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

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.