The nociception level index (NOL) is a multi-parameter index that incorporates changes in autonomic parameters to evaluate nociception, with more painful stimuli causing more pronounced index variations. How this nociception monitor relates to the pain experience is uncertain, and patients with chronic pain may respond differently to acute pain due to alterations in pain processing. The goal of this pilot study was to evaluate NOL index variations after a painful physiotherapy exercise in patients with upper limb complex regional pain syndrome. Baseline NOL indexes were recorded using a finger probe (PMD-200™ Monitor, Medasense, Israel) and patient reported baseline pain scores using an 11-point numeric rating scale (NRS). Patients then performed a painful physiotherapy exercise and NOL index and pain scores were again recorded. The same procedure and recordings were repeated after a stellate ganglion block. Data were analyzed using a paired Student T test and a P value < 0.05 was considered statistically significant. Twenty patients (12/20 female, 10/20 right-sided) were included in this study. Patients reported moderate baseline pain (4.0 ± 2.7) despite having a low baseline NOL index (7.66 ± 5.76 out of 100). NRS and NOL index scores increased significantly during exercise, both before and after the block. The NOL index increased significantly when patients reported increased pain, indicating that it could eventually be useful in the objective assessment of acute pain in the chronic pain patients. However, NOL index was not able to reflect pain levels at rest, before the painful stimulation, in this chronic pain population. Further studies are needed to better assess NOL index utility at rest and to confirm these findings in this specific chronic pain population.
Keywords: Chronic pain; Complex regional pain syndrome; NOL index; Objective pain assessment.
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