Ultrasound assessment of gastric volume in children with raised intracranial pressure undergoing neurosurgeries

This is a prospective observational study involving pediatric neurosurgical patients with raised intracranial pressure undergoing neurosurgeries admitted to NIMHANS.

After obtaining written, informed consent from the parents or legal guardian data will be collected for the study. Preoperative assessment will be done by the attending anesthesiologist.

Gastric ultrasound examination:

Assessments will be conducted in the operating room, ward or preoperative holding area as per convenience so as not to delay the surgery. It will be done in two positions; Supine and Right lateral decubitus. Both qualitative (type of content) and quantitative (volume) assessments of gastric content will be performed and documented. A low-frequency curvilinear transducer will be used for large pediatric patients, while a linear high- frequency transducer will be used for patients under 40kg.

The patient will be placed on the operating table with their upper abdomen exposed, and conducting gel will be utilised as an acoustic medium. The patient will first be scanned while supine, and subsequently when they are in the right lateral decubitus (RLD) position. The stomach is visualised in the epigastric region on a sagittal plane, directly beneath the xiphoid and above the umbilicus. The antrum is located directly inferior to the left lobe of the liver. It resembles a superficial hollow viscus with a thick, multilayered wall. The inferior vena cava and the aorta are located posterior to the antrum. The amount of stomach fluid is quantitatively assessed using a standardised plane at the level of the aorta.

Using a high- frequency transducer, the five sonographic layers of the stomach wall will be seen while it is empty. From the inner to the outer surface, the five layers are as follows; The mucosal-air contact, muscularis mucosa, submucosa, muscularis propria and serosa. Only the muscularis propria is reliably seen when using a low-frequency transducer. Based on qualitative data, the nature of stomach content (empty, clear fluid, thick fluid/solid) can be determined.

1. Empty stomach- antrum flat or ovoid with no content.

2. Clear fluid content- antrum distended with homogenous hypoechoic or anechoic content.

3. Thick fluid or solid content- antrum distended with heterogenous hyperechoic or grossly particular content.

Qualitative assessment of gastric antrum will be done by the 3-point grading system

Grade 0- absence of content in a flattened antrum in both positions

Grade 1- fluid content visible only in the right lateral decubitus position

Grade 2- fluid content noticeable in both the RLD and supine positions

If clear fluid is present (grade 1 and grade 2 antrum) cross-sectional area will be calculated in the RLD position using the free tracing method (FTM) by using an ultrasound machine’s calipers to trace the circumference of the antrum including the outermost serosal layer.

The gastric volume will then be derived from the formula

Volume (ml)= -7.8 + (3.5 x CSA in RLD in cm2)) + (0.127 x age in months)

After qualitative and quantitative assessment, findings will be summarised as

1. empty stomach (no fluid or solid content visible)

2. low volume of clear fluid (<1.25ml/kg) consistent with baseline gastric secretions

3. high volume of clear fluid (>1.25ml/kg) suggesting greater than baseline gastric secretions

4. thick fluid or solid content.

A stomach will be categorised as "full" if there is evidence of any solid, echogenic content in the antrum with volume >1.5ml/kg) and "high risk" if there is evidence of any solid, echogenic content in the antrum with volume >1.25ml/kg. Peri-intubation events such as vomiting and aspiration of gastric contents will be noted.