Anisocoria in the ICU (AICU study): Diagnostic Implications and Clinical Outcomes

Assessment of the pupils regarding symmetry and reactivity to light are important parts of the neurological evaluation of critically ill patients treated in intensive care units. Thereby, anisocoria can be found in up to 60% of patients with acute neurologic injuries(2). Furthermore, anisocoria or pupillary areflexia can be signs of increasing intracranial hypertension with brain herniation, ischemia in traumatic brain injury, cerebrovascular accidents, intoxication with psychotropic and neurotropic drugs including anticholinergic, opioids, and cannabinoids. While anisocoria or impaired pupillary reactivity may result from such devastating cerebral injuries, they can also be caused by more benign and potentially reversible scenarios, such as pharmacological effects (e.g. agents such as ipatroprium bromide) or as part of the Horner’s syndrome following jugular central venous cannulation. Despite these well-known underlying pathomechanisms of pupillary anomalias, data on the prevalence and associated clinical consequences of anisocoria in non-selected general ICU populations is scarce. Due to the lack of data on the prognostic implications of anisocoria or changes in pupillary reactivity for non-neurological ICU patients, the new onset of any pupillary abnormality necessitates a rapid and thorough evaluation usually including clinical neurological examination and the performance of neuroimaging, such as a cerebral computed tomography (CT) or magnetic resonance imaging (MRI). Considering the the variety of more benign and reversible causes of pupillary abnormalities, alongside the potential for missed underlying pathomechanisms with severe clinical implications, it is highly probable that a significant number of unremarkable CT or MRI scans are conducted to investigate acute pupillary abnormalities. This practice may expose patients to unnecessary risks and contribute to increased healthcare costs. While quantitative pupillometry with dynamic pupil assessments after light has shown some promise to distinguish between clinically relevant anisocoria and benign variations, further validation is still lacking. Unfortunately, studies elucidating to what extent a cerebral CT or MRI detects clinically relevant findings in specific patient groups with particular clinical contexts, and in which clinical scenarios CTs are likely to provide no clinical relevance beyond exposing the patient to radiation are still pending.

This retrospective single-center cohort study has four primary objectives. 

-   First, it aims to determine the prevalence of acute "new onset" pupillary abnormalities (anisocoria and/or impaired light-reactive pupillary response) in adult ICU patients. 

-   Second, it seeks to assess the clinical impact of these abnormalities, particularly in terms of the frequency of diagnostic tests ordered, such as neuroimaging (i.e., head CT or MRI scans, and ophthalmologic and neurologic consultations. 

-   Third, the study aims to identify specific clinical contexts in which significant pathological findings lead to treatment modifications, as well as those scenarios where no clinically relevant findings are detected.

-   Finally, it evaluates the prognostic implications of these pupillary abnormalities on patient outcomes.