During the early weeks of life, developmental immaturity and clinical fragility of
extremely preterm (EPT) infants limit oral and enteral feeding. Parenteral nutrition
(PN) allows provision of energy requirements and essential nutrients, including fatty
acids. The optimization of nutrition presents a critical opportunity to attenuate
the adverse neurological consequences of prematurity and potentially to improve neurodevelopmental
outcome.[1 ]
The last trimester of gestation is a critical period for brain growth and maturation;
during this period, the cerebellum and cortical gray matter exhibit the highest growth
rates, with 4- to 5-fold increase in volume.[2 ] Fat intake has been shown to have a large effect on brain growth.[3 ]
For many years soybean-based lipid emulsion (SLE) has been the principal source of
intravenous fat. SLE is rich in omega-6 (ω-6) polyunsaturated fatty acids (PUFAs),
with minimal omega-3 (ω-3) PUFAs. In the last decade, newer lipid emulsions (LEs)
have been introduced to offer a more balanced provision of lipids derived from multiple
sources. Multicomponent lipid emulsion (MLE) includes medium-chain triglycerides,
which are rapidly metabolized lipids; soybean oil, which is a source of essential
fatty acids; olive oil, which naturally contains the antioxidant vitamin E; and fish
oil, rich of ω-3 PUFAs, which are known for their anti-inflammatory effects.
Fish oil has a higher ratio of ω-3 to ω-6, as compared with soybean oil, especially
because of the high content of ω-3 long-chain PUFAs, such as docosahexaenoic acid
(DHA) and eicosapentaenoic acid, which seem to be crucial for growth of preterm infants.[4 ]
[5 ]
[6 ]
[7 ]
[8 ]
In our previous study, we found that the use of MLE (SMOFlipid 20%, Fresenius Kabi,
Italy) in very low birth weight (VLBW) infants significantly reduces the loss of head
circumference (HC) and length z -scores from birth to 36 weeks' postmenstrual age (PMA) or at discharge home compared
with the use of pure SLE (Intralipid 20%, Fresenius Kabi, Italy).[8 ]
We hypothesized that the use of MLE in PN would be related to larger volume of the
cerebellum on brain magnetic resonance at term of equivalent age (TEA) in extremely
low birth weight (ELBW) infants.
Materials and Methods
Study Design and Patients
We retrospectively analyzed the brain magnetic resonance imaging (MRI)—acquired at
TEA—of a cohort of preterm infants with gestational age (GA) ≤28 weeks and/or birth
weight (BW) <1,000 g, admitted to the Neonatal Intensive Care Unit of the Fondazione
Policlinico Universitario Agostino Gemelli, IRCCS in Rome, Italy, between December
1, 2015, and May 31, 2019. The enrolled infants were a cohort of subjects randomly
assigned in our previous trial to receive an MLE (SMOFlipid 20%, Fresenius Kabi, Italy)
or SLE (Intralipid 20%, Fresenius Kabi, Italy).[8 ]
Infants with congenital or chromosomal malformations, inborn errors of metabolism,
and/or congenital infections of the central nervous system, and with major brain pathology
such as intraventricular hemorrhage (IVH)[9 ] grade 3 or higher, periventricular leukomalacia (PVL),[10 ] and/or parenchymal hemorrhagic infarction on cerebral ultrasound were excluded.
The study protocol was approved by Institutional Review Board (Prot. ID 2759). Written
informed consent was obtained from the parents.
Data Collection
Baseline databased on sex, BW and BW z -score, HC and HC z -score, length and length z -score, GA (based on the last menstrual period, ultrasound in early pregnancy, and
postnatal physical examination), the number of prenatal (two doses of intramuscular
betamethasone 12 mg 24 h apart), and postnatal steroid course were recorded. Furthermore,
BW, HC, length, and their z -scores at time of MRI scan were included.
The following clinical outcomes were recorded for each infant: respiratory distress
syndrome; pharmacologically treated patent ductus arteriosus; bronchopulmonary dysplasia,
diagnosed according to consensus definition[11 ] and only moderate and severe degrees were considered; necrotizing enterocolitis
(NEC), diagnosed using modified Bell's criteria[12 ] and only degrees >2A were considered; any stage of retinopathy of prematurity[13 ]; late-onset sepsis, defined as a positive blood culture or suggestive clinical and
laboratory findings leading to treatment with antibiotics for at least 7 days despite
absence of a positive blood culture; and length of hospital stay.
