Features of postoperative pain relief in patients with a low level of consciousness: a prospective randomised study

AIM: To determine the possibility of using analgonociception monitoring (analgesia nociception index, ANI) to assess the need for postoperative analgesia in patients with prolonged impairment of consciousness.

MATERIAL AND METHODS: This pilot prospective randomized study enrolled 34 consecutive patients with chronic impairment of consciousness (vegetative state/minimal state of consciousness) who underwent neurosurgical interventions. Randomization was made by the envelope method for the grouping of the patients: study group (SG, n=17), received anesthesia with intravenous paracetamol 1000 mg according to ANI in the postoperative period; control group (CG, n=17), without additional anesthesia in the postoperative period. Patients with arrhythmias were excluded. The groups are comparable in terms of the main clinical parameters (all parameters p >0.05). The ANI (MetroDoloris device, France) was recorded at 1, 4, 8, 12, and 24 h after surgery. The valuation was based on the revised scale for assessing pain in a coma, i.e., Nociception Coma Scale–Revised (NCS-R) [7], after 4, 12, and 24 h.

RESULTS: An intragroup comparison of the changes in ANI during postoperative day 1 showed an adequate level of pain relief (60.1 [55.3–62.5]), whereas in the group without postoperative analgesia with paracetamol, by 4 h after the operation, ANI dropped to the lower limit (46.3 [40.2–51.9]). In an intergroup comparison in the first 8 h after surgery, ANI was significantly higher than in the group without anesthesia (p=0.04) and had values of >55, which indicates the absence of pronounced vegetative reactions indicating the presence of pain. From 12 o’clock, the values are leveled out, not going beyond the limits of indicators of inadequate anesthesia (p=0.69). When assessing nociception on the NCR-R scale during the postoperative day in both groups, a tendency to the appearance of weak autonomic responses was observed (6 [5; 8] in SG and 6 [5; 7] in CS, respectively), which did not differ significantly. The presence of pain 4 h after surgery was confirmed by increased levels of cortisol and salivary alpha-amylase in patients without postoperative analgesia (p=0.03).

CONCLUSION: No generally recognized and available evidence-based instrumental methods are available for the assessment of pain intensity in patients with chronic impairment of consciousness. There is no single position of the professional community on the need for postoperative analgesia in such patients. Further studies to evaluate the effectiveness of using the ANI Metro Doloris monitoring system with a significant number of observations will lead to the determination of adequate perioperative analgesia regimens in patients with various forms of prolonged impairment of consciousness.