One of the guiding principles in the management of traumatic brain injury (TBI) is based on the Munro-Kellie doctrine. According to this principle, the volume of the intracranial compartment is fixed and comprises of the brain parenchyma (80%), intracranial blood volume (10%), and the cerebrospinal fluid volume (10%). An increase in the intracranial volume is compensated to a limited extent by a shift of the cerebrospinal fluid out of the intracranial compartment. However, beyond a certain threshold level of increase in the intracranial volume, compensatory mechanisms fail, and the intracranial pressure (ICP) begins to rise steeply. The rise in ICP compresses the brain parenchyma, leading to a drop in the cerebral perfusion pressure (CPP).
CPP = Mean arterial pressure (MAP) – ICP
If the ICP continues to rise unabated, cerebral perfusion is compromised, leading to secondary brain injury, which is usually fatal.
Early studies, ICP thresholds
Lundberg et al. first reported the use of an intraventricular catheter connected to a strain gauge transducer for the continuous measurement ICP in 30 patients with TBI. They proposed that continuous ICP measurement offers a more rational basis to optimize interventions in TBI.1 More than a decade later, Miller et al., in their series of 160 patients, suggested that an ICP higher than a threshold level of 20 mm Hg led to poor outcomes after TBI. They proposed that ICP measurement needs to be considered as part of the management protocol for severe TBI.2 In another early landmark study of patients with intracranial hematoma, clinical features were not helpful in predicting the requirement for surgical intervention; however, an ICP of more than 20 mm Hg was associated with deterioration of the neurological status and the requirement for surgical intervention.3
Advantages and disadvantages of ICP monitoring
ICP monitoring enables CPP-targeted therapeutic interventions. Severe TBI requires controlled ventilation with sedatives, and muscle relaxants for ICP control. Meaningful clinical assessment is often not feasible in this setting. Repeated interruption of sedation at regular intervals to enable clinical assessment may be detrimental in patients with intracranial hypertension. An increase in the ICP alerts the clinician to possible neurological deterioration that may call for re-imaging or surgical intervention. An intraparenchymal catheter is relatively easy to insert and reasonably safe; besides, staff familiarity with this modality of monitoring may improve the level of care.
However, paradoxically, aggressive interventions to normalize ICP, including the excessive use of mannitol and hypertonic saline in elderly patients, with compromised cardiovascular and renal function, may lead to harm. Decompressive craniectomy aimed at alleviating intracranial hypertension may also lead to poor functional outcomes in patients with TBI.4 Although ICP monitoring is recommended by the Brain Trauma Foundation guidelines, in the Trauma Quality Improvement Program database study that included 13,188 patients, only 11.5% of eligible patients underwent ICP monitoring. This finding probably suggests ambivalence among neurosurgeons regarding the efficacy of ICP monitoring in the setting of severe TBI.5
What is the evidence for the usefulness of ICP monitoring?
ICP monitoring is commonly used to titrate interventions including osmotherapy, optimize sedation and ventilator management, and for decision making regarding surgical intervention such as decompressive craniectomy. Most of the information available regarding the efficacy of ICP monitoring and its impact on clinical outcomes is based on observational studies.
The relationship between ICP monitoring and mortality was evaluated among centers participating in the American College of Surgeons Trauma Quality Improvement Program (TQIP). After adjustment for possible confounders, mortality was significantly lower in patients who underwent ICP-guided management. Besides, centers that performed ICP monitoring more often revealed lower mortality.6 A 2-year observational study was performed in patients with severe TBI (GCS of 8 or less) from 14 trauma centers in the US. In-hospital mortality was evaluated after adjusting for confounders using propensity score matching. On both unadjusted and propensity-matched analysis, ICP-based care resulted in a significantly lower in-hospital mortality compared to patients who did not receive ICP monitoring.7
However, other studies have revealed conflicting results. In a two-center Dutch study, one of the study centers used therapeutic interventions based on clinical features and computed tomography (CT) findings. The other study center utilized interventions to maintain an ICP of less than 20 mm Hg and CPP of more than 70 mm Hg. The Glasgow outcome score was used to assess functional outcomes after 12 months. After adjustment for confounders, there was no difference in functional outcomes between centers. The median duration of ventilator support was significantly lower among patients who did not undergo ICP-based management.8 A large US National Trauma Databank (NTDB) study compared patients with TBI who underwent ICP monitoring with those who did not. Patients with blunt TBI with a GCS of 8 or less, with an abnormal brain CT scan, and ICU stay of 3 days or more were included. On multivariate analysis, after adjustment for possible confounders, ICP monitoring resulted in a 45% reduction in survival.9
In a study based on the Trauma Quality Improvement Program (TQIP) database, the investigators assessed compliance with the BTF guidelines for ICP monitoring and the impact of ICP monitoring on clinical outcomes. The study included patients with isolated TBI with a GCS of less than 9 and a score of 3 or more on the head Abbreviated Injury Scale (AIS). This study included 13,188 patients. ICP monitoring was carried out only in 11.5% of eligible patients. Overall, no mortality benefit was discernible among patients who underwent ICP monitoring. Placement of an ICP monitor was an independent predictor of overall complications, infectious complications, and was associated with poor functional outcomes. In the subgroup of patients with the most severe injuries according to the AIS, ICP monitoring was an independent predictor of mortality.5
The only randomized controlled trial comparing ICP-based vs. clinical assessment and imaging-based management was conducted in 324 patients who had suffered severe TBI. The study was conducted across six centers in Bolivia and Ecuador. The composite primary outcome included the duration of survival, the level and duration of impairment of conscious level, the functional status at 3 and 6 months, and the neuropsychological state at 6 months. There was no significant difference in the composite primary outcome between groups. The 6-month mortality and the median duration of ICU stay were also similar in both groups. The duration of cerebral protective therapy was longer in the clinical assessment and imaging-based group; the incidence of adverse events was similar in both groups. Thus, ICP-guided management of severe TBI was not superior to clinical assessment and imaging-based management in this study.10 This study has evoked intense debate and may need to be interpreted against the background of a clinical setting in which ICP monitoring may not be the standard of care.
