Ultrasound Assessment of Gastric Residual Volume in Obese Patients

Gastric emptying is a major risk factor for aspiration of gastric contents.Aspiration into the lungs represents a fatal complication that can occur during anesthesia.

Not only gastric emptying importance to anesthetists is related to aspiration but also it is important to determine the systemic availability of substances given through the mouth. Delayed gastric emptying represents a major danger as it causes nausea and vomiting and prevents a return to oral feeding. Lastly it may cause morbidity and mortality.

Both humoral and neural influences have their impact on emptying. Volume and composition of gastric food act as major determinants for the rate of gastric emptying. The effect of body weight on gastric emptying are inconsistent.

ASA fasting guidelines application represents the primary method to avoid aspiration as it ensures that stomach is empty before induction of anesthesia.

These guidelines cannot be applied on all cases as in urgent or emergent situations or in morbidities associated with delayed gastric emptying.

Ultrasound can be used perioperatively to asses gastric content and volume at bedside.

The objective of the current study is to evaluate gastric residual volume in obese patients versus healthy controls scheduled for elective surgery, using gastric ultrasound.

This prospective observational study was performed on 100 patients undergoing elective surgery from July 2019 to June 2020 at Fayoum University hospital after approval of the local institutional ethical committee (M420). A detailed informed consent was signed by the eligible participants before enrollment.

Our study adheres to the CONSORT guidelines. The study was conducted on 100 Patients were assigned to one of two groups of (50) patients in each group. Group obese ASA II from( 30-40) BMI, ASA III above 40 BMI without other comorbidities and group non obese ASA I control.Obese patients whose BMI \>30 and healthy patients whose BMI = 18-24.9 who was scheduled for an elective surgery were included in this trial. All patients were enrolled in the study aged above \>20 y. This study included patients scheduled for elective surgery after 8-hour overnight fast after a light meal.

Ultrasound scanning:

Focused gastric ultrasound by was performed by a trained physician in semi-sitting position then right lateral position using low frequency (2-5MHz) mindray curved transducer and mindray DP-20 ultrasound system. The antrum of the stomach was located in the epigastrium after a sweep of the probe from left to right subcostal margins. This could be done using left lobe of liver as an anterior landmark and descending abdominal aorta as a posterior landmark.

The antrum was considered to be empty if flat with juxtaposed anterior and posterior walls, fluid-containing if distended with thin walls and hypoechoic contents, solid -containing if distended with a content with mixed echogenicity according to antral shape and contents .

The antral cross sectional area (CSA) was measured using the two antral dimensions, craniocaudal (D1) and anteroposterior (D2) dimensions, according to the following equation: π \[D1×D2\]/4 provided that π = 22/7.

The gastric residual volume was calculated according to patient position as follows:

Bouvet and colleagues equation for semi-sitting position: gastric residual volume (ml) =215 + 57 log CSA (mm2) - 0.78 age (year) - 0.16 height (cm) - 0.25 weight (kg) - 0.80 ASA.

Perlas and colleagues equation for right lateral position: gastric residual volume (ml) = 27.0 + 14.6 × right-lateral CSA - 1.28 × age.

Using the classification of Ven de Putte and perlas, the study could asses the risk of aspiration as follows: (a) low risk of aspiration: patients with empty antrum and patients with gastric residual volume less than 1.5 ml/kg.(b) high risk of aspiration: patients with solid contents and patients with gastric residual volume more than 1.5 ml/kg.

Nasogastric tube (18-french) was inserted after induction of anaesthesia and endotracheal intubation. Aspiration of gastric contents was performed through gentle suction using 50 ml syringe with synchronous epigastric massage and gentle movement of nasogastric tube in and out for 10 minutes after confirmation of nasogastric tube position.

Statistical Analysis The collected data were organized, tabulated and statistically analyzed using SPSS software statistical computer package version 22 (SPSS Inc, USA). Numerical variables were not normally distributed and were presented as median and interquartile range (IQR); Mann-Whitney U test was used as a test of significant. Qualitative data were presented as numbers and percentages, and the chi-squared test was used to determine significance. A two-sided P-value of \<0.05 was considered statistically significant.

Sample size Sample size calculated using G-Power© software version 3.1.7 results with effect size (0.57), two sided (two tails) type I error 0.05 and power of 80%, each group should include at least (50) Subjects. the authors expected no dropout rates or missing data.

Eligibility Criteria:
Inclusion Criteria:

* Adult patients aged from 20 years to 60 years
* Patients scheduled for elective surgery after an 8-hour overnight fast after a light meal (200 ml milk, 50 g white cheese, and 120 g bread).
* American society of anesthesiologists physical status I-III.

Exclusion Criteria:

* Pregnancy
* Renal failure
* Liver cell failure
* History of upper GIT morbidity (hiatus hernia and gastric cancer)
* History of upper abdominal surgery.