All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The exams can be performed using either a sector array (sometimes colloquially referred to as a &#34;phased array&#34;) or a low-frequency curvilinear transducer based on the sonographers&#39; preference. For the figures and scans, a curvilinear probe was used for the anterior sagittal views, while a sector array probe was used for the gastric body scans. The commercial details of the probes are provided in the Table of Materials.
1. Subxiphoid sagittal gastric antrum views (aka &#34;Subxiphoid Views&#34;)
<ol>
	<li>Supine view
	<ol>
		<li>Patient positioning: place the patient in the supine position. If the patient is unable to tolerate being fully supine, up to 30 degrees head up is an acceptable alternative.</li>
		<li>Probe selection: select any low-frequency probe (e.g., curvilinear or sector array) (see Table of Materials).</li>
		<li>Mode selection: set the preset to abdominal mode.</li>
		<li>Probe placement
		<ol>
			<li>Place the probe on the patient&#39;s sub-xiphoid region in the sagittal plane (Figure 1).</li>
			<li>Orient the probe marker in a cephalad direction.</li>
		</ol>
		</li>
		<li>Image optimization
		<ol>
			<li>Fan the probe from the patient&#39;s left to right until one can visualize the following structures on the screen: (1) liver on the left side of the screen; (2) pulsatile aorta in the long-axis deep in the image; and (2) gastric antrum just caudal and deep to the superficial liver edge (Figure 2).</li>
			<li>Ensure the abdominal aorta is positioned at the deeper edge of the image. If the inferior vena cava (IVC) is seen instead, correct the ultrasound beam angle if angled too far towards the patient&#39;s right. In this case, visualize the stomach at the pylorus level rather than the antrum. If that happens, adjust by fanning leftward until the aorta becomes visible. This is the appropriate position to analyze the gastric antrum (Figure 3). 
			NOTE: If only the stomach is visible at the IVC level and not the aorta, the qualitative sonographic data is still valuable, but remember that this view has lower sensitivity for detecting a &#34;high-risk&#34; stomach. In such cases, a volume assessment will probably underestimate gastric volume (Figure 3).</li>
			<li>Identify the muscularis propria (hypoechoic, thickest gastric wall layer) to ensure focusing on the stomach. Large, dilated bowel can be misidentified as the gastric antrum (Figure 4). 
			NOTE: The pancreas may be visible posterior to the gastric antrum (Figure 2).</li>
		</ol>
		</li>
		<li>Image acquisition: click on Acquire to save a video clip of this sonographic view.</li>
	</ol>
	</li>
	<li>Right lateral decubitus view
	<ol>
		<li>Patient positioning: position the patient in the right lateral decubitus (Figure 5).</li>
		<li>Probe selection: follow step 1.1.2.</li>
		<li>Mode selection: follow step 1.1.3.</li>
		<li>Probe placement: follow step 1.1.4.</li>
		<li>Image optimization: follow step 1.1.5.</li>
		<li>Image acquisition: follow step 1.1.6.</li>
		<li>Quantitative estimation of gastric volume
		<ol>
			<li>If the gastric antrum appears to contain only clear liquids, quantify the total gastric volume by obtaining an image of the gastric antrum as described above, with the patient in the RLD position (refer to step 1.2.5).</li>
			<li>When a view of the gastric antrum is obtained during its maximal expansion, freeze the image.</li>
			<li>Activate the Trace tool and trace out the cross-sectional area of the gastric antrum along the outer hyperechoic layer of the wall representing the serosa (Figure 6). 
			NOTE: An antral area greater than 10 cm2is unlikely consistent with normal baseline volume and suggests a &#34;full stomach&#34;.</li>
			<li>Click on Save.</li>
			<li>Estimate the gastric fluid volume using the following formula13: stomach volume (mL) = 27 + 14.6 ACSA (in RLD) cm2&#160;&#8722; 1.28 x age (years). 
			&#8203;NOTE: This formula has been validated for clear liquids in the antrum. This formula was also validated in a separate study of morbidly obese individuals14.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
2. Left upper quadrant (LUQ) gastric body views
<ol>
	<li>If subxiphoid views are inadequate or inaccessible, proceed to evaluate left upper quadrant views (step 2.2 and step 2.3).</li>
	<li>LUQ coronal gastric body view
	<ol>
		<li>Patient positioning: follow step 1.1.1.</li>
		<li>Probe selection: follow step 1.1.2.</li>
		<li>Mode selection: follow step 1.1.3.</li>
		<li>Probe positioning
		<ol>
			<li>Place the probe on the left mid-axillary line in the longitudinal plane with the orientation marker pointed toward the patient&#39;s head (Figure 7). 
			NOTE: With the probe marker oriented in this direction, the thoracic cavity will appear on the left side of the ultrasound scanner and the right side will be the abdominal cavity.</li>
		</ol>
		</li>
		<li>Image optimization
		<ol>
			<li>Identify the spleen and left hemidiaphragm. The spleen is identified by its rounded capsular shape. The left hemidiaphragm appears as a hyperechoic line, superior to the spleen, and moves with the normal respiratory cycle.</li>
			<li>Once the spleen is identified, fan posteriorly to identify the kidney, which will appear as the oblong structure inferior and posterior to the spleen. 
			NOTE: The spleen offers less of an acoustic window than the liver does on the right abdomen</li>
			<li>Once these landmarks are identified, angle the transducer in an anterior direction to obtain a view of the gastric body (Figure 7). 
			NOTE: The anatomic structures will likely shift as the diaphragm moves. If possible, consider asking the patient to briefly hold his/her breath while the scans are being performed.</li>
		</ol>
		</li>
		<li>Acquire the images following step 1.1.6.</li>
	</ol>
	</li>
	<li>LUQ anterior transverse gastric body view
	<ol>
		<li>Patient positioning: follow step 1.1.1.</li>
		<li>Probe selection: follow step 1.1.2.</li>
		<li>Mode selection: follow step 1.1.3.</li>
		<li>Probe positioning
		<ol>
			<li>Place the probe on the anterior surface of the patient&#39;s abdomen at approximately the mid-clavicular line, just caudal to the ribs (Figure 8). In order to fully assess the gastric body, it might be necessary to rotate the probe clockwise to an oblique view.</li>
		</ol>
		</li>
		<li>Image optimization: fan the probe cranial-to-caudal until the gastric body is seen deep into the spleen.</li>
		<li>Acquire images folllowing step 1.1.6.</li>
	</ol>
	</li>
</ol>

