weight loss (4) and in the 
occurrence of adverse events such as nausea, vomiting, acute gastroparesis (5) and 
gastro-esophageal reflux disease (GERD) (4). 
 
Tirzepatide, however, presents a dual agonist action, combining GLP-1 agonism with 
glucose-dependent insulinotropic polypeptide (GIP) agonism (6). Its use has been 
approved by the Food and Drug Administration (FDA) and by the European Medicines 
Agency (2) and is associated with weight loss, glycaemic control and improvements in 
other metabolic parameters in individuals with obesity, with or without type 2 diabetes 
mellitus (7,8). 
 
The presence of gastric content during anaesthesia may lead to pulmonary aspiration 
and the development of chemical pneumonitis, a potentially devastating complication 
(9), with an incidence of 1 in 3,000 to 4,000 elective procedures (10). To avoid such 
complications, in healthy patients, fasting of 8 hours for solids and 2 hours for clear 
liquids is recommended (11). However, when there is a risk factor for delayed gastric 
emptying, despite adequate fasting, the stomach may still present residual content, and 
bedside ultrasonography is an effective, non-invasive and rapid method to measure this 
content and stratify aspiration risk (12). 
 

Some studies corroborate a higher occurrence of a full stomach in patients using 
semaglutide despite adequate fasting (13,14). However, the association between the use 
of this class of medications and the occurrence of gastric aspiration remains uncertain. 
 
Due to the scarcity of data associating the use of dual GLP-1 and GIP analogues with 
increased aspiration risk in individuals who have undergone adequate fasting for 
anesthesia, there is no evidence-based consensus recommendation for the suspension of 
these medications (15), nor for routine preoperative gastric ultrasonography. Some 
institutions and societies empirically recommend preoperative suspension. 
 
Given the severity of broncho aspiration, the biological action of GLP-1 analogues on 
gastric function and the increasing use of these medications, a better understanding of 
gastric content in fasting individuals using a dual GLP-1 and GIP analogue is required. 
Thus, through ultrasonography, we aim to evaluate the gastric content of volunteers who 
have no risk factors for broncho aspiration, who will not undergo anesthesia, but who 
have adhered to recommended fasting and are using tirzepatide, a dual GLP-1 and GIP 
analogue. 
 
Our hypothesis is that most individuals using tirzepatide present a full stomach even 
after fasting times recommended in the literature. Therefore, safety criteria during 
anesthesia should be adjusted for this population. 
 
 
 
 
2. OBJECTIVES 
2.1 Primary objective 
To evaluate the prevalence of a full stomach using gastric ultrasonography in 
volunteers using tirzepatide who have fasted for at least 8 hours for solids and 2 hours 
for clear liquids. 
 
 
2.2 Secondary objectives 
 

 
To evaluate whether demographic characteristics, duration of medication use, 
time since the last dose of tirzepatide, dose and dosing regimen, indication for use, and 
the presence of symptoms such as nausea, vomiting and a sensation of gastric fullness 
influence gastric emptying when assessed by ultrasonography. 
 
 
3. Study design 
Observational, cross-sectional, non-interventional study. 
 
4. Study population 
 
Thirty volunteers will be included, of whom 15 will be current users of 
tirzepatide and 15 will not be using the medication. 
Potential volunteers may be invited in person, such as colleagues, individuals 
from the investigators’ social environment, or patients already referred to the 
Interventional Medicine Centre for other examinations or procedures. 
Thirty healthy volunteers, 15 using tirzepatide analogues and 15 not using the 
medication, both groups having fasted for at least 8 hours for solids and 2 hours for 
clear liquids. 
The informed consent process will be conducted by the principal investigator or 
a trained and delegated member of the research team, in person, before the ultrasound 
examination. After understanding the study and voluntary agreement to participate, 
written informed consent will be obtained prior to participation. A copy signed by both 
parties will be provided to the participant, and a note will be recorded in the medical 
record indicating the date of consent. 
After inclusion, gastric ultrasound will be performed at Hospital Israelita Albert 
Einstein by an anesthesiologist experienced in gastric ultrasound. Images will be 
recorded in the PACS system and reviewed by a radiologist. 
 
