# Pupillometry as a Novel Tool for Pain Monitoring: Evaluating the Antinociceptive Effect of Intravenous Lidocaine During Orotracheal Intubation

## TL;DR

This study shows that intravenous lidocaine reduces pupillary dilation during intubation, suggesting it helps manage pain during anesthesia.

## Contribution

The study introduces pupillometry as a novel, non-invasive method to monitor pain during orotracheal intubation.

## Key findings

- Intravenous lidocaine significantly reduced pupillary reflex dilation compared to placebo during intubation.
- Pupillometry showed a positive correlation with BIS values, indicating lighter anesthesia increases pupillary response.
- PPI scores were not significantly affected by lidocaine, suggesting it does not influence this pain index.

## Abstract

Background/Objectives: Pupillometry offers a non-invasive method for assessing nociceptive responses during anesthesia. This study aimed to evaluate the effects of intravenous lidocaine on pupillary reflex dilation (PDR) and the Pupillary Pain Index (PPI) during general anesthesia with orotracheal intubation. Methods: In this prospective, randomized, single-blind trial, 90 ASA I–II patients aged 18–65 years, scheduled for elective surgery under general anesthesia, were enrolled. Participants were randomized into three groups: control, study (lidocaine 1.5 mg/kg), and placebo. Standardized anesthesia induction was performed using propofol, fentanyl, and rocuronium. Pupil diameter was measured using the Algiscan pupillometer. PDR was assessed during intubation, while PPI was measured five minutes post-intubation through controlled electrical stimulation. Hemodynamic parameters and BIS values were recorded throughout. Eighty-six patients completed the study. No significant differences in demographics, anesthetic drug doses, or hemodynamic parameters were noted between groups. Results: PDR during intubation showed no significant difference between the control and study groups (median dilation: 0.34 mm vs. 0.33 mm; p = 0.76), but was significantly lower in the lidocaine group compared to placebo (median dilation: 0.33 mm vs. 0.50 mm; p = 0.02). PPI scores did not differ significantly between groups (p > 0.05). A positive correlation was observed between PDR and BIS values, indicating that lighter anesthesia depth increased PDR response. No such correlation was found with PPI. Conclusions: Intravenous lidocaine attenuates the pupillary response to nociceptive stimuli during orotracheal intubation but does not influence PPI scores. Pupillometry remains a valuable adjunct for intraoperative nociceptive monitoring.