Reviewer Comments:
REVIEWER 1:
Thank you for the opportunity to review this article. The time involved in submitting your
manuscript is greatly appreciated. This is an important topic for nurses caring for preterm
infants in both NICU's and transitional nurseries. It is also an important topic to parents of
preterm infants as it has implications for length of hospitalization. Your manuscript is well
organized and shows great potential.
Problem Statement.
Although no problem statement is listed the purpose of the paper is clearly stated at the
end of the literature section. Feeding challenges and the achievement of feeding milestones
with the preterm infant impact length of hospitalization, family stress and ultimately the
cost of care. Greater understanding of how specific medical conditions impact this
progression is needed in order to develop appropriate care paths for this population.
Utilization of hypothesis and problem statement would have provided further clarity to the
reader. For example was there a primary and secondary purpose or was it a combined
purpose such as suggested in the first sentence of your discussion section? The numerous
variables (infant illness characteristics) are stated in this section and further defined within
the methods section providing clarity to the reader.
Background Literature.
The literature section needs to set the ground work for justifying the need for your study.
You have made a good start. Within this section you speak of five milestones in preterm
feeding. Literature to support these points as milestones and the impact on progression to
full feeds would strengthen this section.
Theoretical framework.
No theoretical framework was identified. A theoretical framework would have strengthened
the manuscript by helping to make the link between preterm feeding milestones, infant's
illness characteristic and feeding plans.
Concepts utilized and how they were operationalized was well defined, thus providing clarity
to the reader.
Research design and method.
This study utilized a descriptive exploratory approach as secondary analysis of another
study focusing on an unrelated variable. A retrospective chart review confirming the data
strengthened the design. A plan for assessing reliability was implemented. Ethical approval
was obtained and stated.
Please ensure consistency in terminology across the manuscript. Changing terminology to
describe the same variable the clarity. (line 6 page 3: Medical complications is used in the
Literature section; Line 10 page 5: Infant illness characteristics is used in the Measures
section; Line 14, page 6: seven Infant characteristics are used in the Data Analysis section;
and Line 16 page 13 back to medical complications in the discussion section).
Data analysis.
Analysis chosen was appropriate for the data collected. Utilization of linear mixed model was
appropriate for examining patterns of infant feeds across feeding milestones looking at both
gestational age and infant illness characteristics.
Results.
Utilizing a table to present the data would help the reader better see the differences
between gestational ages and specific medical conditions. Individual figures helped provide
clarity to the individual variable results. The sample characteristics need to be provided;
specifically the overall gestational age at birth and sex of infants. Again this could be
presented in a table along with the medical conditions.
Discussion.
The discussion needs to reflect back on the literature review. Results need to be discussed
within the context of current literature. New research was introduced in the discussion. This
literature would have strengthened the support for the need of this research if introduced in
background section of this paper. Literature addressed should have been introduced in the
literature review at the beginning of the manuscript.
A major limitation of this study is the failure to mention the type of infant feeding. Breast
milk feeding has a gastric emptying time that is half that of infant formula. The type of
infant feeding can drastically impact the achievement of feeding outcomes as the milestones
would be very different for preterm infants receiving breast milk compared to formula.
Organization and style of presentation.
Overall the manuscript is well organized and well written.
Summary.
The key Strength of this study is the importance of the research problem as preterm infant
feeding greatly impacts the length of hospitalization. This study is relevant to the nursing
profession and adds to the body of work looking at preterm feeding.
This manuscript shows great potential. The literature review which has begun to set the
foundation for the importance of this project needs to be expanded to include the literature
that was introduced within the discussion section. With an expanded literature review
section that may encompass some of these references, the argument for the need for this
research will be strengthened.
Failing to report the type of infant feeding within each group is a serious concern. If an
imbalance existed between the groups (e.g. one group was predominantly formula fed) the
results would be skewed. If this data is available it should be reported. This limitation also
needs to be indicated within the discussion section.
The key Strength of this study is the importance of the research problem as preterm infant
feeding greatly impacts the length of hospitalization. This study is relevant to the nursing
profession and adds to the body of work looking at preterm feeding.
