Critical Thresholds for Cerebrovascular Reactivity After Traumatic Brain Injury
Pressure-reactivity index (PRx) is a useful tool in brain monitoring of trauma patients, but the question remains about its critical values. Using our TBI database, we identified the thresholds for PRx and other monitored parameters that maximize the statistical difference between death/survival and favorable/unfavorable outcomes. We also investigated how these thresholds depend on clinical factors such as age, gender and initial GCS.
A total of 459 patients from our database were eligible. Tables of 2 × 2 format were created grouping patients according to survival/death or favorable/unfavorable outcomes and varying thresholds for PRx, ICP and CPP. Pearson’s chi square was calculated, and the thresholds returning the highest score were assumed to have the best discriminative value. The same procedure was repeated after division according to clinical factors.
In all patients, we found that PRx had different thresholds for survival (0.25) and for favorable outcome (0.05). Thresholds of 70 mmHg for CPP and 22 mmHg for ICP were identified for both survival and favorable outcomes. The ICP threshold for favorable outcome was lower (18 mmHg) in females and patients older than 55 years. In logistic regression models, independent variables associating with mortality and unfavorable outcome were age, GCS, ICP and PRx.
The prognostic role of PRx is confirmed but with a lower threshold of 0.05 for favorable outcome than for survival (0.25). Results for ICP are in line with current guidelines. However, the lower value in elderly and in females suggests increased vulnerability to intracranial hypertension in these groups.
KeywordsICP CPP PRx TBI Prognosis Head injury Prognostic factors Thresholds
The project was supported by the National Institute of Health Research, Biomedical Research Centre, Cambridge University Hospital Foundation Trust – Neurosciences Theme and Senior Investigator Awards (JDP, DKM), Technology Foresight Challenge Fund (Grant FCA 234/95), MRC Programme Grant (MRC G9439390). Clifford and Mary Corbridge Trust (KPB) and Foundation for Polish Science (MK). Many thanks to all colleagues participating in head injury monitoring program in Cambridge, UK in 1991-2009, whose experience, knowledge and clinical material helped us to write this study: Mrs. P. Al-Rawi, Mrs. D. Chattfield, Mrs. C.Turner, Dr. M. Balestreri, Miss. M.Hiler, Dr. SK Piechnik, Dr. LA Steiner, Mr. E. Guazzo, Mr. PC Whetfield, Mr. P. Minhas, Dr. M.Soehle, Mr. R. Kett-White, Dr. E. Schmidt, Mr. I. Timofeev, Mr. A.Helmy. Mr. PJ Kirkpatrick, Dr. B. Matta, Dr. J. Coles, Prof. A.Gupta, nursing and research staff from Neurosciences Critical Care Unit and Wolfson Brain Imaging Centre. Dr. M. Czosnyka is on leave from Warsaw University of Technology, Poland.
- 1.Hyam JA, Welch CA, Harrison DA, Menon DK. Case mix, outcomes and comparison of risk prediction models for admissions to adult, general and specialist critical care units for head injury: a secondary analysis of the ICNARC Case Mix Programme Database. Crit Care. 2006;10:1–11.Google Scholar
- 4.Brain Trauma Foundation; American Association of Neurological Surgeons; Congress of Neurological Surgeons; Joint Section on Neurotrauma and Critical Care, AANS/CNS, Bratton SL, Chestnut RM, Ghajar J, et al. Guidelines for the management of severe traumatic brain injury. Introduction. J Neurotrauma. 2007;24 Suppl 1:S1–2.Google Scholar
- 7.Brain Trauma Foundation; American Association of Neurological Surgeons; Congress of Neurological Surgeons; Joint Section on Neurotrauma and Critical Care, AANS/CNS, Bratton SL, Chestnut RM, Ghajar J, McConnell et al. Guidelines for the management of severe traumatic brain injury. VIII. Intracranial Pressure thresholds IX. Cerebral perfusion thresholds. J Neurotrauma. 2007;24 Suppl 1:S54–58 and S59–64.Google Scholar
- 30.Chambers IR, Treadwell L, Mendelow AD. Determination of threshold levels of cerebral perfusion pressure and intracranial pressure in severe head injury by using receiver-operating characteristic curves: an observational study in 291 patients. J Neurosurg. 2001;94(3):412–6.PubMedCrossRefGoogle Scholar