Gastric Ultrasound Technique for Mitigating Peri-Procedural Aspiration Risk

<ol>
	<li>Sakai, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+incidence+and+outcome+of+perioperative+pulmonary+aspiration+in+a+university+hospital:+a+4-year+retrospective+analysis.">The incidence and outcome of perioperative pulmonary aspiration in a university hospital: a 4-year retrospective analysis.</a> Anesthesia &amp; Analgesia. 103 (4), 941-947 (2006).</li><li>Delamarre, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anaesthesiologists'+clinical+judgment+accuracy+regarding+preoperative+full+stomach:+Diagnostic+study+in+urgent+surgical+adult+patients.">Anaesthesiologists' clinical judgment accuracy regarding preoperative full stomach: Diagnostic study in urgent surgical adult patients.</a> Anaesthesia Critical Care &amp; Pain Medicine. 40 (3), 100836 (2021).</li><li>Committee ASoA. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Practice+guidelines+for+preoperative+fasting+and+the+use+of+pharmacologic+agents+to+reduce+the+risk+of+pulmonary+aspiration:+application+to+healthy+patients+undergoing+elective+procedures:+an+updated+report+by+the+American+Society+of+Anesthesiologists+Committee+on+Standards+and+Practice+Parameters.">Practice guidelines for preoperative fasting and the use of pharmacologic agents to reduce the risk of pulmonary aspiration: application to healthy patients undergoing elective procedures: an updated report by the American Society of Anesthesiologists Committee on Standards and Practice Parameters.</a> Anesthesiology. 114 (3), 495-511 (2011).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Practice+Guidelines+for+Preoperative+Fasting+and+the+Use+of+Pharmacologic+Agents+to+Reduce+the+Risk+of+Pulmonary+Aspiration:+Application+to+Healthy+Patients+Undergoing+Elective+Procedures:+An+Updated+Report+by+the+American+Society+of+Anesthesiologists+Task+Force+on+Preoperative+Fasting+and+the+Use+of+Pharmacologic+Agents+to+Reduce+the+Risk+of+Pulmonary+Aspiration.">Practice Guidelines for Preoperative Fasting and the Use of Pharmacologic Agents to Reduce the Risk of Pulmonary Aspiration: Application to Healthy Patients Undergoing Elective Procedures: An Updated Report by the American Society of Anesthesiologists Task Force on Preoperative Fasting and the Use of Pharmacologic Agents to Reduce the Risk of Pulmonary Aspiration.</a> Anesthesiology. 126 (3), 376-393 (2017).</li><li>Koenig, S. J., Lakticova, V., Mayo, P. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Utility+of+ultrasonography+for+detection+of+gastric+fluid+during+urgent+endotracheal+intubation.">Utility of ultrasonography for detection of gastric fluid during urgent endotracheal intubation.</a> Intensive Care Medicine. 37 (4), 627-631 (2017).</li><li>Perlas, A., Chan, V. W., Lupu, C. M., Mitsakakis, N., Hanbidge, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasound+assessment+of+gastric+content+and+volume.">Ultrasound assessment of gastric content and volume.</a> Anesthesiology. 111 (1), 82-89 (2009).</li><li>Perlas, A., Van de Putte, P., Van Houwe, P., Chan, V. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=I-AIM+framework+for+point-of-care+gastric+ultrasound.">I-AIM framework for point-of-care gastric ultrasound.</a> British Journal of Anaesthesia. 116 (1), 7-11 (2016).</li><li>Yasuda, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Monitoring+of+gastric+residual+volume+during+enteral+nutrition.">Monitoring of gastric residual volume during enteral nutrition.</a> Cochrane Database of Systematic Reviews. 9 (9), CD013335 (2021).</li><li>Kothekar, A. T., Joshi, A. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gastric+Ultrasound:+POCUSing+an+Intolerant+GUT.">Gastric Ultrasound: POCUSing an Intolerant GUT.</a> Indian Journal of Critical Care Medicine. 26 (9), 981-982 (2022).</li><li>Lamm, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+role+for+gastric+point+of+care+ultrasound+in+postoperative+delayed+gastrointestinal+functioning.">A role for gastric point of care ultrasound in postoperative delayed gastrointestinal functioning.</a> Journal of Surgical Research. 276, 92-99 (2022).</li><li>Valla, F. V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gastric+point-of-care+ultrasound+in+acutely+and+critically+Ill+Children+(POCUS-ped):+A+Scoping+Review.">Gastric point-of-care ultrasound in acutely and critically Ill Children (POCUS-ped): A Scoping Review.</a> Frontiers in Pediatrics. 10, 921863 (2022).</li><li>Tankul, R., Halilamien, P., Tangwiwat, S., Dejarkom, S., Pangthipampai, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Qualitative+and+quantitative+gastric+ultrasound+assessment+in+highly+skilled+regional+anesthesiologists.">Qualitative and quantitative gastric ultrasound assessment in highly skilled regional anesthesiologists.</a> BMC Anesthesiology. 22 (1), 5 (2022).</li><li>Perlas, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Validation+of+a+mathematical+model+for+ultrasound+assessment+of+gastric+volume+by+gastroscopic+examination.">Validation of a mathematical model for ultrasound assessment of gastric volume by gastroscopic examination.</a> Anesthesia &amp; Analgesia. 116 (2), 357-363 (2013).</li><li>Kruisselbrink, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasound+assessment+of+gastric+volume+in+severely+obese+individuals:+a+validation+study.">Ultrasound assessment of gastric volume in severely obese individuals: a validation study.