REVIEWER 2:
Problem Statement
Attainment and progression to full oral feeds is a major milestone in the overall wellbeing of
infants born prematurely and heralds their readiness for hospital discharge. Studies
conducted to provide insight into the myriad of issues surrounding these issues is important
and necessary. This study provides helpful insights into this process.
Background Literature
The review of the literature is not current and not comprehensive enough to provide a
foundation for understanding the scope of the problem related to the significance and
importance of attaining full oral feeds in an extremely-low-birth-weight infant. Of the 23
articles cited ten were published before 2008. As with most things in health care,
tremendous strides have been made in the care of infants born prematurely. Practices
commonplace five years ago have been replaced with methods incorporating revised
thinking. A more thorough review of the literature is recommended.
Theoretical Framework (TF)
There was no TF mentioned.
Research design and method
A retrospective chart review was conducted using records of infants previously enrolled in a
larger study between 2003 and 2006. This methodology is accepted as a valid means by
which to gain important health information about a specified group of patients, in this case,
extremely low birth weight infants. The author(s) appropriately disclosed this use, stated
the purpose of the parent study and the potential impact any interventions in the parent
study may have had on the current study. In this case the use of "piggybacking" on to
another study is appropriate. There is concern about the length of time elapsed since the
data were collected. Much can change in a 6-9 year time period, especially in healthcare.
Any conclusions drawn from study results will need to take this time lag into account.
Gestational age birth weight ranges were provided. There was no mention of whether
infants were appropriate for gestational age, small for gestation age, or large for gestational
age. This information would provide another data point by which to evaluated the ultimate
timeliness of progression to full oral feeds.
Data analysis
The interpretation of analyzed data is logical and easy to follow; their statistical significance
evident. The Figures used to depict the data results provide a clear picture of the findings.
The details of the statistics will need to be evaluated by someone other than myself.
Results
See above comments.
Discussion
In this section the author(s) adequately contrasts and compares their study findings with
those described in the literature. Limitations of study design and method were discussed.
REVIEWER 3/statistical reviewer:
A review of 'factors associated with feeding progression in extremely preterm infants',
NRES-D-14-00160.
Summary
The manuscript examined the timings of acquisition of five early feeding milestones (first
enteral feeding, full enteral feeding, first oral feeding, half oral feeding, and full oral
feeding) among extremely preterm (EP) infants. Factors affecting such timings are also
considered. These factors include treatment conditions, gestational age, neurological risk,
severity of lung disease, necrotizing entercolitis, patent ductus arteriosus, and
gastroesophageal reflux disease. Linear mixed models are employed to answer these
research questions. The conclusions include (a) EP infants achieved feeding milestones, and
(b) slow attainments of the feeding milestones were associated with younger GA at birth
and the presence of neurological risk, BPD, NEC and PDA, but not GERD.
Major Comments
I am a methodologist whose expertise is statistical methods. My comments focus on data
analysis. Substantive significance of the findings will be left for more qualified reviewers. On
page 6, the authors describe how the data analysis was conducted. The main statistical
method is linear mixed models. The authors may consider providing more details about the
model and its implementation, for example, the software used to conduct the analysis,
model specification for the error (repeated measures) term, and the model estimation
method.
At lines 11 to 12 (page 6), the authors write 'the covariance structure accounted for
correlation and variance of PMAs at each feeding milestones with the same infant.' Being
more flexible in handling error covariance structure is one of most important advantages of
Linear Mixed models over Repeated-measures ANOVA. How is the covariance structure
modelled? Is it through a random effect of the categorical variable of milestones, or a model
(a diagonal matrix, an AR model, or an unstructured matrix) for error (repeated measures)
covariance matrix?
At line 13, the authors write '(fixed and random effects = infant's PMA at feeding
milestone).' Should the fixed and random effects be a categorical variable of feeding
milestones? Are infant's PMAs at feeding milestones dependent variables? If feeding
milestones are treated as random effects, the linear mixed model seems non-identified. Are
these random effects confounded by errors?
Minor Comments
P7-P10, many F-tests are reported. In these F-tests, the degrees of freedom for the
denominators are all integers. When a linear mixed model with random effects, such
degrees of freedom need to be estimated from the data. These estimates are often not
whole numbers. Are the degrees of freedom reported in the manuscript rounded to
integers? Or are they exact integers?