5. Inclusion and exclusion criteria 
 
 
 

5.2 Inclusion criteria 
 
• Adults aged 18 years or older. 
• Individuals currently using tirzepatide. 
• Individuals fasting for at least 8 hours for solids and 2 hours for clear liquids without 
residue. 
 
5.3 Exclusion criteria 
 
• Pregnant or postpartum individuals. 
• Technical limitation for gastric ultrasound assessment. 
• Presence of risk factors for gastroparesis. 
• Use of prokinetic medications such as bromopride, metoclopramide or domperidone. 
 
 
5.4 Sample size calculation 
 
Based on the literature (16), control individuals presented residual gastric fluid 
areas ranging from 3 to 7 cm², with a median of 5.1 cm², corresponding to residual 
volumes of 32.4 mL, 90.8 mL and 63.1 mL after 8 hours of fasting. Assuming a mean 
increase of at least 20 mL in patients using semaglutide, with 95% confidence and 80% 
power, the required sample size is 14 patients per group. To compensate for possible 
losses, the sample was increased by 10%, resulting in 15 volunteers per group. 
 
 
6. Risks and benefits 
 
6.1 Risks 
 
Abdominal ultrasonography is a non-invasive examination that does not emit 
radiation. There is no evidence that ultrasound causes harm to health. Participants may 
experience discomfort related to fasting. There is a risk of data confidentiality breach; 
however, all precautions will be taken to ensure data confidentiality. 
 

 
6.2 Benefits 
There is no direct benefit to participants. However, they may benefit from the 
study results if undergoing surgery in the future, as the findings may guide safety 
measures for individuals using tirzepatide. 
 
7. Methods 
 
7.1 Study outcomes 
7.1.1 Primary outcome 
 
Comparison of the prevalence of a full stomach after fasting using gastric 
ultrasonography in volunteers using tirzepatide versus those not using the medication. 
The outcome is binary: a full stomach is defined as the presence of solids or clear liquid 
volume greater than 1.5 mL/kg. 
 
7.1.2 Secondary outcomes 
• Demographic characteristics 
• Dose and dosing regimen 
• Indication for medication use 
• Presence of symptoms (nausea, vomiting, gastric fullness, early satiety, abdominal 
pain) 
• Use of other medications 
 
 
7.2 Randomization 
Not applicable. 
 
7.3 Definitions 
 
 
 
7.3.1 Ethnicity 
 

Caucasian, Black, Hispanic, Asian, Indigenous or Other (self-declared). 
 
 
7.3.2 Risk factors for broncho aspiration 
 
• Diabetes mellitus with neuropathy or gastroparesis 
• Obesity (BMI ≥ 30 kg/m²) 
• Active cancer 
• Gastro-esophageal reflux disease 
• Opioid use 
• History of bariatric surgery 
• Neurological disease 
• Chronic or acute kidney disease 
• Symptomatic hypothyroidism 
 
 
7.3.3 Technical limitations 
 
• Previous gastric surgery 
• Large hiatal hernia 
 
 
7.3.4 Adequate fasting 
 
Clear liquids: 2 hours 
General diet: 8 hours 
(*Clear liquids: water, pulp-free juices) 
 
 
7.3.5 GLP-1 analogue 
 
• Tirzepatide (Mounjaro®, Zepbound®) 
 
 

