Monitoring of feeding tolerance in preterm infants

Introduction

Preterm infants who tolerate enteral nutrition have more favorable outcomes. Yet, feeding a very premature baby via the enteral route can be challenging, particularly if the baby is born weighing less than 1500 grams. These premature babies require either a nasogastric or orogastric feeding tube because they are unable to coordinate sucking, swallowing, and breathing. Effective integration of these skills is necessary for safe oral feeding.

Because of gastrointestinal immaturity and the risk of feeding intolerance, enteral feeds via a gavage feeding tube are advanced slowly. Soon after birth, intravenous nutrition is necessary until full enteral nutrition is achieved. The practice of initiating and advancing enteral feeds can vary significantly among clinicians. Furthermore, feeding guidelines differ among NICUs. Some clinicians employ a slow, cautious approach, while others employ a faster approach.

In addition to variable feeding guidelines and practices, current clinical measures for monitoring feeding tolerance (gastric residual volume, abdominal circumference, bowel sounds, emesis, stool patterns, apnea, bradycardia, and desaturation) are nonspecific and poor indicators of gut maturity, tolerance, and feeding readiness. As a result, the interpretation of these findings can be subjective, leading to clinical interventions that vary among clinicians. There is great concern among some clinicians that a fast feeding advancement may lead to necrotizing enterocolitis (NEC), the most common gastrointestinal cause of morbidity and mortality affecting predominantly very-low-birth-weight preterm infants. The concern for NEC and the use of these nonspecific, unreliable measures contribute to delays, slow advancement, and frequent interruptions of enteral feeds in babies who otherwise may tolerate a faster advancement. This delay leads to prolonged intravenous nutrition that results in complications such as cholestasis, infection, and increased hospital stay and cost. However, no specific, reliable measure to monitor for feeding tolerance currently exists. Therefore, we depend on these unreliable clinical techniques that are poor predictors of tolerance and feeding readiness. Objective measures of feeding tolerance are needed for better assessment of gastrointestinal maturity and prediction of feeding readiness so that feeds can be advanced quickly and safely to help decrease morbidity and mortality in premature infants.

Feeding intolerance in preterm infants

Feeding intolerance is a combination of clinical signs suggestive of an inability by the patient to tolerate enteral nutrition. The definition of feeding intolerance varies among different authors. The most comprehensive definition in the literature is “the inability to digest enteral feedings presented as gastric residual volume more than 50%, abdominal distension or emesis or both, and the disruption of the patient’s feeding plan.” However, this definition of feeding intolerance is based on nonspecific clinical signs such as gastric residual volume, abdominal distension, and emesis. It does not provide the clinician with an instrument to differentiate between developmental feeding intolerance (DFI) resulting from gastrointestinal immaturity and dysmotility and pathologic feeding intolerance (PFI), which is associated with the ileus due to several conditions including NEC, spontaneous intestinal perforation, and bowel obstruction. Additionally, the “inability to follow a feeding plan” or guideline may depend on clinician preference or hesitancy, which can be unrelated to the presence of feeding intolerance. For example, the feeding plan may be altered if the clinician routinely stops enteral feeding during administration of indomethacin or pressors and during a sepsis evaluation or a procedure. Thus a more objective, specific definition of feeding intolerance is needed to guide clinical care and further research.

Feeding intolerance remains a major cause of morbidity in preterm infants, resulting in prolonged need for parenteral (intravenous) nutrition and central line access, which can lead to sepsis, cholestasis, prolonged length of hospital stay, malnutrition, and poor neurodevelopmental outcomes. In most cases, feeding intolerance represents a developmental condition that is related to anatomical and functional immaturity of the gastrointestinal tract; however, its clinical presentation can overlap with that of more serious gastrointestinal pathology. As a result, the clinician must interpret the clinical and prognostic significance of nonspecific clinical signs and symptoms, which is one of the most uncertain and unidentified problems in the nutritional management of preterm infants. Often, these nonspecific signs are interpreted incorrectly as PFI, leading to the inappropriate and prolonged cessation of enteral feeding or the limitation of feeding advancement in preterm infants who do not have any gastrointestinal pathology. The evaluation for PFI also exposes infants to the risks of intravenous antibiotics and radiographs. Thus morbidity that is associated with feeding intolerance is likely a result of our inability to differentiate DFI from PFI.

The lack of objective biomarkers makes it difficult to diagnose feeding intolerance and predict gastrointestinal pathology. There is a critical need to develop specific, reliable, and objective biomarkers that are validated to differentiate DFI from PFI in preterm infants. Development of these biomarkers will serve as a cornerstone for future research on early detection and treatment of PFI.

Current clinical assessment of feeding tolerance

The clinical assessment of feeding tolerance in preterm infants is limited by nonspecific measures. The following subsections describe the most common tools that are used daily in NICUs to monitor for feeding tolerance.