From head trauma to stroke: analyzing the eyes to understand what happens in the brain
How many things can our pupils tell us? More than you might think. Depending on how much they dilate or shrink, they can give us valuable information about the health of not only our eyes but also other parts of the body. They can, for example, help us understand whether the brain has suffered acute injuries, traumatic or otherwise, in emergency situations, such as in the case of a violent fall, a car accident, a stroke or an aneurysm. And today it is possible to analyze the pupils in an increasingly objective and reliable way, thanks to the pupillometer, a tool that also allows you to predict the evolution of the lesions. This is confirmed by a study published in Lancet Neurology: the results have demonstrated how quantitative pupillometry can play a crucial role in monitoring the progression of acute brain lesions and how it is able to predict the neurological outcome and mortality of a patient in a period of 6 months.
Acute brain injuries
Brain injuries can be traumatic and non-traumatic. We speak of acute lesions when they arise suddenly and without antecedents. The causes can be different: craniocerebral trauma for traumatic ones; a cerebral hemorrhage, a stroke or a disease such as meningitis, encephalitis or acute hydrocephalus, for non-traumatic ones. Depending on the severity, brain function may be temporarily or permanently impaired.
The importance of pupil reactivity
In the first phases of helping the patient, a clinical neurological evaluation is carried out on the ability to respond to simple commands and on the functionality of the reflexes regulated by the deep pathways of the brainstem, such as the response of the pupils to light. This allows us to determine the brain damage affecting the deep structures of the brainstem. “Normally, when we go from darkness to light – he explains Giuseppe Citerio, Principal Investigator of the study and professor of Anesthesia and Resuscitation at the Department of Medicine and Surgery of the University of Milan-Bicocca – our pupil narrows physiologically to avoid being dazzled. In the patient with acute brain damage this does not happen: the pupillary reflex can be compromised due to a compression caused by an expansive lesion, traumatic or non-traumatic, which occupies space inside the skull, compressing the brainstem and the structures responsible for vigilance. One or both pupils therefore dilate, indicating the presence of unilateral compression or much more serious bilateral compression. With diagnostic imaging in the acute phase we can then understand the type of lesion we are faced with and whether to intervene surgically or with other procedures.”
I study
Pupillary reactivity can thus give immediate information on the presence or absence of a neurological emergency, and automated pupillometry represents a way to measure it more precisely than the subjective assessments made until some time ago with a flashlight. The ORANGE study, Outcome Prediction of Acute Brain Injury Using the Neurological Pupil Index, coordinated by the University of Milan-Bicocca, adds something more: it shows that automated pupillometry can also have predictive value. The research involved 514 patients (224 with traumatic brain injury, 139 with aneurysmal subarachnoid hemorrhage and 151 with intracerebral hemorrhage) in 13 hospitals in eight countries between Europe and the United States, including San Gerardo in Monza, the first Italian facility to adopt a pupillometer in 2015 in the neurological intensive care unit directed by Citerio.
The objective was to clarify the association between pupil assessments in the first seven days of hospitalization and neurological outcome at six months. Through the infrared camera of the pupillometer, capable of acquiring 90 images in 2.7 seconds, the patients (who were in a coma at the time of admission) underwent an automated pupillometric evaluation to calculate the NPi (Neurological Pupil Index) , the neurological index of the pupil with values from 0 to 5 (where values less than 3 are considered abnormal). “The NPi brings together all the elements analyzed by pupillometry – underlines Citerio – i.e. the speed and amplitude of the patient’s response to the pupillary reflex to light, and how the pupil returns to a normal condition. By integrating all these values, the index gives us information quantified in a precise, repeatable and standardized number. When NPi values are low they indicate a serious alarm and are associated with unfavorable outcomes, but when the NPi falls within a range of values considered normal, the risk of unfavorable outcomes decreases”.
Pupil analysis can monitor the evolution of lesions
During the study, 40,071 NPi measurements were taken, an average of approximately 40 measurements on each patient. The 6-month outcome was evaluated in 497 patients, of whom 160 died and 241 achieved at least one abnormal NPi detection associated with poor neurologic outcome and in-hospital mortality. “Our analysis, the first at an international level with such important numbers, has shown us how quantitative pupillometry allows us to standardize the evaluation of anomalies. And also to track subtle changes over time that could provide an early warning of potentially very serious developmental lesions – comments Citerio again – In fact, if the patient responds well to therapy or surgery, the NPi is able to report and monitor in precise and dynamic way possible improvements and these are associated with a distant outcome that improves, making the examination of the pupils a dynamic monitoring tool”.
The use of the pupillometer in Italy
In America the use of the pupillometer is now widespread, but in Italy it is starting to catch on. “It has been used in our department for several years now – concludes Citerio – but in general also in other Italian structures it is becoming a standard monitoring system in neurological resuscitations. This is undoubtedly a significant step in reducing the manual subjective assessment of the pupils.”
