Utility of M-mode ultrasound for pupillary assessment in patients with traumatic brain injury

Abstract Background Pupillary assessment is an important index to evaluate changes in the conditions of patients with traumatic brain injury (TBI). This study assessed the utility of M-mode ultrasound as a non-invasive bedside assessment to evaluate pupillary light reflex (PLR) sensitivity in patients with TBI. Methods This is a prospective observational study of patients with TBI. Patients were divided into brisk, sluggish, or absent groups based on their PLR sensitivity. M-mode ultrasound was performed according to standard operation guidelines using a standardized light stimulus.Pupillary diameter (PD) and PLR sensitivity were recorded. At the same time, the pupil was examined by M-mode ultrasound, and the diameter and pupillary contraction time (PCT) were measured at rest, ipsilateral opposite PLR, and contralateral opposite PLR. Results A total of 150 participants were included. In the briskgroup, during the ipsilaterallight reflex, the left and right PCTs were 0.09 ± 0.02s and 0.10 ± 0.09s, respectively, and the pupillary diameter variation rates (PDVRs) were 0.36 ± 0.10 and 0.35 ± 0.09. In the sluggish group, during the ipsilateral light reflex, the left and right PCTs were 0.20 ± 0.05s and 0.19 ±0.03s, respectively. PDVRs were 0.18 ± 0.07 and 0.19 ± 0.11, respectively. In the brisk group, the cut-off value of PDVR of ipsilateral PLR was 0.205, AUC value was 0.957, and sensitivity and specificity were 95.3% and 90.8%, the cut-off value of PDVR of contralateral PLR was 0.146, AUC value was 0.962, and sensitivity and specificity were 95.3% and 86.2%. Conclusions This study demonstrated the usefulness of M-mode ultrasound for quantitative evaluation of pupillary changes. It is a simple, rapid, and objective method that can accurately monitor PD and sensitivity to light reflex, especially in patients with eyelid edema or TBI, where pupils cannot be examined visually.