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 Table of Contents  
Year : 2023  |  Volume : 13  |  Issue : 1  |  Page : 40-44

Comparison of ultrasound measured gastric volume in term-pregnant patients posted for elective cesarean section with nonpregnant elective surgery patients---An observational study

Department of Anaesthesia and Intensive Care and Obstetrics and Gynecology, PGIMER, Chandigarh, India

Date of Submission25-Mar-2022
Date of Acceptance03-Jun-2022
Date of Web Publication09-Mar-2023

Correspondence Address:
Dr. Subrata Podder
Department of Anaesthesia and Intensive Care, PGIMER, Chandigarh - 160 012
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/JOACC.JOACC_25_22

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Background: The pregnant patients undergoing anesthesia are at increased risk of aspiration due to decreased lower esophageal sphincter tone and mass effect of gravid uterus on gastric antrum. Ultrasound used as a noninvasive bedside imaging tool to measure gastric volume in term pregnant patients immediately before elective caesarian section (CS) may help in reducing aspiration induced morbidity and mortality. Methods: This observational prospective case--control study was conducted in 33 nonlaboring term pregnant patients immediately before elective CS and 30 nonpregnant patients immediately before elective surgeries, enrolled according to inclusion and exclusion criteria. A 2-5 MHz curvilinear probe was used to scan the participants in supine and right lateral decubitus (RLD) position in pre-recovery room. Visibility, qualitative grading (0,1, 2), anteroposterior (AP), and craniocaudal (CC) diameter, and cross-sectional area (CSA) of gastric antrum was measured. Gastric volume was derived from CSA using equations formulated by previous investigators. Results: Gastric antrum was visible in 27 (82%) of pregnant and 30 (100%) of nonpregnant patients in supine position (P = 0.014). In RLD position, 25 (75.7%) pregnant and 29 (96.7%) nonpregnant patients had antrum visible (P = 0.018). The qualitative grading was comparable (P = 0.064) in both the groups. In supine position, (P = 0.615), CSA in cm2 was 3.37 ± 1.31 and 3.54 ± 1.33, while in RLD position (P = 0.012), CSA was 3.98 ± 1.13 and 5.09 ± 1.85, in pregnant and nonpregnant patients, respectively. Conclusion: Gravid uterus sometimes impedes visualization of antrum by ultrasound in term pregnant patients immediately before elective CS and shows clinically similar gastric CSA when compared to nonpregnant patients, though statistically different in RLD position.
Trial registration number- NCT03380637

Keywords: Aspiration, gastric-antrum, gravid-uterus, term-pregnant, ultrasound

How to cite this article:
Bellapukonda S, Podder S, Kajal K, Prasad G R. Comparison of ultrasound measured gastric volume in term-pregnant patients posted for elective cesarean section with nonpregnant elective surgery patients---An observational study. J Obstet Anaesth Crit Care 2023;13:40-4

How to cite this URL:
Bellapukonda S, Podder S, Kajal K, Prasad G R. Comparison of ultrasound measured gastric volume in term-pregnant patients posted for elective cesarean section with nonpregnant elective surgery patients---An observational study. J Obstet Anaesth Crit Care [serial online] 2023 [cited 2023 Apr 1];13:40-4. Available from: https://www.joacc.com/text.asp?2023/13/1/40/371307

  Introduction Top

Gastric content aspiration remains a major perioperative complication and can cause significant morbidity and mortality.[1] In NAP4 study, reported anesthesia-related deaths due to aspiration was around 1 in 350,000.[2] Aspiration may result in aspiration pneumonitis, caused by sterile acidic gastric content induced chemical injury or aspiration pneumonia, caused by pathogenic bacteria colonized oropharyngeal secretion.[3],[4] Pregnancy increases the risk of aspiration and is a challenge to the anesthetist. Lower esophageal sphincter incompetence, distortion of the gastric antrum and pylorus, increased intraabdominal pressure predisposes pregnant to aspiration.[3] Marked airway edema, breast enlargement, obesity, emergency surgeries, results in a 3 to 11 times increased chances of failed intubation and aspiration.[5],[6] Ultrasonography as a noninvasive, bedside, imaging technique can be used to estimate preoperative gastric volume and likely aspiration risk in patients undergoing anesthesia and surgery.[7]

This study evaluates ultrasound as a noninvasive tool for estimating gastric volume immediately before elective cesarean delivery in term pregnant patients who are not in labor and compare it with nonpregnant females scheduled for elective surgeries. The visibility, qualitative grading and gastric antrum cross-sectional area (CSA) were measured in each participant and compared between the pregnant and nonpregnant population.

