INTRODUCTION

The growing scientific and technological development in the area of health, and neonatology in particular, has contributed unequivocally to lower infant mortality rates worldwide, with the survival rates of newborns (NBs) at 24 weeks of gestation being situated between 35-84% and at 29 weeks a rate of 92-98% ¹. Despite all of these developments, prematurity has increased in developed countries, many of the preterm NBs have a high risk of morbidity, which is accentuated by long hospitalisations in the neonatology unit (NU) ². Major morbidities, such as grade III and grade IV intraventricular haemorrhage, are highlighted in 10.6% of newborns up to 32 weeks and 13.6% of these are still associated with other morbidities, such as bronchopulmonary dysplasia ³.

In this especially vulnerable population, stability will be achieved through neuroprotective care, which is supported by interventions to support neurodevelopment, or which facilitate it after a neuronal injury, by building an environment that recognises multidimensionality and the complex needs of preterm NBs, as well as their family ^4,5. It is, therefore, essential to carry out neuroprotective care, in order to minimise factors that contribute to an aggressive NU environment, such as constant activity, noise and light that influence preterm Nbs' brain development ^2,4,5.

One of the neuroprotective measures is nutrition optimisation. Oral feeding, which is a highly complex and demanding sensory motor activity in relation to the oral motor coordination of the preterm NB, requires the nurses to effectively implement neuroprotective care ^{(4; 6)}. In this sense, on an oral feeding level, this type of care aims to provide a successful and quality experience, in which the NB's maturity level is respected ⁴. This should contribute to help the NB to reach their ideal state of wellness, that is, increase their existing strengths and reduce the influence of environmental conditions in the transition to oral feeding and, consequently, to feeding autonomy. Autonomy is one of the hospital discharge criteria for preterm NBs ², so it is crucial to implement strategies that improve oral feeding skills in preterm NBs ².

The development of oral motor skills for feeding in these NBs depends on several factors, namely the ability to organise and coordinate their oral functions in order to promote an efficient consumption of calories, progressing their growth and development. These skills also involve the NB's ability to maintain interest in food at a physiological and behavioural level; organise their oral motricity and breathing coordination, with suction and swallowing and maintaining their physiological stability ⁷. This complex process involves the balanced development of brain maturation and its relationship with physiological and behavioural development ². The acquisition of oral motor skills is considered one of the development milestones of preterm Nbs ⁸, as these are skills that allow a safe, functional and pleasurable feeding experience for both the NB and their parents ⁹.

Physiologically, oral feeding involves a complex interaction between the brain and the central nervous system, as well as oral-motor reflexes and the multiple muscles of the mouth, pharynx, oesophagus and face. It also requires rhythmic coordination between sucking and swallowing, simultaneously with effective breathing.

Conceptually, oral feeding is defined as a consequence of multiple events that involve activities in search of food, ingestion and swallowing. Both in practice and in scientific literature, there is no consensus regarding the ideal time to start oral feeding. Recommendations have emerged that 32/34 weeks of gestational age (GA) or adjusted age (AA) are not criteria to begin feeding ¹⁰, which should be delayed until 34 weeks¹¹. The coordination maturation between sucking, swallowing and breathing usually occurs between 34-36 weeks ¹², therefore a tailored assessment by nurses is essential, allowing them to identify when it is safe to start feeding.

In nursing care, there is a lack of consensuson a daily basis regarding the most appropriate oral feeding technique for the development of the oral motor skills and the consequent feeding autonomy of the preterm NB. For the NB to be autonomous in oral feeding, they will have to ingest all the daily feeding intakes, with no instances of haemodynamic instability, even subtle ones, and show no signs of neurobehavioural stress. For this reason, it is essential that during feeding, the nurse performs an tailored and systematic assessment of the NB's oral motor skills through oral skills assessment scales, such as the Observation Scale for Early Skills in Oral Feeding ⁷. Additionally, it is imperative to discover which feeding techniques positively influence the development of feeding skills and the preterm NB's consequent autonomy, so that the technique selection is standardised in care practices ¹³.