***
ADDITIONAL COMMENTS FROM THE EDITOR
Review of Literature/Discussion
The review of literature (introduction) is short, and many new citations are introduced in the
discussion section. Following APA style, please use the intro/review of literature to present
what is known, and then reserve the discussion for consideration of findings in light of
what's known (i.e., introduction of new citations should be minimal).
In addition to the literature about feeding progression in extremely premature infants, some
other issues need to be addressed to contextualize the research. For example, reviewer 2
noted the time elapsed since the data used for this analysis were obtained and observed
that care practices have changed during this time. To argue the continued relevance of the
dataset, background about changes (or lack thereof) in the survival of extreme prematures
and care practices should be summarized in a paragraph or two (e.g., Mohamed, Nada, &
Aly, 2010, Table 5; Stoll et al., 2010, Table 4). Likewise, trends in feeding protocols for
prematures from the time data were collected to the present time should be described.
Use of postmenstrual age (PMA) at the time of reaching a milestone as the outcome needs
justification. Explain why it was selected and why other age-related variables were not
used.
Compare Results in your abstract with the last sentence in paragraph 1 of the literature
review/introduction (p. 2, lines 9-12). The statements are very similar. Please take a closer
look at the composition to be sure that "what's known" and "what this paper adds" are
clearly delineated.
"Continuous process" of attaining feeding milestones (p. 2, lines 21-22ff): Please try to
describe this concept more fully, and link it to the research problem/statistical
model/interpretation of outcomes.
METHODS
Design (p. 3, lines 14-20)/Parent study: Say what was found (one sentence, if possible),
and provide citation to the primary report.
Feeding progression (p. 5, lines 8-9): state how gestational age was determined (LNMP,
ultrasound, physical exam, etc)
Data Analysis
Co-occurrences of the infant characteristics need to be provided. As presented, focusing on
the effects of each characteristic separately gives the impression that the characteristics are
independent, but this isn't likely (for example, more NEC would be associated with more
severe respiratory disease and more neurological risk). (The comment about this issue in
the limitations was not adequate.) Separate models for each of the characteristics can be
useful, but should come with a caution about co-morbidity.
The data analysis section lacked the detail needed to understand what models were
estimated. Provide an explicit representation of the models (equations or computer input).
Clarify how many models were actually estimated.
RESULTS
Please provide a table describing infant characteristics.
So that the report is complete, parameter estimates and standard errors should be
provided; it is suitable to submit computer output them for use as supplemental digital
content if the paper is accepted.
DISCUSSION--Key Finding
"This was the first study to show a more pronounced delay as EP infants moved from
enteral to oral feeding milestones." This statement seems to refer back to your earlier
comment about the "continuous process" of feeding progression. If you elaborate on the
conceptual and empirical components of this idea in the background/review of literature, I
think you would be able to make stronger statements about what you found and why/how
the findings matter.
DISCUSSION--minor points
phrase: "significantly by weeks": please be more precise
phrase: "have totally recovered" with respect to NEC (p. 12, line 5): include decision rules
used to determine that complete recovery has occurred
LIMITATIONS
I'm concerned about the inferential implications of not including infants who died before
achieving all feeding milestones or who transferred to a non-study nursery (p. 4, lines 3-5).
Also, information about how age at attainment of a milestone was coded when the infant did
not reach a milestone before discharge was not provided (9.6% of the cases that were
analyzed; p. 7, line 1). In all these situations, observations were right censored. How did
excluding some of them affect your definition of the conceptual population of interest? How
did including those who had not reached milestones affect parameter estimates, and
interpretation of their meaning?
Figures: The superscript in the x-axis label isn't needed.
REFERENCES in Editorial Comments
Mohamed, M. A., Nada, A., & Aly, H. (2010). Day-by-day postnatal survival in very low birth
weight infants. Pediatrics, 126, e360-e366.
Stoll, B. J., Hansen, N. I., Bell, E. F., Shankaran, S., Laptook, S. S., Walsh, M. C., ...Euncie
Kennedy Shriver National Institute of Child Health and Human Development Neonatal
Research Network. (2010). Neonatal outcomes of extremely premature infants from the
NICHD Neonatal Research Network. Pediatrics, 126, 443-456.