I’m a nurse in a pediatric cardiac ICU. There is a debate within our unit about whether slow flow nipples, or standard nipples are best for feeding our complex kids. There is a belief among some of the staff that using a slow flow nipple makes the baby have to work harder to get the milk, thus tiring them out. Most of the studies I found about slow flow nipples don’t directly address whether they cause the baby to “work harder”/expend more calories, and many of the studies that I found are over 10 years old. I was wondering if you could advise me on what is the current, evidence based best practice.
Many preterm infants in the NICU and the vast majority of our infants in pediatric cardiac intensive care have a baseline increase in WOB and often intermittent if not frequent tachypnea related to their cardiac pathology. Clearly our HLHS infants are among the most fragile, but not unlike many of our NICU infants with CLD and typical cardiac infants, it is their baseline respiratory work that creates both endurance and safety concerns during PO feeding (Jadcherla, 2009). Our cardiac infants who are also former preterms have then an added co-morbidity that typically increases cardio-respiratory workload.
In addition, any cardiac surgery that involves the aortic arch (reconstruction, dissection nearby, the ductus arteriosus or L pulmonary artery; S/P Norwood procedure) presents a high risk for post-surgical LVCP (Averin et al, 2012) This then can add another level of concern for safety during PO feeding.
The aerobic demands of feeding superimposed on a baseline of increased cardiorespiratory work serve to increase the risk for aspiration in the pediatric cardiac.
Yet there is pressure sometimes on professional caregivers to “get our cardiac infants to eat”, with a well-intentioned goal of getting them home. Indeed, well-intentioned strategies, which are volume-driven, may include increasing the flow rate to empty the bottle, which can cause the infant to “fight the flow” to breathe. While medium and high flow nipples help to “empty the bottle”, there is no evidence that increasing the flow facilitates a safe swallow or promotes cardio-respiratory stability.
A faster flow rate can result in both physiologic stress and negative feeding behaviors for the infant, who may struggle to breathe when swallowing and breathing compete. It can lead to learned feeding refusals to feed and long-term feeding aversions. How often we observe feeding refusals and aversions in cardiac infants. This indeed may be a direct result of struggling to feed, given the inherent aerobic demands of feeding. Respiratory fatigue then sets in and compounds the negative experience. In addition, unfortunately, a well-intentioned caregiver may steer the infant back to sucking and ask him to continue, when he has disengaged. The risk then to aspirate increases.
Clearly our cardiac infants require instead an “infant-guided” approach to feeding, which optimizes respiratory stability, swallowing safety and positive learning experiences for the infant. This supports our long-term goal of good growth with a lifelong joy in eating.
There has been minimal research regarding flow rate and cardiac infants per se. Much of our understanding of flow rate and its impact on both intake and cardio-respiratory workload comes from research regarding preterm infants, who by their nature, typically have respiratory co-morbidities.
Offering a flow rate that is manageable promotes what Goldfield (2007) calls “islands of stability” for breathing and avoids the need for an urgent breath. The need for an urgent breath can be due to sucking too fast and then “running out of air”, which can in turn lead to desaturation, apnea, bradycardia and a cascade of physiologic decompensation; swallowing and its integrity will “defer” if you will, to breathing, and result in movement of the bolus into/toward the airway with that breath, leading to either symptomatic or silent aspiration. A flow which is not manageable inhibits “windows of opportunity” (Goldfield et al, 2006) to breathe, and thus the infant has to fight the flow” to breathe. Sucking, swallowing and breathing are complex processes even when considered separately. When an infant is fed, these processes must act together, working smoothly and efficiently, with highly accurate timing and coordination, to result in safe and efficient feeding. When both breathing frequency and depth are not optimally supported because too much time is spent in swallowing a larger volume of fluid delivered by a faster flowing nipple, ventilation is adversely affected. Al-Sayed and colleagues (1994) showed that slowing the rate of milk flow reduced ventilatory compromise. They reported that in term infants, taking more with a faster flow was at the cost of ventilation. An increased rate of consumption typical with a faster flow required an increased metabolic rate and increased swallowing frequency, which reduced ventilation. There work suggests that any feeding strategy that maintains intake with reduced frequency of swallowing (such as with a slow flow nipple) is likely to be ventilatory sparing. This is a critical component for our cardiac infants and can avoid the onset of respiratory fatigue and its attendant sequelae
