The Effect of Fasting on GI Motility

Ileus, a known postoperative side effect in humans, is estimated to occur in approximately 10% to 25% of surgical cases.

Potential contributing factors of ileus include the use of anesthesia and analgesia, as well as preoperative fasting. Ileus also has potential negative effects, including vomiting, prolonged surgical recovery time, and increased mortality.

Researchers at the University of Calgary in Canada recently performed a study to examine the effect of fasting on gastrointestinal (GI) motility in healthy dogs using 2-dimensional ultrasound techniques.

Study Design

Dogs included in the study were determined to be healthy based on normal physical examination findings, complete blood count, and serum biochemistry panel. Participants were excluded if they had acute or chronic GI problems, anorexia, or had been administered medications with GI effects within 2 weeks preceding the study.

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All dogs were fed twice daily. On the day of the study, dogs were fasted for 24 hours after receiving a regular morning meal. Abdominal ultrasound was performed for each dog at the following postprandial time points: 30 minutes and 3, 6, 12, and 24 hours. Dogs were fed after the 24-hour scan, and ultrasound was performed 30 minutes thereafter (the equivalent of 24.5 hours after baseline). Other than a 10-minute walk after each scan, dogs were not walked during the study.

The ultrasound examination consisted of placing the dog in left lateral recumbency and scanning the stomach, duodenum, and jejunum/ileum. Two observers independently recorded the number of GI contractions at each site over two 3-minute periods, then used the values to calculate average number of contractions per minute. The researchers also recorded whether food was present or absent in the GI lumen at each site.

Results

Two neutered male and 8 spayed female dogs with a median age of 6 years (range, 10 months to 13.5 years) participated in the study. Participating dogs represented 5 breeds and 5 mixed breeds.

Mean GI contraction rates at all 3 examined sites decreased steadily over the 24-hour fasting period, then increased at 24.5 hours (30 minutes after feeding was resumed). Contraction rates at the 12- and 24-hour time points were significantly lower than those at the 30-minute and 3-, 6-, and 24.5-hour time points.

Food material was present in the stomach, duodenum, and jejunum/ileum of all dogs at 30 minutes, 3 hours, 6 hours, and 24.5 hours during the study. One dog and 7 dogs lacked food at 1 or more sites after fasting for 12 and 24 hours, respectively. In all cases where food material was observed, GI contractions were also observed at the same site.

Major Finding

A 24-hour fasting period decreased peristalsis in all 3 examined sections of the GI tract; however, motility returned to normal when feeding resumed. According to the authors, the next research step should examine longer fasting periods, which may be more likely to cause persistent ileus.

Dr. Stilwell received her DVM from Auburn University, followed by a MS in fisheries and aquatic sciences and a PhD in veterinary medical sciences from the University of Florida. She provides freelance medical writing and aquatic veterinary consulting services through her business, Seastar Communications and Consulting.