Sucking behaviour using feeding teats with and without an anticolic system: a randomized controlled clinical trial

Infantile colic portrays a widespread problem with an uncertain prevalence of 5%–40% [1] within the first 4 [2] or 6 months [1] of an infant’s life. The occurrence is difficult to identify due to differences in classification, methods of data collection, study design, and parents’ perception of defining colic [1].

Although the history of research now reaches over 115 years, based on the paper of Zahorsky [3], the etiology of infantile colic still remains unknown [4]. As a result, therapeutic interventions to reduce the severity of symptoms and crying episodes are lacking their effectiveness [4, 5] and stressed parents seeking alternative methods to cope with their suffering infants. In this situation parents are susceptible to promises made by manufacturers of feeding bottles. Numerous bottle-nipple systems (BNSs) are available on the market, advertised to reduce infantile colic. The idea behind those so-called “anticolic” teats is to prevent excessive air swallowing (aerophagia) during feeding. It is estimated that 70% of the gastrointestinal gas is swallowed [6] and it was hypothesized that a substantial proportion of air could accumulate, leading to symptoms of distension, discomfort [7, 8], or colic [9, 10].

Studies on the relationship between vented BNS and reduction of infant colic symptoms are limited. Available information is based on subjective assessments like expert opinion [11], parents’ recordings of infant’s level of arousal, sleep states [12] and questionnaires to rank infant’s symptoms on a Likert-type scale [13].

Studies on direct measurement of air swallowing during bottle-feeding are not available. However, BNSs were assessed concerning suck-swallow-breath coordination in relation to breastfeeding [7, 14]. It was speculated that increased air swallowing leads to air accumulation in the stomach which may cause gastric upset and that pulse oximetry measures may help to clarify post feeding distress [7].

To examine the effect of a vented “anticolic” teat on suck-swallow-breath coordination we investigated the sucking behaviour of infants bottle-fed with vented teats (VTs) and nonvented teats (NVTs). We hypothesize that an uncoordinated random-like sucking behaviour implies more stress in terms of increased sucking frequency, oxygen desaturation, increased cardiorespiratory parameters, leading to a higher risk of aerophagia.

The aim of this study was to investigate differences in sucking behaviour of infants bottle-fed with vented and nonvented teats. We hypothesized that possible differences of milk flow may result in uncoordinated sucking, implying more stress in terms of oxygen desaturation, increased heart and respiratory rates, and increased sucking frequency, leading to a higher risk of aerophagia. We used a mixed approach consisting of a parents’ self-administered, non-validated questionnaire and a monitoring of infants’ heart and respiratory rates and oxygen saturation before, during, and after feeding.

Various studies have investigated topics related to nutritive and nonnutritive sucking and their mechanisms and various BNSs and how they influenced the infant, but as far as we are aware, no previous studies have been published, comparing the sucking behaviour in full term infants using vented and nonvented teats. For this reason, our results cannot be discussed in view of comparable investigations.

One focus of research is the comparison of breast- and bottle-feeding. Despite high variability in breastfeeding studies, sucking behaviour improves with maturation [14] and bottle fed term infants show lower breathing frequency [17], lower oxygen saturation [7, 17], higher heart rate and lower blood pressure [18], lower suck frequency [15, 17], less coordinated (random) sucks [7], and less sucking pauses [15].

Nipple units differ in size, shape, consistency and mechanics and these factors are thought to influence suck-swallow-breath coordination in both term and preterm infants [7, 16, 19‐21].

We found that sucking frequency using VTs was lower in the ITT analysis and significantly lower in the subgroup B analysis (p = .01). A comparative investigation of vented and nonvented bottles in preterm infants showed results nearly similar to ours [21]. The authors observed that sucking frequency is lower in a vacuum-free bottle system which confirmed “a more mature stage of sucking” [21]. The preterm infants showed a sucking frequency of 0.6 sucks/s with a vacuum-free bottle system and 0.9 sucks/s with a standard bottle, which corresponds to 36 sucks/min with a vacuum-free bottle system and 54 sucks/min using a standard bottle, closely matching our results (Table 3).

Moral and coworkers used the same VT as in our study when comparing breast- and bottle-feeding [15]. They found in a group of exclusively bottle-fed infants 37.9 ± 13.5 sucks/min which corresponds closely to our findings (Tables 2, 3). Infants 3–5 months of age showed significantly less pauses during bottle-feeding compared to breast-feeding [15]. In contrast, other studies found higher sucking values when different nonvented nipples were used [16].

