Pain assessment in the postanaesthesia care unit using pupillometry: A cross-sectional study after standard anaesthetic care.

BACKGROUND: Patients assess their own pain with a numerical rating scale (NRS). In the postanaesthesia care unit (PACU), NRS helps to determine and monitor analgesic administration, but is useless in patients who are unable to communicate. In non-PACU patients, acute pain increases pupillary diameter and pupillary light reflex amplitude (PLRA), the difference between pupillary diameter before and after light stimulation.

OBJECTIVES: To study the association between postoperative pain (NRS) and pupillary diameter or PLRA in PACU patients after routine anaesthetic care.

DESIGN: Cross-sectional cohort study.

SETTING: Bichat-Claude Bernard Hospital, Paris.

PATIENTS: One hundred and forty-five patients undergoing planned surgery under general anaesthesia.

INTERVENTIONS: NRS, pupillary diameter and PLRA were measured on arrival in the PACU. When NRS was more than 4, intravenous morphine titration was started and a second measurement performed.

MAIN OUTCOME MEASURES: Association between NRS and pupillary diameter or PLRA was assessed with Pearson correlation coefficient (r) as was association between changes in these variables after morphine titration.

RESULTS: Mean NRS was 4.7, and was more than 4 in 79 patients (55%). No statistically significant association was observed between NRS and pupillary diameter (r = 0.10, P = 0.54) or PLRA (r = 0.03, P = 0.72). Twenty-seven patients (19%) received morphine titration with significant decreases in NRS, pupillary diameter and PLRA afterwards. No association was observed between NRS changes and pupillary diameter or PLRA changes.

CONCLUSION: Acute postoperative pain is not associated with pupillary diameter or PLRA. Further research is required to develop tools to assess pain in the PACU.