Synbiotics for preventing necrotising enterocolitis in preterm infants
Abstract
Objectives
This is a protocol for a Cochrane Review (intervention). The objectives are as follows:
To evaluate the effect of enteral supplementation with synbiotics (versus placebo or no treatment, or versus probiotics or prebiotics alone) on the risk of necrotising enterocolitis and associated morbidity and mortality in very preterm or very low birth weight infants.
Background
This review will assess the trial evidence for the effectiveness of enteral synbiotics (combinations of probiotic micro‐organisms and prebiotic oligosaccharides) for preventing necrotising enterocolitis (NEC) in very preterm or very low birth weight (VLBW) infants. Other Cochrane Reviews assess the evidence for prebiotics alone or probiotics alone (Sharif 2020).
Description of the condition
Necrotising enterocolitis is a syndrome of acute intestinal necrosis which affects about one in twenty very preterm (born before 32 weeks' gestation) or VLBW (birth weight less than 1500 g) infants (Horbar 2012). The risk factors for NEC include being extremely preterm (born before 28 weeks' gestation) or extremely low birth weight (ELBW; birth weight less than 1000 g), and intrauterine growth restriction or compromise indicated by absent or reversed end‐diastolic flow velocities in antenatal Doppler studies of the umbilical artery or fetal aorta (Samuels 2017). Infants who develop NEC experience more infections, have lower levels of nutrient intake, grow more slowly, and have longer durations of intensive care and hospital stay than gestation‐comparable infants who do not (Battersby 2018; Berrington 2012). The associated mortality rate is about 20%. Infants who survive NEC, especially if associated with bloodstream infections, have a higher risk of neurodevelopmental problems and disability compared with their peers (Hickey 2018).
The pathogenesis of NEC is not fully understood but is speculated to involve intestinal dysbiosis, infection and inflammation (Eaton 2017; Mara 2018; Stewart 2016). Evidence exists that the pattern, diversity and stability of the intestinal microbiome is associated with the risk of developing NEC (Masi 2019; Olm 2019; Stewart 2012; Warner 2016). Feeding with human milk compared with cow milk formula reduces the risk of NEC in very preterm or VLBW infants (Cleminson 2015; Quigley 2019). A putative mechanism for this protective effect is that “prebiotic” human milk oligosaccharides promote the growth of non‐pathogenic probiotic micro‐organisms, such as lactobacilli and bifidobacteria, that modulate the intestinal microbiome and promote mucosal barrier functions (Embleton 2017; Granger 2020; Walsh 2019). Compared with human milk‐fed term infants, however, very preterm or VLBW infants tend to harbour fewer intestinal probiotic micro‐organisms, and more potential pathogens, which might be due to dysbiotic effects of enteral fasting and antibiotic exposure (Stewart 2017).
Description of the intervention
Synbiotics (probiotic‐prebiotic combinations)
Synbiotics are combinations of probiotics and prebiotics. The prebiotic content is intended to enhance probiotic growth and intestinal colonisation (Nolan 2020).
Probiotics
Probiotics are live micro‐organisms (predominantly bifidobacteria and lactobacilli) that benefit the host by modulating the intestinal microbiome and promoting mucosal barrier functions and resistance to pathogens (Berrington 2019; Esaiassen 2018). Preterm infants supplemented enterally with bifidobacteria and lactobacilli establish an intestinal microbiome that is dominated by probiotics and contains fewer potential pathogens compared with non‐supplemented infants (Alcon‐Giner 2020). Meta‐analysis of data from more than 50 randomised controlled trials (RCTs) ‐ which used a variety of probiotic strains and multi‐organism combinations ‐ suggests that probiotic supplementation may reduce the risk of NEC, and probably reduces mortality and late‐onset infection in very preterm or VLBW infants (Sharif 2020). The certainty of this evidence, however, is low because of concerns that effect estimates are inflated by methodological weaknesses in the (mainly small) trials and by publication bias. Consequently, and because of ongoing issues about safety and the availability of regulated products, probiotic supplementation has not become established as a common practice in most neonatal care facilities (Duffield 2019; Fleming 2019; Pell 2019; Vermeulen 2020).
Prebiotics
Prebiotics are a diverse family of complex glycans that promote intestinal colonisation with probiotic micro‐organisms. Human milk contains numerous prebiotic substances, predominantly galacto‐oligosaccharides and fructo‐oligosaccharides, that influence the intestinal microbiome in preterm infants (Boehm 2008; Nolan 2020). Natural human milk oligosaccharides vary markedly between individual women, and vary temporally (depending on the stage of lactation) within individual woman. The quantity and types of oligosaccharides affect the pattern of the probiotic microbiome of a woman’s colostrum (Aakko 2017; Smilowitz 2013). Newborn infants do not digest human milk oligosaccharides. Rather, these are primarily nutrient sources for intestinal probiotic micro‐organisms, particularly bifidobacteria (Alcon‐Giner 2020; Jost 2015). There is emerging evidence about how specific human milk oligosaccharides promote probiotic predominance and reduce intestinal dysbiosis in very preterm infants (Masi 2020; Underwood 2015).
