Abstract
BackgroundElevated intracranial pressure (ICP) is frequent after traumatic brain injury (TBI) and may cause abnormal pupillary reactivity, which in turn is associated with a worse prognosis. Using automated infrared pupillometry, we examined the relationship between the Neurological Pupil index (NPi) and invasive ICP in patients with severe TBI.MethodsThis was an observational cohort of consecutive subjects with severe TBI (Glasgow Coma Scale [GCS] < 9 with abnormal lesions on head CT) who underwent parenchymal ICP monitoring and repeated NPi assessment with the NPi-200® pupillometer. We examined NPi trends over time (four consecutive measurements over intervals of 6 h) prior to sustained elevated ICP > 20 mmHg. We further analyzed the relationship of cumulative abnormal NPi burden (%NPi values < 3 during total ICP monitoring time) with intracranial hypertension (ICHT)—categorized as refractory (ICHT-r; requiring surgical decompression) vs. non-refractory (ICHT-nr; responsive to medical therapy)—and with the 6-month Glasgow Outcome Score (GOS).ResultsA total of 54 patients were studied (mean age 54 ± 21 years, 74% with focal injuries on CT), of whom 32 (59%) had ICHT. Among subjects with ICHT, episodes of sustained elevated ICP (n = 43, 172 matched ICP-NPi samples; baseline ICP [T− 6 h] 14 ± 5 mmHg vs. ICPmax [T0 h] 30 ± 9 mmHg) were associated with a concomitant decrease of the NPi (baseline 4.2 ± 0.5 vs. 2.8 ± 1.6, p < 0.0001 ANOVA for repeated measures). Abnormal NPi values were more frequent in patients with ICHT-r (n = 17; 38 [3–96]% of monitored time vs. 1 [0–9]% in patients with ICHT-nr [n = 15] and 0.5 [0–10]% in those without ICHT [n = 22]; p = 0.007) and were associated with an unfavorable 6-month outcome (15 [1–80]% in GOS 1–3 vs. 0 [0–7]% in GOS 4–5 patients; p = 0.002).ConclusionsIn a selected cohort of severe TBI patients with abnormal head CT lesions and predominantly focal cerebral injury, elevated ICP episodes correlated with a concomitant decrease of NPi. Sustained abnormal NPi was in turn associated with a more complicated ICP course and worse outcome.
Highlights
Elevated intracranial pressure (ICP) is frequent after traumatic brain injury (TBI) and may cause abnormal pupillary reactivity, which in turn is associated with a worse prognosis
The results of this study can be summarized as follows: (1) sustained elevations of ICP > 20 mmHg are associated with a concomitant and clinically relevant decrease of quantitative Neurological Pupil index (NPi), on average below normal values (NPi < 3); (2) treatment of elevated ICP with hyperosmolar agents was in turn associated with a normalization of the NPi; (3) the cumulative burden of abnormal NPi was a marker of an increased severity of intracranial hypertension, a more complicated ICP course, and a worse 6-month neurological outcome; and (4) failure of the NPi to recover to normal values was associated with very poor prognosis
Pupillary light reactivity is a known prognostic predictor in patients with TBI [21] and is a validated variable used in both the CRASH (Corticosteroid Randomization after Significant Head Injury) and the IMPACT (International Mission of Prognosis and Analysis of Clinical Trials) prognostic models [9]. Previous studies and both the CRASH and IMPACT models are based on the standard manual qualitative pupillary examination, and there are only limited data regarding the potential value of quantitative pupillometry in the monitoring of TBI complications and outcome
Summary
Elevated intracranial pressure (ICP) is frequent after traumatic brain injury (TBI) and may cause abnormal pupillary reactivity, which in turn is associated with a worse prognosis. In the current clinical practice pupillary examination is generally performed using a manual, hand-held light source (e.g., pen torch); the evaluation of pupillary size and reactivity is essentially based on a visual qualitative assessment (i.e., absent or present, slow or brisk) This subjective, qualitative method has various limitations, including limited precision (especially in patients with small pupil size) and significant intra- and inter-observer variability, due to the inconsistent experience and visual acuity of the assessing clinician, differences in ambient light exposure between measurements, or the technique used to direct the stimulus (i.e., intensity, proximity, duration, and orientation of the light source) [10,11,12]
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