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Direct Measures of Intestinal
Responses to Feeding

by Carol Lynn Berseth, MD

As increasing numbers of immature infants now survive, an important determinant of hospital length of stay is the time to establish full enteral feeding. However, approximately half of all very preterm infants experience feeding intolerance or an inability to achieve full enteral intake within the 10-day period after the initiation of feeding. Until recently, only indirect methods were available to assess whether infants were tolerating feeding, such as body weight measurements or the number of daily stools. Several new measures of intestinal function have been adapted for use in preterm infants to directly assess gut responses to feeding. One such measure used at Baylor College of Medicine is antroduodenal manometry—the measurement of muscle contractions in the wall of the stomach and upper portion of the small bowel.

These muscle contractions mix foods with hormones and other chemicals that the stomach and intestine produce. This mixing permits better digestion and absorption of foods. After foods have been fully utilized, muscle contractions then push the non-absorbable portion through the intestine for elimination. Studies have shown that the muscles in the intestinal wall of an infant do not contract the same way that they do in adults. The normal mixing activity of the muscles after feeding fails to occur in about half of very preterm infants. In addition, the coordinated contractions that are needed to achieve stooling are absent in most of these same infants. By measuring the absence or presence of these two types of muscle activity, investigators have shown that providing small feedings – as little as 20 mL per day – can hasten the ability of the intestinal muscles to work appropriately in the small immature infant and, thus, shorten the time to reach full enteral feedings. Other studies have shown that the use of specific feeding methods, such as infusing feedings over 60 or 120 minutes, triggers more adult-like muscle responses and a better ability to empty stomach contents. It should be remembered that other factors may impact appropriate muscle responses. For example, the use of routine medications, such as mydriatics, inhibits intestinal muscle contractions and results in worse feeding tolerance on the day of a screening eye examination for ROP.

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