REVIEW 4 major objections 4 minor 10 references
Pain Analysis, in Premature Infants, Using Near Infrared Spectroscopy (NIRS)
T0 review · 4 major / 4 minor · reviewed 2026-08-14 · deepseek-v4-flash
Pith's one-line read NIRS brain-oxygen readings drop measurably after painful procedures in premature infants.
desk verdict A small, honestly written pilot that adds little to Slater/Ranger's established NIRS-pain link; the lone p=0.01 cannot support a pain-specific claim without a control period. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the regional cerebral oximetry value rSO2, computed by the INVOS 5100C as the ratio of oxygenated hemoglobin to total hemoglobin and sampled every 30 seconds. The protocol places the probe on the side of the forehead opposite the procedure, records roughly 10 minutes of baseline, marks the painful procedure, records another 10 minutes, and then compares pre and post medians with a Wilcoxon signed rank test. The mechanism being tested is the hypothesis that cortical activation from pain increases oxygen demand faster than oxygenated blood arrives, so the ratio dips.
What would settle it
Collect NIRS continuously in the same preterm infants during 20-minute windows with no procedure and during a matched non-painful handling event; if the median oximetry falls by about 1.8 percentage points in those control windows as often as it does after a heel stick, then the negative deflection is not specific to pain.
Extended reading notes
Core claim
The central claim is that an acute painful procedure is typically followed by a negative deflection in NIRS regional cerebral oximetry in preterm infants. Comparing each infant's first collection event, the median of the medians was 78.3% before the procedure and 76.5% after it, and a Wilcoxon signed rank test at the 0.05 level reported p = 0.01. The paper interprets this drop as nociceptive cortical activity registered through oxygen supply and demand in the brain, and it presents NIRS as a candidate technology for automated neonatal pain detection.
Load-bearing premise
The paper treats the entire 10-minute post-procedure window as the pain response, without a no-pain control procedure or correction for spontaneous drift, so the observed drop is assumed to be caused by the painful event.
Editorial extensions
If this is right
- If the result holds, NIRS regional oximetry offers a continuous numeric pain signal in preterm infants, unlike intermittent behavioral scores.
- A negative deflection after heel sticks, blood draws, and vaccinations could serve as a common endpoint in studies of pain-relief interventions.
- Pairing NIRS with behavioral or facial-expression monitoring could close the sensitivity gap the authors saw in their earlier automated pain detection.
- Continuous NIRS recording across an infant's NICU stay could reveal whether the cortical pain response strengthens or distorts after repeated procedures.
- A persistent or exaggerated deflection might become an early marker of abnormal pain processing and guide earlier analgesia.
Reading between the lines
- Editorial extension: The 10-minute post-window conflates the pain response with settling, feeding, and handling effects; a matched no-pain control session would test how much of the 1.8-point drop is specifically nociceptive.
- Editorial extension: Because rSO2 is a ratio, the same deflection could arise from a rise in total hemoglobin rather than a true oxygen deficit; separating HbO2 and HbH changes would clarify the physiology.
- Editorial extension: If the drop replicates in a larger cohort, NIRS could be combined with heart-rate and oxygen-saturation time series to build a multimodal pain detector; that is a testable next step the paper does not spell out.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. This manuscript reports a prospective pilot study of using near-infrared spectroscopy (NIRS) regional cerebral oximetry to detect acute pain in preterm infants. NIRS data were collected for about 10 minutes before and 10 minutes after a clinically indicated painful procedure (heel stick or vaccination) in NICU infants with birth gestational age under 37 weeks. Among 15 consented infants, 25 data collection events were reportedly completed. For each infant's first collection event, the median of the infant-level median pre-procedure rSO2 was 78.3% and the post-procedure value was 76.5%, with a Wilcoxon signed-rank p-value of 0.01. The authors conclude that an acute painful procedure is typically followed by a negative deflection in NIRS readings and that NIRS may be useful for automated neonatal pain detection. The manuscript explicitly acknowledges the pilot nature and the insufficient data for longitudinal conclusions.
Significance. If the reported effect is real and specifically attributable to pain, this pilot would provide a useful proof-of-concept that a commercially available bedside NIRS monitor can detect nociceptive cortical responses in preterm infants, complementing previous evoked-potential and behavioral studies. The authors use an appropriate nonparametric test for paired small-sample data and are appropriately cautious about longitudinal conclusions. However, the central claim is currently supported only by a within-session pre/post comparison with no control condition, no artifact handling, and internal inconsistencies in the reported enrollment numbers. As presented, the result cannot be distinguished from sensor drift, probe settling, or handling-related changes, so the significance for pain monitoring is plausible but not established.
major comments (4)
- [II-D (Study Protocol)] The design lacks any sham procedure, no-pain control period, or probe-stability run. The pre-procedure 10-minute window is immediately followed by the clinical procedure and then a 10-minute post window, and the entire post window is summarized by its median. Any slow downward drift in the NIRS signal, settling after the INVOS auto-baseline, or changes due to the infant's positioning and handling during the procedure would be scored as a pain response. Because the comparison is only pre versus post within each infant, the p-value of 0.01 cannot be attributed to nociception without evidence that the post-procedure deflection would not occur in the absence of a painful procedure. At minimum, the manuscript should report a no-procedure control recording of comparable duration or reanalyze the data time-locked to the procedure onset, and the conclusions should be tempered accordingly.
