Comparison of three stimulation sites on the pupillary dilation reflex amplitude evoked by a standardized noxious test

Depth of Anesthesia and Nociception Monitoring: Current State and Vision For 2050

Anesthesia objectives have evolved into combining hypnosis, amnesia, analgesia, paralysis, and suppression of the sympathetic autonomic nervous system. Technological improvements have led to new monitoring strategies, aimed at translating a qualitative physiological state into quantitative metrics, but the optimal strategies for depth of anesthesia (DoA) and analgesia monitoring continue to stimulate debate. Historically, DoA monitoring used patient's movement as a surrogate of awareness. Pharmacokinetic models and metrics, including minimum alveolar concentration for inhaled anesthetics and target-controlled infusion models for intravenous anesthesia, provided further insights to clinicians, but electroencephalography and its derivatives (processed EEG; pEEG) offer the potential for personalization of anesthesia care. Current studies appear to affirm that pEEG monitoring decreases the quantity of anesthetics administered, diminishes postanesthesia care unit duration, and may reduce the occurrence of postoperative delirium (notwithstanding the difficulties of defining this condition). Major trials are underway to further elucidate the impact on postoperative cognitive dysfunction. In this manuscript, we discuss the Bispectral (BIS) index, Narcotrend monitor, Patient State Index, entropy-based monitoring, and Neurosense monitor, as well as middle latency evoked auditory potential, before exploring how these technologies could evolve in the upcoming years. In contrast to developments in pEEG monitors, nociception monitors remain by comparison underdeveloped and underutilized. Just as with anesthetic agents, excessive analgesia can lead to harmful side effects, whereas inadequate analgesia is associated with increased stress response, poorer hemodynamic conditions and coagulation, metabolic, and immune system dysregulation. Broadly, 3 distinct monitoring strategies have emerged: motor reflex, central nervous system, and autonomic nervous system monitoring. Generally, nociceptive monitors outperform basic clinical vital sign monitoring in reducing perioperative opioid use. This manuscript describes pupillometry, surgical pleth index, analgesia nociception index, and nociception level index, and suggest how future developments could impact their use. The final section of this review explores the profound implications of future monitoring technologies on anesthesiology practice and envisages 3 transformative scenarios: helping in creation of an optimal analgesic drug, the advent of bidirectional neuron-microelectronic interfaces, and the synergistic combination of hypnosis and virtual reality.

Malewicz N, Ebel M, K. Zahn P, H. Meyer-Frießem C. Pupillometric Monitoring of Nociception in Cardiac Anesthesia

BACKGROUND

High-dose opioids are conventionally used for cardiac anesthesia, but without monitoring of nociception. In non-cardiac surgical procedures the intra - operative dose of opioids can be individualized and reduced with pupillometric monitoring of the pupillary pain index (PPI; scale 1-9). A randomized controlled trial was carried out to explore whether pupillometry can be used for nociception monitoring in cardiac anesthesia and whether it leads to opioid reduction.

METHODS

A sample of 57 cardiac surgery patients receiving continuously administered sufentanil (initial dosage 0.7 μg*kg-¹*h-¹) was divided into a PPI group (sufentanil reduction if PPI<3 up to a minimum of 0.15 μg*kg-¹*h-¹, n=32) and a control group (standard anesthesia; n = 25). The primary outcome was the time from the end of anesthesia to extubation. The secondary outcomes were total intraoperative dose of sufentanil/noradrenaline, postoperative pain intensity (numeric rating scale [NRS] 0-10) and intraoperative awareness. German Clinical Trials Registry no. DRKS 00012329.

RESULTS

The primary outcome, extubation time, did not differ between the two groups (1.14 h, 95% confidence interval [-0.99; 3.27], p = 0.592). Compared with the control patients (68% male, age 70 ± 10.4 years, PPI 1.1 ± 0.2), the mean sufentanil infusion rate in the PPI patients (81% male, age 68 ± 10.3 years, PPI 1.1 ± 0.2) decreased by 81.8% (-0.68 μg*kg-¹*h-¹ [-0,7; -0.67], p<0.001) to the predetermined minimum level, without intraoperative awareness. Moreover, the noradrenaline dose was reduced by 56% (1235.51 μg [321.91; 2149.12], p = 0.005) and the postoperative pain intensity by 45% (2.11 NRS [0.93; 3.3] after 24 h, p = 0.003).

CONCLUSION

Pupillometry is appropriate for nociception monitoring in cardiac anesthesia. Thereby a considerable reduction of intraoperative opioids as well as increased intraoperative hemodynamic stability was achieved and postoperative opioid-induced hyperalgesia was prevented. The consistently low PPI scores, indicating adequate analgesia, suggest that further reduction of opioid doses is feasible.