Preoperative Gastric Volume Assessment in Full-Term Pregnant and Non-Pregnant Females: A Prospective Observational Study

Introduction: Perioperative pulmonary aspiration (PA) of gastric contents is a serious anesthetic complication that can lead to significant morbidity and mortality. Obstetric patients, due to substantial anatomical and physiological changes, face a significantly higher risk of PA compared to non-pregnant individuals undergoing planned gynecological or other procedures.

Objective: The objective of this study is to compare gastric contents and volume through point-of-care gastric ultrasound (PoCUS) in full-term pregnant women and non-pregnant females scheduled for elective surgeries.

Methods: This single-center, prospective, observational study included 140 patients who underwent surgery between March 2022 and July 2023. Quantitative and qualitative measurements of the stomach were performed using PoCUS.

Results: The study included 140 patients with a mean age of 25±2.5 years (pregnant, range: 22-31 years) and 29±6 years (non-pregnant, range: 21-30 years), respectively. Patients in the pregnant group are classified as ASA II (70 (100%)), while those in the non-pregnant group (ASA I: 22 (31%); ASA II: 48 (69%)) are mixed. In Perlas, a 3-point grading system was used to classify the antrum based on the presence or absence of clear fluid in the supine position. The majority of the pregnant patients’ antrum levels were reported to contain clear fluid (37 (53%)), while in non-pregnant patients, they were empty (45 (64%)). The average gastric antrum cross-sectional area (302.63±4.87 cm²) and gastric volume (1.85±0.5 mL) were found to be high in pregnant females.

Conclusion: PoCUS was proven to be a simple, non-invasive method that can evaluate and offer a more precise bedside measurement of gastric volume, both qualitatively and quantitatively, in patients at risk for PA.

INTRODUCTION

Perioperative pulmonary aspiration (PA) of stomach contents is a rare event; its consequences can be catastrophic, especially in obstetrics, causing anesthesia-related morbidity and mortality (¹). Major morbidity events include conditions like acute respiratory distress syndrome, aspiration pneumonitis, aspiration pneumonia, brain damage, multiple organ dysfunction, and subsequent bacterial infections (²). The degree of PA-related morbidity is also largely dependent on pH, volume, and nature of the aspirated contents (³).

Incidents of PA are largely varied and highly dependent on the area of work or department. In a clinical setting, the general incidence of PA was reported at 2-7 per 20,000 anesthetic cases. However, its incidence was reported to be increased from 0.5% to 3% in emergency situations in the hospitals that were not within the operating room (⁴). To avoid any such instances and given patients' safety, preoperative fasting guidelines were designed by anesthesiology societies and the American Society of Anesthesiologists (ASA), providing direction for clinical practice in healthy patients undergoing elective surgeries (⁵). Even after considering all the set guidelines, fasting intervals are not reliable or applicable in emergency surgeries. Changes in anatomical and physiological conditions particularly affect obstetric patients.

Advanced technologies have emerged, yet there are no validated non-invasive tests available to assess the contents of the stomach. The application of point-of-care gastric ultrasound (PoCUS) as a diagnostic tool for assessing gastric volume was deemed straightforward and practical in clinical environments, particularly when gastric contents are unclear or uncertain (⁴,⁶-¹⁰). In these situations, clinicians evaluate the gastric antrum with strong intra-and inter-rater reliability and simultaneously obtain real-time data on the amount and type of gastric contents (solid, thick liquid, clear liquid, or none) utilizing PoCUS.

In this study, we aimed to compare gastric contents and volumes between fasting term pregnant patients and fasting non-pregnant surgical women posted for elective surgeries using PoCUS.

METHODS

Study Design

Ethical permissions were obtained from Saveetha College of Allied Health Sciences (SCAHS/IRB/2021/MARCH/060) on March 25, 2021 and from the Clinical Trials Registry -India (CTRI/2022/06/043329). This observational, prospective, comparative single-center study was conducted at a tertiary medical center from March 2022 to July 2023. Consent from all study participants was obtained before the start of the research.

Study Sample and Eligibility Criteria

A total of 140 eligible patients participated and were grouped as group A (n=70), representing the term pregnant females undergoing elective lower segment caesarean section (LSCS), and group B (n=70), representing non-pregnant female patients undergoing elective surgeries.

Patients aged between ≥18 and ≤45 years, with ASA scores of 1 and 2, and pregnant/nonpregnant female patients posted for elective surgeries were included. Whereas, patients of ASA score of 3 and 4, with multiple gestations, pre-existing abnormalities of the upper GI anatomy (previous surgery of the lower esophagus or stomach, hiatal hernia, and gastric malignancy), and who refused to give consent were excluded.

Fasting guidelines

Before going for elective surgery, all the patients have followed the recommended ASA fasting guidelines as presented: a minimum of two hours for consuming clear liquids, six hours for consuming light meals, and a minimum of eight hours for meals that include fried or fatty foods.

Preoperative procedures

A day prior to surgery, preoperative visits and thorough clinical evaluations were conducted by a multidisciplinary team, as required. All the patients were kept nil oral prior to surgery for 8 hours, and as a pre-medication, H2 blockers were given at night. On the next day after shifting to the operating theater, all the vital parameters were checked and recorded. Preoperatively, all the patients were examined using PoCUS (both qualitatively and quantitatively) by staff anesthesiologist.

Qualitative assessment of the antrum and patient’s classification as per the Perlas grading system

As per the Perlas’ grading system 1112(,) a 3-point grading system was used to classify the antrum according to the detection of clear fluid while in the right lateral decubitus (RLD) and supine positions.

Grade 0 – the antrum is empty in both RLD and supine.

Grade 1 – antrum with appreciable clear fluid in the RLD.

Grade 2 – antrum with clear fluid in both RLD and supine.

From the third trimester, instead of supine, semi-recumbent positions are preferred.

Quantitative assessment

The quantitative assessment was based on evaluating gastric volume by measuring the gastric cross-sectional area (GCSA). Whereas the gastric fluid volume was calculated using the formula by Schmitz:

Gastric volume (ml/kg) = [0.0093 X gastric central area (sq.mm) − 0.9]

Where gastric fluid volume ≤1.5 ml is considered safe, and more than >1.5 ml is considered higher risk.

Statistical Analysis

Data was descriptively analyzed using SPSS (Version 24.0, USA). The data is presented in frequency and percentation for each parameter.

RESULTS AND DISCUSSION

All 140 patients were divided into two groups with 70 patients each (group A for pregnant and group B for non-pregnant) to study the gastric volume. All participants were female, with a mean age of 25 ± 2.5 years for group A (range: 22-31 years) and 29 ± 6 years for group B (range: 21-30 years), respectively. All the patients of group A are of ASA II (70, 100%), and group B (ASA I: 22, 31%; ASA II: 48, 69%) is mixed.

Parameters	Pregnant (n=70)	Non-pregnant (n=70)
Qualitative
Age (years) [mean±SD]	25±2.5	29±6
Height (cm) [mean±SD]	157±6	158±6
Weight (kg) [mean±SD]	63±6	58±7
ASA Score [n (%)]
ASA I	--	22 (31)
ASA II	70

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