This review will consider a feeding technique as the way in which oral feeding is given to preterm NBs to develop their feeding skills. The technique chosen to begin oral feeding, on the part of the nursing team, should fall on factors such as the mother's desire or not to breastfeed, the NB's GA and AA, their weight and feeding readiness behaviours demonstrated.

Oral feeding, as a nursing intervention, incurs the nurse's responsibility in decision making, regarding the feeding technique to be used in order to guarantee suitable nutrition, that is, that which is necessary for growth and development. This decision should be based on scientific evidence, made in partnership with the parents and that which will meet the NB's needs. Thus, the relevance of carrying out this review is related to the importance of identifying and mapping out in the scientific literature the oral feeding techniques that promote the preterm newborn's oral motor skills.

METHOD

A scoping review was selected in order to carry out this review, as it contributes to a greater understanding of the subject under study. In this type of review, a systematic approach is followed to map out evidence on a topic and identify the main concepts, theories, sources and gaps in knowledge on the topic ¹⁴. This type of review can be a preliminary exercise before conducting a systematic review of the literature, because it allows us to verify emerging evidence when it is not yet possible to ask and address more specific questions ¹⁵.

According to Peters et al.¹⁵ the structure of the scoping review must follow the following steps: defining and outlining the issues and objectives; defining the inclusion criteria according to the questions and definitions; outlining research strategies and study selection; researching and selecting studies; extracting results; summarising the evidence in relation to the objectives and consulting experts and specialists.

The questions outlined for this review are: What are the most common techniques to support oral feeding for preterm newborns? What are the techniques to support oral feeding of preterm newborns, and what is their influence on the development of their oral motor skills?

This review considered studies that include preterm NBs, with a GA greater than or equal to 32 weeks, of GA and/or AA up to 36 plus 6 of GA and/or AA that are undergoing intervention in oral feeding. The feeding techniques must be implemented on haemodynamically stable newborns admitted to the NU. Studies whose participants were preterm NBs with central nervous system and orofacials malformations, intra-ventricular haemorrhages of a degree greater than II, chromosopathies and bronchopulmonary dysplasia were excluded.

The review considered studies that focus on the various techniques to support the preterm NB feeding and their influence on the development of oral feeding skills. Studies that relate oral feeding techniques to feeding autonomy in preterm NBs were also considered.

All types of scientific articles will be considered, including quantitative and qualitative studies, as well as systematic literature reviews. The articles were limited to Portuguese, Spanish and English. Chronologically, articles from 2000 to 2018 were considered.

Research Strategy

The research strategy outlined for the preparation of this review aimed to scan published and unpublished articles, having been divided into three distinct stages. In the first stage, the research was limited to the Medline and CINAHL databases in order to analyse the words present in the titles and abstracts and the indexing terms used to describe the articles on the topic.

In the second stage, a search was carried out in each database with the descriptors in natural language and the indexing terms corresponding to each of them, having analysed the definitions of the indexing terms and their use to describe the articles, thus proceeding to their validation. Of the existing articles, initially only the titles and respective abstracts were taken into account and read, this was in order to exclude those that did not meet the previously defined inclusion criteria. After selecting the articles that were considered to be relevant, they were read in full.

In the third stage, using the list of references of previously selected articles, we proceeded to search for possible additional studies that could be relevant, in order to increase the sensitivity of the research.

The databases in which the research was carried out were Medline, CINAHL, Cochrane Central Register of Controlled Trials and Scielo. The search for unpublished studies was carried out through Google Scholar, master's and doctoral theses with access via the Nursing School of Lisbon's virtual library.

Two reviewers carried out the search for and selection of articles and then proceeded to select titles and then abstracts, taking the inclusion and exclusion criteria of the review into account. Subsequently, duplicate studies were removed.

The complete research strategy is shown in Table 1.

Table 1.  Research Strategy 

A similar process was followed for the eligibility of the full text. (Figure 1) ¹⁴.

Figure 1.  Flowchart 

The results were extracted using a data table. The complete data extraction was previously validated between the two reviewers, and as this process is interactive, a table was built as the extraction was carried out. The extraction table contains the key information for all selected articles.

