This study was a prospective, randomized controlled trial, which has been approved by the Medical Ethics Committee of Sichuan Orthopaedic Hospital, and all the enrolled subjects signed informed consent. It was also registered prior to patient enrollment at Chinese Clinical Trial Registry (http://www.chictr.org.cn; Registration number: ChiCTR2100043166; Scientific title: Safety Evaluation by Gastric Ultrasound for Drinking Glucose Beverages on Demand at 3 Hours Before Surgery; Principal investigator: Gang Zhang).
Inclusion criteria: Aged 18–60 years old, previously healthy, ASA grade I, BMI 18-25kg/m2. Exclusion criteria: Subjects with pregnancy, diabetes, metabolic disease, kidney disease, organic digestive disease, no use of drugs affecting the digestive system within one week before the examination. In order to better approach the patients with elective surgery, all subjects began fasting and abstaining satrictly adherence to guidelines before ultrasound evaluation. After at least 6 hours of fasting and drinking, the subjects were randomly divided into group C (Oral carbohydrate less than 400ml as needed) and group D (continue fasting and abstaining).
Several Important Time Points In This Study Were Defined As Follows
T0: the time the subjects in group C drank water immediately after 6 hours of fasting and abstinence, or the time the subjects in group D have been fasting and abstinence for 6 hours. T1: the time 1 hours after subjects in group C drinking water, or the time the subjects in group D have been fasting and abstinence for 7 hours; T2: the time 2 hours after subjects in group C drinking water, or the time the subjects in group D have been fasting and abstinence for 8 hours; T3: the time 3 hours after subjects in group C drinking water, or the time the subjects in group D have been fasting and abstinence for 9 hours
Gastric ultrasound was performed at T0, T1, T2, T3.
Ultrasound Scan Of Stomach
Antral antrum ultrasound examination was performed by an anesthesiologist with more than three years of ultrasound experience to observe gastric empties. The subjects were asked to lie on their backs and fully expose their abdomen. Ultrasound scans of the gastric antrum were performed in the supine position and the right supine position respectively. The specific scanning method was as follows: the abdominal low frequency convex probe with the frequency set at 2-5HZ was placed slightly to the right under the xiphoid. After slightly pressing down the probe, the left lobe of liver can be clearly seen in the scanning window, and the gastric antrum is usually located on the left side of the liver. At the same time, the superior mesenteric artery and abdominal aorta should be scanned in the ultrasound section, and this section was defined as the standard section. (Fig. 1)
Assessment Of Gastric Contents By Ultrasound
First, Perlas A semi-quantitative scale was used to evaluate reflux aspiration: Perlas 0, no stomach contents were found in neither supine or right lateral decubitus. Perlas 1: no stomach contents were found in supine position, but on the right side. Perlas 2, stomach contents were visible in both positions. Secondly, antero posterior diameter (AP) and CC craniocaudal diameter (CC), the long and short diameters of the gastric antrum in the patient's right lateral position, were measured in the standard interface at the end of expiration. The mean values of AP and CC were calculated after three measurements. The next step was to calculate the cross-sectional area of the gastric antrum (CSA) with the elliptic area calculation formula, namely CSA = π × D1×D2/4. Finally, the following mathematical models can be established to calculate gastric volume (GV) according to the cross-sectional area of the antrum (CSA): GV = 27.0+(14.6×right lateral antral CSA)-(1.28×age). This model is suitable for non-pregnant adult patients and the gastric volume can be reliably predicted to 500 ml. (Fig. 1)
According to the Perlas grading standard,[17] if the gastric antrum scan of both supine position and right decubitus position showed empty stomach, it was Perlas 0 of gastric antrum, indicating no gastric contents. If the supine position was empty, the gastric contents could be seen in the right decubitus position, it was Perlas 1 of the gastric antrum. If the gastric contents were visible in both positions, it was grade 2 of the gastric antrum. Based on this classification, the evaluation criteria of risk stomach is as follows: if the antrum is grade 0 or grade 1 with antrum area less than 340 mm2, it indicates an empty stomach. If it was grade 2 of antrum with an area larger than 340 mm2, indicating moderate gastric contents. If the antrum is grade 2, no matter how much the antrum area is, it indicates risk stomach.
At the same time, it is considered reliable to define a risk stomach with a volume greater than 1.5ml/kg.[13, 18] Based on this, dangerous stomach was defined in this study as Perlas grade 2, Perlas grade 1 with antral transsection area of 340mm2, or a gastric volume greater than 1.5ml/kg.
Measurement of outcomes
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Primary outcome measures: incidence of risk stomach:
Definition of dangerous stomach (meeting any of the following): Perlas semi-quantitative grade 2; Perlas semi-quantitative grade 1 with CSA greater than 340mm2; GV greater than 1.5ml/kg.
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Secondary outcome measures
The gastric volumes: The gastric volumes calculated by formula GV = 27.0+(14.6×right lateral antral CSA)-(1.28×age) at different time points;
Visual Analog Scale (VAS): In this study, 0–3 scale was used to evaluate hunger and thirst;
Hunger score: 0 indicates no hunger; A score of 1 indicates mild hunger; A score of 2 indicates obvious but tolerable hunger; A score of 3 is very hungry, can not stand or even appear dizzy, cold sweat and other symptoms;
Thirst score: 0 indicates no thirst; A score of 1 is slightly thirsty; A score of 2 indicates a significant but tolerable thirst; 3 points represents severe thirst.
Statistical analysis
SPSS20.0 statistical software was used for statistical processing and analysis of data. Measurement data conforming to normal distribution were expressed as mean ± standard deviation (x ± S), and Independent sample t test was used for comparison between groups. The statistical data were represented by the number of cases (percentage) n(%)), and the χ2 test was used for comparison. Non-parametric test was used to compare measurement and counting data that did not conform to normal distribution. α = 0.05 was used as the test level, P < 0.05 was considered to be statistically significant.