Measuring “pain load” during general anesthesia

Abstract

fNIRS allows for ongoing measures of brain functions during surgery. The ability to evaluate cumulative effects of painful/nociceptive events under general anesthesia remains a challenge. Through observing signal differences and setting boundaries for when observed events are known to produce pain/nociception, a program can trigger when the concentration of oxygenated hemoglobin goes beyond ±∆0.3 mM from 25 seconds after standardization. fNIRS signals were retrieved from patients undergoing knee surgery for Anterior Cruciate Ligament (ACL) repair under general anesthesia. Continuous fNIRS measures were measured from the primary somatosensory cortex (S1), which is known to be involved in evaluation of nociception, and the medial polar frontal cortex (mPFC), which are both involved in higher cortical functions (viz., cognition, emotion). A ± ∆0.3 mM threshold for painful/nociceptive events was observed during surgical incisions at least twice, forming a basis for a potential near-real time recording of pain/nociceptive events. Evidence through observed true positives in S1 and true negatives in mPFC are linked through statistically significant correlations and this threshold. Our results show that standardizing and observing concentrations over 25 seconds using the ±∆0.3 mM threshold can be an arbiter of the continuous number of incisions performed on a patient, contributing to a potential intraoperative pain load index.

Evaluation of Nociception during Pediatric Surgery: A Topical Review

“…Spectral entropy monitor analyzes the EEG entropy (i.e., the degree of perturbation or randomness) and the electromyography (EMG) signal to calculate the response entropy (RE) and the state entropy (SE) as a measure of intraoperative analgesia [ 12 , 18 , 19 ]. The RE is computed from a frequency range of 0.8–47 Hz and integrates both EEG and EMG signals, whereas the SE derives from an EEG frequency range of 0.8–32 Hz and represents the depth of hypnosis [ 18 ]. A difference between the two (ΔRE-SE) less than 10 was associated with a decrease of intraoperative opioid administration [ 9 , 18 ].…”

“…The RE is computed from a frequency range of 0.8–47 Hz and integrates both EEG and EMG signals, whereas the SE derives from an EEG frequency range of 0.8–32 Hz and represents the depth of hypnosis [ 18 ]. A difference between the two (ΔRE-SE) less than 10 was associated with a decrease of intraoperative opioid administration [ 9 , 18 ]. Whether the ΔRE-SE simply measures the level of (in)adequate anesthesia rather than nociception is still unclear.…”

“…The electrical intensity needed to elicit a spinal polysynaptic withdrawal reflex can be used as surrogate of the level of nociception [ 18 ]. A clinically adequate, opioid-based general anesthesia (absence of somatic and hemodynamic responses to high intensity tetanic stimulations) abolishes only 59% of the spinal cord and brain nociception, which is still detectable with functional magnetic resonance imaging [ 2 ].…”

“…The Nociceptive flexor reflex (NFR or RIII reflex, Dolosys GmbH, Berlin, Germany) measures the EMG activity secondary to the electrical stimulus (on the biceps femoris muscle) and has been studied during general anesthesia [ 18 , 23 ]. Current data show a 63% probability of predicting nociception [ 22 ].…”

“…Current data show a 63% probability of predicting nociception [ 22 ]. However, age, gender, weight, neuromuscular blockers, and muscular diseases limit its application [ 18 ]. Data in pediatrics are not available.…”