Video versus ultrasound pupillometry for detecting increased pupillary diameters due to nociceptive stimuli: a prospective observational study.

Purpose: Ultrasound pupillometry (UP) is a potential alternative to video pupillometry (VP) for assessing changes in patients' pupillary diameter (ΔPD) due to surgical nociception, but the reproducibility of UP and VP has been unclear. We evaluated the reproducibility of nociceptive ΔPD measured with both methods.

Subjects And Methods: This prospective observational trial with 15 healthy volunteers aged ≥ 18 years was conducted at a Japanese teaching hospital. The ΔPD due to tetanic stimuli randomly applied at 10-60 mA was measured with VP and UP. The primary outcome was the correlation between the ΔPD measured with VP and that measured with UP. The secondary outcome was the agreement between the methods. We also evaluated ΔPD pattern changes due to the raised pain intensity in each method.

Results: The noxious ΔPD values of UP were weakly but significantly correlated with those of VP (Spearman's ρ = 0.38, p < 0.001). A significant constant error was identified between the two measurements (Bland-Altman: mean of the difference in ΔPD (VP - UP), - 0.4 [95% CI: - 0.52 to - 0.28, p < 0.001], generalized estimating equation: a beta estimator of ΔPD: 0.41, [95% CI: 0.26-0.56, p < 0.001]). The ΔPD pattern changes due to the raised tetanic stimuli were almost the same in the two methods.

Conclusion: Due to the significant constant error, we consider the reproducibility of the measured ΔPD between UP and VP moderate. Trial registry number UMIN 000047145. Prior to the subjects' enrollment, the trial was registered with the University Hospital Medical Information Network (Principal investigator: Mao Konno, Date of registration: 3.11.2022). https://center6.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000053778 .