Functional near-infrared spectroscopy and neonatal pain

Myron Yaster MD

It’s really hard to believe, but over most of human history, neonates were thought to neither experience nor remember pain or painful experiences.  Indeed, when I was a resident and fellow in anesthesiology in the late 1970s, surgery in the newborn was a ‘resuscitation” and often performed without general anesthesia (paralysis plus oxygen). There were a lot of reasons for this.  The newborn presenting for surgery was fragile, hemodynamically unstable, monitoring consisted of a finger on the pulse and a precordial stethoscope  (no pulse oximeters, agent analyzers, automated blood pressure cuffs, etc.!), and the vapor anesthetic was halothane which profoundly depressed the myocardium of newborns at MAC (which wasn’t clearly established either).  Fortunately, there have been remarkable changes and progress over the years and today there is no longer a need to “justify” general anesthesia for newborn surgery (see the January 20 Remembering the classics PAAD by Rob Friesen).  Today’s PAAD and accompanying editorial was an “ah ha” moment for me as I read it and is research I wish I had thought of and/or been involved with. Myron Yaster MD

Editorial

Vutskits L, Skowno J. Near-infrared spectroscopy: More than just monitoring brain oxygenation. Paediatr Anaesth. 2022 Mar;32(3):394-395. PMID: 35170164

Original article

Yuan I, Nelson O, Barr GA, Zhang B, Topjian AA, DiMaggio TJ, Lang SS, Christ LA, Izzetoglu K, Greco CC, Kurth CD, Ganesh A. Functional near-infrared spectroscopy to assess pain in neonatal circumcisions. Paediatr Anaesth. 2022 Mar;32(3):404-412. PMID: 34747096

Most of you have used near-infrared spectroscopy (NIRS) to non-invasively monitor cerebral oxygenation in infants with congenital heart disease undergoing cardiac surgery. Clinical observations suggest an association of “low” NIRS with ischemia and “bad” outcomes, thus, monitoring NIRS values, and actively keeping them in a “physiological range” during anesthesia sounds like a plausible and valuable strategy.  Yuan and colleagues at the Children’s Hospital of Philadelphia using forehead NIRS monitoring, recorded the functional temporal pattern and magnitude of changes in oxyhemoglobin and total hemoglobin content (fNIRS) during circumcision in healthy, awake, newborn males while simultaneously measuring observational pain responses with the Neonatal Infant Pain Scale (NIPS). The authors divided circumcision into several discrete events: preop before local, local injection (penile nerve block), prep before incision, sucrose, incision, Gomco applied, Gomco off.  They found: “Noxious stimuli elicited an increase in fNIRS parameters, especially in cerebral blood volume reflected by HbT, whereas innocuous or soothing stimuli caused a decrease in fNIRS parameters. The magnitude of fNIRS changes varied with the type of stimuli; pressure noxious stimuli elicited a larger fNIRS response compared to sharp noxious stimuli; (2) Local anesthetic injection was effective in attenuating the fNIRS response to subsequent incision sharp pain, but not to Gomco-related pressure pain. Local anesthetic was not able to prevent an increase in NIPS during subsequent incision; and (3) Although fNIRS and NIPS changed in the same direction for most events, only fair positive correlations were noted for events 5-Incision and 7-Gomco On”. Their results suggest that fNIRS can be used to monitor perioperative pain and analgesia and could replace current pain assessment tools which rely on behavioral and physiological observations to pain like the CRIES, FLACC, and NIPS.

Will it work in anesthetized newborns is unknown, but if it does, it will open the flood gates to a stampede of future research that can, if successful, fundamentally change the practice of neonatal anesthesia.  Think of it like this: currently we have no real method of assessing pain in anesthetized patients other than movement to surgical stimulus (MAC) which obviously doesn’t work in paralyzed patients, or proxies, like elevations in heart rate, blood pressure or pupillary responses. A routinely placed fNIRS monitor could guide us in how much opioid (or no opioid) we administer, how we adjust our vapor anesthetics etc.  Obviously, it may also be useful outside of the operating room like the NICU where painful procedures are still exceedingly common.

Finally, where to place the fNIRS monitors?  In this study the authors used the forehead (frontal neocortex).  The somatosensory cortex where a lot of pain transmission is processed would probably be better but much more difficult to use.  This too, I’m sure, will also be a hot topic for future research.