Measurement of the nociceptive flexion reflex threshold in critically ill patients - a monocentric prospective observational study

Abstract

Background Pain detection and treatment is a major challenge in the care of critically ill patients. However, in addition to the risk of analgesic undersupply, there is also the risk of overanalgesia. In the perioperative context, the measurement of the nociceptive flexion reflex threshold has become established for measuring the level of analgesia. To date, however, it is unclear whether measurement of NFRT can be usefully applied to noncommunicating, ventilated, and analgosedated ICU patients. Therefore, the aim of the present study was to investigate whether NFRT measurement correlates with the Behavioral Pain Scale (BPS) in critically ill, analgosedated, and mechanically ventilated patients and whether it can also detect possible overanalgesia.Methods In this prospective, observational, single-center study, 114 patients were included. All patients were admitted to the surgical Intensive Care Unit of the University hospital Ulm, Germany. First measurements of the NFRT and the Behavioral Pain Scale (BPS) were conducted within 12 hours after admission. In the further observation period, a structured pain assessment was performed at least twice daily until extubation (Group A: BPS + NFRT, Group B: BPS). Univariate analysis was performed to evaluate possible associations between NFRT measurement and baseline characteristics. Furthermore, mixed linear regression modeling was used to evaluate possible effects of administered analgesics or sedatives on NFRT. Results NFRT correlates negatively with the Behavioral Pain Scale. NFRT was almost twice as high in patients with a RASS of -5 compared with patients with a RASS ≥ -4 (RASS -5 - NFRT: 59.40 vs. RASS -4 - NFRT: 29.00, p < 0.001). By means of NFRT measurement, potential overanalgesia could not be detected.Conclusion The NFRT measurement reliably correlates negatively with the Behavioral Pain Scale in critically ill patients. In patients with RASS scores ≤ -4, in whom analgesia level is often difficult to assess, NFRT measurement provides guidance in the assessment of nociceptive processes. However, in order to detect possible overanalgesia and to derive therapeutic consequences, a defined stimulus threshold must be determined for the critically ill patient, above which the absence of pain can be safely assumed.Trial Registration Retrospectively registered at German Clinical Trials Register, registration number DRKS00021149, date of registration: March 26, 2020. https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00021149