The bottom line
- ICP monitoring-based care in severe TBI remains contentious with conflicting results from observational studies.
- The only randomized controlled trial on this topic did not demonstrate any clinical outcome benefit with ICP monitoring-based care compared to clinical examination and CT imaging-based care; however, the generalizability of this study remains uncertain.
- Patients with severe TBI require controlled ventilation with sedatives and muscle relaxants as part of neuroprotective therapy; clinical assessment is often not feasible in such patients. Continuous ICP monitoring enables early detection of neurological deterioration.
- There is persisting uncertainty regarding the usefulness of ICP monitoring in patients with severe TBI. Equipoise needs to be maintained on this unresolved issue until more robust evidence is available.
1. Lundberg N, Troupp H, Lorin H. Continuous Recording of the Ventricular-Fluid Pressure in Patients with Severe Acute Traumatic Brain Injury. J Neurosurg. 1965;22(6):581-590. doi:10.3171/jns.1965.22.6.0581
2. Miller JD, Becker DP, Ward JD, Sullivan HG, Adams WE, Rosner MJ. Significance of intracranial hypertension in severe head injury. J Neurosurg. 1977;47(4):503-516. doi:10.3171/jns.1977.47.4.0503
3. Gallbraith S, Teasdale G. Predicting the need for operation in the patient with an occult traumatic intracranial hematoma. J Neurosurg. 1981;55(1):75-81. doi:10.3171/jns.1981.55.1.0075
4. Cooper DJ, Rosenfeld JV, Murray L, et al. Decompressive craniectomy in diffuse traumatic brain injury. N Engl J Med. 2011;364(16):1493-1502. doi:10.1056/NEJMoa1102077
5. Aiolfi A, Benjamin E, Khor D, Inaba K, Lam L, Demetriades D. Brain Trauma Foundation Guidelines for Intracranial Pressure Monitoring: Compliance and Effect on Outcome. World J Surg. 2017;41(6):1543-1549. doi:10.1007/s00268-017-3898-6
6. Alali AS, Fowler RA, Mainprize TG, et al. Intracranial pressure monitoring in severe traumatic brain injury: results from the American College of Surgeons Trauma Quality Improvement Program. J Neurotrauma. 2013;30(20):1737-1746. doi:10.1089/neu.2012.2802
7. Dawes AJ, Sacks GD, Cryer HG, et al. Intracranial pressure monitoring and inpatient mortality in severe traumatic brain injury: A propensity score-matched analysis. J Trauma Acute Care Surg. 2015;78(3):492-501; discussion 501-502. doi:10.1097/TA.0000000000000559
8. Cremer OL, van Dijk GW, van Wensen E, et al. Effect of intracranial pressure monitoring and targeted intensive care on functional outcome after severe head injury. Crit Care Med. 2005;33(10):2207-2213. doi:10.1097/01.ccm.0000181300.99078.b5
9. Shafi S, Diaz-Arrastia R, Madden C, Gentilello L. Intracranial pressure monitoring in brain-injured patients is associated with worsening of survival. J Trauma. 2008;64(2):335-340. doi:10.1097/TA.0b013e31815dd017
10. Chesnut RM, Temkin N, Carney N, et al. A trial of intracranial-pressure monitoring in traumatic brain injury. N Engl J Med. 2012;367(26):2471-2481. doi:10.1056/NEJMoa1207363