</a> British Journal of Anaesthesia. 118 (1), 77-82 (2017).</li><li>Perlas, A., Davis, L., Khan, M., Mitsakakis, N., Chan, V. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gastric+sonography+in+the+fasted+surgical+patient:+a+prospective+descriptive+study.">Gastric sonography in the fasted surgical patient: a prospective descriptive study.</a> Anesthesia &amp; Analgesia. 113 (1), 93-97 (2011).</li><li>Bouvet, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clinical+assessment+of+the+ultrasonographic+measurement+of+antral+area+for+estimating+preoperative+gastric+content+and+volume.">Clinical assessment of the ultrasonographic measurement of antral area for estimating preoperative gastric content and volume.</a> Anesthesiology. 114 (5), 1086-1092 (2011).</li><li>Cubillos, J., Tse, C., Chan, V. W., Perlas, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bedside+ultrasound+assessment+of+gastric+content:+an+observational+study.">Bedside ultrasound assessment of gastric content: an observational study.</a> Canadian Journal of Anesthesia. 59 (4), 416-423 (2012).</li><li>Van de Putte, P., Perlas, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrasound+assessment+of+gastric+content+and+volume.">Ultrasound assessment of gastric content and volume.</a> British Journal of Anaesthesia. 113 (1), 12-22 (2014).</li><li>El-Boghdadly, K., Kruisselbrink, R., Chan, V. W., Perlas, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Images+in+anesthesiology:+gastric+ultrasound.">Images in anesthesiology: gastric ultrasound.</a> Anesthesiology. 125 (3), 595 (2016).</li><li>Perlas, A., Arzola, C., Van de Putte, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Point-of-care+gastric+ultrasound+and+aspiration+risk+assessment:+a+narrative+review.">Point-of-care gastric ultrasound and aspiration risk assessment: a narrative review.</a> Canadian Journal of Anesthesia. 65 (4), 437-448 (2018).</li><li>Deslandes, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sonographic+demonstration+of+stomach+pathology:+Reviewing+the+cases.">Sonographic demonstration of stomach pathology: Reviewing the cases.</a> Australasian Journal of Ultrasound in Medicine. 16 (4), 202-209 (2013).</li><li>Kitai, Y., Sato, R., Inoue, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gastric+volvulus+suspected+by+POCUS+finding+in+the+emergency+department.">Gastric volvulus suspected by POCUS finding in the emergency department.</a> BMJ Case Reports. 15 (8), e250659 (2022).</li><li>Shokraneh, K., Johnson, J., Cabrera, G., Kalivoda, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emergency+physician-performed+bedside+ultrasound+of+gastric+volvulus.">Emergency physician-performed bedside ultrasound of gastric volvulus.</a> Cureus. 12 (8), e9946 (2020).</li><li>Cohen, A., Foster, M., Stankard, B., Owusu, M., Nelson, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+&amp;#34;Black-and-White+Cookie&amp;#34;+sign+-+a+case+series+of+a+novel+ultrasonographic+sign+in+gastric+outlet+obstruction.">The &amp;#34;Black-and-White Cookie&amp;#34; sign - a case series of a novel ultrasonographic sign in gastric outlet obstruction.</a> Clinical Practice and Cases in Emergency Medicine. 2 (1), 21-25 (2021).</li><li>Gottlieb, M., Nakitende, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+gastric+outlet+obstruction+using+point-of-care+ultrasound.">Identification of gastric outlet obstruction using point-of-care ultrasound.</a> American Journal of Emergency Medicine. 35 (8), 1207.e1-1207.e2 (2017).</li><li>Barbera, P., Campo, I., Derchi, L. E., Bertolotto, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emergency+ultrasound+in+trauma+patients:+beware+of+pitfalls+and+artifacts.">Emergency ultrasound in trauma patients: beware of pitfalls and artifacts.</a> Journal of Emergency Medicine. 60 (3), 368-376 (2021).</li><li>Di Serafino, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Common+and+uncommon+errors+in+emergency+ultrasound.">Common and uncommon errors in emergency ultrasound.</a> Diagnostics (Basel). 12 (3), 631 (2022).</li><li>Bouvet, L., Barnoud, S., Desgranges, F. P., Chassard, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+body+position+on+qualitative+and+quantitative+ultrasound+assessment+of+gastric+fluid+contents.">Effect of body position on qualitative and quantitative ultrasound assessment of gastric fluid contents.</a> Anaesthesia. 74 (7), 862-867 (2019).</li><li>Kruisselbrink, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diagnostic+accuracy+of+point-of-care+gastric+ultrasound.">Diagnostic accuracy of point-of-care gastric ultrasound.</a> Anesthesia &amp; Analgesia. 128 (1), 89-95 (2019).</li><li>Arzola, C., Carvalho, J. C., Cubillos, J., Ye, X. 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YB is an Editor for the American Society of Anesthesiologists Editorial Board on Point-of-Care Ultrasound and is the Section Editor for POCUS for OpenAnesthesia.org. SH is Editor-in-Chief of the American Society of Anesthesiologists Editorial Board on Point-of-Care Ultrasound. AP is an Editor for the American Society of Anesthesiologists Editorial Board on Point-of-Care Ultrasound. She also performs consulting work for FujioFilm Sonosite.

