Different perspectives for monitoring nociception during general anesthesia

Safe anesthesia is achieved using objective methods that estimate the patient's state during different phases of surgery. A patient's state under anesthesia is characterized by three ma-jor aspects, which are linked to the main effects produced by each of the families of anes-thetic agents administered: hypnosis, analgesia, and muscular relaxation. While quantifi-cation techniques designed to assess muscular relaxation under neuromuscular blocking agents have a relatively long history with a high degree of standardization and understand-ing (e.g., the train-of-four), the knowledge and techniques used to the depth of hypnosis assessment suffer from a lesser degree in both standardization and interpretation due to brain complexity. The problem of standardization and interpretation in the analgesia and nociception assessment increases since it involves more systems, the central nervous sys-tem, and the autonomic nervous system. This helps to explain why there are multiple a priori valid approaches to develop nociception monitoring from different interpretations and physiological bases of noxious stimuli processing. Thus, in this review, the current monitoring technologies clinically available for estimating a patient's nociception under general anesthesia are described.