  Materials and Methods Top

This prospective observational case--control study was conducted for a period of one year. Approval was taken from the Institutional ethics committee (INT/IEC/2016/2703) and the clinical trial was registered with Clinical Trial.Gov (NCT03380637). Written informed consent was taken from all the participants. No fetal sex determination was done during ultrasound and declaration regarding the same was mentioned in the consent form.

All participants were thoroughly evaluated for the primary purpose of their admission and posted for elective surgeries by the concerned departments. Patients with any gastrointestinal pathology, any medication delaying gastric motility, Systemic lupus erythematous, Diabetes mellitus, gestational diabetes, hypothyroidism and those not willing to give consent were excluded. Thirty-three term pregnant patients and 30 nonpregnant female patients of ASA I & II, aged between 18 to 45 years, having BMI between 18.5 to 30 kg/m2, scheduled for elective lower segment cesarean section (LSCS) and elective surgeries, respectively, were included in the study.

They were instructed to fast according to the ASA fasting guidelines.[8] Ranitidine tablet 150 mg was given at night and in the morning 2 hours before surgery, in both the groups. Both the groups were scanned in the pre-recovery room immediately before anesthesia with ultrasound (Sonosite, FUJIFILM M-Turbo, USA) in supine and right lateral decubitus (RLD) position for gastric antrum. A 2--5 MHz frequency curvilinear probe was used to scan the patient in the sagittal and parasagittal plane. Gastric antrum image was made in the parasagittal plane in epigastric region between left lobe of liver anteriorly and pancreas posteriorly.[7],[9],[10],[11],[12],[13],[14] Aorta or inferior vena cava with superior mesenteric artery or vein were used as important vascular landmarks to determine the scanning plane of gastric antrum.[7],[9],[11],[12],[13] The largest and the best possible cross-sectional view was obtained at resting state. After the gastric antrum was clearly visualized, both quantitative and qualitative measurements were done. Quantitative assessment was done using two perpendicular diameters of anterio-posterior (AP), and craniocaudal (CC), with the largest possible cross-sectional area (CSA) of the gastric antrum. An average of three measurements was taken.

Outcome measures

The age, body mass index (BMI) and fasting interval were noted. The primary outcome measure was if the gastric antrum was visible or not (yes/no). The secondary outcome measures were grading of antrum, AP and CC diameters and CSA. Gastric volumes (GV) were derived from these measurements. The ultrasound scan was tried for 5 minutes and repeated three times before deciding about sonical nonvisibility of antrum. The image of gastric antrum, when visible, was evaluated qualitatively and 'classified as follows[11],[15] Grade 0---the antrum appears empty on both supine and RLD positions; Grade 1---gastric fluid is visible on the RLD position only, suggesting a small fluid volume; Grade 2---gastric fluid is observed in the antrum in both supine and RLD, suggesting a larger fluid volume.

For quantitative grading, AP and CC diameter was measured and formula for area of an ellipse (AP×CC×π/4) was used to calculate CSA. Gastric volume (GV) was derived from CSA using equation (1) "GV (mL) = 1199.99 + 4830.09 × log (CSA-Supine) – 5.84 × age – 90.94 × Height",[7] and (2) "GV (mL) = –3720.54 + 282.49 × log (CSA-RLD) –1.68 × weight"[7]

(These equations work well within the variable range used to create the model as, "age = 19 to 58 years, weight = 45 to 105 kg, height = 150 to 192 cm, CSA-Supine = 2.3 cm2 to 16.27 cm2, CSA-RLD = 4.88 cm2 to 20.18 cm2"). And also (3) "GV (mL) = 27.0 + 14.6 × CSA-RLD –1.28 × age",[14] in adult, nonpregnant, BMI ≤40 kg/m2, and can predict volume up to 500 mL.

Statistical analysis

The sample size was calculated from "gastric antral CSA" in pregnant and nonpregnant patients,[7],[16] using model for cohort studies, by methods of "Kelsey, Fleiss, and Fleiss".[17],[18] A sample size of 26 was obtained with a confidence interval of 95%, power of 90%. After accounting possible losses, a sample size of 30 was considered adequate for each group.

