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Review article: Biomedical intelligence

Vol. 141 No. 2930 (2011)

Actual evidence for neuromonitoring-guided intensive care following severe traumatic brain injury

  • J Stover
Cite this as:
Swiss Med Wkly. 2011;141:w13245


Therapeutic interventions following severe traumatic brain injury (TBI) are substantially influenced by complex and interwoven pathophysiological cascades involving both, local and systemic alterations. Our main duty is to prevent secondary progression of the primary damage. This, in turn, obliges us to actively search and identify secondary insults related, for example, to hypoxia, hypotension, uncontrolled hyperventilation, anaemia, and hypoglycaemia. During pharmacological coma we must rely on specific cerebral monitoring which is indispensable in unmasking otherwise occult changes. In addition, extended neuromonitoring (SjvO2, ptiO2, microdialysis, transcranial Doppler sonography, electrophysiological studies, direct brain perfusion measurement) can be used to define individual pathological ICP levels which, in turn, will support our decision making. Extended neuromonitoring expands the limited knowledge derived from ICP and CPP values, thereby allowing us to adequately adapt the type, extent and speed of different therapeutic interventions. A more individualised and flexible treatment concept depends on extended neuromonitoring.

The present review addresses current evidence in favour of extended neuromonitoring used to guide treatment options aimed at improving intensive care treatment of patients with severe TBI. With increasing experience gained by the use of extended neuromonitoring in clinical routine we may expect that the evidence obtained within the individual patient will translate to convincing evidence on a larger scale for the entire study population.


  1. Maegele M, Engel D, Bouillon B, Lefering R, Fach H, et al. Incidence and outcome of traumatic brain injury in an urban area in Western Europe over 10 years. Eur Surg Res. 2007;39(6):372–9.
  2. von Elm E, Osterwalder JJ, Graber C, Schoettker P, Stocker R, Zangger P, et al. Severe traumatic brain injury in Switzerland – feasibility and first results of a cohort study. Swiss Med Wkly. 2008;138(23-24):327–34.
  3. Smith M. Monitoring intracranial pressure in traumatic brain injury. Anesth Analg. 2008;106(1):240–8.
  4. Belli A, Sen J, Petzold A, Russo S, Kitchen N, Smith M. Metabolic failure precedes intracranial pressure rises in traumatic brain injury: a microdialysis study. Acta Neurochir (Wien). 2008;150(5):461–9.
  5. Sahuquillo J, Poca MA, Arribas M, Garnacho A, Rubio E. Interhemispheric supratentorial intracranial pressure gradients in head-injured patients: are they clinically important? J Neurosurg. 1999;90(1):16–26.
  6. Rosner MJ, Rosner SD, Johnson AH. Cerebral perfusion pressure: management protocol and clinical results. J Neurosurg. 1995;83(6):949–62.
  7. Møller K, Paulson OB, Hornbein TF, Colier WN, Paulson AS, Roach RC, et al. Unchanged cerebral blood flow and oxidative metabolism after acclimatization to high altitude. J Cereb Blood Flow Metab. 2002;22(1):118–26.
  8. Holbein M, Béchir M, Ludwig S, Sommerfeld J, Cottini SR, Keel M, et al. Differential influence of arterial blood glucose on cerebral metabolism following severe traumatic brain injury. Crit Care. 2009;13(1):R13.
  9. Kiening KL, Unterberg AW, Bardt TF, Schneider GH, Lanksch WR. Monitoring of cerebral oxygenation in patients with severe head injuries: brain tissue PO2 versus jugular vein oxygen saturation. J Neurosurg. 1996;85(5):751–7.
  10. Vigué B, Ract C, Benayed M, Zlotine N, Leblanc PE, et al. Early SjvO2 monitoring in patients with severe brain trauma. Intensive Care Med. 1999;25(5):445–51.
  11. Chan MT, Ng SC, Lam JM, Poon WS, Gin T. Re-defining the ischemic threshold for jugular venous oxygen saturation – a microdialysis study in patients with severe head injury. Acta Neurochir Suppl. 2005;95:63–6.
  12. Gopinath SP, Robertson CS, Contant CF, Hayes C, Feldman Z, Narayan RK, et al. Jugular venous desaturation and outcome after head injury. J Neurol Neurosurg Psychiatry. 1994;57(6):717–23.
