The impact of pupil diameter on assessing illness severity and outcome after out-of-hospital cardiac arrest in patients with unreactive pupils

Background and purpose

Absent pupillary light reflex (PLR) has been implicated as an indicator of poor prognosis following cardiac arrest; however, few studies report on pupil size. We evaluated the association between pupil size and reactivity immediately following return of spontaneous circulation (ROSC) and post-arrest illness severity and clinical outcomes.

Methods

In this retrospective, single-center study between 2018 and 2024, out-of-hospital cardiac arrest (OHCA) patients with early pupil size and reactivity data were identified. Dilated pupils were defined as $\ge$4 mm in diameter. Pupil size and reactivity were subjectively assessed by the clinical team and documented as part of the standardized note template. We evaluated the association between post-ROSC pupil size, reactivity and illness severity, clinical outcomes.

Results

In our cohort of 382 OHCA patients, 50.8 % had absent PLR (n = 194). Patients with absent PLR were younger, had less premorbid medical conditions, worse cardiac arrest features, and higher illness severity. The false positive rate for absent PLR was 10.9 % for mortality and 5.9 % for poor neurologic outcome. Amongst those with absent PLR, dilated pupils were present in 68 % (n = 132). Patients with absent PLR and dilated pupils were younger, had less premorbid medical conditions, were less likely to have a shockable rhythm arrest, had higher illness severity scores and worse post-arrest labs. Patients with absent PLR and dilated pupils had a higher incidence of brain death (34.8 % vs. 9.7 %, p < 0.001). Amongst patients with absent PLR, the presence of dilated pupils improved the prediction of brain death [ AUC (CI) 0.733 (0.672–0.793) vs. 0.683 (0.628–0.738), p = 0.026].

Conclusion

Absent PLR immediately following ROSC is associated with poor outcomes but does not preclude good outcome. Pupil size and reactivity immediately post-ROSC may help to differentiate brain injury phenotypes. Prospective work using quantitative pupillometry is important to validate our findings.