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A Stepwise Approach to Locating the Antrum During Gastric Ultrasound

  • Brandon Foster
    Affiliations
    Department of Anesthesiology and Pain Medicine, Stanford University School of Medicine, Stanford, CA
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  • Jeffrey Chen
    Affiliations
    Department of Anesthesiology and Pain Medicine, Stanford University School of Medicine, Stanford, CA
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  • Ban C.H. Tsui
    Correspondence
    Corresponding author: Dr. BCH Tsui, Professor of Anesthesia, Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University School of Medicine, 300 Pasteur Drive, Stanford, CA 94305, USA, Phone: (650)723-5728, Fax: (650)725-8544
    Affiliations
    Department of Anesthesiology and Pain Medicine, Stanford University School of Medicine, Stanford, CA
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Published:November 24, 2022DOI:https://doi.org/10.1053/j.jvca.2022.11.030
      We read with great interest the excellent work by Sharkey et al.1 on the national Delphi survey of anesthesia resident training in perioperative ultrasonography. We found the outcome of unanimity for gastric ultrasound intriguing. While the article provides no detailed explanation for why a consensus among experts cannot be reached, it may provide insight into why an objective evaluation with ultrasound is not commonly employed to confirm time-based "NPO" information. Most literature focuses on interpreting gastric ultrasound and whether it is a sensitive approach for evaluating stomach contents and NPO status. However, the technical and practical challenge of obtaining a view of the antrum has received little attention. Currently, anesthesiologists are not routinely receiving training in gastric ultrasound, and there is limited information on the learning curve for gastric ultrasound competency. In a cohort study of anesthesiologists who had both prior ultrasound experience and completed a training program, only 50 % attained proficiency.2 In another study,3 the investigators, who had completed 50 supervised gastric ultrasound scans, still found that 13% of their examinations were uninterpretable. These studies imply that the field could benefit from gastric ultrasound instruction that makes the skill accessible to novices. While the antrum is crucial for determining aspiration risk, many trainees need help visualizing it during ultrasonography workshops. Zhou et al.4 found that even the expert anesthesiologists could not visualize the antrum in 6 of 108 adult patients. Patient body mass index, bowel gas, and patient position significantly impact how easy it is to see the antrum. When first learning the technique, it can be challenging as there is no consistent method for using other anatomical landmarks as a reference point.
      From our teaching experience, we realize that one of the effective ways to educate trainees on performing gastric scanning for patients is first focusing on locating the antrum using a stepwise approach (Video 1; Figure 1). The key to the “RLSA” (rectus muscles, liver, stomach, antrum) stepwise approach. The scanning (Step 1) begins with a curved linear probe placed inferior to the xiphoid process in a transverse view, with the patient in a semi-recumbent position. The bilateral rectus muscles and their connecting fascia form a characteristic “bowtie” shape that can establish the patient's midline. (Step 2) Minimizing misperception from the various layers of subcutaneous tissues and fat, the plane of the liver can be quickly identified just below the rectus muscles (i.e., depth) and will eventually be seen with continued caudal probe movement down the midline. Continue to move caudally down the liver until a pancake/nugget shape of the stomach is visible. (Step 3) Once the stomach is located, the probe is rotated 90 degrees into the sagittal view to reveal the characteristic image of the cross-section of the antrum at the liver margin (“bullseye” appearance if the patient has an empty stomach). Additionally, we have found that first locating the cross-section antrum with this method and positioning can aid in visualizing the antrum in the right lateral decubitus.
      Figure 1
      Figure 1Stepwise gastric ultrasound. The patient's midline is first established by the bowtie shape formed by the bilateral rectus (R) muscles and its connecting fascia. Continue to move caudally down the liver (L) until a pancake/nugget shape of the stomach (S) is visible. The probe is rotated 90 degrees into the sagittal view to reveal the characteristic "bullseye" image of the antrum (A) if empty at the liver margin. (see video)
      Declaration of interests
      The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
      Contribution list:
      Brandon Foster: contributed, revised, approved, and is accountable for the final manuscript
      Jeffrey Chen: contributed, revised, approved, and is accountable for the final manuscript.
      Ban C.H. Tsui, MD: conceived, supervised, contributed, approved, and is accountable for the final manuscript

      Reference

      1. Sharkey A, Mitchell JD, Fatima H, et al: National Delphi Survey on Anesthesiology Resident Training in Perioperative Ultrasound. [Internet]J. Cardiothorac. Vasc. Anesth. [Internet]2022Retrieved from: https://linkinghub.elsevier.com/retrieve/pii/S1053077022005353
      2. Arzola C, Carvalho JCA, Cubillos J, et al: Anesthesiologists’ learning curves for bedside qualitative ultrasound assessment of gastric content: a cohort study. [Internet]Can. J. Anesth. Can. d'anesthésie [Internet] 60:771–9, 2013Retrieved from: http://link.springer.com/10.1007/s12630-013-9974-y
      3. Holtan-Hartwig I, Johnsen LR, Dahl V, et al: Preoperative Gastric Ultrasound in Surgical Patients who Undergo Rapid Sequence Induction Intubation. [Internet]Trends Anaesth. Crit. Care [Internet] 38:30–5, 2021Retrieved from: https://linkinghub.elsevier.com/retrieve/pii/S2210844021000599
      4. Zhou L, Yang Y, Yang L, et al: Point-of-care ultrasound defines gastric content in elective surgical patients with type 2 diabetes mellitus: a prospective cohort study. [Internet]BMC Anesthesiol. [Internet] 19:179, 2019Retrieved from: https://bmcanesthesiol.biomedcentral.com/articles/10.1186/s12871-019-0848-x

      Appendix. Supplementary materials

      Linked Article

      • National Delphi Survey on Anesthesiology Resident Training in Perioperative Ultrasound
        Journal of Cardiothoracic and Vascular AnesthesiaVol. 36Issue 11
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          Objective: To establish agreement among nationwide experts through a Delphi process on the key components of perioperative ultrasound and the recommended minimum number of examinations that should be performed by a resident upon graduation.Design: A prospective cross-sectional study.Setting: A survey on multiinstitutional academic medical centers.Participants: Anesthesiology residency program directors and/or experts in perioperative ultrasound.Interventions: A list of components and examinations recommended for anesthesiology resident training in perioperative ultrasound was developed based on guidelines and 2 survey rounds among a steering committee of 10 experts.
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