Age, height, weight, BMI, fasting interval, CSA of antrum, gastric volumes were presented in Mean ± SD. Visibility of antrum, grading in USG findings were represented as frequencies or percentage. Normality of the continuous data is checked, applying the Kolmogorov--Smirnov test. Unpaired student t-test was used to compare quantitative variable. Ultrasound visibility and grading were analyzed with Chi-square test. Age, height, weight, BMI, fasting interval, and various dimensions of gastric antrum were analyzed using Unpaired Student t-test. The association of BMI with CSA, and fasting interval with CSA, were analyzed using Pearson correlation coefficient. Comparability of derived formulae for measuring gastric volume was determined using Bland--Altman plot. Data analysis was done using SPSS Version 22.0 (IBM, USA) and Microsoft Excel 2010 (Microsoft, USA). All tests were two-tailed with 95% confidence interval and level of significance at 5% (P < 0.05).

  Results Top

The study had 33 ASA-2 pregnant patients and 30 ASA-1 nonpregnant patients (all the patients consented for study---no dropouts). The baseline parameters are depicted in [Table 1]. The pregnant patients were significantly younger (P = 0.003) when compared to nonpregnant patients. The fasting hours of pregnant patients was less (P = 0.002) when compared to nonpregnant patients. The visibility of gastric antrum is presented in [Table 2], the qualitative ultrasound grading is presented in [Table 3], and the measured dimensions are presented in [Table 4]. Calculated gastric volumes all three equations were comparable and presented in [Table 4]. Bland--Altman plot depicting gastric volumes obtained from equation 1 and equation 2 in the pregnant patients is shown in [Figure 1].
Figure 1: Bland-Altman plot depicting gastric volumes obtained from equation 1 and equation 2 in the pregnant patients

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Table 1: Baseline Parameters

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Table 2: Comparison of gastric antrum visibility in supine and right lateral decubitus position

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Table 3: Comparison of USG grading (Only if antrum is visible in both the positions)

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Table 4: Various dimensions of the gastric antrum

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  Discussion Top

The present study evaluated ultrasound as a noninvasive modality to measure gastric antral CSA and volume in term nonlaboring patients just before undergoing elective cesarean section and compared it with nonpregnant female patients posted for elective surgery.

All demographic variables between the groups were comparable except the age and duration of fasting. The pregnant group contained significantly younger patients and their duration of fasting was significantly less when compared with nonpregnant patients. However, these values were not clinically significant.

The antral visibility was significantly less in pregnant group when compared with nonpregnant group in both supine and RLD position [Table 2]. The gravid uterus may have displaced and subsumed the gastric antrum, thus decreasing the possibility to make a window with the ultrasound. According to our observation, the gastric antrum was more in the epigastric region towards the left in the pregnant patients, while it was visible in right hypochondrium in the parasagittal plane in the nonpregnant group. The visibility is comparatively less in the RLD position when compared to the supine position, as it is difficult to make the window in this position. The posterior wall of the gastric antrum was less visible in the pregnant population. It was observed in current study, that grade 0 patients were more in the pregnant group. The nonpregnant group patients had more 1 and 2 antral grading. The observed differences in grading were not statistically significant (P = 0.233).

Perlas et al.[7] commented in their study that gastric antrum was visible by ultrasound in 100% nonpregnant population. Carp et al.[19] in his study, among pregnant patients in active labor, stated that gastric antrum was visible in only 60% of them. Bataille et al.[16] observed that ultrasound is feasible in 96% of pregnant population in labor. Bouvet et al.[9] in two studies using ultrasound observed gastric antrum in 98.5% and 98.4% of nonpregnant population.[20] Zieleskiewicz et al. stated that ultrasound results were conclusive in 82.6% of fasted pregnant females in labor.[21],[22] Arzola et al.[23] in his study mentioned that gastric antrum was visible in 98% of the scanned term pregnant patients posted for elective caesarean section. Hakak et al.[24] assessed gastric contents in term nonlaboring pregnant patients, after a standardized light meal and fasting guidelines. This prospective study reported visibility of 90% with 13% grade 0 antrum, 78% grade 1 antrum, and 9% grade 2 antrum after 6 hours of fasting. Current study found that the ultrasonographic visibility of gastric antrum in pregnant population is less and this is statistically significant when compared to nonpregnant population. The findings are similar to other studies of antral visibility in term pregnant patients.

