Evaluation of the Effect of Body Mass Index on Gastric Volume With Ultrasound in Term Pregnant Women

After approval by the Institutional Review Board, the investigators will obtain consent from patients. The consent will be obtained by the authorized personnel as per protocol, in which the investigators will explain to the patient the procedure, benefit, risk, cost and, confidentiality. The investigators plan to get the consent immediately after the patient arrived at the unit to avoid any interference with the delivery process. If the patient needs to go to an emergency cesarean section. This patient is not going to be included in the study. A gastric ultrasound with a low frequency (1-5 Hz) curvilinear array transducer using a Philips (CX-50) (Bothell, WA. USA) with image compounding technology, will be performed in each patient. The ultrasound procedure will be performed in the supine position and in a semi-recumbent right lateral position. The antrum will be identified in the sagittal plane between the liver, pancreas and aorta between peristaltic contractions. The ultrasound will be performed in each patient, in each position by three operators: two staff anesthesiologists and an anesthesia resident in presence of a medical student who will make sure that the standards for the procedure are uniform between operators (three images will be recorded by each operator per position in each patient). A qualitative assessment will be initially made, consisting of three grades: Grade 0, no fluid evidenced; Grade 2, clear fluid is evidenced only in right lateral decubitus position, and Grade 3, fluid is evidenced in both positions. Quantitative measurement of the cross-sectional area of the antrum (CSA) will be done by means of free tracing calipers. The full-thickness of the gastric wall will be included in the measurement and the average from the three images of each operator will be recorded. CSA will be calculated using the following formula:

CSA =(π x mean anteroposterior diameter x mean longitudinal diameter)/4

In addition to qualitative and quantitative ultrasound measures, the investigators will record demographic variables including age, BMI, weeks of gestation, gravity and parity.

The investigators plan to evaluate the existence of a relationship between cross-sectional area of the antrum (CSA) and BMI in term pregnant women using measurements of the CSA taken with free tracing calipers in ultrasound