A recent article by Pados and colleagues (2016) looks at effects of milk flow on the physiologic and behavioral responses to feeding in infants with HLHS (Hypoplastic Left Heart Syndrome). They remind us that feeding is a physiologically stressful event due to the need to coordinate suck-swallow-breathe and maintain adequate oxygenation during those aerobic demands. From their baseline, which often includes increased WOB and intermittent tachypnea, our cardiac infants have limited tolerance for further aerobic “work” that adversely affects ventilation. During frequent swallows, there is a repeated and prolonged disruption in ventilation during the time the airway is closed for swallowing. This may result in considerable physiologic distress for the cardiac baby with limited respiratory reserves, and may lead to disengagement, apnea, bradycardia and inadvertent bolus mis-direction leading to aspiration. A slower flow rate may assist the cardiac infant with maintaining baseline respiratory reserves and timing of the dynamic adjustments of airway opening and closing that surround the actual swallow. In their study, Pados et al observed physiologic and behavioral responses to a standard flow (Dr. Brown’s level 2) and a slow flow (Dr. Brown’s preemie). Results included the finding that the slower flow allowed the infant to maintain heart rate closest to baseline, and indeed a lower heart rate overall compared to the standard flow rate, suggesting the slow flow feeding was less physiologically stressful. Respiratory rate was significantly higher during slow flow feedings and change from baseline to feeding was greatest for the standard flow feedings. They suggest that the higher respiratory rate during slow flow feedings may be interpreted as being an indicator that slow flow feedings are more supportive, as the infant is able to breathe more often and more readily during feeding. Yet the infant’s average respiratory rate of 72 across all (both standard and slow flow) feedings is still worrisome. Given that integrating a pharyngeal swallow, which takes an average of one second, creates concern for inherent risk for airway protection, despite the flow rate offered. Because the study infant experienced adverse events with both flow rates, it reminds us that safe feeding for our cardiac infants is about much more than just a manageable flow rate. It takes understanding the physiology of infant swallowing, considering pertinent research that considers flow rate and physiologic stability, and then learning from the “communication” of our cardiac infants when they feed with a slow flow nipple and we provide co-regulated pacing and resting – how much calmer they look, how less excessive their WOB is, and how their volumes actually do increase (Shaker, 2013a).
Lau et al (1997, 2000) hypothesized in her study that preterm infants would feed more if the flow rate was unrestricted versus if milk flow occurred only when the infant was sucking. This was a great way to look at the difference in intake when flow was faster (less controllable) compared to a slower, more manageable “infant-guided” flow rate. Oral feeding performance was documented when milk delivery was “unrestricted”, as routinely administered in nurseries, versus “restricted” when milk flow occurred only when the infant was sucking. Proficiency (% volume transferred during first 5 minutes of a feeding/total volume ordered), efficiency (volume transferred per unit time) and overall transfer (% volume transferred) were calculated. Restricted flow rate enhanced all three parameters. With a slower flow rate, infants were less likely to have to struggle with milk flow when they need to pause to breathe. This is what Goldfield postulates is essential to coordinated swallowing with breathing. The infant’s ability to take more with a slower flow rate reflects how a manageable flow rate enhances intake. It promotes the essential respiratory reserves to “go the distance” like marathon runners, as it allows for frequent and deep breaths.
Although increasing the flow rate is considered a way to help a preterm infant ingest more volume, flow rate is actually negatively correlated with feeding efficiency. Using a randomized controlled trial, Chang and colleagues (2007) evaluated the effects of a crosscut nipple (faster flow) versus a single-hole nipple (slower flow rate) on feeding ability and stability. Preterm infants were more physiologically stable and used a more efficient sucking pattern with the slower flowing nipple than with the crosscut nipple. The infants ingested a greater volume with the slower flowing nipple as well (Chang et al, 2007).
It is important to note that any nipple ring tightened excessively will create a vacuum that does indeed require “more work” and could in effect create an artifact of fatigue. I always suggest we just “hand turn” the nipple ring to close it, but not “man turn it”. I find too tight a nipple ring is often an adverse factor when slow flow nipples are used, which does then indeed create too much “work”. But this is not flow-related, its caregiver related.
Parents of our cardiac infants need help learning to “listen” to their infant during feeding, responding sensitively to the infant’s communication during feeding about how the infant is tolerating the feeding, and titrating interventions accordingly (Shaker 2013a, Thoyre et al, 2013; Thoyre et al, 2012). If parents are focused on volume, that can then have adverse effects on the parent-infant relationship, which is established early on through co-regulated and communicative feeding interactions that build trust Shaker 2013b). This is not to say that volume is not one of the important measures of feeding integrity required for discharge. However, volume must be viewed in the context of the infant’s developmental strivings, and as the by- product of a quality feeding, in which the infant’s cues of both engagement and disengagement, despite the volume, are respected and honored (Shaker 2013a). When this happens, there is physiologic stability during feeding, and both underlying good nutrition and growth are optimized.
In both our large Level III NICU and our large cardiac surgical unit at Florida Hospital for Children in Orlando, we have started to make wonderful strides with staff and family in changing the misconception regarding slow flow nipples” making babies “work harder”. The improved feeding outcomes, more pleasant infant-guided feedings, and happier families speak for themselves.
I hope this is helpful! Thank you for asking how to best support successful feeding for our little ones in PCVICU.
Catherine S. Shaker, MS/CCC-SLP, BCS-S
Neonatal/Pediatric Speech-Language Pathologist
Florida Hospital for Children – Orlando
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