As stated previously, the primary purpose of gastric ultrasound is to evaluate gastric contents and assess risk before airway management or procedural sedation. The provided protocol outlines two main methods to capture images of the gastric antrum and body, aiding in this risk assessment. Additionally, reviewing the representative results section assists gastric sonographers in developing image interpretation skills. While a comprehensive discussion of medical decision-making is beyond this protocol's scope, this manusc...

Pulmonary aspiration of gastric contents can cause pneumonitis, pneumonia, and even death1. Higher volume, the presence of particulate matter, and higher acidity of aspirate have been shown to increase the severity of this scenario. Numerous factors help guide a clinician in assessing the risk of aspiration, including comorbid diseases that may slow gastric emptying times, mechanical gastrointestinal obstruction, and timing of the last oral intake. Historically, the latter relies solely on an assessment of the patient&#39;s history, which can be unreliable and inaccurate. In addition, clinician judgment has been shown to be poor to fair at diagnosing a full stomach2.
In 2011, a special task force appointed by the American Society of Anesthesiology (ASA) first published the guidelines for preoperative fasting, and these were updated in 20173,4. Although the ASA fasting guidelines are helpful, they are population-based and not tailored to specific clinical situations, and they recommend further consideration for patients with altered pathology, such as delayed gastric emptying or bowel obstruction. Furthermore, these guidelines rely on a patient who is an accurate historian and can correctly recall their last oral intake. Finally, the guidelines&#39; recommended fasting intervals may not be sufficient to ensure an empty stomach in urgent or emergency situations.
To address gaps in the published fasting guidelines and identify patients at high risk of aspiration, diagnostic point-of-care ultrasound (POCUS) imaging protocols of the stomach have been developed and validated by two separate author groups: one group consisting of intensive care unit (ICU) physicians, and the other of anesthesiologists. The ICU group5 focused on critically ill patients requiring urgent endotracheal intubation and developed a method to screen these patients for gross gastric distension by evaluating the stomach through the left upper quadrant (LUQ). In the LUQ, the authors used the spleen as a sonographic window to visualize the gastric body in the coronal and transverse planes to screen for qualitative signs of gastric distension. When gross gastric distension was identified, the authors took special airway precautions to minimize the chance of aspiration (e.g., by placing a nasogastric tube for gastric decompression [if not contraindicated] before induction of general anesthesia and endotracheal intubation). Separately, a group of anesthesiologists focused on perioperative patients developed a technique for screening stomach contents that would not be expected in properly fasted patients with normal gastric emptying6. This technique involves placing the ultrasound probe in a sagittal plane in the epigastrium to visualize the gastric antrum. The technique allows for both qualitative detection of high-risk stomach contents and, in cases of clear fluid, quantitative estimation of gastric fluid volume.
By combining these two protocols into a hybrid approach, this manuscript will abide by the I-AIM framework to categorize the key steps in gastric ultrasonography: indications, acquisition, image interpretation, and medical decision-making7. However, since this Special Collection is focused on diagnostic POCUS image interpretation, this manuscript will only briefly cover image interpretation and will largely defer the discussion of medical decision-making, as this falls outside the scope of this Collection.
Indications 
Gastric ultrasound has at least four possible indications. First, gastric ultrasound is indicated to screen for high-risk stomach contents prior to intubation or procedural sedation in situations when the patient&#39;s stomach volume and/or contents are either unknown or the history about gastric volume/contents is unreliable. In this setting, the gastric ultrasound exam is performed to risk-stratify the likelihood of pulmonary aspiration and adjust the patient&#39;s care to minimize this risk. Second, some intensivists have used gastric ultrasound to measure gastric residual volumes (GRV) in patients receiving enteral feeding8. In this case, assessing the gastric antrum can aid in the diagnosis of enteral feed intolerance and subsequently decrease the risk of aspiration pneumonia. Recently, gastric ultrasonography has been evaluated as a tool to measure antral cross-sectional area and has shown a strong correlation with GRV in ICU patients9. Third, gastric POCUS has been used to assess delayed bowel function and post-operative ileus in patients following surgical procedures10. Fourth, in pediatric patients, gastric ultrasound has been utilized to diagnose foreign body ingestion and pathologies such as pyloric stenosis11. For other pediatric applications of gastric ultrasound, readers are referred to other sources. The remainder of this article will focus on gastric ultrasound in adults11.
There are very few contraindications to gastric ultrasound because the exam is a non-invasive test that poses negligible direct harm to patients. The main absolute contraindication is patient refusal. Relative contraindications include any of the following: (1) dressings/wounds in the area of the usual scanning windows; (2) a lack of time to attempt the exam due to rapid deterioration of a patient&#39;s hemodynamic or clinical status; and (3) a very high or very low pre-test probability of a full stomach. Fortunately, the presence of intervening dressings/wounds can sometimes be addressed by choosing an alternate sonographic window. For example, if the anterior abdominal approach is obstructed, one can attempt a left lateral view and vice versa. A shortage of time can also be managed through deliberate practice, as studies have shown that gastric ultrasound can be performed expeditiously in expert hands12. Finally, there are cases where the pre-test probability of a full stomach is either very low (e.g., a healthy patient properly fasted for surgery) or very high (e.g., a patient presenting with a known, fixed intestinal obstruction). In such cases, gastric ultrasound is relatively contraindicated because the test - like all diagnostic tests - is imperfect and has the potential to generate false positive and false negative results that can lead patients in an inappropriate direction.
Acquisition 
For acquisition, it is recommended to begin with the subxiphoid sagittal approach to visualize the gastric antrum. The antrum represents an optimal anatomical location to measure gastric contents due to its consistent and superficial location. It constitutes the most dependent portion of the stomach and can be quickly identified in most patients6. Additionally, the gastric antrum dilates in a linear fashion as its contents increase, making it a suitable target for qualitatively assessing stomach contents and suggesting a risk stratification of gastric aspiration6. If the anterior sagittal window is not accessible (e.g., due to wounds/dressings) or provides indeterminate data, the left lateral window may offer useful qualitative data regarding a patient&#39;s gastric contents.
Regarding image interpretation and medical decision-making, the manuscript reviews a range of potential outcomes and explains how gastric ultrasound can be collaboratively used in distinct patient populations. Finally, the common pitfalls and limitations of these methods will be described.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>High Frequency Ultrasound Probe (HFL38xp)</td>
			<td>SonoSite (FujiFilm)</td>
			<td>P16038</td>
			<td></td>
		</tr>
		<tr>
			<td>Low Frequency Ultrasound Probe (C35xp)</td>
			<td>SonoSite (FujiFilm)</td>
			<td>P19617</td>
			<td></td>
		</tr>
		<tr>
			<td>SonoSite X-porte Ultrasound</td>
			<td>SonoSite (FujiFilm)</td>
			<td>P19220</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrasound Gel</td>
			<td>AquaSonic</td>
			<td>PLI 01-08</td>
			<td></td>
		</tr>
	</tbody>
</table>

