Can pain under anesthesia be measured? Pain-related brain function using functional near-infrared spectroscopy during...

Quantitative measurement of perisurgical brain function may provide insights into the processes contributing to acute and chronic postsurgical pain.

We evaluate the hemodynamic changes in the prefrontal cortex (medial frontopolar cortex/mFPC and lateral prefrontal cortex) and the primary somatosensory cortex/S1 using functional near-infrared spectroscopy (fNIRS) in 18 patients ($18.2\pm 3.3$ years, 11 females) undergoing knee arthroscopy.

We examined the (a) hemodynamic response to surgery and (b) the relationship between surgery-modulated cortical connectivity (using beta-series correlation) and acute postoperative pain levels using Pearson's $r$ correlation with 10,000 permutations.

We show a functional dissociation between mFPC and S1 in response to surgery, where mFPC deactivates, and S1 activates following a procedure. Furthermore, the connectivity between (a) left mFPC and right S1 (original $r=-0.683$, $p_{\text{permutation}}=0.001$), (b) right mFPC and right S1 (original $r=-0.633$, $p_{\text{permutation}}=0.002$), and (c) left mFPC and right S1 (original $r=-0.695$, $p_{\text{permutation}}=0.0002$) during surgery were negatively associated with acute postoperative pain levels.

Our findings suggest that greater functional dissociation between mFPC and S1 is likely the result of inadequately controlled nociceptive barrage during surgery leading to more significant postoperative pain. It also supports the utility of fNIRS during the perioperative state for pain monitoring and patient risk assessment for chronic pain.