Study objectives: To describe a method of the authors' design for estimating gastric volume quantitatively using ultrasound and to evaluate the usefulness of this method in the clinical setting.
Design: Prospective, two-phase clinical study.
Setting: University hospital. PATIENTS AND VOLUNTEERS: Phase 1 study: 31 patients who were undergoing general anesthesia and had no gastrointestinal disorder. Phase 2 study: 8 healthy volunteers.
Interventions: With each subject in the sitting position, a cross-sectional view of the stomach was obtained via ultrasound along the median line of the epigastric region. The cross-sectional area of the stomach (CSA) was measured by the analysis unit on the basis of the trace-enclosure method, and a mean value was obtained from triplicate measurements.
Measurements and main results: In the phase 1 study, CSA was measured after the patient had fasted for 1 hour, 4 hours, and more than 8 hours. CSA (cm2) was 19.2 +/- 0.9 cm2 at 1 hour, 11.0 +/- 0.7 cm2 at 4 hours, and 5.5 +/- 0.4 cm2 at more than 8 hours. That is, CSA significantly decreased as fasting time was prolonged (p < 0.001 for 1 hour vs. more than 8 hours and 4 hours vs. more than 8 hours). Most of the patients (87%) who fasted for more than 8 hours had a CSA less than 8.0 cm2. In the phase 2 study, after patients had fasted for more than 8 hours, CSA was measured both before and 5 minutes after the patient drank 50 ml of milk. CSA was 5.0 +/- 0.5 cm2 before and 8.5 +/- 0.9 cm2 after ingestion of the milk (p < 0.001). All subjects had a CSA less than 8.0 cm2 before drinking the milk, whereas only 2 of 8 patients had a CSA less than 8.0 cm2 after.
Conclusions: This method would be useful to estimate gastric contents quantitatively, and a CSA of 8.0 cm2 might be a valid indicator of an empty stomach.