Ultrasound assessment of gastric content in preoperative patients. Implications for anesthetic management

Nº de DOI:10.34896/RSI.2025.86.59.001

AUTHORS

1. Ronie Hugo Crespo Tonato. General Practitioner. Attached to Private Clinics of Ecuador. Independent Researcher at the Matilde Hidalgo of Procel Research and Teaching Department. Graduate of the Regional Autonomous University of Los Andes. (Salcedo -Ecuador). https://orcid.org/0009-0003-4070-9575
2. Elías Josue Del Pezo Matovelle. General Practitioner. Attached to APROFE. Graduate of the University of Guayaquil. (⁠Guayaquil -Ecuador). https://orcid.org/0009-0003-2558-177X
3. Roberto Carlos Rodríguez Arias. General Practitioner. Master’s Degree in Public Health. Attached to the Baba Health Centre. Graduate of the National University of Chimborazo. (⁠Riobamba-Ecuador). https://orcid.org/0009-0004-1779-3315
4. Noelia Deyanira Choez Abendaño. General Practitioner and Specialisation in Occupational Health and Safety. Attached to the Chorora Rural Health Centre of the Social Security Institute (IESS). Graduate of the Particular Technical University of Loja. (Loja-Ecuador). https://orcid.org/0009-0009-3576-3394
5. Marlith Gabriela Mora González. General Practitioner. Attached to San Vicente de Paul Basic Hospital. Graduate of the National University of Loja. (Arenillas-Ecuador). https://orcid.org/0000-0002-8782-3012

ABSTRACT

This paper aims to explore the various techniques employed for ultrasound assessment of gastric content, analyze their impact on anesthetic management strategies, and discuss the clinical challenges encountered in implementing this technology effectively, ultimately highlighting its potential to enhance patient safety and optimize perioperative care.

KEY WORDS

Gastric ultrasound, gastric content assessment, preoperative evaluation, aspiration risk, anesthetic management and perioperative care.

RESUMEN

Este artículo tiene como objetivo explorar las diversas técnicas empleadas para la evaluación ecográfica del contenido gástrico, analizar su impacto en las estrategias de manejo anestésico y analizar los desafíos clínicos que presenta la implementación eficaz de esta tecnología, destacando su potencial para mejorar la seguridad del paciente y optimizar la atención perioperatoria.

PALABRAS CLAVE

Ecografía gástrica, evaluación del contenido gástrico, evaluación preoperatoria, riesgo de aspiración, manejo anestésico y atención perioperatoria.

INTRODUCTION

The evaluation of gastric content in preoperative patients has become an essential aspect of anesthetic practice, primarily aimed at minimizing the risk of aspiration pneumonia, a rare but potentially fatal complication associated with anesthesia. Traditionally, assessment of gastric emptying and content has relied on clinical history and standard fasting protocols; however, these methods often lack precision and can be unreliable, especially in patients with conditions that alter gastric motility or in emergency scenarios. In recent years, point-of-care ultrasound has emerged as a valuable, non-invasive tool for directly visualizing gastric contents, allowing clinicians to assess both the volume and type of gastric material with greater accuracy. Techniques for gastric ultrasound assessment typically involve standardized approaches, such as the use of specific transducers and patient positioning, to optimize visualization of the gastric antrum, which serves as a reliable surrogate for overall gastric content. Ultrasound differentiation between clear fluids, solids, and mixed contents is achieved through real-time imaging and, in some cases, quantitative measurements, although challenges such as operator dependency, patient anatomy, and varying gastric conditions can limit the accuracy and reproducibility of assessments. The implications of these ultrasound findings are significant; they influence risk stratification for aspiration, guide adjustments in anesthetic induction techniques—such as choosing rapid sequence induction or delaying anesthesia—and inform protocols for managing patients with unexpectedly full or solid gastric contents preoperatively. Despite its promise, the integration of gastric ultrasound into routine clinical practice faces limitations related to training requirements, equipment availability, and the need for standardized protocols to ensure consistent and reliable results.

