Brain injury

Intracranial pressure monitoring, cerebral perfusion pressure estimation, and ICP/CPP-guided therapy: a standard of care or optional extra after brain injury?

Authors: Kirkman MA, Smith M.

Measurement of intracranial pressure (ICP) and mean arterial pressure (MAP) is used to derive cerebral perfusion pressure (CPP) and to guide targeted therapy of acute brain injury (ABI) during neurointensive care. Here we provide a narrative review of the evidence for ICP monitoring, CPP estimation, and ICP/CPP-guided therapy after ABI. Despite its widespread use, there is currently no class I evidence that ICP/CPP-guided therapy for any cerebral pathology improves outcomes; indeed some evidence suggests that it makes no difference, and some that it may worsen outcomes. Similarly, no class I evidence can currently advise the ideal CPP for any form of ABI. 'Optimal' CPP is likely patient-, time-, and pathology-specific. Further, CPP estimation requires correct referencing (at the level of the foramen of Monro as opposed to the level of the heart) for MAP measurement to avoid CPP over-estimation and adverse patient outcomes. Evidence is emerging for the role of other monitors of cerebral well-being that enable the clinician to employ an individualized multimodality monitoring approach in patients with ABI, and these are briefly reviewed. While acknowledging difficulties in conducting robust prospective randomized studies in this area, such high-quality evidence for the utility of ICP/CPP-directed therapy in ABI is urgently required. So, too, is the wider adoption of multimodality neuromonitoring to guide optimal management of ICP and CPP, and a greater understanding of the underlying pathophysiology of the different forms of ABI and what exactly the different monitoring tools used actually represent.

Decreased risk of acute kidney injury with intracranial pressure monitoring in patients with moderate or severe brain injury

Authors: Zeng J, Tong W, Zheng P.

Object The authors undertook this study to evaluate the effects of continuous intracranial pressure (ICP) monitoring-directed mannitol treatment on kidney function in patients with moderate or severe traumatic brain injury (TBI). Methods One hundred sixty-eight patients with TBI were prospectively assigned to an ICP monitoring group or a conventional treatment control group based on the Brain Trauma Foundation guidelines. Clinical data included the dynamic changes of patients' blood concentrations of cystatin C, creatinine (Cr), and blood urea nitrogen (BUN); mannitol use; and 6-month Glasgow Outcome Scale (GOS) scores. Results There were no statistically significant differences with respect to hospitalized injury, age, or sex distribution between the 2 groups. The incidence of acute kidney injury (AKI) was higher in the control group than in the ICP monitoring group (p < 0.05). The mean mannitol dosage in the ICP monitoring group (443 ± 133 g) was significantly lower than in the control group (820 ± 412 g) (p < 0.01), and the period of mannitol use in the ICP monitoring group (3 ± 3.8 days) was significantly shorter than in the control group (7 ± 2.3 days) (p < 0.01). The 6-month GOS scores in the ICP monitoring group were significantly better than in the control group (p < 0.05). On the 7th, 14th, and 21st days after injury, the plasma cystatin C and Cr concentrations in the ICP-monitoring group were significantly higher than the control group (p < 0.05). Conclusions In patients with moderate and severe TBI, ICP-directed mannitol treatment demonstrated a beneficial effect on reducing the incidence of AKI compared with treatment directed by neurological signs and physiological indicators.

Mathematical Modelling of Near-Infrared Spectroscopy Signals and Intracranial Pressure in Brain-Injured Patients

Authors: Highton D, Panovska-Griffiths J, Smith M, Elwell CE.

Raised intracranial pressure (ICP) is a key concern following acute brain injury as it may be associated with cerebral hypoperfusion and poor outcome. In this research we describe a mathematical physiological model designed to interpret cerebral physiology from neuromonitoring: ICP, near-infrared spectroscopy and transcranial Doppler flow velocity. This aims to characterise the complex dynamics of cerebral compliance, cerebral blood volume, cerebral blood flow and their regulation in individual patients. Analysis of data from six brain-injured patients produces cohesive predictions of cerebral biomechanics suggesting reduced cerebral compliance, reduced volume compensation and impaired blood flow autoregulation. Patient-specific physiological modelling has the potential to predict the key biomechanical and haemodynamic changes following brain injury in individual patients, and might be used to inform individualised treatment strategies.