Nutritional Intake
The composition of the two LEs are detailed in [Table 1 ]. Daily total parenteral and enteral protein, fat, and caloric intakes for the first
28 days of life were available for all infants.
Table 1
Composition of the multicomponent lipid emulsion and the pure soybean oil emulsion
Lipid emulsion
MLE (SMOF lipid)
SLE (Intralipid)
Oil source, %
100
Soybean
30
Coconut (MCT)
30
Olive
25
Fish
15
Composition of major fatty acids, %
MCTs
Caproic acid (6:0)
Trace
–
Caprylic acid (8:0)
17
–
Capric acid (10:0)
12
–
Lauric acid (12:0)
0.2
–
Long-chain triacylglycerols
Myristic acid (14:0)
1
0.2
Palmitic acid (16:0)
9
11
Palmitoleic acid (16:1n-7)
2
–
Stearic acid (18:0)
3
4
Oleic acid (18:1n-9)
29
24
ω-6 long-chain triacylglycerols
Linoleic acid (18:2n-6)
19
53
Arachidonic acid (20:4n-6)
0.5
–
ω-3 long-chain triacylglycerols
α-Linolenic acid (18:3n-3)
2
8
Eicosapentaenoic acid (20:5n-3)
3
–
Docosahexaenoic acid (22:6n-3)
2
–
Phytosterols, mg/L
47.6
348
α-Tocopherol, mg/L
200
38
Abbreviations: MCT, medium-chain triacylglycerols; MLE, multicomponent lipid emulsion;
SLE, soybean-based lipid emulsion.
Intravenous lipids were administered at a dose of 1.5 g/kg/d within first 24 hours
of life and were gradually increased by 0.5 g/kg/d until the dose of 3 g/kg/d was
reached within the first week of life. According to our local protocol, the parenteral
lipid intake was reduced by 25 to 50% when plasma triglycerides concentrations were
between 265 and 442 mg/dL and was stopped when they exceeded 442 mg/dL. The feeding
protocol provided that a minimal enteral feeding was started on the first day of life.
Enteral feeding was increased by 20–30 mL/kg/d. All infants received human milk (own
mother's milk or donor milk); human milk was enriched with fortifier (Aptamil BMF,
Milupa, Germany) when enteral feeding of 100 mL/kg/d was reached.
Magnetic Resonance Imaging
All MRI investigations were performed according to a standard protocol on a 1.5 Tesla
MRI system (Philips Healthcare) with a standard head coil.
Infants were sedated using Sevoflurane in O2 and administered by vaporization or intravenous midazolam before the examination
as the clinical local protocol.
Heart rate, transcutaneous oxygen saturation, and respiration rate were continuously
monitored, and an expert anesthetist was present throughout the entire examination.
The scanning protocol included T2- and T1-weighted imaging. Parameters of the scanning
protocol included: axial three-dimensional (3D) T1-weighted image, coronal 3D T1-weighted
image, axial T2-weighted image, and coronal T2-weighted image.
We used axial T2-weighted MRI to measure supratentorial volume (SuV), cerebellar volume
(CeV), brainstem volume (BsV), total brain volume (TBV), and CeV corrected for TBV.
SuV was defined as the volumes of the cerebral hemispheres, including cortical gray
matter, basal ganglia, and white matter, without the lateral ventricles, the III ventricle,
and the cerebrospinal fluid (CSF) spaces. BsV was defined as the volumes of the midbrain,
pons, and medulla oblongata without the CSF spaces, the IV ventricle, and the Silvian
acqueduct. CeV was defined as the volume of the entire cerebellum (vermis and hemispheres),
without the CSF spaces and the IV ventricle. TBV was defined as the volume of all
brain structures, that is, intracranial volume without the volume of the ventricles
and CSF ([Fig. 1 ]). All measures were corrected for PMA at the time of scan with linear regression
analysis.
Fig. 1 Volumetric measurements, T2-weighted axial MR images. Supratentorial volume is shown
in blue-shaded areas (A , B ); cerebellar volume is shown in red-shaded areas (B , C ); brainstem volume is shown in green-shaded areas (B , C ).