gastric point of care ultrasound in adults: image acquisition and interpretation

Over the past two decades, diagnostic point-of-care ultrasound (POCUS) has emerged as a rapid and non-invasive bedside tool for addressing clinical inquiries related to gastric content. One emerging concern pertains to patients about to undergo sedation and/or endotracheal intubation: the elevated risk of aspiration from the patient&#39;s stomach contents. Aspiration of gastric contents into the lungs poses a serious and potentially life-threatening complication. This occurs more frequently when the stomach is considered &#34;full&#34; and can be affected by the techniques employed for airway management, making it potentially preventable. To mitigate the risk of peri-procedural aspiration, two distinct medical specialties (anesthesiology and critical care medicine) have independently developed techniques to utilize ultrasonography for identifying patients requiring &#34;full stomach&#34; precautions. Due to these separate specialties, the work of each group remains relatively unfamiliar outside its respective field. This article presents descriptions of both techniques for gastric ultrasound. Furthermore, it explains how these approaches can complement each other when one of them falls short. Regarding image acquisition, the article covers the following topics: indications and contraindications, selection of the appropriate probe, patient positioning, and troubleshooting. The article also delves into image interpretation, complete with example images. Additionally, it demonstrates how one of the two techniques can be employed to estimate gastric fluid volume. Lastly, the article briefly discusses medical decision-making based on the findings of this examination.

To ensure accurate visualization of the gastric antrum, it is necessary to probe deep enough to identify the aorta. Detecting the IVC instead places the scan at the gastric pylorus level, causing findings to underestimate genuine gastric content. While diagnostic utility remains for the gastric pylorus level, it iss less straightforward to interpret compared to the gastric antral view (Figure 3). Hence, a crucial task is to scan the great vessels and distinguish between the gastric antrum an...

Watch this Scientific Journal Video about Point-of-Care Ultrasound for Gastric Content Assessment and Risk Stratification in Perioperative Care at JoVE.com

Author Spotlight: Point-of-Care Ultrasound for Gastric Content Assessment and Risk Stratification in Perioperative Care 

This protocol introduces two methods for image acquisition in gastric ultrasonography. Additionally, tips are provided for interpreting this information to assist in medical decision-making.

Gastric Point of Care Ultrasound in Adults: Image Acquisition and Interpretation

Over the past two decades, diagnostic point-of-care ultrasound (POCUS) has emerged as a rapid and non-invasive bedside tool for addressing clinical ...

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2.4K Views.  George Washington University. This protocol introduces two methods for image acquisition in gastric ultrasonography. Additionally, tips are provided for interpreting this information to assist in medical decision-making.

