Neurological pupil index

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Clinicians routinely check the pupils of critically injured and ill patients to monitor neurological status. However, manual pupil measurements (performed using a penlight or ophthalmoscope) have been shown to be subjective, inaccurate, and not repeatable or consistent. [1] Automated assessment of the pupillary light reflex has emerged as an objective means of measuring pupillary reactivity across a range of neurological diseases, including stroke, traumatic brain injury and edema, tumoral herniation syndromes, and sports or war injuries. Automated pupillometers are used to assess an array of objective pupillary variables including size, constriction velocity, latency, and dilation velocity, which are normalized and standardized to compute an indexed score such as the Neurological Pupil index (NPi) or the Quantitative Pupillometry index (QPi).

Contents

Pupillary evaluation

Pupillary evaluation involves the assessment of two components—pupil size and reactivity to light.

Neurological Pupil index (NPi)

The Neurological Pupil index, or NPi, is an algorithm developed by NeurOptics, Inc., that removes subjectivity from the pupillary evaluation. A patient's pupil measurement (including variables such as size, latency, constriction velocity, dilation velocity, etc.) is obtained using a pupillometer, and the measurement is compared against a normative model of pupil reaction to light and automatically graded by the NPi on a scale of 0 to 4.9. Pupil reactivity is express numerically so that changes in both pupil size and reactivity can be trended over time, just like other vital signs.

The numeric scale of the NPi allows for a more rigorous interpretation and classification of the pupil response than subjective assessment.

Neurological Pupil index(tm) (NPi(r)) Pupil Reactivity Assessment Scale (NeurOptics, Inc.) NeurOptics' NPi-300 Screens.png
Neurological Pupil index™ (NPi®) Pupil Reactivity Assessment Scale (NeurOptics, Inc.)

Interpreting the Neurological Pupillary index (NPi)

Each NPi measurement taken is rated on a scale ranging from 0 to 4.9. A score equal to or above 3 means that the pupil measurement falls within the boundaries of normal pupil behavior as defined by the NPi. However, a value closer to 4.9 is more normal data than a value closer to 3. An NPi score below 3 means the reflex is abnormal, i.e., weaker than a normal pupil response, and values closer to 0 are more abnormal than values closer to 3. A difference in NPi between Right and Left pupils of greater than or equal to 0.7 may also be considered an abnormal pupil reading.

Validity of score indices in pupillometry

Automated pupillometer (NPi-300 by NeurOptics, Inc.) NeurOptics' NPi-300 Pupillometer.png
Automated pupillometer (NPi-300 by NeurOptics, Inc.)

More than 100 studies published in peer-reviewed academic journals indicate the effectiveness of automated pupillometry and the NPi scale for use in critical care medicine, neurology, neurosurgery, emergency medicine, and applied research settings.

Others:

Clinical equivalence between NPi and QPi indexes

Several clinical publications have demonstrated the clinical equivalence of the QPi (Quantitative Pupillary Index) and NPi (Neurological Pupillary Index) in critical care settings. These indices have been studied in various contexts, including the assessment of comatose patients following cardiac arrest (CA) and the evaluation of traumatic brain injury (TBI).

The first abstract, titled "Comparison between Neurological Pupil Index and Quantitative Pupillometry Index to prognosticate outcome after cardiac arrest", by Pasetto et al., investigated the prognostic accuracy of QPi and NPi in predicting unfavorable neurological outcomes after CA. This prospective observational study revealed significant correlations between QPi and NPi values. The study concluded that both indices are interchangeable for assessing neurological outcomes in CA patients, further supporting their reliability in clinical practice.

A second abstract, "Equivalence between Quantitative Pupillary Index (QPi) and Neurological Pupil Index (NPi) in Critical Care Settings" , by Blandino Ortiz et al., also highlighted the equivalence of the two indices across diverse neurocritical applications. This study demonstrated that QPi and NPi provide strongly correlated results when used to monitor pupillary reactivity, reinforcing their role as reliable tools for early decision-making in neurocritical care.

A third abstract, "Quantitative Pupillometry Index (QPi) in Comatose Patients After Cardiac Arrest", by Zorzi et al., expanded on these findings by evaluating the QPi and NPi in a larger cohort of 98 patients across two centers. This study showed strong correlations between the indices over multiple time points (e.g., Ps = 0.70 at 24 hours, Ps = 0.68 at 72 hours, p < 0.001). A QPi ≤ 2 at 72 hours demonstrated a specificity of 100% for predicting UO, further underscoring its prognostic value. The authors concluded that QPi and NPi are strongly correlated and can be interchangeably used for prognosticating neurological outcomes in comatose patients after CA.

Together, these studies reinforce the equivalence and utility of QPi and NPi as interchangeable tools in critical care, particularly for monitoring pupillary reactivity and predicting neurological outcomes in patients with acute brain injuries or post-cardiac arrest comas.

See also

References

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