Patient-specific thresholds of intracranial pressure in severe traumatic brain injury

Clinical article

Christos Lazaridis M.D. 1 , 2 , Stacia M. DeSantis Ph.D. 3 , Peter Smielewski Ph.D. 1 , David K. Menon M.D., Ph.D., F.Med.Sci. 4 , Peter Hutchinson F.R.C.S.(SN), Ph.D. 1 , John D. Pickard F.R.C.S., M.Chir., F.Med.Sci. 1 , and Marek Czosnyka Ph.D. 1
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  • 1 Academic Neurosurgical Unit, University of Cambridge Clinical School, Cambridge;
  • 2 Department of Neurology, Divisions of Neurocritical Care and Vascular Neurology, Baylor College of Medicine, Houston;
  • 3 Division of Biostatistics, School of Public Health at Houston, University of Texas, Houston, Texas; and
  • 4 University Department of Anaesthesia, Addenbrooke's Hospital, University of Cambridge, United Kingdom
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Object

Based on continuous monitoring of the pressure reactivity index (PRx), the authors defined individualized intracranial pressure (ICP) thresholds by graphing the relationship between ICP and PRx. These investigators hypothesized that an “ICP dose” based on individually assessed ICP thresholds would correlate more closely with the 6-month outcome when compared with ICP doses derived by the recommended universal thresholds of 20 and 25 mm Hg.

Methods

This study was a retrospective analysis of prospectively collected data from 327 patients with severe traumatic brain injury.

Results

Individualized thresholds were visually identified from graphs of PRx versus ICP; PRx > 0.2 was the cutoff. Intracranial pressure doses were then computed as the cumulative area under the curve above the defined thresholds in graphing ICP versus time. The term “Dose 20” (D20) was used to refer to an ICP threshold of 20 mm Hg; the markers D25 and DPRx were calculated similarly. Separate logistic regression models were fit with death as the outcome and each dose as the predictor, both alone and adjusted for covariates. The discriminative ability of each dose for mortality was assessed by receiver operating characteristic AUC analysis in which 5-fold cross-validation was used. A clearly identifiable PRx-based threshold was possible in 224 patients (68%). The DPRx (AUC 0.81, 95% CI 0.74–0.87) was found to have the highest area under the curve (AUC) over both D20 (0.75, 95% CI 0.68–0.81) and D25 (0.77, 95% CI 0.70–0.83); in the cross-validation model, DPRx remained the best discriminator of mortality (DPRx: AUC 0.77 [95% CI 0.68–0.89]; D20: 0.72 [95% CI 0.66–0.81]; and D25: 0.65 [95% CI 0.56–0.73]).

Conclusions

The authors explored the importance of different ICP thresholds for outcome by calculating patient-specific ICP doses based on the continuous monitoring of cerebrovascular pressure reactivity. They found that these individualized doses of intracranial hypertension were stronger predictors of death than doses derived from the universal thresholds of 20 and 25 mm Hg. The PRx could offer a method that can be directed toward individualizing the ICP threshold.

Abbreviations used in this paper:ABP = arterial blood pressure; AUC = area under the curve; BTF = Brain Trauma Foundation; CPP = cerebral perfusion pressure; DECRA = decompressive craniectomy; D20, D25, DPRx = ICP doses based on thresholds of 20 mm Hg, 25 mm Hg, and PRx > 0.2; GCS = Glasgow Coma Scale; GOS = Glasgow Outcome Scale; ICP = intracranial pressure; MAP = mean arterial pressure; PRx = pressure reactivity index; ROC = receiver operating characteristic; TBI = traumatic brain injury.

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Contributor Notes

Address correspondence to: Christos Lazaridis, M.D., Department of Neurology, Divisions of Neurocritical Care and Vascular Neurology, Baylor College of Medicine, 6501 Fannin St., Mail slot NB320, Houston, TX 77030. email: lazaridi@bcm.edu.

Please include this information when citing this paper: published online February 7, 2014; DOI: 10.3171/2014.1.JNS131292.

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