Measurements were performed twice, with an automatic segmentation method and then
with a semiautomatic segmentation open-source program called ITK-SNAP (version 3.8.0,
University of Pennsylvania, Philadelphia, PA), using the Cavalieri's principle.[14 ]
[15 ]
Two neonatologists with experience in the field of neonatal neuroimaging (M.L.T. and
C. Cocca) and a neuroradiologist (G.D.A.) evaluated the MRI scans for brain injury
according to Kidokoro et al.[16 ]
Primary and Secondary Outcomes
The primary outcome of the study was the CeV valued on MRI acquired at TEA.
Secondary outcomes included TBV, SuV, BsV, and CeV corrected for TBV evaluated on
MRI acquired at TEA.
Sample Size and Statistical Analyses
The sample size calculation was based on the literature data according to which premature
infants with a mean GA of 28 weeks, and without severe IVH (grades 3–4), have a mean
CeV measured with MRI equal to 18.3 ± 3.2 cm3 .[17 ] Expecting an 18% gain in CeV (equal to 3.3 cm3 ) in premature infants who received the MLE, a sample of at least 16 infants per arm
is required, considered an α error of 0.05 and a study power of 80%.[18 ]
Data were analyzed with Statistical software SPSS for Windows version 25.0 (SPSS,
Inc., Chicago, IL). Continuous variables are expressed as mean and standard deviation
or as median and interquartile range, whereas categorical variables are expressed
as numbers and percentages. Continuous variables were first tested for normal distribution
by using the Shapiro–Wilk test. Categorical variables were compared using the chi-squared
test or the Fisher's exact test. Continuous variables were compared using student
t -test for independent samples (to compare data with normal distribution) or Mann–Whitney
U test (to compare the others continuous data).
Because the volumes increase with PMA, we corrected the volume with linear regression
analysis according to the following equation: corrected volume = measured volume + the
slope × (40 − PMA on MRI). The level of significance was set at p < 0.05.
Results
In our institution, according to local care protocol, preterm infants with GA ≤ 28
weeks and/or BW <1,000 g, and those neonates with cerebral abnormalities at echography,
regardless of GA and BW, underwent cerebral MRI. Then, 51 patients from the original
trial were studied with MRI at TEA. Seventeen patients were excluded: 5 because of
IVH > grade 2, 11 because of PVL, and 1 because of parental informed consent refusal.
MRIs at TEA of 34 infants were then analyzed: 17 in the MLE group and17 in the SLE
group ([Fig. 2 ]).
Fig. 2 Flowchart of included infants. IVH, intraventricular hemorrhage; MRI, magnetic resonance
imaging; PVL, periventricular leukomalacia; TEA, term of equivalent age.
No differences were observed between groups at baseline and for the main clinical
outcomes ([Table 2 ]). The mean PN and enteral nutrition intakes, including energy, protein, and lipid
intake, were similar for both groups over the first 28 days of life. Moreover, there
were no differences between the groups regarding the number of days required to reach
full enteral feeding and the cumulative days of PN ([Table 3 ]).
Table 2
Demographics and clinical characteristics
MLE (n = 17)
SLE (n = 17)
p
Gestational age (wk)
25.9 ± 1.8
27.0 ± 1.8
0.10
Male sex (n)
7 (41)
6 (35)
0.7
Birthweight (g)
665 (575–781)
735 (645–815)
0.26
Birthweight (z -score)
−0.38 ± 1.1
−0.42 ± 1.1
0.92
Length, cm
32.3 ± 2.5
33.5 ± 2.6
0.17
Length z -score
−0.35 ± 0.93
−0.24 ± 1.53
0.8
Head circumference (cm)
22.0 (21.0–24.1)
23.1 (21.5–25.3)
0.21
Head circumference z -score
−0.81 ± 0.84
−0.71 ± 1.06
0.76
Prenatal steroids (n )
7 (41)
8(47)
0.73
Postnatal steroids (n )
6 (35)
3 (18)
0.44
NEC > 2A (n )
1 (5.8)
0 (0)
1
PDA (n )
10 (59)
9 (53)
0.73
RDS (n )
17 (100)
17 (100)
1
BPD (moderate/severe; n )
7 (41)
5 (29)
0.47
ROP (all stages; n )
16 (94)
13 (76)
0.34
Treated ROP (n )
3 (18)
2 (12)
1
Sepsis (n )
10 (59)
10 (59)
1
Length of stay (d)
114 (99–177)
105 (64–124)
0.077
Weight at time of MRI (g)
2,020 (± 429)
1,925 (± 493)
0.52
Weight z -score at time of MRI
−1.5 (± 0.99)
−1.6 (± 0.98)
0.81
Length at time of MRI (cm)
42.8 (± 2.1)
42.0 (± 3.3)
0.41
Length z -score at time of MRI
−1.8 (± 0.87)
−1.9 (± 1)
0.74
Head circumference at time of MRI (cm)
30.5 (± 1.4)
29.6 (± 1.8)
0.14
Head circumference z -score at time of MRI
−1.7 (± 0.94)
−2 (± 0.95)
0.3
Abbreviations: BPD, bronchopulmonary dysplasia; MLE, multicomponent lipid emulsion;
MRI, magnetic resonance imaging; NEC, necrotizing enterocolitis; PDA, patent ductus
arteriosus; RDS, respiratory distress syndrome; ROP, retinopathy of prematurity; SLE,
soybean-based lipid emulsion.