  13. Poca MA, Sahuquillo J, Vilalta A, Garnacho A. Lack of utility of arteriojugular venous differences of lactate as a reliable indicator of increased brain anaerobic metabolism in traumatic brain injury. J Neurosurg. 2007;106(4):530–7.
  14. Pérez A, Minces PG, Schnitzler EJ, Agosta GE, Medina SA, Ciraolo CA. Jugular venous oxygen saturation or arteriovenous difference of lactate content and outcome in children with severe traumatic brain injury. Pediatr Crit Care Med. 2003;4(1):33–8.
  15. Glenn TC, Kelly DF, Boscardin WJ, McArthur DL, Vespa P, Oertel M, et al. Energy dysfunction as a predictor of outcome after moderate or severe head injury: indices of oxygen, glucose, and lactate metabolism. J Cereb Blood Flow Metab. 2003;23(10):1239–50.
  16. Rosenthal G, Hemphill JC 3rd, Sorani M, Martin C, Morabito D, Obrist WD, et al. Brain tissue oxygen tension is more indicative of oxygen diffusion than oxygen delivery and metabolism in patients with traumatic brain injury. Crit Care Med. 2008;36(6):1917–24.
  17. Jaeger M, Soehle M, Schuhmann MU, Winkler D, Meixensberger J. Correlation of continuously monitored regional cerebral blood flow and brain tissue oxygen. Acta Neurochir (Wien). 2005;147(1):51–6.
  18. Sarrafzadeh AS, Sakowitz OW, Callsen TA, Lanksch WR, Unterberg AW. Bedside microdialysis for early detection of cerebral hypoxia in traumatic brain injury. Neurosurg Focus. 2000;9(5):e2.
  19. Meixensberger J, Kunze E, Barcsay E, Vaeth A, Roosen K. Clinical cerebral microdialysis: brain metabolism and brain tissue oxygenation after acute brain injury. Neurol Res. 2001;23(8):801–6.
  20. Meixensberger J, Renner C, Simanowski R, Schmidtke A, Dings J, Roosen K. Influence of cerebral oxygenation following severe head injury on neuropsychological testing. Neurol Res. 2004;26(4):414–7.
  21. Maloney-Wilensky E, Gracias V, Itkin A, Hoffman K, Bloom S, Yang W, et al. Brain tissue oxygen and outcome after severe traumatic brain injury: a systematic review. Crit Care Med. 2009;37(6):2057–63.
  22. Jaeger M, Schuhmann MU, Soehle M, Meixensberger J. Continuous assessment of cerebrovascular autoregulation after traumatic brain injury using brain tissue oxygen pressure reactivity. Crit Care Med. 2006;34(6):1783–8.
  23. Tisdall MM, Smith M. Cerebral microdialysis: research technique or clinical tool. Br J Anaesth. 2006;97(1):18–25.
  24. Vespa P, Bergsneider M, Hattori N, Wu HM, Huang SC, Martin NA, et al. Metabolic crisis without brain ischemia is common after traumatic brain injury: a combined microdialysis and positron emission tomography study. J Cereb Blood Flow Metab. 2005;25(6):763–74.
  25. Engström M, Polito A, Reinstrup P, Romner B, Ryding E, Ungerstedt U, et al. Intracerebral microdialysis in severe brain trauma: the importance of catheter location.J Neurosurg. 2005;102(3):460–9.
  26. Reinert M, Barth A, Rothen HU, Schaller B, Takala J, Seiler RW. Effects of cerebral perfusion pressure and increased fraction of inspired oxygen on brain tissue oxygen, lactate and glucose in patients with severe head injury. Acta Neurochir (Wien). 2003;145(5):341–9.
  27. Nordström CH, Reinstrup P, Xu W, Gärdenfors A, Ungerstedt U. Assessment of the lower limit for cerebral perfusion pressure in severe head injuries by bedside monitoring of regional energy metabolism. Anesthesiology. 2003;98(4):809–14.
  28. Marcoux J, McArthur DA, Miller C, Glenn TC, Villablanca P, Martin NA, et al. Persistent metabolic crisis as measured by elevated cerebral microdialysis lactate-pyruvate ratio predicts chronic frontal lobe brain atrophy after traumatic brain injury. Crit Care Med. 2008;36(10):2871–7.