- [II-B and Figure 1 (Infant Data Collection)] The participant counts are internally inconsistent. The text states that data were obtained on thirteen infants because consent was withdrawn on one infant and one was discharged, yet it then says 'A total of twenty-five data collection events were performed on the fourteen infants that maintained informed consent.' Section II-A says fifteen infants were consented. These numbers cannot all be correct, and Figure 1 should clarify the flow. This inconsistency directly affects the sample size underlying the statistical test and must be resolved before the p-value can be interpreted.
- [II-E and III-B (Statistical Analysis and Results)] The analysis plan compares ordered collection events (1st, 2nd, etc.) but only the first-collection result is reported as significant. The manuscript does not state whether any correction for multiple comparisons was applied, and it does not report effect sizes, confidence intervals, or any measure of variability beyond medians. Figure 3 shows only the median pre and post values without error bars, spread, or individual trajectories. Given the small sample and the modest 1.8 percentage-point difference in the median of medians, these omissions make it difficult to judge the stability or clinical meaningfulness of the effect.
- [II-C and II-D (Equipment and Protocol)] The NIRS device samples at 30-second intervals, yet the manuscript describes a pain response that may be brief and transient. The protocol also does not describe any screening or rejection of motion artifacts, probe displacement, or signal-quality indicators. With a 30-second sampling period, the median of a 10-minute post window may be dominated by slow drift rather than the acute response, and without artifact handling the reported negative deflection could be an artifact of movement during the heel stick or vaccination. The authors should report signal-quality measures, justify the temporal window, and acknowledge the sampling-rate limitation in interpreting the negative deflection.
minor comments (4)
- [Throughout] There are several typographical errors: 'heal sticks' should be 'heel sticks', 'Wilcoxson' should be 'Wilcoxon', 'indentified' should be 'identified', and 'studys' should be 'study's'.
- [References] Reference 9 is cited as '(Zamami)' in the text without a year, and the reference list entry for Zamzami et al. is missing the publication year in the citation call-out. Please make all citations consistent.
- [Section II-D] The phrase 'Post-procedure data were then collected for an additional 10 additional minutes' is redundant; it should read 'for an additional 10 minutes'.
- [Figure 3] The figure would be much more informative if it displayed the paired pre/post values for each infant, the direction of change, and some measure of spread (e.g., interquartile range) rather than only the medians.
Circularity Check
No circularity: the p-value is computed directly from measured pre/post NIRS medians, with no fitted parameters and no load-bearing self-citation.
full rationale
The paper's central claim is an empirical comparison: pre-procedure and post-procedure regional cerebral oximetry medians were recorded and tested with a Wilcoxon signed-rank test. The reported p value of 0.01 follows directly from the measured data rather than from any equation, model, or fitted parameter. No derivation step uses the conclusion as an input, and no result is defined in terms of the outcome it is supposed to predict. The only self-citation (Zamzami et al. on facial recognition) is mentioned as prior motivation for the broader device goal, not as evidence for the NIRS finding. The cited external literature (Slater, Taddio, Ranger) is used only to motivate the hypothesis and interpret the direction of the response, not to generate the statistical result. The study has important experimental-design limitations, such as the absence of a sham or no-pain control period, but those are validity/correctness concerns, not circularity: the statistical test is computed from independent pre and post measurements. Therefore no circular step is present, and the appropriate score is 0.
Assumptions & free parameters
assumptions (4)
- domain assumption NIRS rSO2 reflects nociceptive cortical hemodynamic activity.
- domain assumption The contralateral forehead probe placement captures the cortical response to a painful stimulus in the limb.
- domain assumption The 10-minute post-procedure window captures the pain-evoked response.
- domain assumption The painful procedure is accurately time-stamped and the NIRS data are free of significant artifacts.
Cite this review
Pith. "Pith review of Pain Analysis, in Premature Infants, Using Near Infrared Spectroscopy (NIRS)." pith.science (2026). https://pith.science/paper/W35AQSHH
@misc{pith2026190810240,
author = {Pith},
title = {Pith review of: Pain Analysis, in Premature Infants, Using Near Infrared Spectroscopy (NIRS)},
year = {2026},
howpublished = {\url{https://pith.science/paper/W35AQSHH}},
note = {Machine review of arXiv:1908.10240}
}
read the original abstract
Background: The role of neonatal pain on the developing nervous system is not completely understood, but evidence suggests that sensory pathways are influenced by an infants pain experience. Research has shown that an infants previous pain experiences lead to an increased, and likely abnormal, response to subsequent painful stimuli. We are working to improve neonatal pain detection through automated devices that continuously monitor an infant. The current study outlines some of the initial steps we have taken to evaluate Near Infrared Spectroscopy (NIRS) as a technology to detect neonatal pain. Our findings may provide neonatal intensive care unit (NICU) practitioners with the data necessary to monitor and perhaps better manage an abnormal pain response. Methods: A prospective pilot study was conducted to evaluate nociceptive evoked cortical activity in preterm infants. NIRS data were recorded for approximately 10 minutes prior to an acute painful procedure and for approximately 10 minutes after the procedure. Individual data collection events were performed at a weekly maximum frequency. Eligible infants included those admitted to the Tampa General Hospital (TGH) NICU with a birth gestational age of less than 37 weeks. Results: A total of 15 infants were enrolled and 25 individual studies were completed. Analysis demonstrated a statistically significant difference between the median of the pre- and post-painful procedure data sets in each infants first NIRS collection (p value = 0.01). Conclusions: Initial analysis shows NIRS may be useful in detecting acute pain. An acute painful procedure is typically followed by a negative deflection in NIRS readings.
Figures
Reference graph
Works this paper leans on
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American Society of Anesthesiologists
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Reviewed August 14, 2026 · model on record in the stance chip above.
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