Relationship Between Near-Infrared Spectroscopy and Transabdominal Ultrasonography: Noninvasive Monitoring of Intestinal Function in Neonates

Abstract

Background: Near-infrared spectroscopy (NIRS) has the potential to continuously and noninvasively monitor intestinal function. This technology may be valuable because among neonates, intestinal maturity is highly variable and difficult to assess based solely on clinical signs. The aim of this study was to determine if there is an association between NIRS-based StO2 measurements and peristaltic activity assessed by transabdominal ultrasonography (US).

Material/methods: Nineteen neonates of gestational age >32 weeks were categorized according to "no/low" versus "normal/hyperactive" motility levels, based on blinded US scan results. StO2 was recorded every 2 s for 24 h, following the ultrasound recording. Differences between the resulting estimates of average StO2 (bias of fits) and goodness-of-fit (residuals) were evaluated.

Results: Newborns with normal/hyperactive motility had higher mean StO2 than newborns with no/low motility (72.3±4.4 vs. 65.5±7.9, p<0.05, F=5.65). Residual errors were not significantly different between the 2 groups (p=0.213, F=0.213). A multivariate linear regression model using the means, residuals, and pairwise products of both, demonstrated more significant separation (0.47±0.26 vs. -0.24±0.33, p<0.01, F=27.4). A non-linear variant of the multivariate linear regression model demonstrated greatest separation (0.68±0.24 vs. -0.49±0.53, p<0.01, F=41.9).

Conclusions: This is the first study to demonstrate an association between NIRS-based StO2 measurements and peristaltic activity visualized by ultrasound imaging. NIRS may offer a continuous, noninvasive method to assess motility. This may have significant implications in premature infants at risk for feeding intolerance or necrotizing enterocolitis.

Figure 1

(A) Diagram that summarizes the approximate position of ultrasound transducer and NIRS probe. (B) Sample image of an abdominal ultrasound scan of the right side of the abdomen. Multiple short echogenic lines representing bowel lines can be seen. (C) StO₂ vs. Time plot of an 8-min sample of tissue oximetry. The solid blue line is the line of best fit for the first 4 minutes of the 8-min sample. The solid red line is the line of best fit of the second 4 minutes of an 8-min sample.

Figure 2

Consort flow diagram.

Figure 3

Relationship between StO₂ measurements and US categories. Four sets of 19 horizontal box plots. Each box plot summarizes the mean and interquartile ranges for each StO₂ parameter, obtained from the 4-min linear fits over a 24-h period. Green box plots correspond to neonates with normal/hyperactive motility. Yellow box plots correspond to neonates with no/low motility. Solid blue vertical lines represent the mean of each category. Dashed blue vertical lines were added as continuations of the solid lines for comparison. (A) Neonates assigned to normal/hyperactive group had higher average StO₂ than those assigned to no/low motility (72.25±4.36 vs. 65.53±7.93; p<0.05, F value=5.65). (B) The variability (average of residual error of 4 min linear fits) was not significantly different between the 2 categories (1.48±0.26 vs. 1.73±0.58, p=0.213, F=0.213). (C) The multivariate linear regression model utilizing a combination of means, residuals, and pairwise products of both described higher separation (0.47±0.26 vs. −0.24±0.33, p<0.01, F=27.4). (D) The highest separation was found utilizing a multivariate nonlinear regression model (0.47±0.26 vs. −0.24±0.33 vs., p<0.01, F=27.4).