The secondary aim was to grade the visibility and measure the CSA. Volume was then calculated from equations formulated in previous studies7 Current study showed that despite the pregnant patients having significantly less fasting interval compared to nonpregnant patients, CSAs were less in the pregnant group when compared with nonpregnant group [Table 3]. This possibly is the result of mass effect of gravid uterus on the gastric antrum distorting, displacing, and compressing it. This compression decreases CSA, in contrast to the belief that the pregnant patients have increased CSA resulting in increased aspiration risk. The increased risk of aspiration in pregnancy is likely due to the distorted gastric antrum and decreased esophageal sphincter tone under the effect of the altered level of various hormones during pregnancy.[25]

A Bataille and colleagues,[16] in a prospective cohort study to determine the quality of gastric contents and its changes in pregnant patients in labor, who were given epidural analgesia reported decrease in antral CSA from 319 mm2 to 203 mm2 during labor. The subject of present study was not under the effect of labor. But the mass of uterus on the gastric antrum causing a decrease in CSA in parturient when compared to nonparturient were similar to our study.

A cross over study by Cynthia Wong et al.[26] assessed gastric motility in term, nonlaboring pregnant women without comorbidities and with normal BMI. They used both, serial ultrasound in 9 pregnant and paracetamol absorption in 11 pregnant females. This study observed that there is no delay in gastric emptying in this class of pregnant females after ingestion of 300 mL water compared to that of overnight fasting. Another cross-over study conducted by Cynthia Wong et al.[27] in term, nonlaboring, obese pregnant patients with similar methodology attained the same result. Our study showed that gastric antral CSA was less in pregnant group than nonpregnant group supporting the fact that there is no gastric delay.

Arzola et al.[23] conducted an observational cohort study in term pregnant patients. An ultrasound was done in 103 pregnant women after well-defined fasting guidelines. A qualitative grading was made based on the grading system proposed by Perlas et al.[11] Quantitative assessment was done after attaining still images of gastric antrum in the RDL position. This study concluded that perioperative ultrasound can be used for assessment of individual risk of aspiration. The upper limit of confidence interval for antral cross-sectional area in RDL position (95 percentile of normal findings) was decided to be 10.3 cm2. In our study, the largest CSA in RDL position was 4.2 cm2 in pregnant group and 7.5 cm2 in nonpregnant group, thus supports the conclusion of the above study about using ultrasound to assess the risk of aspiration.

Van de Putte et al.[28] conducted a single-center cohort study in nonlaboring term pregnant patients who were fasting and were scheduled for cesarean section. A standardized qualitative, semi-quantitative (Perlas grades) and quantitative (volume) assessment was made in pregnant patients and compared with nonpregnant females from a historical cohort. This study found similar baseline gastric volume in nonlaboring pregnant females and nonpregnant females. Our study agrees that the gastric antral volume is similar in both the groups.

Roukhomovsky et al.[29] analyzed gastric antral volume and antral contents in 34 pregnant patients by magnetic resonance imaging (MRI). This study was done assuming that stomach anatomical position is changed by the gravid uterus in parturient. Based on it, the authors developed a new mathematical model to predict gastric volume in pregnant patients. The study also proposed that a combination of qualitative and quantitative grading is more useful than a single entity. Our study with ultrasound also found a likely displacement of stomach by gravid uterus.

Perlas and colleagues,[7] from their study derived formulae for gastric volume calculation, which was used in our study. Mean gastric volume of 284.16 mL in pregnant patients and 297.78 mL in nonpregnant patients were derived from formula 1 and 303 mL in pregnant patients and 279.27 mL in nonpregnant patients were derived from formula 2. Formula 3 was not applicable to pregnant patients but was applicable to nonpregnant patients. Mean gastric antral volume derived from formula 3 was 57 mL. Negative gastric volume is physically not possible and so it should ideally be considered as zero. But as these are calculated volume and substituting all negative values as zero makes statistical analysis impossible, for calculating differences in volume we used the calculated negative values. Hence, Formulae 1 and 2 were comparable and were in agreement with each other as seen in the Bland--Altmann plot. [Table 3], [Figure 1]

The study has certain limitations, a strict fasting protocol was not followed with patients having 8 or more hours of fasting, inability to control patient's last meal composition, the possible effect of pregnancy on gastric motility, and the small sample size. Hence, more studies need to be done to improve the strength of the findings.

We conclude that ultrasound is a useful tool for assessing gastric volume in term pregnant patients but is more challenging than nonpregnant patients due to the mass effect of term uterus. Although, ultrasound measured antral cross-sectional area is statistically less in pregnant than nonpregnant population it is clinically negligible.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1]

  [Table 1], [Table 2], [Table 3], [Table 4]


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