7.4 Gastric ultrasound protocol 
It consists of scanning the abdomen in the sagittal plane in the 45° dorsal 
decubitus position, in the supine position, and in the right lateral decubitus position with 
a curvilinear, low-frequency (2 to 5 mHz) ultrasound probe and locating the gastric 
antrum by identifying the main reference points – the left lobe of the liver and a main 
vessel, the aorta or inferior vena cava.(12) Gastric emptying will be assessed 
quantitatively and qualitatively by evaluating the composition of its contents and 
measuring the gastric volume, respectively. 
The qualitative assessment will evaluate whether the stomach is empty, with 
clear liquid, or with solids. The stomach is considered empty when the antrum presents 
with the anterior and posterior walls juxtaposed, denoting a "buffalo eye" or "target" 
pattern, a characteristic attributed by the identification of a thick, hypoechoic outer ring. 
(12) In this case, there is no risk of aspiration of gastric contents during the induction of 
anesthesia and it is classified as low risk. When fluid is identified in the antrum, 
hypoechoic content is observed in the center and distended walls. The antrum may 
appear empty in the supine position and contain fluid in the right lateral decubitus 
position. The fluid volume should be measured in this position, and if it is less than 1.5 
ml/kg (average of 100 ml in adults), it is considered normal in fasting individuals, and 
the risk of broncho aspiration is considered low (12). On the other hand, the 
visualization of fluid in both the supine and right lateral decubitus positions is 
suggestive of a large gastric volume. When the fluid measurement is greater than 1.5 
ml/kg, the patient presents a high risk for broncho aspiration (18). Thick liquid, milk, or 
suspensions have a hyperechoic appearance, generally homogeneous. After ingestion of 
solid foods, the air content mixed with the solid bolus during mastication forms an air-
mucosa interface along the anterior wall of the distended antrum. This area of air 
artifacts is referred to as a "ground-glass" pattern. After a time interval, this air is 
displaced and the antrum then appears distended with content of typically mixed 
echogenicity (16) 
Whenever clear liquids are visualized, gastric volume is measured by means of 
the cross-sectional area of the gastric antrum (AA) using the outer wall of the stomach, 
which has a linear correlation with gastric volume. This is performed in the right lateral 
decubitus position with two perpendicular diameters of the antrum, from serosa to 
serosa, the longitudinal or craniocaudal diameter (CC) and the anteroposterior diameter 
(AP), using the ellipse formula developed by Bolondi (19) where AA = (CC × AP × π) 

/4. With the value of π = 3.14. After calculating AA, the total stomach volume 
(“predicted volume”) will be evaluated in each volunteer using a previously tested and 
validated mathematical model (18), where stomach volume (mL) = 27 + 14.6 AA (cm2) 
− 1.28 age (in years). 
 
8 Statistical analysis plans 
Patients included will be divided into two groups according to the ultrasound 
result: high risk for broncho aspiration and low risk for broncho aspiration. Differences 
between the groups regarding continuous numerical variables will be analyzed using the 
Student's t-test (normal distribution) or the Mann-Whitney U test (variables not 
normally distributed). Proportions will be compared using the Chi-square test or Fisher's 
Exact Test, if the assumptions for using the Chi-square test are violated. 
We will use the Kolmogorov-Smirnov test to assess the distribution pattern of 
continuous numerical variables. Continuous variables with a normal distribution will be 
expressed as mean ± standard deviation or as median and interquartile range when 
appropriate. Categorical variables will be presented as absolute and relative frequencies. 
All significance probabilities (p-values) presented will be two-tailed. P-values 
will be considered statistically significant when less than 0.05. All analyses will be 
performed using R 3.4.1 software (R Foundation for Statistical Computing, Vienna, 
Austria). 
 
9 Safety and ethical considerations 
9.1 Adverse Events 
Abdominal ultrasound is a non-invasive examination that does not emit 
radiation. There is no evidence to support that the use of ultrasound may cause any 
harm to health. The research participant may experience some discomfort related to 
fasting for 8 hours for solids and 2 hours for liquids. There are risks related to the loss 
of data confidentiality, and the research team is responsible for taking all precautions to 
ensure data confidentiality. 
 
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