Various studies focus on the influence of a specific bottle or nipple design on a particular health parameter of the infant. These studies comparing BNSs focused, inter alia, on vital parameters such as oxygen saturation during bottle-feeding with a particular feeding teat design [7, 20, 22] and sucking skills [7, 21].

Fucile et al. investigated skills of suck-swallow-respiration coordination and observed higher sucking stages when fed with the VT bottle [21]. This more mature sucking [21] corresponds to our own findings: We found no differences between the amount of formula intake and feeding time throughout the feeding procedure, meaning that, with the same amount of feeding medium for the same time, subgroup B needed fewer sucks and less pauses with the VTs than with the NVTs. Clinically, lower mean suck frequency suggests that the nipple enables to lengthen the intrasuck interval to allow the time necessary for swallowing larger volume of milk [22]. Our findings indicate that, on the one hand, the VTs did not hasten the formula flow nor did they increase formula intake. On the other hand, they did foster a more constant nonrandom drinking process.

Even though the drinking process is different between the VT and NVT group, we found no differences concerning cardiorespiratory measurements. Our results support the findings of Fadavi et al. who observed no differences in oxygen saturation when term neonates were bottle-fed with different nipples [22]. This is in contrast to other studies that found decreased oxygenation saturation during feeding of term neonates [7, 17]. One possible explanation for our results may be that we included older infants who maintained stable oxygen saturation.

Preterm infants have significant desaturation during bottle-feeding [23], but it could be shown that oxygen saturation increases significantly if a vented BNS is used [20]. Interestingly, some authors reported significantly lower SpO2 after feeding and attribute this to aerophagia in terms of burping and gastric distress [7, 24]. In general, higher oxygen levels during bottle-feeding is seen as a more coordinated sucking, swallowing, and breathing pattern [7]. The authors stated, “If a system can be designed that promotes less swallowing, babies can feed more like the natural physiologic norm of breast-feeding.” [7].

Results from the literature and our own findings suggest that nonvented teats have a higher risk for aerophagia. The mechanism behind nonvented teats is the vacuum that builds up within the bottle and results in a net decrease of milk flow [21]. The infant tries to compensate for the negative pressure by increasing sucking frequency or amplitude until nipple release after air reflux from the oral cavity. Vented teats allow the nipple to deliver formula in an uninterrupted process [20].

The hypothesis that aerophagia causes colic symptoms [3, 10, 25] is unproven, and the evidence of vented BNS on infant colic is very low. Subjective assessments like expert opinion [11] and questionnaires [12, 13] attribute a positive effect of vented BNS on infant colic. Other studies found that aerophagia could be seen as a consequence of increased sucking frequency, which may cause gastric upset [7, 24]. Our own results also support the findings that increased sucking implies the risk of aerophagia which could be reduced by using vented BNSs. In our investigation, the used questionnaire by itself did not show any differences between the two types of feeding teats in connection with colic symptoms. However, valid tools to assess infant colic are not available [26] and further studies are needed to prove the relation between aerophagia and infant colic.

The age of the infants is a confounding factor and a potential limitation of this study. Sucking behaviour improves with age and the inclusion of infants older than 6 months may have biased the sample. We included older infants due to a disappointing recruitment rate of exclusively bottle-fed healthy infants. Complementary diet increased with age and showed an effect on the ITT and PP analysis. Therefore, 6 to 8 months old infants were excluded.

Maturation may also be the reason why both groups maintain stable cardiorespiratory parameters and the effect of a ventilation is too small to create significant differences between the groups. Preterm or other impaired infants may be more vulnerable to this effect.

Specific bottle or nipple designs have an influence on sucking behaviour. We therefore used the same “orthodontic” shape of one manufacturer for both groups. The different base size may have an effect but lip resting was not disturbed with both teats.

Our hypothesis that an uncoordinated sucking behaviour implies more stress in terms of increased sucking frequency could be confirmed, whereas the effect of oxygen desaturation and cardiorespiratory parameters must be rejected. Compared with an NVT group, infants aged 1–6 months need fewer sucks and pauses when fed with VTs. In both groups, equal amounts of feeding medium and feeding time was observed. With NVT feeding, disruption occurs when the bottle vacuum is released by air from the oral cavity. Therefore, higher sucking frequency is needed to rebuild the oral vacuum for bottle milk flow, which implies a higher risk of aerophagia. The role of aerophagia in the occurrence of infantile colic is vague and must be investigated further. Overall, we suggest that the VTs provided a more coordinated drinking pattern than did the NVTs, which may have a positive effect on gastric distress.