PERIOPERATIVE MEDICINE • Ultrasound Evaluation of Gastric Emptying Time in Healthy Term Neonates after Formula Feeding

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PERIOPERATIVE MEDICINE • Ultrasound Evaluation of Gastric Emptying Time in Healthy Term Neonates after Formula Feeding

Source: ANESTHESIOLOGY 2021; 134:845–51


The current American Society of Anesthesiologists (ASA) fasting guideline for formula-fed infants in the periprocedural setting is 6 h before elective procedures requiring general anesthesia, regional anesthesia, or sedation/analgesia. For breastfed infants, the recommendations advise fasting “from intake of breast milk at least 4 h before elective procedures requiring general anesthesia, regional anesthesia, or sedation/analgesia (i.e., monitored anesthesia care)”.

These recommendations are based on category C3 level of evidence (equivocal literature from observational studies reporting inconsistent findings or do not permit inference regarding benefit or harm) regarding gastric volume and pH, and category D (insufficient evidence from literature) with regard to risks of pulmonary aspiration.

These recommendations do not consider the physiologic effects of prolonged fasting in very young infants and while many practitioners encourage babies to have clear fluids up to 2 h before the procedure, neonates and young infants may not accept clear fluids. Therefore, the current guidelines may put neonates and young infants at risk for dehydration and hypoglycemia.

Based on recent studies documenting the use of gastric ultrasound as a valid tool for the assessment of antral area in adults and older children to accurately predict gastric volume, this aim of this study was to generate evidence to support or refute current preprocedural non per os (NPO) guidelines for neonates. The authors hypothesis was that the gastric emptying time in healthy neonates after formula feeding would be less than the current guideline of 6 h of fasting.


All mothers in two NY hospitals on the postpartum well-baby units were screened to identify healthy full-term (postmenstrual age greater than or equal to 36 weeks) neonates aged 0 to 5 days who were formula-fed for possible recruitment.

Exclusion criteria included individuals who (1) required resuscitation at delivery; (2) were admitted to the neonatal intensive care unit; (3) were diagnosed with gastroesophageal reflux or other feeding difficulty; or (4) received any medication known to accelerate or delay gastric emptying, including but not limited to opioid-containing medications and antacids.

Participants underwent an initial ultrasound scan immediately before feeding to determine the baseline gastric antral cross-sectional area, then fed formula. This feeding volume was recorded. After feeding, serial ultrasounds of the gastric antral area were obtained every 15 min until the antral area returned to “baseline,” which was defined as within 10% of prefeeding measurements. The time lapse from gastric antral cross-sectional area before feeding until its return to baseline was considered the gastric emptying time, which was the primary outcome of this study.

Ultrasound Measurements and Calculations

Gastric antral ultrasound was performed with a high-frequency linear transducer in the sagittal plane with patients positioned in the right lateral decubitus position. Gastric antral cross-sectional area was measured using the two-diameter method where two perpendicular diameters (A, B) were measured and then the cross-sectional area was calculated by the formula for area of an ellipse: cross-sectional area = ¼ABπ. Cross-sectional area was then used to estimate the gastric antral volume using the following formula: gastric antral volume = (weight) × [0.009 × cross-sectional area − 1.36].


Forty-six neonates were included in the final analysis. There was an equal distribution of sex in the overall study group (males: 23 of 46 [50.0%]; females: 23 of 46 [50.0%]). Ages of participants were 1.5 ± 0.7 days. Their weights were 3.3 ± 0.5 kg, and gestational ages were 39.4 ± 1.4 weeks. Apgar score at 1 min was 8.6 ± 0.1 and at 5 min, 9.0 ± 0.2. The majority (91.3%) of neonates were of Hispanic race/ethnicity (42 of 46), and 58.7% were delivered via cesarean section (27 of 46).

The volume of formula fed in the participants was 29.7 ± 10.6 ml (9.0 ± 3.2 ml/k g). Overall, gastric emptying times ranged from 45 to 150 min, with a mean of 92.9 min (95% CI, 80.2 to 105.7 min; 99% discussion CI, 76.0 to 109.8 min). The median gastric emptying time was 90 min (interquartile range, 75 to 105 min).

Gastric emptying time was significantly less than the current NPO guideline of 6 h for formula.


In this study, the authors assessed gastric emptying times in healthy neonates in order to provide evidence to support or refute current NPO guidelines for formula as established by the ASA. Using serial ultrasonography in the neonatal population, the authors report gastric emptying times in this well-powered clinical trial.

They found that in 46 healthy full-term neonates aged 0 to 5 days, it took 92.9 ± 42.6 min to return to baseline antral cross-sectional area. The upper range of gastric emptying time was 150 min. There were no significant differences in gastric emptying time in subgroup analyses according to sex or mode of delivery.

These findings suggest that the current fasting guidelines may be more stringent than necessary by more than 3 h. These findings suggest that liberalizing fasting times may not only improve patient/ parental satisfaction but also minimize the risks of hypoglycemia and dehydration for the very young infant.