Video: Author Spotlight: Point-of-Care Ultrasound for Gastric Content Assessment and Risk Stratification in Perioperative Care 

Point-Of-Care Ultrasound Screening for Proximal Lower Extremity Deep Venous Thrombosis

Acute lower extremity deep venous thrombosis (DVT) is a serious vascular disorder that requires accurate and early diagnosis to prevent life-threatening sequelae. While whole leg compression ultrasound with color and spectral Doppler is commonly performed in radiology and vascular labs, point-of-care ultrasound (POCUS) is becoming more common in the acute care setting. Providers appropriately trained in focused POCUS can perform a rapid bedside examination with high sensitivity and specificity in critically ill patients. This paper describes a simplified yet validated approach to POCUS by describing a three-zone protocol for lower extremity DVT POCUS image acquisition. The protocol explains the steps in obtaining vascular images at six compression points in the lower extremity. Beginning at the level of the proximal thigh and moving distally to the popliteal space, the protocol guides the user through each of the compression points in a stepwise manner: from the common femoral vein to the femoral and deep femoral vein bifurcation, and, finally, to the popliteal vein. Further, a visual aid is provided that may assist providers during real-time image acquisition. The goal in presenting this protocol is to help make proximal lower extremity DVT exams more accessible and efficient for POCUS users at the patient&#39;s bedside.

Traditionally, lower extremity deep venous thrombosis (DVT) is diagnosed by radiology-performed venous duplex ultrasound. Providers appropriately trained in focused point-of-care ultrasound (POCUS) can perform a rapid bedside examination with high sensitivity and specificity in critically ill patients. We describe the scanning technique for focused POCUS DVT lower extremity examination.

Acute lower extremity deep venous thrombosis (DVT) is a serious vascular disorder that requires accurate and early diagnosis to prevent life-threatening ...

Troubleshooting FoCUS Image Acquisition: Patient Positioning, Transducer Manipulation, and Image Optimization

Focused cardiac ultrasound (FoCUS) is a limited, clinician-performed application of echocardiography to add real-time information to patient care. These bedside exams are problem oriented, rapidly and repeatedly performed, and largely qualitative in nature. Competency in FoCUS includes mastery of the stereotactic and psychomotor skills required for transducer manipulation and image acquisition. Competency also requires the ability to optimize the setup, troubleshoot image acquisition, and understand the sonographic limitations because of complex clinical environments and patient pathology. This article presents concepts for successful, high-quality two-dimensional (B-mode) image acquisition in FoCUS.
Concepts of high-quality image acquisition can be applied to all established sonographic windows of the FoCUS exam: the parasternal long-axis (PLAX), parasternal short-axis (PSAX), apical four chamber (A4C), subcostal fourchamber (SC4C), and the inferior vena cava (IVC). The apical five-chamber (A5C) and subcostal short-axis (SCSA) views are mentioned, but are not discussed in-depth. A pragmatic figure illustrating the movements of the phased array transducer is also provided to serve as a cognitive aid during FoCUS image acquisition.

Here, we present a protocol to allow providers to perform focused cardiac ultrasound (FoCUS) in the clinical environment. We describe methods of transducer manipulation, review common pitfalls of transducer movements, and suggest tips to optimize phased array transducer use.

Focused cardiac ultrasound (FoCUS) is a limited, clinician-performed application of echocardiography to add real-time information to patient care. These ...

Point-of-Care Lung Ultrasound in Adults: Image Acquisition

Consultative ultrasound performed by radiologists has traditionally not been used for imaging the lungs, as the lungs&#39; air-filled nature normally prevents direct visualization of the lung parenchyma. When showing the lung parenchyma, ultrasound typically generates a number of non-anatomic artifacts. However, over the past several decades, these artifacts have been studied by diagnostic point-of-care ultrasound (POCUS) practitioners, who have identified findings that have value in narrowing the differential diagnoses of cardiopulmonary dysfunction. For instance, in patients presenting with dyspnea, lung POCUS is superior to chest radiography (CXR) for the diagnosis of pneumothorax, pulmonary edema, lung consolidations, and pleural effusions. Despite its known diagnostic value, the utilization of lung POCUS in clinical medicine remains variable, in part because training in this modality across hospitals remains inconsistent. To address this educational gap, this narrative review describes lung POCUS image acquisition in adults, including patient positioning, transducer selection, probe placement, acquisition sequence, and image optimization.

Point-of-care ultrasound (POCUS) of the lungs provides quick answers in rapidly changing clinical scenarios. We present an efficient and informative protocol for image acquisition for use in acute care settings.

Consultative ultrasound performed by radiologists has traditionally not been used for imaging the lungs, as the lungs&#39; air-filled nature normally ...

Point-of-Care Ultrasound: A Review of Ultrasound Parameters for Predicting Difficult Airways

Airway management remains a crucial part of perioperative care. The conventional approach to assessing potentially difficult airways emphasizes the LEMON method, which looks for and evaluates the Mallampati classification, signs of obstruction, and neck mobility. Clinical findings help predict a higher likelihood of difficult tracheal intubation, but no clinical result reliably excludes difficult intubation. Ultrasound as an adjunct to clinical examination can provide the clinician with a dynamic anatomical airway assessment, which is impossible with clinical examination alone. In the hands of anesthesiologists, ultrasound is becoming more popular in the perioperative period. This method is particularly applicable for identifying proper endotracheal tube positioning in specific patient populations, such as those who are morbidly obese and patients with head and neck cancer or trauma. The focus is on identifying the normal anatomy, correctly positioning the endotracheal tube, and refining the parameters that predict difficult intubation. Several ultrasound measurements are clinical indicators of difficult direct laryngoscopy in the literature. A meta-analysis revealed that the distance from the skin to the epiglottis (DSE) is most associated with a difficult laryngoscopy. An ultrasound of the airway could be applied in routine practice as an adjunct to the clinical examination. A full stomach, rapid sequence intubation, gross visual anatomical abnormalities, and restricted neck flexibility prevent using ultrasound to assess the airway. The airway evaluation is performed with a linear array transducer of 12-4 MHz, with the patient in the supine position, with no pillow, and with the head and neck in a neutral position. The central axis of the neck is where the ultrasound parameters are measured. These image acquisitions guide the standard ultrasound examination of the airway.

