Electrophysiological monitoring of pain provides objective measures that allow for pain control and adjustment of analgesia in non-communicative patients. Among the available electrophysiological devices, automated infrared pupillometry, Analgesia Nociception Index (ANI), and Nociception Level Index (NOL®) stand out. These non-invasive measurement systems analyze the sympathetic or parasympathetic nervous system response to painful stimuli by observing pupillary dilatation and reactivity (pupillometry), heart rate during respiration (ANI), or a combination of multiple parameters from the nociceptive-autonomic medullary circuit (NOL®). These methods have mainly been used in the monitoring of nociception related to procedures in critically ill patients. Furthermore, they have allowed for the prediction, adjustment, and customization of analgesia administration prior to painful procedures. To obtain accurate measurements and properly interpret the values provided by these devices, it is important to consider certain limitations in their use, such as the administration of specific medications or the presence of certain pathologies, due to their influence on the autonomic nervous system response. It is also important to note that the reported level of evidence is limited, as randomized clinical trials in the context of intensive care unit regarding these devices are currently lacking.