The infant will have physiologic responses to the work of feeding. If an infant is not able to cope with these responses physiological changes, stress reactions, and poor endurance may result. To assess physiologic control during feeding each parameter is evaluated at baseline, during feeding, and after feeding.
Heart Rate: In term infants heart rate is typically in the range of 120 to 140 beats per minute. It is not uncommon for see heart rate increases of about 10 beats per minute during feeding. Larger increases may indicate that feeding is placing excessive demands on the infant. Bradycardia (a drop in heart rate to below 100 beats per minute) can also be observed during feeding in the high-risk infant, and is a potentially life threatening event. Bradycardia might occur after oxygen desaturation, or with a suspected reflux event, or with position change. In some cases it is a vagally mediated response to stimulation of sensory receptors in the pharyngeal-laryngeal area. Bradycardia may be triggered via stretch receptors within the pharynx that may be stimulated by a large bolus. Touch-pressure receptors can be stimulated by the presence of nasogastric tubes, or chemoreceptors can be stimulated by microaspiration of food or by reflux of gastric content. Decreases in oxygen saturation can also lead to bradycardia.
Respiratory Rate: The most accurate method of measuring respiratory rate (RR) is counting the infant’s breaths. Normal values for term infants are 30 to 60 breaths per minute. During bottle feeding the respiratory rate is low while the infant is actively sucking. It is higher during pauses. This leads to an overall RR that is adequate for effective ventilation. During the early part of feeding, when the infant is sucking eagerly, the respiratory rate decreases significantly from baseline values. As the feeding progresses and the infant sucks less eagerly, taking more pauses to breathe, the respiratory rate increases toward baseline.
In infants with respiratory compromise RR can be significantly elevated. Infants who require a high respiratory rate to maintain homeostasis may not be able to tolerate the suppression in respiration that occurs in the early part of feeding. The infant may fatigue easily or may be at risk for aspiration as he or she tries to gasp for air. Respiratory rate during feeding is measured during pauses in sucking. IF RR is above 80 breaths per minute during these pauses, it often indicates that work of feeding is too great for the infant.
Studies indicate that term and preterm infants experience light, but measurable oxygen desaturation with feeding. For the compromised infant with borderline saturations, such reduction may be significant. If desaturation is observed during feeding evaluation, the pattern of desaturation should be noted. Sudden dips may be associated with apnea or bradycardic episodes, whereas a gradual decline may indicate inadequate respiratory support for feeding.
During feeding assessment without oxymetry, attention should be focused on the infant’s color around the mouth and eyes. If cyanosis is noted it is recommended that the infant be fed with an oximeter in place. A lack of color change with feeding, however does not necessarily imply that oxygen saturation is normal. Many infants can have relatively low oxygen saturation without external evidence such as cyanosis.
Endurance: Poor endurance may result in the infant terminating the feeding before taking the required volume, or demonstrating poor weight gain despite acceptable intake. Endurance is a reflection of the infant’s work to maintain homeostasis, work for other activity (such as feeding) and the infant’s cardiopulmonary reserve. Endurance is compromised by many disease processes that are more common in LBW infants.
Problems in any one of these processes or lack of coordination among these processes can have a profound effect on the infant’s feeding abilities. Within the pharynx, feeding and breathing share a common space. This dual role of the pharynx underlies the difficulties observed when sucking, swallowing, and breathing are not well coordinated.
Sucking: Sucking involves the rhythmic movements of the tongue and jaw, with support from the lips and cheeks, which create changes in pressure that cause liquid to flow out of a nipple. Sucking is comprised of two types of pressure, positive pressure (compression) and negative pressure (suction). Non-nutritive sucking occurs in a highly organized, repetitive pattern of bursts and pauses with a high ratio of sucks per swallow (6 to 8: 1) and 1 to 4 swallows per burst. Assessment of non-nutritive sucking on a gloved finger allows evaluation of the strength of the suck and relative amounts of suction and compression.
Nutritive sucking occurs during active feeding and has a more complex pattern than non-nutritive sucking. Preterm infants often have fewer or shorter bursts of nutritive sucking. At the beginning of a feeding the sucking pattern usually consists of long sucking outbursts with few or brief sucking pauses. The suck-swallow ratio is usually 1:1, but may increase toward the end of a feeding. In assessment of sucking in bottle-fed infants, return of bubbles into the bottle is a reflection of liquid flow out of the bottle. The strength of the infant’s suck is reflected in both the resistance to pulling the nipple out of the infant’s mouth and the rate of liquid flow. On the breast, the rate of sucking and the suck-swallow ratio can give indications of the rate of milk flow. The slower the sucking rate and lower the suck-swallow ratio, the faster the milk flow. When differences are noted in the quality of sucking between nutritive and non-nutritive sucking it is suggestive of problems with some aspect of suck-swallow-breath coordination.
Swallowing: Coughing or choking during swallowing can indicate that liquid is impinging on the airway. This can be liquid that is actually aspirated into the airway or that merely penetrates the airway and then is expelled. Aspiration can result from a primary swallowing dysfunction or from lack of coordination between sucking, swallowing, and breathing. Aspiration can be descending (during feeding), but can also be ascending (during gastroesophageal reflux). A history of frequent upper respiratory infection or pneumonia may be an indication that “silent” aspiration is taking place.
Clinical assessment of swallowing function includes: ability to handle secretions, presence of noise or wet sounding breathing during or after feeding. (Noises arising from the nasopharynx may indicate nasal reflux during swallowing, while noises in the pharynx may indicate residue left in the pharynx after the swallow), and the need for multiple swallows to clear a single bolus.
Infants who show signs of swallowing dysfunction should be referred for further assessment. The most comprehensive evaluation of swallowing occurs radiologically during the videofluoroscopic swallowing study (VFSS) or modified barium swallow.
· Respiratory effort: evaluation before, during, and after feeding. Increased respiratory effort is indicated by retractions at the neck, trunk, or rib cage, head bobbing, grunting or forced exhalation.
· Changes in respiratory pattern: observe whether there are excessive pauses or irregularities in breathing pattern. Short respiratory pause of 15 seconds can be considered normal at any age, but longer periods or those associated with cyanosis, pallor, or bradycardia are pathologic.
· Sounds of respirations. Noise heard during any part of the respiratory cycle may indicate airway obstruction or alteration in airway patency.
Coordination of Sucking, Swallowing, and Breathing: This is assessed by listening to the ratio of sucks to swallows and the timing and adequacy of respiratory efforts during sucking bursts. The normal rhythmic sucking pattern during bottle feeding consists of a series of bursts and pauses that begins as a continuous sucking pattern and changes to an intermittent sucking pattern over the course of the feeding. Normally recovery in all respiratory parameters occurs within the sucking pauses.
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