Note: Data are reported as mean (± standard deviation), median (interquartile range),
and number (%).
Table 3
Nutritional data during the first 28 days of life
MLE (N = 17)
SLE (N = 17)
p
Parenteral nutrition duration (d)
50.0 ± 29.5
44.0 ± 28.6
0.53
Time to full enteral feeding (d)
40 (34–52)
36 (28–59)
0.57
Total caloric intake (kcal/kg/d)
92.6 ± 9.6
93.3 ± 18
0.89
Total intravenous caloric intake (kcal/kg/d)
76.2 ± 12
66.7 ± 24
0.16
Total enteral caloric intake (kcal/kg/d)
18.8 ± 18
33.7 ± 0.4
0.11
Total protein intake (g/kg/d)
3.3 ± 0.4
3.4 ± 0.39
0.22
Total intravenous protein intake (g/kg/d)
2.8 ± 0.4
2.5 ± 0.9
0.3
Total enteral protein intake (g/kg/d)
0.6 ± 0.6
1.1 ± 1.1
0.1
Total lipid intake (g/kg/d)
3.1 ± 0.7
3.2 ± 1.2
0.65
Total intravenous lipid intake (g/kg/d)
2.2 ± 0.38
1.8 ± 0.7
0.14
Total enteral lipid intake (g/kg/d)
1.2 ± 1
1.8 ± 1.7
0.21
Abbreviations: MLE, multicomponent lipid emulsion; SLE, soybean-based lipid emulsion.
Note: Data are presented as mean (±standard deviation) or median (interquartile range).
The PMA at which MRIs were performed were comparable between the two study groups.
The CeV as well as the PMA-corrected CeV were significantly higher in the MLE group
than in the SLE group. No difference was found among the other brain volumes considered,
and also CeV corrected for TBV was similar between groups ([Table 4 ]).
Table 4
Study outcomes
MLE (N = 17)
SLE (N = 17
p
Postmenstrual age at MRI study
43.5 ± 8
42.8 ± 10
0.8
Cerebellum volume (cm3 )
24.0 ± 9.6
18.2 ± 6.2
0.045
Cerebellum volume corrected for PMA (cm3 )
22.3 ± 6.5
16.9 ± 7.2
0.027
Cerebellar volume corrected for total brain volume (%)
5.1 (4.3–7.3)
5.1 (3.9–7.2)
0.87
Supratentorial volume (cm3 )
284.7 (253.8–407.9)
283.4 (233.1–297.8)
0.16
Supratentorial volume corrected for PMA (cm3 )
358.3 (179.0–396.8)
294.9 (191.5–345.8)
0.25
Brainstem volume (cm3 )
6.0 ± 0.9
5.3 ± 9.9
0.053
Brainstem volume corrected for PMA (cm3 )
5.7 ± 9.6
5.2 ± 1.1
0.11
Total brain volume (cm3 )
379.5 (208.6–419.6)
316.6 (211.6–364.7)
0.21
Abbreviations: MLE, multicomponent lipid emulsion; MRI, magnetic resonance imaging;
PMA, postmenstrual age; SLE, soybean-based lipid emulsion.
Note: Data are reported as mean (± standard deviation), and median (interquartile
range). Bold p -values are statistically significant.
Discussion
In this retrospective study, we found that the use of MLE in PN positively influences
the CeV in ELBW infants, valued with MRI at TEA. Our previous randomized controlled
trial showed that the use of MLE in VLBW infants significantly reduces the loss of
HC and length z -scores from birth to 36 weeks' PMA or at discharge home compared with the use of
pure SLE.[8 ] MRI study at TEA of a cohort of ELBW infants randomized in this previous study confirms
the beneficial effect of MLE on CeV. However, we could not confirm these results when
we adjusted the CeV for TBV.