OBJECTIVE

Explore the various techniques used for ultrasound assessment of gastric contents, analyse their impact on anaesthetic management strategies, and discuss the clinical challenges involved in implementing this technology effectively, ultimately highlighting its potential to improve patient safety and optimise perioperative care.

METHODOLOGY

The methodology for this scientific review article, follows a systematic approach to identify, evaluate, and synthesize current evidence regarding the use of gastric ultrasound as a tool for preoperative risk assessment. A comprehensive literature search is conducted in major medical databases including PubMed, Embase, Scopus, and Web of Science. Search terms include combinations of controlled vocabulary and free-text keywords such as “gastric ultrasound,” “gastric content assessment,” “preoperative evaluation,” “aspiration risk,” “anesthetic management,” and “perioperative care.” Boolean operators and filters are used to refine the search to include studies published in English over the past 15 years.

Inclusion criteria encompass original research articles, systematic reviews, meta-analyses, and clinical guidelines that evaluate the use of point-of-care ultrasound (POCUS) to assess gastric volume and content in adult patients undergoing elective or emergency surgery. Studies are selected if they report on the accuracy, safety, feasibility, or clinical utility of gastric ultrasound for anesthetic decision-making. Exclusion criteria include case reports, pediatric-only studies, studies involving non-surgical patients, and those lacking methodological rigor or relevance to anesthetic practice.

Extracted data are synthesized qualitatively, with summary tables and figures used to illustrate key findings, clinical applications, and limitations. Particular attention is given to the correlation between ultrasound findings and aspiration risk classification, as well as how these findings influence fasting guidelines, airway management decisions, and perioperative safety protocols.

RESULTS

Techniques for Ultrasound Assessment of Gastric Content in Preoperative Patients:

What are the standard approaches for gastric ultrasound examination?

Standard approaches for gastric ultrasound examination encompass a combination of qualitative and quantitative assessments, leveraging both imaging techniques and specific anatomical landmarks to determine gastric content and volume. Typically, the procedure begins by identifying the gastric antrum, commonly achieved through visualization of adjacent structures such as the left lobe of the liver and the pulsation of the aortic or superior mesenteric artery, which provides a consistent starting point for reliable imaging¹. For most patients, a low-frequency (2 to 5 MHz) curved array probe is recommended, while a higher-frequency linear probe may be appropriate for pediatric populations, ensuring sufficient penetration and resolution based on patient size and anatomy². The examination usually involves positioning the patient in both the full supine and right lateral decubitus positions, as the emptying status of the antrum in these postures can distinguish between low-risk and high-risk stomachs, with an empty antrum in both suggesting a low aspiration risk³. Furthermore, ultrasonographic images are collected and analyzed to calculate the antral cross-sectional area (CSA), with specific cut-off values—such as 340 mm² in the supine position with the head elevated at 45°—serving to differentiate between high-risk and low-risk gastric states³. These quantitative assessments are often complemented by qualitative evaluations, wherein the presence of solids or thick fluids in the antrum denotes a high-risk stomach, emphasizing the necessity of integrating both approaches for a comprehensive risk assessment³. The interconnection of these methods not only enhances diagnostic accuracy but also supports the development of personalized perioperative management strategies, ultimately reducing aspiration risk and improving patient safety. Given these practices, ongoing refinement and standardization of gastric ultrasound protocols are essential to ensure consistent application and optimal outcomes across diverse patient populations.

How is gastric content volume and type differentiated using ultrasound?

