In this investigation we elucidated characteristics of feeding performance among healthy, non-dysphagic breast- and bottle-fed infants throughout the first month of life using three commonly used measures of infant feeding performance. Key findings from this investigation indicate 1) what are commonly considered ‘imperfections’ in feeding performance appear to in fact be a normal developmental variant of healthy non-dysphagic infants within the first month of life; 2) these imperfections do not decline throughout the first month of life; and 3) breast feeding may offer some infants advantages in feeding quality when compared to bottle feeding.
This investigation is the first to the authors’ knowledge to delineate the frequency that healthy non-dysphagic infants exhibit what are commonly considered indices of feeding impairment. Of potentially greatest clinical significance are our findings suggesting it is likely a normal developmental variant for healthy term infants to periodically cough during feeds. Almost all of the infants in our investigation coughed during at least one of their monitored feeds, with the average infant coughing during 2 feeds per day. Of equal importance as the average values is consideration of the full range of performance across our sample, which indicates some infants did not cough at all, while others coughed the majority of feeds. These findings relating to coughing during feeds have tremendous clinical significance, where it is common practice for clinicians evaluating infants for feeding deficits to interpret a cough during a feed as an indicator of a physiologic swallowing impairment resulting in bolus airway entry that warrants instrumental evaluation and treatment.
Our findings suggest that coughing during feeds in itself does not necessarily signify the presence of a swallowing impairment that warrants treatment. Instead, they support the need to evaluate the clinical significance of these coughing episodes in the context of the infant’s respiratory health, weight gain, and the overall psychosocial components of the infant-caregiver feeding dynamic. All of the infants in the current investigation were in good respiratory health, following appropriate growth trajectories, and not exhibiting significant enough impairments to cause caregivers to seek the offered medical attention. As such, application of clinical interventions was not of clinical concern or clinically indicated. Future investigations examining how these measures of feeding performance differ among infants found to have documented physiologic impairments using videofluoroscopy to help aid clinicians in the interpretation of coughing reports among patients.
The cough reflex is an airway protective response that emerges from the early laryngochemoreflex to prevent the entry of foreign materials into the lungs (21). Previous research in human and animal models indicates this reflex can be triggered by stimulation not only to the laryngeal or tracheal region, but also the interarytenoid space and the underbelly of the epiglottis (21). In the first weeks of life, stimulation to these regions rarely manifests as a cough, and instead commonly manifests as obstructed apnea with rapid swallows to clear the bolus (21, 22). Within the first weeks of development, however, the maturation of the reflex causes the cough response to predominate (22). Understanding of the etiology and the purpose of the cough reflex raises important considerations in its interpretation. The first of these being whether the presence of a cough during a feed is viewed as a pathology, or if in fact it is viewed as an indicator of a functioning pulmonary protective reflexive system. One could argue that the absence of a cough during a feed could raise more questions regarding whether the integrity of these reflexive pathways that are key to facilitating pulmonary health are intact, and that potentially the patient who does not cough in response to stimuli is at greater risk for pulmonary morbidities. The other consideration this raises is the source of the stimulation. While the cough reflex can be stimulated by a bolus as it is ingested (anterograde), it is equally probable that the reflex is being stimulated by a retrograde refluxate event resulting from esophageal sphincter relaxation during the pharyngeal swallow (23). In this case it is important to note that gastroesophageal reflux, in moderation, is an established normal manifestation of immature infant neuromuscular immaturity (24) to which the cough response is a functional healthy protective mechanism.
Our findings relating to milk ingestion and caregiver perceived feeding performance also hold tremendous clinical relevance as they provide a form of clinician calibration for their expectations of infant feeding performance. It is common clinical practice in the acute care setting to schedule infants' feedings at rigid three-hour intervals, stopping feeds when the infant exhibits reduced levels of arousal, and limiting feeds to no longer than 20 minutes. Our results, however, indicate these practices are not being used to allow healthy term infants to thrive. For example, though we found infants consumed their feeds in an average of 20 minutes, there were many infants whose feeds were occasionally provided for 40–60 minutes. Likewise, 38% of caregivers reported their child falling asleep before the end of the feed with many needing to stimulate the baby to finish the feed to enable adequate hydration and nutrition in the first weeks of life. While the modification of these feeding variables is sometimes clinically necessitated for medically fragile infants to ensure adequate weight gain and rest for recovery, it is important for clinicians and caregivers of these infants to keep in mind that these artificial clinical confines may not fit normal developmental patterns as these infants become more stable and can tolerate the weaning of these clinical supports.
There are several important limitations that warrant attention in the consideration of these results. The first being these results were collected by caregivers without any video monitoring by study personnel for verification of findings. While such a methodology was necessary to enable accrual with the proposed study design, it is likely this had an impact on the provision of reporting when compared to monitoring in a lab environment. Despite the limitations in precision, this method offers the greatest clinical relevance to therapists gathering caregiver report. Another key consideration in the interpretation of these findings is the timing during which this study was completed. The vast majority of the participants underwent feeding and health monitoring during the peak of the COVID-19 pandemic. While COVID-19 certainly posed an exponential increase in health complications for much of the population, infants were largely unaffected by the early COVID-19 variants and in fact, had better systemic health during this time due to mandatory social distancing and mask wearing that stopped the spread of many common illnesses. This is likely reflected in our astoundingly healthy infants that rarely experienced illness as indicated on the systemic health questionnaire. Lastly, the sample size used in this investigation was used as it provided sufficient power to detect changes in feeding parameters within the first month of life, while also providing a feasible number of infants for longitudinal data collection. It is important to note that the establishment of true normative data requires substantially larger samples, often in the hundreds, that include patients with diverse demographic and social backgrounds. Future work using cohort or single time point data collection methods may enable greater accrual for more refinement in normative value establishment.