Manufactured (synthetic) prebiotic oligosaccharides are less heterogeneous than natural human milk oligosaccharides, typically consisting of short chains of galactose or fructose, usually with a terminal glucose monomer (Johnson‐Henry 2016). Evidence exists that giving supplemental synthetic prebiotic oligosaccharides to formula‐fed very preterm infants stimulates the growth of an intestinal microflora that is similar to that found in infants fed with maternal milk (Autran 2018; Boehm 2008; Kapiki 2007; Veereman‐Wauters 2011). RCTs, however, have not provided evidence of their effectiveness in preventing NEC or associated morbidity or mortality (Chi 2019; Johnson‐Henry 2016; Srinivasjois 2013).
How the intervention might work
It is postulated that administering supplemental prebiotic oligosaccharides enhances both exogenous and endogenous probiotic growth and intestinal colonisation (Nolan 2020; Underwood 2019). Probiotic bacteria and fungi use prebiotic oligosaccharides as a major nutrient source (Alcon‐Giner 2020). Bifidobacteria and lactobacilli ferment prebiotic oligosaccharides to produce short‐chain fatty acids that inhibit adhesion of pathogenic bacteria and modulate intestinal epithelial integrity and barrier function (Johnson‐Henry 2016). Synbiotic combinations, therefore, may be more effective than supplementation with either a probiotic or prebiotic alone (Zmora 2018). A recent RCT involving more than 4500 newborn infants (birth weight at least 2000 grams or gestation greater than 34 weeks) in rural India showed that enteral synbiotic supplementation (Lactobacillus plantarum plus fructo‐oligosaccharide) was associated with a reduced risk of neonatal sepsis (Panigrahi 2017).
Why it is important to do this review
Necrotising enterocolitis and associated complications, particularly infection, are the commonest causes of mortality and serious morbidity beyond the early neonatal period in very preterm or VLBW infants (Berrington 2012). Current trial data do not provide high certainty evidence that probiotic or prebiotic supplementation alone reduces the risk of NEC (Quigley 2019). Given the plausibility that synbiotics might have an advantage over probiotics or prebiotics alone, appraising and synthesising the trial evidence about the effectiveness and safety of synbiotic supplementation could inform practice, policy and research.
Objectives
To evaluate the effect of enteral supplementation with synbiotics (versus placebo or no treatment, or versus probiotics or prebiotics alone) on the risk of necrotising enterocolitis and associated morbidity and mortality in very preterm or very low birth weight infants.
Methods
Criteria for considering studies for this review
Types of studies
Randomised or quasi‐randomised controlled trials (including cluster‐randomised controlled trials). Cross‐over studies will not be eligible for inclusion.
Types of participants
Very preterm (< 32 weeks' gestation) or VLBW (< 1500 grams) infants.
Types of interventions
Intervention
Enteral synbiotics: any combination or dose of probiotic organisms and prebiotic oligosaccharides, commenced within 14 days of birth and continued (at least) daily for (at least) one week. Probiotics and prebiotics need not be given simultaneously, but should be given (at least) on the same day.
Types of outcome measures
Primary outcomes
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NEC confirmed at surgery or autopsy or using standardised clinical and radiological criteria (VON 2020):
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at least one of: bilious gastric aspirate or emesis; or abdominal distention; or blood in stool; and
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at least one of: abdominal radiograph showing pneumatosis intestinalis; or gas in the portal venous system; or free air in the abdomen.
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All‐cause mortality before discharge from hospital.
Secondary outcomes
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Late‐onset invasive infection, as determined by culture of bacteria or fungus from blood or cerebrospinal fluid or from a normally sterile body space (> 48 hours after birth).
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Late‐onset infection with the supplemented probiotic micro‐organism.
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Duration of hospitalisation since birth.
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Neurodevelopmental impairment assessed by a validated test after 12 months' post‐term: neurological evaluations, developmental scores, and classifications of disability, including cerebral palsy and auditory and visual impairment.
Search methods for identification of studies
We will use the criteria and standard methods of Cochrane Neonatal.
Electronic searches
We will search the Cochrane Central Register of Controlled Trials (CENTRAL, 2020, current issue), Ovid MEDLINE (1946 to date), OVID Embase (1974 to present), OVID Maternity & Infant Care Database (1971 to present), and the Cumulative Index to Nursing and Allied Health Literature (1982 to present) using a combination of text words and MeSH terms described in Appendix 1. We will limit the search outputs with the relevant search filters for clinical trials as recommended in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2020). We will not apply any language restrictions.