Continuous Optical Monitoring of Cerebral Hemodynamics During Head-of-Bed Manipulation in Brain-Injured Adults

Authors: Kim MN, Edlow BL, Durduran T, Frangos S, Mesquita RC, Levine JM, Greenberg JH, Yodh AG, Detre JA.

INTRODUCTION: Head-of-bed manipulation is commonly performed in the neurocritical care unit to optimize cerebral blood flow (CBF), but its effects on CBF are rarely measured. This pilot study employs a novel, non-invasive instrument combining two techniques, diffuse correlation spectroscopy (DCS) for measurement of CBF and near-infrared spectroscopy (NIRS) for measurement of cerebral oxy- and deoxy-hemoglobin concentrations, to monitor patients during head-of-bed lowering.

Induced and Sustained Hypernatremia for the Prevention and Treatment of Cerebral Edema Following Brain Injury

Authors: Ryu JH, Walcott BP, Kahle KT, Sheth SA, Peterson RT, Nahed BV, Coumans JV, Simard JM.

Cerebral edema develops in response to and as a result of a variety of neurologic insults such as ischemic stroke, traumatic brain injury, and tumor. It deforms brain tissue, resulting in localized mass effect and increase in intracranial pressure (ICP) that are associated with a high rate of morbidity and mortality. When administered in bolus form, hyperosmolar agents such as mannitol and hypertonic saline have been shown to reduce total brain water content and decrease ICP, and are currently the mainstays of pharmacological treatment. However, surprisingly, little is known about the increasingly common clinical practice of inducing a state of sustained hypernatremia. Herein, we review the available studies employing sustained hyperosmolar therapy to induce hypernatremia for the prevention and/or treatment of cerebral edema. Insufficient evidence exists to recommend pharmacologic induction of hypernatremia as a treatment for cerebral edema. The strategy of vigilant avoidance of hyponatremia is currently a safer, potentially more efficacious paradigm.

Wide variation and systematic bias in expert clinicians' perceptions of prognosis following brain injury

Authors: Moore NA, Brennan PM, Baillie JK.

Background. The heterogeneous nature of traumatic brain injury (TBI) makes outcome prediction difficult. Although a considerable evidence base exists in the form of well-validated predictive models, these models are not widely used. We hypothesised that this prognostic gap, between the availability and use of prognostic data, leads to inaccurate perceptions of patient outcome. We investigated whether outcome predictions in TBI made by expert clinicians were consistent and accurate when compared to a well-validated prognostic model (IMPACT). Methods. Neurosurgeons and neurointensivists were asked to predict probability of death at 6 months for 12 case vignettes describing patients with isolated TBI. Predictions were compared to IMPACT prognosis for each vignette. To interrogate potential sources of bias in clinical predictions, respondents were given one of two sets of vignettes (A or B) identical apart from one critical factor known to make a large difference to outcome. Results. 27 of 33 questionnaires were returned. Clinicians were consistently more pessimistic about outcomes than the IMPACT model, predicting a significantly greater probability of death (mean difference + 16.3%, 95% CI 13.3-19.4, p < 0.001). There was wide variation between clinicians predicting outcomes for any given vignette (mean range 68.3%), and within the predictions made by each individual: 30% of clinicians were both the most pessimistic respondent, and the most optimistic, for at least one vignette. Clinicians modified their predictions appropriately for most of the factors altered between corresponding vignettes. However when the reported blood glucose was changed, clinicians' predictions deviated widely from IMPACT predictions, indicating that clinicians systematically overlooked the prognostic relevance of this information. Conclusion. Clinical experts' predictions of outcome in TBI are widely variable and systematically pessimistic compared to IMPACT. Clinicians overlook important factors in formulating these predictions. Use of well-validated outcome models may add value and consistency to prognostication.

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