  29. Timofeev I, Carpenter KL, Nortje J, Al-Rawi PG, O’Connell MT, Czosnyka M, et al. Cerebral extracellular chemistry and outcome following traumatic brain injury: a microdialysis study of 223 patients. Brain. 2011;134(Pt 2):484–94.
  30. van Santbrink H, Schouten JW, Steyerberg EW, Avezaat CJ, Maas AI. Serial transcranial Doppler measurements in traumatic brain injury with special focus on the early posttraumatic period. Acta Neurochir (Wien). 2002;144(11):1141–9.
  31. Rasulo FA, De Peri E, Lavinio A. Transcranial Doppler ultrasonography in intensive care. Eur J Anaesthesiol Suppl. 2008;42:167–73.
  32. Moppett IK, Mahajan RP. Transcranial Doppler ultrasonography in anaesthesia and intensive care. Br J Anaesth. 2004;93(5):710–24.
  33. Brandi G, Béchir M, Sailer S, Haberthür C, Stocker R, Stover JF. Transcranial color-coded duplex sonography allows to assess cerebral perfusion pressure noninvasively following severe traumatic brain injury. Acta Neurochir (Wien). 2010;152(6):965–72.
  34. Carter BG, Butt W (2005) Are somatosensory evoked potentials the best predictor of outcome after severe brain injury? A systematic review. Intensive Care Med 31(6):765–75.
  35. Roche RA, Dockree PM, Garavan H, Foxe JJ, Robertson IH, O’Mara SM. EEG alpha power changes reflect response inhibition deficits after traumatic brain injury (TBI) in humans. Neurosci Lett 2004;362(1):1–5.
  36. Hebb MO, McArthur DL, Alger J, Etchepare M, Glenn TC, Bergsneider M, et al. Impaired percent alpha variability on continuous electroencephalography is associated with thalamic injury and predicts poor long-term outcome after human traumatic brain injury. J Neurotrauma. 2007;24(4):579–90.
  37. Leao AAP. Spreading depression of activity in cerebral cortex. J Neurophysiol. 1944;7:359–90.
  38. Dreier JP, Woitzik J, Fabricius M, Bhatia R, Major S, Drenckhahn C, et al. Delayed ischaemic neurological deficits after subarachnoid haemorrhage are associated with clusters of spreading depolarizations. Brain. 2006;129(Pt 12):3224–37.
  39. Fabricius M, Fuhr S, Bhatia R, Boutelle M, Hashemi P, Strong AJ, Lauritzen M. Cortical spreading depression and peri-infarct depolarization in acutely injured human cerebral cortex. Brain. 2006;129(Pt 3):778–90.
  40. Strong AJ, Hartings JA, Dreier JP. Cortical spreading depression: an adverse but treatable factor in intensive care? Curr Opin Crit Care. 2007;13(2):126–33.
  41. Parkin M, Hopwood S, Jones DA, Hashemi P, Landolt H, Fabricius M, et al. Dynamic changes in brain glucose and lactate in pericontusional areas of the human cerebral cortex, monitored with rapid sampling on-line microdialysis: relationship with depolarisation-like events. J Cereb Blood Flow Metab. 2005;25(3):402–13.
  42. Krajewski KL, Orakcioglu B, Haux D, Hertle DN, Santos E, Kiening KL, et al. Cerebral microdialysis in acutely brain-injured patients with spreading depolarizations. Acta Neurochir Suppl. 2011;110(Pt 1):125–30.
  43. Feuerstein D, Manning A, Hashemi P, Bhatia R, Fabricius M, Tolias C, et al. Dynamic metabolic response to multiple spreading depolarizations in patients with acute brain injury: an online microdialysis study. J Cereb Blood Flow Metab. 2010;30(7):1343–55.
  44. Jaeger M, Soehle M, Schuhmann MU, Winkler D, Meixensberger J. Correlation of continuously monitored regional cerebral blood flow and brain tissue oxygen. Acta Neurochir (Wien). 2005;147(1):51–6.
  45. Rosenthal G, Sanchez-Mejia RO, Phan N, Hemphill JC 3rd, Martin C, Manley GT. Incorporating a parenchymal thermal diffusion cerebral blood flow probe in bedside assessment of cerebral autoregulation and vasoreactivity in patients with severe traumatic brain injury. J Neurosurg. 2011;114(1):62–70.
