Prefrontal Cortical Near-Infrared Spectroscopy for Acute Pain Assessment in Infants: A Feasibility Study

Abstract

Background: Assessing pain in infants is challenging due to their inability to communicate discomfort. Accurate pain evaluation is essential, as unaddressed pain might lead to long-term neurological consequences. This study investigates the use of conventional two-site near-infrared spectroscopy (NIRS) to evaluate hemodynamic responses in the prefrontal cortex during nociceptive stimuli. Methods: Data were prospectively collected from ten infants undergoing elective heel lance/squeeze (HLS) after surgery. Continuous bilateral NIRS oxygenation monitoring was performed alongside cardiorespiratory and behavioral (Children's and Infant's Postoperative Pain Score (CHIPPS)) pain assessments before, during, and after HLS. The primary outcome was the correlation between NIRS response and CHIPPS. Results: The average gestational and postnatal ages were 39 weeks and 49 days. No significant changes in prefrontal oxygenation levels (left, right, combined, ipsilateral, contralateral) were observed during the first ten seconds of HLS compared with baseline. Although CHIPPS and heart rates increased, oxygenation levels remained unchanged throughout the entire HLS event. Significant fluctuations in oxygenation levels from baseline were recorded across all optode configurations, with changes in the lowest oxygenation levels at the contralateral and left hemispheres inversely correlated with CHIPPS and HR changes. Conclusions: While there were subtle alterations in NIRS signals suggesting potential nociceptive-evoked changes, these were inconclusive. By design, the utilized two-site conventional NIRS system may not effectively detect acute pain. Future studies on prefrontal cortical pain processing could benefit from confirmatory NIRS signals from the primary somatosensory and motor regions. Integrating data from fNIRS, fMRI, EEG, along with sympathetic indicators like skin conductance and heart rate variability, would improve the quantification of cortical pain processing in non-verbal infants.

Keywords: NIRS; bilateral frontal near-infrared spectroscopy; cerebral hemodynamics; heel/lance squeeze; infants; nociceptive stimulus; pain assessment; pediatric surgery; personalized interventions; prefrontal cortex; surgical pain management.

Figure 1

(a) A representative c-rSO₂ trace illustrating a contralateral-sided decrease in oxygenation in the prefrontal cortex upon a nociceptive HLS stimulus before (green trace) but not after Bandpass filtering for artifact removal (grey trace). (b) Comparison of normalized 2 min baseline c-rSO₂ levels with normalized c-rSO₂ averages during first 10 s after nociceptive stimulus with no differences among NIRS configurations (p value range: 0.51–1). (c–f) Comparison of 2 min baseline c-rSO₂ levels with the lowest and highest c-rSO₂ levels during an HLS event at various NIRS configurations (left, right, ipsilateral, and contralateral hemisphere). Data are expressed as mean ± SEM. ** (p ≤ 0.01), or *** (p ≤ 0.001).

Figure 1

(a) A representative c-rSO₂ trace illustrating a contralateral-sided decrease in oxygenation in the prefrontal cortex upon a nociceptive HLS stimulus before (green trace) but not after Bandpass filtering for artifact removal (grey trace). (b) Comparison of normalized 2 min baseline c-rSO₂ levels with normalized c-rSO₂ averages during first 10 s after nociceptive stimulus with no differences among NIRS configurations (p value range: 0.51–1). (c–f) Comparison of 2 min baseline c-rSO₂ levels with the lowest and highest c-rSO₂ levels during an HLS event at various NIRS configurations (left, right, ipsilateral, and contralateral hemisphere). Data are expressed as mean ± SEM. ** (p ≤ 0.01), or *** (p ≤ 0.001).

Figure 2

Correlations between the highest and lowest c-rSO₂ changes from baseline (Δc-rSO₂) and the reference pain measures ΔHR and ΔCHIPPS during nociceptive heel lance/squeeze procedures, considering the different NIRS optode configurations—contralateral, ipsilateral, left, and right hemispheres.