By Monique Findlay, Zheng Cheng Zhu
Key reference:
Sidhu, N. S., & Pozaroszczyk, A. J. (2023). “Do you feel hungry?”: Using gastric ultrasound to eliminate guesswork in perioperative airway management. Australasian Anaesthesia, 115–121. https://search.informit.org/doi/10.3316/informit.298917404141486
Key Points
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Gastric ultrasound is emerging as a valuable tool in the pre-operative assessment setting
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It can be used to evaluate gastric contents in patients with active reflux symptoms, uncertain fasting status, or when there are risk factors for delayed gastric emptying.
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Obtaining images of the stomach antrum is relatively straightforward, providing a quick and non-invasive method to estimate gastric content and inform clinical decision making.
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With appropriate training, it provides valuable information at the point of care in predicting the risk of aspiration and informs appropriate modifications to airway management.
Preamble
You are an anaesthetic trainee doing a morning list pre-op assessment for Ms. DM, a lovely 60 year old lady, BMI 30, here for her low risk elective laparoscopic cholecystectomy. Her medical history is significant for GORD and insulin dependent T2DM, for which she is on triple oral antihyperglycaemics + Ryzodeg 70/30 25u BD, and semaglutide weekly injection. She has correctly withheld her diabetic medications, including her semaglutide. When asked if she feels hungry after her fast, she says
“Not at all, I have very minimal appetite”
On your assessment of her aspiration risk, she fasted since 8pm last night and she reports some mild reflux.
You report back to your consultant, and mention that due to the reflux history and the semaglutide injection you are concerned about the risk of aspiration. However, you are not sure if you should cancel her surgery or proceed knowing those risks.
“Should we scan her stomach?”, your consultant asks
Aspiration during anaesthesia refers to the inhalation of stomach contents such as gastric acid and food particles into the lungs. It is a serious and potentially fatal complication. Assessment of aspiration risk is therefore fundamental to safe airway management.
Current practice is largely subjective whereby the anaesthetist must consider a combination of patient fasting status and risk factors for aspiration. This invariably introduces some variation, as depending on the perception of aspiration risk, patients may undergo a rapid sequence induction, surgery postponement, or conversely be at higher risk of aspiration should the risk be under-estimated.
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Impaired GOJ sphincter function |
Delayed gastric emptying |
Impaired airway reflexes |
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Gastro-oesophageal reflux disease Hiatus hernia Previous gastric surgery (gastric sleeve, roux-en-y, fundoplication) Increased abdominal pressure:
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Acute illness / emergency case Bowel obstruction / ileus Autonomic neuropathy
Gastroparesis Severe renal or hepatic impairment Medications
Preoperative anxiety |
Reduced GCS (anaesthesia) Previous major strokes Major trauma |
Table 1: Specific patient risk factors for aspiration
However, gastric ultrasound scan (USS) is emerging as a valuable tool that can be used to eliminate the guesswork and provide a rapid, objective assessment of gastric contents. By using specific probe placement and imaging techniques, the anaesthetist can obtain detailed images of gastric volume and contents.
Recommended approach to USS
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Have the patient positioned on their right side in the right lateral decubitus position- this ensures that gravity pulls any of the stomach contents into the antrum
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Place the USS probe just below the xiphoid process of the sternum, angled slightly toward the left shoulder to allow visualisation of the stomach antrum
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Evaluate the volume and content – gastric contents typically appear as black, fluid filled structure within the abdomen. Assess for the presence of solid material, fluid level and overall gastric distension
Based on the results of the bedside scan, patients can be broadly categorised as either low or high risk for aspiration. This enables a more nuanced approach compared to the traditional black-and-white “fasted” or “not fasted” paradigm. In fact, studies of gastric USS have highlighted concerning rates of “full stomach” in patients who have otherwise adhered to correct fasting times. By categorising gastric content into type of fluid versus solid components and assigning graded risk levels, anaesthetists can tailor their clinical approach based on the specific circumstances of each patient.
For instance, individuals with fluid-filled stomachs may require a shorter waiting period or different airway strategy compared to those with solid contents, allowing for a more individualised and targeted approach to preop planning. This approach acknowledges the variability in gastric emptying rates and the different factors influencing aspiration risk, ultimately enhancing patient safety.
Of course, the major obstacle to adopting bedside gastric scanning into routine clinical practice is its reliance on the skill and training of the operator. Given that ultrasound training is still not integrated in mainstream medical training, it remains under-utilised in clinical settings. With the right training, even novice scanners can achieve very high sensitivity and specificity. Accordingly, dedicated workshops and training are required in order to unlock the full utility of gastric ultrasound in clinical practice.
Conclusion
Your consultant wheels the USS to Ms. DM. After consenting, you apply the USS probe with Ms. DM in the right decubitus position under your consultant’s watchful eyes.
“There’s quite a dilated antrum with what appears to be solid matter”
As the patient’s operation is relatively urgent, she is intubated with a rapid sequence induction and extubated wide awake to ensure minimal risk of aspiration. She had a successful operation and went home the following day.
It is important to note that if patients have significant risk factors for aspiration risk but their gastric USS is that of low risk, many would still recommend adopting a conservative approach while this technique is validated. Next time you are faced with a patient with risk factors, gastric USS may aid in making a tailored decision to treat the patient as high or low risk of aspiration.