Differentiation of gastric content volume and type using ultrasound hinges on the sonographic appearance and anatomical assessment of the gastric antrum, which serves as the most reliable site for these evaluations⁴. Fluid content in the stomach typically presents as anechoic or hypoechoic regions on ultrasound images, clearly indicating the presence of liquid, whereas solid material appears more echogenic and heterogeneous⁵. By assessing both the echogenicity and the distension of the gastric antrum, clinicians can distinguish between solid and fluid contents and estimate overall gastric volume^4,5. This distinction is clinically significant because the type and amount of gastric contents are pivotal for perioperative risk stratification; for example, a fluid volume exceeding 1.5 mL/kg is associated with a heightened risk of regurgitation and aspiration, which necessitates intervention or modification of anesthetic plans⁴. Additionally, specific positioning, such as the right lateral decubitus (RLD), enhances visualization by pooling gastric fluids in the antrum, thereby improving both qualitative and quantitative assessment accuracy⁴. The integration of qualitative findings—such as distinguishing clear fluids from thick fluids or solids—with quantitative measurements informs the clinician’s decision-making and may prompt rescheduling of elective procedures if high-risk gastric contents are detected^2,6. These interrelated ultrasound findings underscore the importance of a systematic approach to gastric content evaluation, with continued research and algorithmic refinement needed to optimize clinical protocols and minimize aspiration risk in vulnerable populations.

What are the limitations and challenges of ultrasound assessment in clinical practice?

Despite its utility in visualizing various anatomical structures such as the stomach’s fluid content, ultrasound assessment in clinical practice faces several notable limitations and challenges that impact its broader application and reliability. One of the primary concerns is the variability in image quality, which is particularly pronounced with handheld devices; these often produce lower-resolution images that can compromise the detailed assessment of cardiac function or detection of small organ pathologies, ultimately affecting diagnostic precision and clinical outcomes⁷. Furthermore, the accuracy of ultrasound examinations is heavily operator-dependent, with significant interobserver variation and potential for misinterpretation, especially when performed by inexperienced^8,9. These challenges are compounded by the steep learning curve required to achieve competence in ultrasound interpretation, as well as limitations in obtaining clear and comprehensive insights during routine practice⁹. Physical constraints also exist, as ultrasound waves do not travel well through air or bone, rendering this modality ineffective for imaging body parts like the lungs or brain, and necessitating the use of alternative imaging techniques such as CT or MRI when deeper or obscured structures must be assessed¹⁰. The interplay between technical, operator-related, and anatomical factors underscores the importance of ongoing training, rigorous protocol development, and judicious clinical judgment to ensure that ultrasound assessment is used effectively and appropriately within diverse clinical settings^7,11. Addressing these multifaceted challenges will require targeted interventions, such as standardized training programs and continued research into optimizing both technology and operator proficiency, to enhance the reliability and diagnostic value of ultrasound in modern medicine.

Impact of Gastric Ultrasound Findings on Anesthetic Management:

How do ultrasound findings influence anesthesia risk stratification?

Ultrasound findings have become integral to anesthesia risk stratification by offering real-time, detailed visualization of patient anatomy and physiological status, which is especially valuable when conventional assessment methods are limited. Cross-sectional imaging with ultrasound enhances the identification of both normal and variant anatomical structures, thus improving procedural success while reducing the likelihood of encountering unexpected anatomical challenges that could elevate anesthesia-related risks¹². This capability is particularly pertinent in patients where surface landmarks are obscured—such as those with obesity, edema, or prior surgical interventions—since ultrasound enables clinicians to accurately assess anatomical relationships and better plan both airway and vascular access procedures¹². Furthermore, ultrasound guidance during preoperative evaluation allows for direct assessment of risk factors such as the presence of potentially dangerous vessels, abnormal masses, or pathologically altered anatomy, thereby minimizing complications associated with blind or landmark-based techniques and supporting more individualized anesthesia planning¹². Additionally, the integration of ultrasound findings into risk stratification protocols facilitates tailored anesthesia approaches, particularly in scenarios where patient-specific factors, such as unclear prandial status or suspected NPO violations, could increase the likelihood of adverse events such as aspiration^13,14. Collectively, these interconnected domains highlight the pivotal role of ultrasound in refining anesthesia risk assessment, underscoring the need for routine preoperative ultrasound evaluation and ongoing training to ensure optimal patient safety and outcomes.

In what ways can anesthetic induction techniques be adjusted based on gastric content assessment?