RESULTS

At the starting point, 431 articles which were potentially eligible for this review were identified. However, upon reading their titles and abstracts, 381 of them were excluded. Two abstracts were not available and there was a duplicate of one article, both present in the CINAHL database. In the complete reading process, 61 articles were selected, of which 8 were duplicates, 25 were excluded and 28 were included in the scoping review, and it was those articles that met the defined inclusion criteria. Of the studies included, 21 are primary studies, 6 are secondary studies and there is one doctoral thesis.

In reviews, it is recommended to consider articles from 10 years prior to the review, in order to increase their reliability. However, in carrying out this review, it was necessary to expand the research to the year 2000, with the purpose of including a greater number of articles, seeking a more solid theoretical support. We can allude that the strategy of temporal expansion was justified by the fact that, at the end of the research, we verified that approximately half of the articles were before the year 2009.

DISCUSSION

The cup technique is the most evident in scientific evidence, however, there is little consensus in the studies analysed regarding the benefits for the development of oral motor skills ^16,17. What can be seen when some authors defend its use is that it is due to the fact that the behaviour of the masseter muscle ^18,19) and that of the temporal muscle is similar to during breastfeeding ¹⁰, and others note that the use of the tongue and muscles differ in cup feeding from those used in breastfeeding ²⁰. One of the muscles that shows greater activity during cup feeding is the suprahyoid, which is not seen in breastfeeding, which may be related to the protruding movement of the tongue, through which the NB obtains the milk ¹⁹.

In cup feeding, when compared to breastfeeding, there is less execution and opening of the jaw, causing the negative intraoral pressure to be lower. This factor can lead to habituation and make breastfeeding difficult, such as that which occurs with nipple confusion. This fact leads us to question whether the use of different muscles during cup feeding, when compared to breastfeeding, may also contribute to the risk of nipple confusion.

Some authors also argue that this technique does not allow the NB to stimulate coordination between sucking-swallowing-breathing ¹², nor stimulate the sucking reflex, and instead only act on the swallowing level, which may cause frustration for preterm NBs ²¹. If this frustration occurs repeatedly, feeding can become a negative stimulus with long-term consequences for feeding.

When cup feeding, the NB actively moves the milk bolus and the small volume of milk ingested and their greater control of the milk flow contribute to haemodynamic stability during outbreaks and in their intervals ²². However, nurses do not always have this perception in their practice, which may be related to the fact that the cup technique is not implemented correctly, as many nurses say they are not comfortable performing the cup feeding technique and consider it to be less safe. Many report that there is more milk waste using this technique, coupled with the fact that NBs show more signs of stress during cup feeding, when compared to bottle feeding.

Regarding bottle feeding, some researchers argue that its use can favour the development of oral motor skills, promoting a more mature suction pattern ⁽²³, in which a greater range and duration of suction translates into a greater transfer of milk volume¹⁸⁾ and less milk waste ¹².

Regarding muscle activity, in a study that aimed to observe the muscular activity of the buccinator and the masseter muscles during bottle feeding, it found that the buccinator showed increased muscle activity and the masseter showed reduced activity ⁽¹⁸. However, the muscle activity of the masseter was further increased in breastfeeding, as previously mentioned, and the muscular activity of the buccinator is absent ⁽²⁴. As bottle feeding is associated with the risk of nipple confusion, the authors of this review consider that indicators that analyse the tongue and jaw position during this technique would have been pertinent. As well as its impact on the development of the breathing and swallowing muscles.

We also emphasise the importance of the physical characteristics of bottles and teats, especially regarding the milk flow, and how they can influence the feeding performance of preterm NBs. The decision to bottle feed should take into account the existence of a vacuum and milk flow control system, in order to have better suction efficiency ²³ and their swallowing and breathing coordination ²⁶. In a standard bottle, the implementation of some strategies, such as having a smaller volume of milk inside the bottle, keeping the milk up at the teat or feeding the NB in a reclined position, can help to reduce the milk flow and consequently facilitate coordination between their swallowing and breathing ¹². Therefore, the importance of nurses being knowledgable regarding feeding techniques is clear, in order to adapt their interventions to control the milk flow when using the bottle. Even more so given that the bottles available in the NU are often standard bottles.