  46. Robertson CS, Valadka AB, Hannay HJ, Contant CF, Gopinath SP, Cormio M, et al. Prevention of secondary ischemic insults after severe head injury. Crit Care Med. 1999;27(10):2086–95.
  47. An G, West MA. Abdominal compartment syndrome: a concise clinical review. Crit Care Med. 2008;36(4):1304–10.
  48. Pinheiro de Oliveira R, Hetzel MP, dos Anjos Silva M, Dallegrave D, Friedman G. Mechanical ventilation with high tidal volume induces inflammation in patients without lung disease. Crit Care. 2010;14(2):R39.
  49. Meier R, Béchir M, Ludwig S, Sommerfeld J, Keel M, Steiger P, et al. Differential temporal profile of lowered blood glucose levels (3.5 to 6.5 mmol/l versus 5 to 8 mmol/l) in patients with severe traumatic brain injury. Crit Care. 2008;12(4):R98.
  50. Cannon-Diehl MR. Transfusion in the critically ill: does it affect outcome? Crit Care Nurs Q. 2010;33(4):324–38.
  51. Rosner MJ, Rosner SD, Johnson AH. Cerebral perfusion pressure: management protocol and clinical results. J Neurosurg. 1995;83(6):949–62.
  52. Marín-Caballos AJ, Murillo-Cabezas F, Cayuela-Domínguez A, Domínguez-Roldán JM, Rincón-Ferrari MD, Valencia-Anguita J, et al. Cerebral perfusion pressure and risk of brain hypoxia in severe head injury: a prospective observational study. Crit Care. 2005;9(6):R670–6.
  53. Longhi L, Pagan F, Valeriani V, Magnoni S, Zanier ER, Conte V, et al. Monitoring brain tissue oxygen tension in brain-injured patients reveals hypoxic episodes in normal-appearing and in perifocal tissue. Intensive Care Med. 2007;33(12):2136–42.
  54. Narotam PK, Morrison JF, Nathoo N. Brain tissue oxygen monitoring in traumatic brain injury and major trauma: outcome analysis of a brain tissue oxygen-directed therapy. J Neurosurg. 2009;111(4):672–82.
  55. Spiotta AM, Stiefel MF, Gracias VH, Garuffe AM, Kofke WA, Maloney-Wilensky E, et al. Brain tissue oxygen-directed management and outcome in patients with severe traumatic brain injury. J Neurosurg. 2010;113(3):571–80.
  56. Ståhl N, Schalén W, Ungerstedt U, Nordström CH. Bedside biochemical monitoring of the penumbra zone surrounding an evacuated acute subdural haematoma. Acta Neurol Scand. 2003;108(3):211–5.
  57. Menzel M, Doppenberg EM, Zauner A, Soukup J, Reinert MM, Clausen T, et al. Cerebral oxygenation in patients after severe head injury: monitoring and effects of arterial hyperoxia on cerebral blood flow, metabolism and intracranial pressure. J Neurosurg Anesthesiol. 1999;11(4):240–51.
  58. Rossi S, Stocchetti N, Longhi L, Balestreri M, Spagnoli D, Zanier ER, Bellinzona G. Brain oxygen tension, oxygen supply, and oxygen consumption during arterial hyperoxia in a model of progressive cerebral ischemia. J Neurotrauma. 2001;18(2):163–74.
  59. Caricato A, Conti G, Della Corte F, Mancino A, Santilli F, Sandroni C, et al. Effects of PEEP on the intracranial system of patients with head injury and subarachnoid haemorrhage: the role of respiratory system compliance. J Trauma. 2005;58(3):571–6.
  60. Muizelaar JP, Marmarou A, Ward JD, Kontos HA, Choi SC, Becker DP, et al. Adverse effects of prolonged hyperventilation in patients with severe head injury: a randomized clinical trial. J Neurosurg. 1991;75(5):731–9.
  61. Davis DP. Early ventilation in traumatic brain injury. Resuscitation. 2008;76(3):333–40.
  62. Hutchinson PJ, Gupta AK, Fryer TF, Al-Rawi PG, Chatfield DA, Coles JP, et al. Correlation between cerebral blood flow, substrate delivery, and metabolism in head injury: a combined microdialysis and triple oxygen positron emission tomography study. J Cereb Blood Flow Metab. 2002;22(6):735–45.
