Ultrasound Assessment of Gastric Volume

Abstract

To the Editor Using ultrasound, Perlas et al.1 assessed the accuracy of a 3-point grading system (0, 1, 2) describing the appearance of the gastric antrum and its correlation with gastroscopically measured fluid volume. As grade 1 was associated with gastric volume >100 mL in 23% of subjects, while gastric fluid volume was >100 mL in 75% of subjects with a grade 2, the authors concluded that this 3-point qualitative grading system could serve as a screening tool to differentiate between low and high gastric fluid volume states. However, based on the results of studies conducted in animals suggesting a volume of 50 mL (or 0.8 mL/kg) as a critical volume for severe aspiration in humans,2 it may be that a threshold of 100 mL above which patients were considered at risk of aspiration was too high. The pathophysiology of aspiration during general anesthesia involves several risk factors, any of which can lead to gastric distension and/or coughing, factors that may cause episodes of gastroesophageal reflux. The combination of a gastric volume >0.8 mL/kg with such risk factors may be sufficient to cause significant aspiration with pulmonary damage.3,4 As previously described, the cutoff value of antral area of 340 mm2 could be useful for diagnosing “risk stomach” (defined by a fluid gastric volume >0.8 mL/kg or presence of solid particles) with a high degree of accuracy.5 Furthermore, this measurement is easy to perform and does not require changing the patient’s position from supine to lateral decubitus; this measurement may also be more accurate than the pure qualitative system, since antral area correlated with gastric fluid volume.5 Therefore, we regret that the authors did not also assess this semiquantitative approach that we previously described to discriminate “empty stomach” from “risk stomach.”