Integrating gastric content assessment into anesthetic induction planning enables a more individualized and risk-adapted approach, particularly when ultrasound examination reveals the type and volume of gastric contents present. For example, when gastric ultrasound identifies an empty stomach, anesthetic induction techniques can be less restrictive and tailored to the specific requirements of the surgical procedure, reducing unnecessary interventions and optimizing perioperative efficiency¹⁵. Conversely, the discovery of clear gastric fluid necessitates careful measurement of its volume, as even apparently benign contents may pose a significant risk of aspiration; hence, the induction approach is adjusted only after this critical assessment is completed¹⁵. When non-clear fluid or solid gastric contents are detected, the risk of aspiration increases substantially, prompting anesthesia providers to adopt more cautious strategies, such as rapid sequence induction, cricoid pressure, awake tracheal intubation, or even the postponement of elective surgery if feasible, thus directly linking the findings of gastric ultrasound to patient safety interventions¹⁵. This process underscores the interconnectedness between preoperative diagnostic imaging, anesthetic management, and surgical scheduling, highlighting the importance of accurate, real-time gastric assessment to inform the safest possible induction plan. Consequently, ongoing education for anesthesia teams in gastric ultrasound interpretation and the development of clear protocols for corresponding induction modifications are essential to further reduce the risk of perioperative aspiration and optimize patient outcomes.

What protocols exist for managing patients with unexpected gastric fullness before anesthesia?

Upon identification of unexpected gastric fullness—particularly fluid content—via preoperative assessment tools such as ultrasound, an integrated protocol is necessary to mitigate the increased risk of aspiration during anesthesia. In such scenarios, rapid sequence induction and intubation (RSI) are strongly recommended as primary airway management techniques, with or without the application of cricoid pressure, to swiftly secure the airway and minimize the potential for regurgitation and aspiration of gastric contents [16]. Prior to induction, the placement of a nasogastric or orogastric tube to empty gastric contents is often advised, especially in patients suspected of having gastrointestinal obstruction or ileus; however, it is important to note that nasogastric tubes may not be fully effective in removing all gastric fluid, and are generally ineffective for solids¹⁶. To further reduce the risk of pulmonary complications in emergency situations, oral administration of non-particulate antacids such as sodium citrate immediately before induction is recommended to elevate gastric pH, thereby decreasing the severity of aspiration should it occur¹⁶. These interventions must be coordinated with ongoing preparedness, such as having a wide bore rigid suction device readily available during both intubation and emergence, to enable prompt clearance of secretions or regurgitated material from the airway¹⁶. Ultimately, a comprehensive approach that includes preoperative assessment, pharmacological prophylaxis, and meticulous airway management is critical in reducing the morbidity associated with unexpected gastric fullness during anesthesia, underscoring the need for robust protocols and multidisciplinary vigilance in perioperative care.

DISCUSSION

The findings of this comprehensive review underscore the significant role of gastric ultrasound as a valuable tool in preoperative assessment and anesthetic management. By facilitating accurate identification and quantification of gastric contents, ultrasound enhances clinicians’ ability to stratify aspiration risk effectively, thereby informing tailored perioperative strategies such as modified induction techniques and prophylactic interventions. The standardization of ultrasound protocols, including specific patient positioning and the use of appropriate probes, appears crucial in minimizing operator dependency and improving diagnostic consistency. However, despite its promising utility, several limitations remain evident. Variability in image quality due to patient anatomy, operator experience, and technical factors such as interference from air and bone can compromise accuracy. These challenges highlight the pressing need for standardized training programs and protocols to ensure reliable application across diverse clinical settings. Moreover, the current reliance on sonographic appearance and cross-sectional area measurements, while useful, may not fully account for the complexities of gastric content composition and volume, especially in patients with abnormal anatomy or comorbidities. Future research should focus on refining quantitative assessment techniques, developing automated image analysis tools, and establishing universally accepted threshold values for aspiration risk. Additionally, large-scale, prospective studies are necessary to validate ultrasound-guided risk stratification models and evaluate their impact on clinical outcomes. Addressing these gaps will be critical for integrating gastric ultrasound more effectively into routine preoperative evaluation, ultimately enhancing patient safety and reducing perioperative complications.