  63. Stocchetti N, Maas AI, Chieregato A, van der Plas AA. Hyperventilation in head injury: a review. Chest. 2005; 127(5):1812–27.
  64. Sarrafzadeh AS, Kiening KL, Callsen TA, Unterberg AW. Metabolic changes during impending and manifest cerebral hypoxia in traumatic brain injury. Br J Neurosurg. 2003;17(4):340–6.
  65. Marion DW, Puccio A, Wisniewski SR, Kochanek P, Dixon CE, Bullian L, et al. Effect of hyperventilation on extracellular concentrations of glutamate, lactate, pyruvate, and local cerebral blood flow in patients with severe traumatic brain injury. Crit Care Med. 2002;30(12):2619–25.
  66. Unterberg AW, Kiening KL, Härtl R, Bardt T, Sarrafzadeh AS, Lanksch WR. Multimodal monitoring in patients with head injury: evaluation of the effects of treatment on cerebral oxygenation. J Trauma. 1997;42(5 Suppl):S32–7.
  67. Soukup J, Bramsiepe I, Brucke M, Sanchin L, Menzel M. Evaluation of a bedside monitor of regional CBF as a measure of CO2 reactivity in neurosurgical intensive care patients. J Neurosurg Anesthesiol. 2008;20(4):249–55.
  68. Soustiel JF, Mahamid E, Chistyakov A, Shik V, Benenson R, Zaaroor M. Comparison of moderate hyperventilation and mannitol for control of intracranial pressure control in patients with severe traumatic brain injury – a study of cerebral blood flow and metabolism. Acta Neurochir (Wien). 2006;148(8):845–51.
  69. Carmona Suazo JA, Maas AI, van den Brink WA, van Santbrink H, Steyerberg EW, Avezaat CJ. CO2 reactivity and brain oxygen pressure monitoring in severe head injury. Crit Care Med. 2000;28(9):3268–74.
  70. Hare GM, Mazer CD, Hutchison JS, McLaren AT, Liu E, Rassouli A, et al. Severe hemodilutional anemia increases cerebral tissue injury following acute neurotrauma. J Appl Physiol. 2007;103(3):1021–9.
  71. Ekelund A, Reinstrup P, Ryding E, Andersson AM, Molund T, Kristiansson KA, et al. Effects of iso- and hypervolemic haemodilution on regional cerebral blood flow and oxygen delivery for patients with vasospasm after aneurysmal subarachnoid haemorrhage. Acta Neurochir (Wien). 2002;144(7):703–12.
  72. Smith MJ, Stiefel MF, Magge S, Frangos S, Bloom S, Gracias V, Le Roux PD. Packed red blood cell transfusion increases local cerebral oxygenation. Crit Care Med. 2005;33(5):1104–8.
  73. Leal-Noval SR, Rincón-Ferrari MD, Marin-Niebla A, Cayuela A, Arellano-Orden V, Marín-Caballos A, et al. Transfusion of erythrocyte concentrates produces a variable increment on cerebral oxygenation in patients with severe traumatic brain injury: a preliminary study. Intensive Care Med. 2006;32(11):1733–40.
  74. Chang JJ, Youn TS, Benson D, Mattick H, Andrade N, Harper CR, et al. Physiologic and functional outcome correlates of brain tissue hypoxia in traumatic brain injury. Crit Care Med. 2009;37(1):283–90.
  75. Van Beek JG, Mushkudiani NA, Steyerberg EW, Butcher I, McHugh GS, Lu J, et al. Prognostic value of admission laboratory parameters in traumatic brain injury: results from the IMPACT study. J Neurotrauma 2007;24:315–28.
  76. Jeremitsky E, Omert LA, Dunham CM, Wilberger J, Rodriguez A. The impact of hyperglycaemia on patients with severe brain injury. J Trauma. 2005;58:47–50.
  77. van den Berghe G, Wouters P, Weekers F, Verwaest C, Bruyninckx F, Schetz M, et al. Intensive insulin therapy in the critically ill patients. N Engl J Med. 2001;345:1359–67.
  78. Bilotta F, Caramia R, Cernak I, Paoloni FP, Doronzio A, Cuzzone V, et al. Intensive Insulin Therapy After Severe Traumatic Brain Injury: A Randomized Clinical Trial. Neurocrit Care. 2008;9(2):159–66.
