Effect of instant oatmeal reconstitution methods on gastric emptying results

Objectives: Instant oatmeal is a common alternative to an egg-based meal for solid-phase gastric emptying (GE) studies for patients that have an egg allergy. However, since no standard of preparation for the instant oatmeal has been established, including within our own department, clinical reliability is limited. The purpose of this study was to determine the most effective reconstitution method of instant oatmeal for GE studies in order to obtain results similar to the egg-based meal.

Methods: Four healthy adult volunteers with normal gastric function, as determined by a detailed medical history questionnaire, were chosen to undergo GE scintigraphy. Participants ingested ^99mTc-sulfer colloid (SC) radiolabeled instant oatmeal on two separate occasions within a 7 day period varying only the oatmeal preparation method. One GE study was performed using “thin” oatmeal reconstituted with 2/3 cup (157 mL) of water, per microwavable instructions listed on the oatmeal box. The second study was performed with “thick” oatmeal prepared using water measured to the packet fill line (125 mL), as directed by the instructions on the oatmeal packet. After the water was added to the oatmeal, the contents were microwaved for a minute and a half in a 1500 watt microwave. ^99mTc-SC (1 mCi) was then added and stirred into the final oatmeal preparation, and served with one sugar packet and 300 mL of water. The patient was instructed to consume the entire contents of the meal within 10 minutes. Anterior and posterior static images of the stomach were acquired immediately upon completion of the meal along with 30, 60, 90, 120, 180, and 240 minutes post-ingestion using a gamma camera equipped with LEAP collimators. Processing was performed by manually drawing regions of interest (ROIs) around the stomach on the anterior images at each time interval and calculating the geometric mean. A time-activity curve was generated and the percent emptying for each time interval was recorded along with the time it took for half of the activity to leave the stomach (T½). The average T½ was then compared to our institution’s current egg-based normal values.

Results: The average emptying percent for the “thick” oatmeal at each time interval produced results of 57%, 76%, 86%, 90%, 97%, and 100% at 30, 60, 90, 120, 180, and 240 minutes, respectively. Meanwhile, the “thin” oatmeal yielded results of 64%, 78%, 85%, 90%, 98%, and 100%, for the 30, 60, 90, 120, 180, and 240 minute intervals, respectively. The average T½ was 36 minutes for the “thick” oatmeal and 23 minutes for the “thin” oatmeal, demonstrating that the “thin” oatmeal emptied 37% faster than the “thick” oatmeal. Additionally, processing of the “thin” oatmeal introduced ROI variances due to a significant amount of small bowel interference making the interpretation of the 0 and 30 minute images questionable.

Conclusions: This study demonstrated that the average T½ of the “thick” oatmeal (36 minutes) increased closer to the egg-based meal at our institution (91 minutes) than the “thin” oatmeal (23 minutes). However, the oatmeal emptying times were still considerably faster than those obtained from an egg-based meal. Implementation of a standard meal preparation for oatmeal gastric emptying studies, along with the creation of normal reference values, may produce more consistent/reliable results between patients and institutions. Further research is still needed to determine if there is an optimal method of instant oatmeal preparation that will more closely simulate a true solid phase gastric emptying study.