CONCLUSIONS

1. The use of ultrasound to assess gastric content in preoperative patients has emerged as a valuable, non-invasive tool that enhances anesthetic management and patient safety. This review confirms that point-of-care gastric ultrasound (POCUS) is effective in providing real-time, dynamic information about the volume and nature of gastric contents, helping clinicians evaluate the risk of pulmonary aspiration—one of the most feared complications during anesthesia induction. The ability to distinguish between an empty stomach, clear fluid, and solid content allows anesthesiologists to make informed decisions regarding airway management strategies, timing of surgery, and the need for additional precautions such as rapid sequence induction.
2. The review also highlights that gastric ultrasound is particularly beneficial in scenarios where fasting status is unclear or unreliable, such as in emergency surgery, obstetric cases, and patients with conditions that delay gastric emptying (e.g., diabetes mellitus, obesity, or gastrointestinal disorders). Moreover, the technique’s bedside applicability and repeatability make it a practical addition to preoperative assessments, especially when traditional fasting guidelines fall short of ensuring safety.
3. Despite these promising advantages, several limitations persist. The technique is operator-dependent and requires adequate training and experience to interpret findings accurately. There is also variability in the quantitative methods used to estimate gastric volume, and standardized thresholds for aspiration risk are still under refinement. Furthermore, most of the existing evidence focuses on select populations, and its generalizability across diverse clinical settings remains limited.

FUTURE DIRECTIONS

1. Future research should aim to standardize ultrasound protocols and risk stratification models across institutions, ensuring greater consistency in practice and improving reliability. The development of user-friendly training programs and validated competency assessments will be essential to expand the safe use of gastric ultrasound, particularly among non-expert users. Large-scale, prospective clinical trials are needed to evaluate the direct impact of gastric ultrasound on perioperative outcomes, including reduction in aspiration events and changes in anesthetic decision-making.
2. Additionally, technological innovations such as automated volume measurement, machine learning integration, and portable devices could further streamline the use of this tool in fast-paced perioperative environments. Studies exploring its role in pediatric populations, in patients with altered gastric physiology, and within enhanced recovery after surgery (ERAS) protocols would also expand its clinical utility.