The biological plausibility of our finding is that the DHA, highly contained in the
MLE, is a structural constituent of cellular membranes of the gray matter structures.[19 ]
[20 ] DHA are also involved in neurogenesis, antiapoptotic effects, and synaptic plasticity.
EPT infants are generally born before the completion of normal placental transfer
and DHA deposition in fetal tissue: MLE may contribute to restoring this DHA loss,
thus helping brain development.
The ω-6 long chain polyunsaturated fatty acids (LCPUFA) arachidonic acid (AA) is another
important component of MLE, that is known for its structural function in cell membranes,
signaling, specific neuroprotective protein activation, and formation of eicosanoids.
Preterm infants are at risk for adverse neurodevelopmental outcome and rely on parenteral
and enteral nutrition for proper DHA and AA intake.[21 ]
[22 ]
Our findings are consistent with those of Hortensius et al, who studied a cohort of
infants derived from a randomized controlled trial evaluating the effect of two parenteral
LEs. They measured serum DHA and AA levels during the first 28 days of life in patients
who received MLE or olive oil–based LE. They found that serum DHA levels were positively
associated with volumes of several brain structures in EPT infants at TEA, including
cerebellum. No effect of AA levels on brain volumes was found.[23 ]
Existing studies demonstrated the beneficial effect of early lipid intake on preterm
brain development using MRI study.[24 ]
[25 ]
[26 ] Schneider et al demonstrated a significant relationship between cumulative energy
and lipid intake in the first 2 weeks of life and cerebellar, basal nuclei, and TBVs
assessed with MRI studies at TEA.[24 ] Coviello et al demonstrated a significant positive association between cumulative
lipid intake in the first 4 weeks of life and cerebellar, basal ganglia and thalamic
volumes.[25 ] Ottolini et al found that early cumulative lipid intake in the first month of life
is associated with significantly greater CeV at TEA in very premature infants, using
MRI study.[26 ] Our study differs from previous ones because our results underlined that the quality,
and not only the cumulative quantity, of the lipids administered with PN plays a role
in the development of brain structures of preterm infants.
We failed to find differences in the volumes of the other considered brain structures;
this is not surprising because the sample size was calculated on the volume of the
cerebellum, which shows the highest growth rate compared with other intracranial structures
during the last trimester of pregnancy.[27 ]
[28 ] For this reason, while a small sample size allowed us to detect the growth differences
of the cerebellum, which experiences a 34-fold increase in volume during this time
period under favorable conditions, the small sample size may have contributed to not
detecting differences between the other brains volumes. Cerebellum growth can, however,
be considered a proxy for overall brain development, because cerebellum seems to play
an essential role not only in sensorimotor and vestibular control, but also in cognition,
emotion, and autonomic function.[29 ]
[30 ]
It is well known that adequate nutrition plays a crucial role for optimal brain growth
and maturation.[31 ]
[32 ] Lipids and energy contributed most to the beneficial effect of nutrition, considering
that lipids provided a third of total energy. Lipids are essential for brain development
and participate in neuronal membrane structure formation and myelin synthesis.[33 ]
[34 ] Also, the optimization of protein and energy intake in the neonatal period has a
positive impact on cognition, with effects persisting until adolescence.[35 ] Our findings suggest that the quality of nutrients composition may play a critical
role for the brain development, at least for the cerebellum.
Strengths and Limitations
The strength of this study is that, despite its retrospective design, the cohort of
infants derived from a randomized and controlled population, partially limiting the
possibility of confounding factors. On the other hand, the small sample size is the
major limitation of this study, reducing the possibility of statistically exploring
whether other variables could have had an effect on CeV.
Conclusion
Our results suggest that the use of MLE in PN could promote CeV growth in ELBW infants,
valued with MRI at TEA. While encouraging, our findings deserve to be confirmed on
larger samples, as well as complemented by a neurological follow-up to assess whether
the better neuroimaging data also correspond to better neurodevelopmental outcomes.
For the original trial, which included the cohort of this study, a neurological follow-up
was planned at 24 months of corrected age. The results of the 24-month follow-up will
provide data on the possible role of LEs quality on neurodevelopmental outcome.
