Clinical and Educational Article
`Water challenge´ to improve diagnostic accuracy in gastric point-of-care ultrasound
N. S. Sidhu
Consultant, Department of Anaesthesia and Perioperative Medicine, North Shore Hospital, Auckland, New Zealand
...
Correspondence to: N. S. Sidhu Email: [email protected] Accepted: 18 October 2022
Keywords: gastric ultrasound; point-of-care ultrasound; ultrasonography Twitter: @DrNavSidhu
Gastric point-of-care ultrasound (POCUS) is an emerging clinical tool. Two important learning elements in using this skill are:
(a) identifying the gastric antrum, including discerning it from other structures, and (b) differentiating an empty stomach from one that contains a small volume of late-stage solids (Fig.1a). The latter is vital if gastric POCUS is to be used to help minimise the risk of aspiration of gastric contents[1]. When faced with challenging sono-anatomy, novice operators mayfind difficulty in image interpretation and experienced help may not always be available, as gastric POCUS is yet to gain widespread adoption.
To solve this problem, the `water challenge´ has been developed, in which the patient drinks 40–50 ml of water followed by immediate rescanning in the right lateral decubitus (RLD) position. A previously unidentified gastric antrum should immediately become visible to the operator if present in the sonovisualfield. In addition, an empty antrum can be confirmed or ruled out because any solid matter can be visualised as `hyperechoicfloaters´ in the now water-filled hypoechoic antrum (Fig.1b–d).
Below, a clinical case is presented to illustrate the utility of this technique.
A previously well 71-kg patient in his mid-30s presented acutely for a laparoscopic appendicectomy with a three day history of abdominal pain, near-normal blood profile and no history of nausea or vomiting. Pre-operatively, he reported minimal pain without need for analgesia in the preceding 12 h. He had last eaten 13 h ago, felt hungry and was passingflatus. In the context of this presentation, regional practice is that a rapid sequence induction (RSI) is only `relatively´ indicated. Gastric POCUS was performed in the RLD position; the image was suspicious of a small volume of late solids. The patient was re-scanned after ingesting 40 ml water. Small hyperechoicfloaters were clearly visible in the water-filled hypoechoic antrum, bobbing in and out of view. The ingested water emptied within 10 min.
The ability to reliably identify and characterise the sonographic appearance of the gastric antrum is key to adopting gastric POCUS into routine clinical practice. A small volume of solid content present in the gastric antrum may be misinterpreted as an empty antrum by less experienced operators, potentially putting the patient at risk of pulmonary aspiration. Ingesting 40–50 ml of water poses no risk to the patient as water empties rapidly with a half-life of 15 min, and is below the 1.5 ml.kg 1safe gastric volume threshold for patients over 34 kg[2].
The `water challenge´ cannot be used in supine scanning because visualisation of fluid requires RLD-dependent positioning. The author teaches scanning in RLDfirst because an empty antrum (the most common finding) can only be confirmed in that position.
In conclusion, a `water challenge´ in gastric POCUS is a novel adjunct to aid identification of the gastric antrum in cases of difficult sono-anatomy and to confirm an empty antrum if the image is non-definitive, especially for operators learning the technique.
©2022 The Author.Anaesthesia Reportspublished by John Wiley & Sons Ltd on behalf of Association of Anaesthetists. 1 of 2 This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use,
distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
Anaesthesia Reports 2022, 10, e12192 doi:10.1002/anr3.12192
26373726, 2022, 2, Downloaded from https://associationofanaesthetists-publications.onlinelibrary.wiley.com/doi/10.1002/anr3.12192 by Cochrane Malaysia, Wiley Online Library on [03/01/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
Acknowledgements
Published with the written consent of the patient . NS is the convener of the POCUS North Shore Gastric Ultrasound Workshop.
No other conflicts of interest, and no external funding to declare. Open access publishing facilitated by The University of Auckland, as part of the Wiley - The University of Auckland agreement via the Council of Australian University Librarians.
References
1. Perlas A, Arzola C, Van de Putte P. Point-of-care gastric ultrasound and aspiration risk assessment: a narrative review.Canadian Journal of Anesthesiology2018;65: 437–48.
2. Fawcett WJ, Thomas M. Pre-operative fasting in adults and children: clinical practice and guidelines.Anaesthesia2019;74: 83–8.
Figure 1 Images from point-of-care ultrasound, obtained in right lateral decubitus position using 5–2 MHz curvilinear probe on
`abdominal´ setting. (a) Gastric antrum with clearly visible gastric wall mucosal folds and possibly containing a small volume of solid content; (b) following ingestion of 40 ml water, solid content is clearly seen as a `hyperechoicfloater´ in the antrum. The solid contentfloats in and out of view, at times appearing larger (c) or disappearing totally (d). Note that (b–d) are scanned at a shallower depth than (a). L: liver; A: antrum; Ao: aorta.
2 of 2 ©2022 The Author.Anaesthesia Reportspublished by John Wiley & Sons Ltd on behalf of Association of Anaesthetists.
Anaesthesia Reports 2022, 10, e12192 Sidhu | `Water challenge´ in gastric ultrasound
26373726, 2022, 2, Downloaded from https://associationofanaesthetists-publications.onlinelibrary.wiley.com/doi/10.1002/anr3.12192 by Cochrane Malaysia, Wiley Online Library on [03/01/2023]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
