Ultrasound Assessment of Gastric Emptying
Condition: Pregnancy
Study type: Observational

Summary: 
      Hypothesis: The volume of gastric contents will be the same for a high protein drink versus
      ice chips as measured by ultrasound at 20 minute intervals for two hours in the laboring
      parturient.

      Specific Aim: To determine the volume of gastric contents at various time intervals (every 20
      minutes for 2 hours) in patients with an epidural that are given a high protein drink versus
      those that are given ice chips, with ultrasound.
    

Detailed description: 
      Since the 1940s women have had restrictions on oral intake during labor. This idea was first
      introduced by Mendelson, who raised awareness on the relationship between oral intake during
      labor and the risk of aspiration of acidic gastric contents if general anesthesia was needed.
      The aspiration of gastric contents could potentially result in severe maternal morbidity or
      mortality. As a result, women in labor who receive analgesia are typically restricted to just
      ice chips in order to prevent aspiration in the rare case that they may require general
      anesthesia for an emergent or stat cesarean section.

      However, recent literature reports that the actual risk of aspiration during labor is
      extremely low. The risk of aspiration is minimized due to improved general anesthetic
      techniques involving the use of non-particulate antacids to neutralize gastric acidity and
      rapid sequence induction to quickly secure the patients airway. Many countries have lenient
      policies on NPO status during labor, including the Netherlands and United Kingdom, who allow
      solid food intake during this period.

      The policy of "nothing by mouth" during labor and the relationship of aspiration of gastric
      contents were explored by Mendelson. He experimented on rabbits to explore the effects of
      gastric contents on their lungs. The rabbits only died when they aspirated material
      containing hydrochloric acid, and no deaths were due to aspiration of fluids with a neutral
      pH. Therefore, if oral intake in labor were to be permitted, the ideal characteristics would
      be for the substance to be in liquid form, isotonic, normothermic, pH of 7.4, and have a low
      residue.

      Labor can be compared to continuous moderate aerobic exercise and these women can experience
      a state of accelerated starvation. This state of starvation results in the production of
      ketones for an alternative source of energy. There is much debate about whether this
      production is harmful to the mother or fetus. A study done by Kubli in 2002 evaluated the
      effects of isotonic sports drinks and the production of ketones. The drinks decreased ketosis
      but proved no benefit regarding labor outcome (i.e. length of labor, spontaneous delivery
      rate). It is important to note that isotonic sports drinks do not contain a significant
      amount of protein.

      It is common for many women in labor to experience nausea and emesis. Protein intake during
      labor may have a beneficial effect in the prevention of nausea and emesis. The feeling of
      nausea is experienced when stomach muscles contract irregularly and protein has been shown to
      re-establish a normal, steadier, and slower rhythm. Protein has been believed to decrease
      incidence of nausea by decreasing these so-called gastric arrhythmias more so than a
      carbohydrate meal can (i.e. non-beneficial effect of isotonic sports drinks). It has also
      been shown that high protein intake decreases nausea and emesis in patients receiving cancer
      chemotherapy. Furthermore, it has been determined that administration of a protein-rich
      intake prevents nausea whether given 5 minutes or 45 minutes prior to the nauseating stimuli
      (i.e. cancer chemotherapy).

      It is traditionally thought that gastric emptying in pregnancy is delayed related to changes
      in hormones such as progesterone as well as the increased abdominal pressure on the gastrum.
      Perlas et al. has determined that bedside ultrasonography can be a useful non invasive tool
      to determine gastric content and volume and that the gastric antrum view is the best view to
      determine gastric volume. In their study of 18 healthy volunteers, a complete cross sectional
      view of the antrum was obtained 100% of the time, and they found the correlation coefficient
      to be 0.86 in the right lateral decubitus position. However, their study was not performed on
      pregnant women.

      Wong and colleagues have done several gastric emptying studies after ingestion of water using
      ultrasound on obese and non-obese non-laboring parturients. In their study of term non
      laboring women, they found gastric emptying half time was shorter (24 min vs. 33 min) after
      the ingestion of 300 ml of water than after 50 ml of water. In term obese pregnant women,
      they did not find any significant difference in gastric emptying after ingestion of 300 ml vs
      50 ml. In effect, all water in both studies was back to baseline level at 60 mins post
      ingestion.

      We are unaware of the gastric emptying time of protein solution in pregnant women. Barret et
      al. has determined that complete gastric emptying of a protein solution takes approximately 2
      hours as compared to 1 hour for a glucose solution, and 3 hours for a solid meal in healthy
      non pregnant adults.

      As a follow up to the protein study (PRO10070074), we plan on evaluating the gastric emptying
      of the protein drink and ice chips using ultrasound to determine gastric volume as described
      above.
    

Intervention name(s): Ice Chips; Protein Drink
Intervention type(s): Other; Other
Intervention description(s): 11 ounces of ice chips given to the laboring parturient; Patients will receive 11 ounces of a protein shake which contains 30 grams of protein
Other intervention name(s): Premier Nutrition Protein Shake (TM)
Observational model: Case-Control
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        All women of childbearing age (including children aged 14 years and above) who request
        epidural analgesia at Magee-Womens Hospital of UPMC will be eligible to participate in the
        study. The racial, gender and ethnic characteristics of the proposed subject population
        reflects the demographics of Pittsburgh and the surrounding area and/or the patient
        population of the University of Pittsburgh Medical Center Health System. Every attempt will
        be made to recruit subjects in respective proportion to these demographics.
      
Keywords: NPO; Gastric Emptying; Ice Chips; Protein Drink; Ultrasound