Pupillometry to detect pain response during general anaesthesia following unilateral popliteal sciatic nerve block: a prospective, observational study

Abstract

Context: Pupillary reflex dilation appears to be a reliable indicator of response to noxious stimulation even under general anaesthesia. The ability of pupillometry to detect the effects of extremity blocks during continuous infusion of opioids remains unknown.

Objective: To explore the performance of pupillometry to detect differences in pupillary reflex dilation response to a standardised noxious stimulus applied to each leg following unilateral popliteal sciatic nerve block during continuous infusion of remifentanil.

Design: Prospective, observational study.

Setting: University hospital anaesthesia department, between June 2010 and December 2010.

Patients: Twenty-four adult patients undergoing elective foot or ankle surgery under general anaesthesia who requested a peripheral nerve block. Unilateral popliteal sciatic nerve block with 0.75% ropivacaine and 1% lidocaine was performed awake. General anaesthesia was maintained with steady-state infusions of propofol and remifentanil.

Main outcome measure: Video-based pupillometer was used to determine pupillary reflex dilation during tetanic stimulation (60 m, 100 Hz) applied to the skin area innervated by the sciatic nerve for 5 s after the onset of general anaesthesia.

Results: Sensory nerve block led to a blunted maximal pupillary reflex dilation response to noxious stimulation compared with the non-blocked leg: median (interquartile range) change from baseline 2% (1 to 4%) versus 17% (13 to 24%), respectively (P < 0.01). The differences in the response persisted throughout the 5-s stimulus and the recovery phase.

Conclusion: These results are a proof of concept. The effects of peripheral nerve block can be detected via the measurement of pupillary reflex dilation response to noxious stimulation of the skin in patients receiving remifentanil.