  79. Van den Berghe G, Wilmer A, Hermans G, Meersseman W, Wouters PJ, Milants I, et al. Intensive insulin therapy in the medical ICU. N Engl J Med. 2006;354:449–61.
  80. Van den Berghe G, Schoonheydt K, Becx P, Bruyninckx F, Wouters PJ. Insulin therapy protects the central and peripheral nervous system of intensive care patients. Neurology. 2005;64:1348–53.
  81. Vespa P, Boonyaputthikul R, McArthur DL, Miller C, Etchepare M, Bergsneider Met al. Intensive insulin therapy reduces microdialysis glucose values without altering glucose utilization or improving the lactate/pyruvate ratio after traumatic brain injury. Crit Care Med. 2006;34:850–6.
  82. Oddo M, Schmidt JM, Carrera E, Badjatia N, Connolly ES, Presciutti M, et al. Impact of tight glycemic control on cerebral glucose metabolism after severe brain injury: a microdialysis study. Crit Care Med. 2008;36(12):3233–8.
  83. Strong AJ, Smith SE, Whittington DJ, Meldrum BS, Parsons AA, Krupinski J, et al. Factors influencing the frequency of fluorescence transients as markers of peri-infarct depolarizations in focal cerebral ischemia. Stroke. 2000;31:214–22.
  84. Hopwood SE, Parkin MC, Bezzina EL, Boutelle MG, Strong AJ. Transient changes in cortical glucose and lactate levels associated with peri-infarct depolarisations, studied with rapid-sampling microdialysis. J Cereb Blood Flow Metab. 2005;25:391–401.
  85. Strong AJ, Hartings JA, Dreier JP. Cortical spreading depression: an adverse but treatable factor in intensive care? Curr Opin Crit Care. 2007;13:126–33.
  86. Meierhans R, Béchir M, Ludwig S, Sommerfeld J, Brandi G, Haberthür C, et al. Brain metabolism is significantly impaired at blood glucose below 6 mM and brain glucose below 1 mM in patients with severe traumatic brain injury. Crit Care. 2010;14(1):R13.
  87. Béchir M, Meierhans R, Brandi G, Sommerfeld J, Fasshauer M, Cottini SR, et al. Insulin differentially influences brain glucose and lactate in traumatic brain injured patients. Minerva Anestesiol. 2010;76(11):896–904.
  88. Vespa PM, McArthur D, O’Phelan K, Glenn T, Etchepare M, Kelly D, et al. Persistently low extracellular glucose correlates with poor outcome 6 months after human traumatic brain injury despite a lack of increased lactate: a microdialysis study. J Cereb Blood Flow Metab. 2003;23(7):865–77.
  89. Jaeger M, Soehle M, Meixensberger J. Effects of decompressive craniectomy on brain tissue oxygen in patients with intracranial hypertension. J Neurol Neurosurg Psychiatry. 2003;74(4):513–5.
  90. Strege RJ, Lang EW, Stark AM, Scheffner H, Fritsch MJ, Barth H, Mehdorn HM. Cerebral oedema leading to decompressive craniectomy: an assessment of the preceding clinical and neuromonitoring trends. Neurol Res. 2003;25(5):510–5.
  91. Jaeger M, Soehle M, Meixensberger J. Improvement of brain tissue oxygen and intracranial pressure during and after surgical decompression for diffuse brain oedema and space occupying infarction. Acta Neurochir Suppl. 2005;95:117–8.
  92. Reithmeier T, Löhr M, Pakos P, Ketter G, Ernestus RI. Relevance of ICP and ptiO2 for indication and timing of decompressive craniectomy in patients with malignant brain oedema. Acta Neurochir (Wien). 2005;147(9):947–51.
  93. Boret H, Fesselet J, Meaudre E, Gaillard PE, Cantais E. Cerebral microdialysis and P(ti)O2 for neuro-monitoring before decompressive craniectomy. Acta Anaesthesiol Scand. 2006;50(2):252–4.
  94. Cooper DJ, Rosenfeld JV, Murray L, Arabi YM, Davies AR, D’Urso P, et al.; DECRA Trial Investigators; Australian and New Zealand Intensive Care Society Clinical Trials Group. Decompressive craniectomy in diffuse traumatic brain injury. N Engl J Med. 2011;364(16):1493–502.