REFERENCES

1. Shubha Srinivasareddy. Gastric Ultrasound for Gastric Content Evaluation. Türk Anesteziyoloji ve Reanimasyon Derneği dergisi [Internet]. 2023 Dec 27 [cited 2024 Apr 19];51(6):465–9. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10758669/
2. Flynn DN, Doyal A, Schoenherr JW. Gastric Ultrasound [Internet]. PubMed. Treasure Island (FL): StatPearls Publishing; 2022 [cited 2024 Jun 19]. Available from: https://www.ncbi.nlm.nih.gov/books/NBK580524/
3. Bouvet L, Chassard D. Ultrasound assessment of gastric contents in emergency patients examined in the full supine position: an appropriate composite ultrasound grading scale can finally be proposed. Journal of Clinical Monitoring and Computing [Internet]. 2019 Dec 18 [cited 2024 Jun 20];34(5):865–8. Available from: https://doi.org/10.1007/s10877-019-00452-3
4. Hu R, Dai W, Qin Y, Meng Z, Xia Z, Wang B, et al. Ultrasonographic Assessment of Gastric Volume in Fasted Patients Undergoing Gastrointestinal Endoscopy Under Sedation. Therapeutics and Clinical Risk Management [Internet]. 2023 Aug 1 [cited 2024 Jun 19];Volume 19(1):685–98. Available from: https://doi.org/10.2147/TCRM.S424890
5. Perlas A, Chan VWS, Lupu CM, Mitsakakis N, Hanbidge A. Ultrasound Assessment of Gastric Content and Volume. Anesthesiology [Internet]. 2009 Jul [cited 2019 Sep 22];111(1):82–9. Available from: http://dx.doi.org/10.1097/ALN.0b013e3181a97250
6. Cubillos J, Tse C, Chan VWS, Perlas A. Bedside ultrasound assessment of gastric content: an observational study. Canadian Journal of Anesthesia/Journal canadien d’anesthésie [Internet]. 2012 Jan 4 [cited 2021 Oct 18];59(4):416–23. Available from: https://doi.org/10.1007/s12630-011-9661-9
7. Spampinato MD, Luppi F, Cristofaro E, Benedetto M, Cianci A, Bachechi T, et al. Diagnostic accuracy of Point Of Care UltraSound (POCUS) in clinical practice: A retrospective, emergency department based study. Journal of clinical ultrasound: JCU [Internet]. 2023 Dec 7 [cited 2024 Jun 19];52(3). Available from: https://doi.org/10.1002/jcu.23619
8. Kalagara H, Coker B, Gerstein NS, Kukreja P, Deriy L, Pierce A, et al. Point-of-Care Ultrasound (POCUS) for the Cardiothoracic Anesthesiologist. Journal of Cardiothoracic and Vascular Anesthesia [Internet]. 2021 Jan [cited 2021 Nov 10];1(1). Available from: https://doi.org/10.1053/j.jvca.2021.01.018
9. Abu-Zidan F, B. Khan M. Point-of-care ultrasound for the acute abdomen in the primary health care. Turkish Journal of Emergency Medicine [Internet]. 2020 [cited 2024 Jun 19];20(1):1. Available from: https://doi.org/10.4103/2452-2473.276384
10. Mayo Clinic. Ultrasound [Internet]. Mayoclinic. 2022 [cited 2024 Jun 19]. Available from: https://www.mayoclinic.org/tests-procedures/ultrasound/about/pac-20395177
11. 11.Höhne E, Recker F, Dietrich CF, Schäfer VS. Assessment Methods in Medical Ultrasound Education. Frontiers in Medicine [Internet]. 2022 Jun 9 [cited 2024 Jun 19];9(1). Available from: https://doi.org/10.3389/fmed.2022.871957
12. Gupta P, Dwivedi AN, Gupta K, Jain M. Potential role of ultrasound in anesthesia and intensive care. Anesthesia: Essays and Researches [Internet]. 2011 [cited 2024 Jun 19];5(1):11. Available from: https://doi.org/10.4103/0259-1162.84172
13. Mecoli MD, Sahu K, McSoley JW, Aronson LA, Suryakumar Narayanasamy. The use of point of care gastric ultrasound and anesthesia management in pediatric patients with preoperative fasting non-adherence scheduled for elective surgical procedures: a retrospective study. BMC Anesthesiology [Internet]. 2024 Jul 15 [cited 2024 Jan 25];24(1). Available from: https://doi.org/10.1186/s12871-024-02628-0
14. Perlas A, Arzola C, Van de Putte P. Point-of-care gastric ultrasound and aspiration risk assessment: a narrative review. Canadian Journal of Anesthesia/Journal canadien d’anesthésie [Internet]. 2017 Dec 11 [cited 2024 Jun 19];65(4):437–48. Available from: https://doi.org/10.1007/s12630-017-1031-9
15. Godschalx V, Vanhoof M, Soetens F, Van P, Hadžić A, Van M, et al. The role of gastric ultrasound in anaesthesia for emergency surgery. European Journal of Anaesthesiology and Intensive Care [Internet]. 2023 Jan 1 [cited 2024 Jun 19];2(4):e0027–7. Available from: https://doi.org/10.1097/ea9.0000000000000027
16. Bassam SA, Zaghw A, Khan MJ, Arun N, Karmakar A. Airway Management in Full Stomach Conditions. wwwintechopencom [Internet]. 2020 Sep 17 [cited 2021 Apr 23];1(1). Available from: https://doi.org/10.5772/intechopen.93591