Regarding the choice of teats, the type of material, the hole, its shape and the size should be considered ²⁵. Several studies mention that straight or single-hole teats decrease the milk flow, thus facilitating swallowing-breathing coordination and consequently reducing milk waste through the labial commissure ^12,26. Some breastfeeding experts even report that the lowest flow teats are those that most support breastfeeding and the NB's physiological stability. However, it is essential that nurses are wary of the signs of stress in NBs, as a very slow flow can cause fatigue and frustration. There are references that wider teats involve the masseter muscle in a way that is similar to breastfeeding ²⁵.

The finger-feeding technique aims to train suction, complement feeding or to feed the NB, when the mother cannot be present ²⁷. In this technique, the sensory stimulation that is created due to the firmness of the finger is more similar to the nipple, facilitating the development of oral motor skills, which are more similar to those that the NB must present during breastfeeding ²⁸. Researchers have shown that this technique promotes suction that is similar to that which occurs during breastfeeding, with their mouth open wide, slow expression and deep sucking ²⁸. In most studies, this technique emerges as that which allows the stimulation of the sucking reflex ^27)(28(29, developing their swallowing and breathing coordination. Two studies also report that less milk is wasted in the finger-feeding technique when compared to the cup or syringe technique ^29,30.

Regarding haemodynamic stability, during finger-feeding, the NB presents less respiratory effort and fewer episodes of low saturation, in comparison to cup feeding ⁽³⁰.

One of the aspects that nurses mention as being less advantageous in this technique is the greater expenditure of time in organising the material for its implementation ²⁹.

It is important to mention that in this review, no study was selected to compare breastfeeding and bottle feeding with finger-feeding.

CONCLUSIONS

Although the research for this review has been temporarily expanded, it found, nevertheless, that there are few studies that effectively address how feeding techniques influence the development of oral motor skills.

The analysed publications focus mainly on aspects of haemodynamic stability, weight gain and feeding autonomy, with consequent early hospital discharge. It is therefore essential to understand how each technique promotes the development of oral motor skills, and it is also essential to consider the parents' wishes and expectations regarding feeding, such as exclusive breastfeeding.

Nurses should not only focus on the act of feeding the NB, they will have to also understand and know the various factors that are inherent to the NBs, such as adjusted age, weight, signs of feeding readiness among others that can interfere with the NB's feeding performance.

In this review, some studies were excluded due to their ineligible population, which could be important for understanding the influence of oral feeding techniques on the development of oral motor skills. Namely, how the characteristics of bottles can influence the milk flow. Therefore, it is plausible to question whether the research results would be different or not, had a population that included full-term NBs been established and the particularities of full-term NBs been taken into account later in the analysis of the studies.

The literature selected in accordance with the inclusion criteria was heterogeneous and relatively scarce. The cup feeding technique is the most evident technique in the scientific literature and in the last few years more research has appeared on the finger-feeding technique. This may be due to the fact that it is increasingly recognised that oral feeding techniques influence the development of oral motor skills and as such, have consequences for breastfeeding and feeding autonomy. Other techniques have also emerged, such as the syringe and the translactation technique, which have emerged with the aim of replacing the use of the bottle in order to promote breastfeeding.

In view of the above, the need for future studies that address oral feeding techniques and their impact on the oral motor skills of preterm NBs is clear. For this reason, the research team considered that it would be appropriate to carry out a study, which is in the course of completion, which intends to learn about the nurses' perception of oral feeding, what motivates their choice of oral feeding techniques and the difficulties experienced in implementing them. A study will be undertaken in order to verify how each feeding technique, bottle feeding, cup feeding and finger-feeding, promote oral motor skills and which ones favour effective feeding autonomy, consistent weight gain and consequent decrease in the length of hospitalisation in the neonatal unit, supporting breastfeeding.