A point-of-care ultrasound (POCUS) is a simple, non-invasive, and portable tool that enables dynamic airway assessment. Several studies have attempted to determine the role of ultrasound parameters as an adjunct to clinical examination in predicting difficult laryngoscopies.

Airway management remains a crucial part of perioperative care. The conventional approach to assessing potentially difficult airways emphasizes the LEMON ...

A Modified Sonographic Algorithm for Image Acquisition in Life-Threatening Emergencies in the Critically Ill Newborn

The use of routine point-of-care ultrasound (POCUS) is increasing in neonatal intensive care units (NICUs), with several centers advocating for 24 h equipment availability. In 2018, the sonographic algorithm for life-threatening emergencies (SAFE) protocol was published, which allows the assessment of neonates with sudden decompensation to identify abnormal contractility, tamponade, pneumothorax, and pleural effusion. In the study unit (with a consulting neonatal hemodynamics and POCUS service), the algorithm was adapted by including consolidated core steps to support at-risk newborns, aiding clinicians in managing cardiac arrest, and adding views to verify correct intubation. This paper presents a protocol that can be applied in the NICU and the delivery room (DR) in relation to three scenarios: cardiac arrest, hemodynamic deterioration, or respiratory decompensation. 
This protocol can be performed with a state-of-the-art ultrasound machine or an affordable handheld device; the image acquisition protocol is carefully detailed. This method was designed to be learned as a general competence to obtain the timely diagnosis of life-threatening scenarios; the method aims to save time but does not represent a substitute for comprehensive and standardized hemodynamic and radiological analyses by a multidisciplinary team, which might not universally be on call but needs to be involved in the process. From January 2019 to July 2022, in our center, 1,045 hemodynamic consultation/POCUS consults were performed with 25 patients requiring the modified SAFE protocol (2.3%), and a total of 19 procedures were performed. In five cases, trained fellows on call resolved life-threatening situations. Clinical examples are provided that show the importance of including this technique in the care of critical newborns.

Here, we present a protocol that can be applied in the neonatal intensive care unit and the delivery room in relation to three scenarios: cardiac arrest, hemodynamic deterioration, or respiratory decompensation. This protocol can be performed with a state-of-the-art ultrasound machine or an affordable handheld device; an image acquisition protocol is carefully detailed.

The use of routine point-of-care ultrasound (POCUS) is increasing in neonatal intensive care units (NICUs), with several centers advocating for 24 h ...

Optic Nerve Sheath Point of Care Ultrasound: Image Acquisition

The goal of this protocol is to develop a standardized method for acquiring images of the optic nerve sheath and measuring the optic nerve sheath diameter (ONSD). Diagnostic ultrasound of the ONSD to detect intracranial hypertension has traditionally faced many problems because of methodologic discrepancies. Due to inconsistencies in the measuring techniques, the potential for ONSD to become a non-invasive bedside monitoring tool for ICP has been hampered. However, establishing a transparent, consistent methodology for measuring the ONSD would support its use as a valid and reliable method of identifying intracranial hypertension. This is important as it has both high sensitivity and specificity in acute care settings. This narrative review describes ONSD POCUS image acquisition, including patient positioning, transducer selection, probe placement, the acquisition sequence, and image optimization. Further, visual aids are provided to assist in real-time during image acquisition. This method should be considered for patients for whom there are concerns regarding intracranial hypertension but who do not have an intracranial monitor in place.

Point-of-care ultrasound (POCUS) of the optic nerve sheath diameter (ONSD) has been shown to be useful in identifying patients with increased intracranial pressure (ICP). However, the non-standardized technique for this POCUS has hampered its use. We present a standardized image acquisition protocol for use in the acute care setting.

The goal of this protocol is to develop a standardized method for acquiring images of the optic nerve sheath and measuring the optic nerve sheath diameter ...

Imaging the Abdominal Aorta with Point-of-Care Ultrasound

An Approach to Point-Of-Care Ultrasound Evaluation of the Abdominal Aorta

Disorders of the abdominal aorta, including aneurysms and dissection, have potentially high rates of morbidity and mortality. While computed tomography (CT) is the current gold standard to image the abdominal aorta, the process of obtaining a CT may be time-consuming, requires the use of intravenous contrast dye, and involves exposure to ionizing radiation. Point-of-care Ultrasound (POCUS) can be performed at the bedside and has excellent sensitivity and specificity for the diagnosis of abdominal aortic aneurysm and excellent specificity for the diagnosis of abdominal aortic dissection. Additionally, POCUS is non-invasive, cost-effective, lacks ionizing radiation, requires no intravenous contrast dye, and can be performed without taking the patient from a critical care area. Screening for abdominal aortic aneurysm (AAA) can be done in primary care settings as well. 
This article will review the approach to POCUS of the abdominal aorta to evaluate such critical pathology. In this paper, we will review the sonographic anatomy of the abdominal aorta as well as the choice of the ultrasound probe, description of POCUS image acquisition, and some pearls and pitfalls of using POCUS to aid in the diagnosis of potentially life-threatening abdominal aortic pathology.