We will search clinical trials registries for ongoing or recently completed trials (clinicaltrials.gov; the World Health Organization’s International Trial Registry and Platform, and the ISRCTN Registry).
Searching other resources
We will examine the reference lists of any articles selected for inclusion in this review.
Data collection and analysis
We will use the standard methods of Cochrane Neonatal.
Selection of studies
Two review authors (SS, PTH or SO) will independently screen the title and abstract of all studies and assess the full articles for all potentially relevant trials. We will exclude those studies that do not meet all of the inclusion criteria and we will state the reason(s) for exclusion. We will discuss any disagreements until consensus is achieved, with referral to WM for final decision as necessary.
Data extraction and management
Two authors (SS, PTH, SO or WM) will extract data independently, using a form to aid extraction of information on design, methodology, participants, interventions, outcomes and treatment effects from each included study. We will discuss any disagreements until we reach a consensus. If data from the study reports are insufficient, we will contact the report authors for further information.
Assessment of risk of bias in included studies
Two review authors (SS, PTH, SO or WM) will assess independently the risk of bias (low, high or unclear) of all included trials using the Cochrane ‘Risk of bias’ tool (Higgins 2011), for these domains:
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sequence generation (selection bias);
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allocation concealment (selection bias);
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blinding of participants and personnel (performance bias);
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blinding of outcome assessment (detection bias);
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incomplete outcome data (attrition bias);
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selective reporting (reporting bias);
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any other bias (including baseline imbalance).
We will resolve disagreements through discussion or by involving a third assessor. See Appendix 2 for a description of risk of bias for each domain.
Measures of treatment effect
We will analyse the treatment effects in the individual trials and report risk ratio (RR) and risk difference (RD) for dichotomous data and mean difference (MD) for continuous data, with respective 95% confidence intervals (CI). We will determine the number needed to treat for an additional beneficial outcome (NNTB) or an additional harmful outcome (NNTH) for analyses with a statistically significant difference in the RD.
Unit of analysis issues
The unit of analysis will be the participating infant in individually randomised trials and the neonatal unit (or sub‐unit) for cluster‐randomised trials. For cluster‐randomised trials, we will undertake analyses at the level of the individual while accounting for the clustering in the data using the methods recommended in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2020).
Dealing with missing data
We will request additional data from trial investigators when data on important outcomes are missing or are reported unclearly. If unavailable, we plan to undertake sensitivity analyses to assess the potential impact of missing outcome data (> 20%).
Assessment of heterogeneity
We will examine the treatment effects of individual trials and heterogeneity between trial results by inspecting the forest plots. We will calculate the I2 statistic for each analysis to quantify inconsistency across studies and describe the percentage of variability in effect estimates that may be due to heterogeneity rather than to sampling error. If we detect high levels of heterogeneity (I2 > 75%), we will explore the possible sources (for example, differences in study design, participants, interventions or completeness of outcome assessments).
Assessment of reporting biases
If at least 10 trials are included in a meta‐analysis, we will examine a funnel plot for asymmetry visually and with Harbord's modification of Egger's test (Harbord 2006).
Data synthesis
We will use a fixed‐effect model for meta‐analyses. When moderate or high heterogeneity is detected, we plan to examine the potential causes in subgroup and sensitivity (by methodological quality) analyses.
Subgroup analysis and investigation of heterogeneity
Where data are available, we will undertake subgroup analyses for the primary outcomes:
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extremely preterm (< 28 weeks' gestation) or ELBW (< 1000 grams) infants);
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genus of probiotics or combinations (Bifidobacterium spp. (species plural)., Lactobacillus spp., Sacchromyces spp., Streptococcal spp., others, and combinations thereof);
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type of prebiotic oligosaccharide: natural versus synthetic
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type of enteral feeding permitted for participating infants (human milk versus formula versus mixed).
Sensitivity analysis
We will undertake sensitivity analyses to determine how estimates are affected by including only studies at low risk of bias: (i) selection bias (adequate randomisation and allocation concealment), (ii) detection or performance bias (adequate masking of intervention and measurement), (iii) attrition bias (< 20% loss to follow‐up for primary outcome assessment), and (iv) reporting bias (selective reporting).
Summary of findings and assessment of the certainty of the evidence
We will use the GRADE approach to assess the certainty of evidence of these outcomes (Schünemann 2013): NEC, all‐cause mortality, late‐onset infection and severe neurodevelopmental impairment.
Two review authors (SS, PTH, SO or WM) will assess independently the certainty of the evidence for each of the outcomes. We will consider evidence from randomised controlled trials as high certainty but downgrade the evidence one level for serious (or two levels for very serious) limitations based upon: design (risk of bias); consistency across studies; directness of the evidence; precision of estimates; and presence of publication bias (Appendix 3).
We will use the GRADEpro GDT Guideline Development Tool to create ‘Summary of findings’ tables to report the certainty of the evidence.
