4 | DISCUSSION
The use of CPAP to treat RDS in premature infants has been associated
with a lower incidence of chronic lung disease than invasive mechanical
ventilation [13]. Therefore, there has been a notable shift to
non-invasive respiratory support for these infants, and the term “less
may be more” has been fully embraced in neonatology. However, increased
use of CPAP requires a closer examination of its potential side-effects.
The presence of an oro- or nasogastric tube in many of these infants may
allow the delivered and swallowed gas to move to the stomach and further
down the GIT. Abdominal distention may restrict diaphragmatic movement
and lung expansion, and serious complications such as intestinal
perforation and necrotizing enterocolitis have been reported
[14,15,16]. Even though we analyzed the incidence of NEC and
intestinal perforation, along with BPD, and found no significant
difference between MD-nCPAP and bCPAP groups, our study was not powered
to detect these differences ( Table 2) .
Studies using scintigraphy to determine the rate of gastric emptying in
healthy term infants have yielded inconsistent results. While some
studies have reported faster gastric emptying in older infants, a large
recent study found that infants less than 3 months of age have faster
gastric emptying than older infants and children [17,18,19]. As
expected, gastric emptying is twice as fast in infants fed breast milk
compared to formula [20]. Conversely, delayed gastric emptying has
been associated with gastro-esophageal reflux in older children
[21]. Using scintigraphy in VLBW infants, Gounaris et al. reported
faster gastric emptying in those treated with MD-nCPAP compared to
healthy controls [5]. However, the utility of scintigraphy is
limited in children and infants because of the need to limit radiation
exposure. US provides a noninvasive method to estimate the gastric
emptying rate and can be performed at the patient’s bedside [22,23].
We found that neither the ACSA nor spheroid method gastric emptying
rates were statistically different between infants treated with MD-nCPAP
and bCPAP, analyzed by multivariable analysis adjusting for emptying
phase (early, late) and GA (25-28 weeks, 28-34 weeks). The caloric
density of the feedings, type of milk (expressed human milk only, donor
human milk only, formula only, or mixed) or volume of milk were not
significantly associated with the ACSA or spheroid rates. Corrected
gestational age (CGA) was significantly different between the MD-nCPAP
and bCPAP infants, but regression analysis of ACSA or spheroid rates and
CGA showed no correlation between the two variables. Our findings are
consistent with a recent meta-analysis that demonstrated no correlation
between postmenstrual age and gastric emptying time [24].
A significantly faster gastric emptying was noted in the early phase
(1-2 hours from the initiation of a feed) compared to the late phase
(2-3 hours after initiation of a feed) when using the spheroid method,
but this was seen only in the 25+0 to 27+6 week GA group using the ACSA
method. This is consistent with previous studies showing faster gastric
half-emptying times in the immediate post-prandial period using
different methods of measurement [5,8,19]. A meta-analysis of 66
studies in various age groups performed by Bonner et al. revealed a
non-linear emptying rate with faster early phase, especially for
liquid-fed subjects compared to those fed solid food [24]. This can
be explained by a high intragastric volume in the early phase, which
stimulates the mucosal stretch receptors [29,30,31,32].
We noted high gastric residual percentages using both methods – 41%
(30.3-49.8) by ACSA and 24.5% (16.8-32.3) by spheroid. Higher gastric
residual percent measured by the ACSA method compared to the spheroid
method is likely due to the antrum being the last part of the stomach to
empty. It appears that traditional measurements of pre-feeding residual
volumes by gastric aspiration underestimate the proportion of retained
feeding by 19-25%. This may be dependent on patient position, feeding
tube size, position of the tip of the tube, milk viscosity and
aspiration technique [25,26,28]. Our subjects at the time of the US
were receiving only non-invasive respiratory support and tolerating full
enteral feeding without clinical evidence of feeding intolerance. This
finding brings into question the reliability and value of using
aspirated gastric residuals to assess feeding intolerance or
gastrointestinal pathology in neonates [27,28].