Author Spotlight: Using Point-of-Care Ultrasound for Comprehensive Evaluation of the Abdominal Aorta

This protocol reviews the steps to image the abdominal aorta with point-of-care ultrasound. We discuss image acquisition, troubleshooting imaging pitfalls and artifacts, and the recognition of life-threatening abdominal aortic pathology.

Disorders of the abdominal aorta, including aneurysms and dissection, have potentially high rates of morbidity and mortality. While computed tomography ...

Ultrasound in Evaluating Diaphragm Dysfunction and Monitoring Treatment

Measuring Diaphragm Thickness and Function Using Point-of-Care Ultrasound

The diaphragm is the main component of the respiratory muscle pump. Diaphragm dysfunction can cause dyspnea and exercise intolerance, and predisposes affected individuals to respiratory failure. In mechanically ventilated patients, the diaphragm is susceptible to atrophy and dysfunction through disuse and other mechanisms. This contributes to failure to wean and poor long-term clinical outcomes. Point-of-care ultrasound provides a valid and reproducible method for evaluating diaphragm thickness and contractile activity (thickening fraction during inspiration) that can be readily employed by clinicians and researchers alike. This article presents best practices for measuring diaphragm thickness and quantifying diaphragm thickening during tidal breathing or maximal inspiration. Once mastered, this technique can be used to diagnose and prognosticate diaphragm dysfunction, and guide and monitor response to treatment over time in both healthy individuals and acute or chronically ill patients.

Author Spotlight: Unraveling the Impact of Mechanical Ventilation on Diaphragm Function and Patient Outcomes 

Diaphragm thickness and function can be assessed in healthy individuals and critically ill patients using point-of-care ultrasound. This technique offers an accurate, reproducible, feasible, and well-tolerated method for evaluating diaphragm structure and function.

The diaphragm is the main component of the respiratory muscle pump. Diaphragm dysfunction can cause dyspnea and exercise intolerance, and predisposes ...

Advancing Bedside Care: A Multidisciplinary Guide to Kidney-Genitourinary POCUS

Point-of-Care Kidney and Genitourinary Ultrasound in Adults: Image Acquisition

A range of conditions involving the kidneys and urinary bladder can cause organ-threatening complications that are preventable if diagnosed promptly with diagnostic imaging. Common imaging modalities include either computed tomography or diagnostic ultrasound. Traditionally, ultrasound of the kidney-genitourinary system has required consultative teams consisting of a sonographer performing image acquisition and a radiologist performing image interpretation. However, diagnostic point-of-care ultrasound (POCUS) has recently emerged as a useful tool to troubleshoot acute kidney injury at the bedside. Studies have shown that non-radiologists can be trained to perform diagnostic POCUS of the kidneys and bladder with high accuracy for a set number of important conditions. Currently, diagnostic POCUS of the kidney-genitourinary system remains underused in actual clinical practice. This is likely because image acquisition for this organ system is unfamiliar to most clinicians in specialties that encounter acute kidney injury, including primary care, emergency medicine, intensive care, anesthesiology, nephrology, and urology. To address this multi-specialty educational gap, this narrative review was developed by a multi-disciplinary group to provide a specialty-agnostic framework for kidney-genitourinary POCUS image acquisition: indications/contraindications, patient positioning, transducer selection, acquisition sequence, and exam limitations. Finally, we describe foundational concepts in kidney-genitourinary ultrasound image interpretation, including key abnormal findings that every bedside clinician performing this modality should know.

Author Spotlight: Developing a Bedside Protocol for Kidney and Genitourinary Ultrasonography

Point-of-care ultrasound (POCUS) of the renal and genitourinary (renal-GU) system can help to screen for certain causes of kidney dysfunction. However, despite its clinical utility, renal-GU POCUS remains underutilized due to a lack of training among clinicians. To address this gap, this article describes renal-GU image acquisition and interpretation.

A range of conditions involving the kidneys and urinary bladder can cause organ-threatening complications that are preventable if diagnosed promptly with ...

Ultrasound Protocol for Perioperative Frailty Assessment

Identifying Frailty Using Point-of-Care Ultrasonography: Image Acquisition and Assessment

Frailty is a significant predictor of a range of adverse outcomes in surgical patients, including increased mechanical ventilation time, longer hospital stays, unplanned readmissions, stroke, delirium, and death. However, accessible tools for screening in clinical settings are limited. Computed tomography of the psoas muscle is the current standard imaging device for measuring frailty, but it is expensive, time-consuming, and exposes the patient to ionizing radiation. Recently, the use of point-of-care ultrasound (POCUS) has emerged as a potential tool to determine the presence of frailty and has been shown to accurately predict frailty and postoperative outcomes. In this article, we will describe the image acquisition of the quadriceps muscles and explain how they can be used to determine frailty and predict postoperative adverse events. We will present information on probe selection, patient positioning, and troubleshooting. Images from a demonstration will be used to present the POCUS technique and example results. The article will culminate in a discussion of the use of these images in medical decision-making and potential limitations.

Author Spotlight: Assessing Surgical Frailty with Point-of-Care Ultrasound of Quadriceps Muscles

Here, we present a protocol to assess frailty in the perioperative setting using point-of-care ultrasound to measure quadriceps thickness. This method offers a practical, non-invasive alternative to traditional assessment methods, potentially enhancing perioperative care by quickly identifying frail patients.

Frailty is a significant predictor of a range of adverse outcomes in surgical patients, including increased mechanical ventilation time, longer hospital ...