Iain Robert Chambers

Objective: To determine the statistical characteristics of blood pressure (BP) readings from a large number of head-injured patients. Methods: The BrainIT group has collected high time-resolution physiological and clinical data from head-injured patients who require intracranial pressure (ICP) monitoring. The statistical features of this dataset of BP measurements with time resolution of 1 min from 200 patients is examined. The distributions of BP measurements and their relationship with simultaneous ICP measurements are described. Results: The distributions of mean, systolic and diastolic readings are close to normal with modest skewing towards higher values. There is a trend towards an increase in blood pressure with advancing age, but this is not significant. Simultaneous blood pressure and ICP values suggest a triphasic relationship with a BP rising at 0.28 mm Hg/mm Hg of ICP, for ICP up to 32 mm Hg, and 0.9 mm Hg/mm Hg of ICP for ICP from 33 to 55 mm Hg, and falling sharply with rising ICP for ICP >55 mm Hg. Conclusions: Patients with head injury appear to have a near normal distribution of blood pressure readings that are skewed towards higher values. The relationship between BP and ICP may be triphasic.

Background: The principal strategy for managing head injury is to reduce the frequency and severity of secondary brain insults from intracranial pressure (ICP) and cerebral perfusion pressure (CPP), and hence improve outcome. Precise critical threshold levels have not been determined in head injured children. Objective: To create a novel pressure–time index (PTI) measuring both duration and amplitude of insult, and then employ it to determine critical insult thresholds of ICP and CPP in children. Methods: Prospective, observational, physiologically based study from Edinburgh and Newcastle, using patient monitored blood pressure, ICP, and CPP time series data. The PTI for ICP and CPP for 81 children, using theoretical values derived from physiological norms, was varied systematically to derive critical insult thresholds which delineate Glasgow outcome scale categories. Results: The PTI for CPP had a very high predictive value for outcome (receiver operating characteristic analyses: area under curve = 0.957 and 0.890 for mortality and favourable outcome, respectively) and was more predictive than for ICP. Initial physiological values most accurately predicted favourable outcome. The CPP critical threshold values determined for children aged 2–6, 7–10, and 11–15 years were 48, 54, and 58 mm Hg. respectively. Conclusions: The PTI is the first substantive paediatric index of total ICP and CPP following head injury. The insult thresholds generated are identical to age related physiological values. Management guidelines for paediatric head injuries should take account of these CPP thresholds to titrate appropriate pressor therapy.

Studies of therapeutic interventions and management strategies on head injured patients are difficult to undertake. BrainIT provides validated data for analysis available to centers that contribute data to allow post-hoc analysis and hypothesis testing.

BrainIT is a multi centre, European project, to collect high quality continuous data from severely head injured patients using a previously defined [6] core data set. This includes minute-by-minute physiological data and simultaneous treatment and management information. It is crucial that the data is correctly collected and validated.

Tympanic membrane displacement (TMD) measurements may be useful in the management of patients with hydrocephalus if they can be directly associated with measurements of ICP. We have compared TMD measurements using the Marchbanks Measurement System with invasive ICP monitoring.

Severe head injury in childhood continues to be associated with considerable mortality and morbidity. Early surgical decompression may be beneficial and the objective of this study was to examine the relationship between age-related thresholds of mean intracranial pressure (ICP) and cerebral perfusion pressure (CPP) over the first 6 hours and age outcome in paediatric head injury patients. A total of 209 head injured children admitted to five UK hospitals were studied. Patients aged 2 to 16 years were included if they had a minimum of six hours of invasive pressure monitoring. Mean values of ICP and CPP over this period were calculated and compared to those with independent (good recovery and moderate disability) and poor outcome (severe disability, and death) for different age groups. There were 148 children with independent outcome (92 good recovery, 56 moderately disabled), and 61 with poor outcome (30 severely disabled, 31 deaths). There was a significant difference between those with independent compared to poor outcome in relation to ICP (p < 0.001) and CPP (p < 0.001). Patients were divided into three groups according to age. The sensitivity of ICP and CPP in predicting outcome was similar for all groups but the specificity differed between groups. At a CPP of 50 mmHg the specificity varied between the age groups (2 to 6 years: 0.47, 7 to 10 years: 0.28 and 11 to 16 years: 0.10) and similarly for an ICP of 25 mmHg (2 to 6 years: 0.53, 7 to 10 years: 0.44 and 11 to 16 years: 0.38). Younger children may be able to tolerate lower perfusion pressures and still have an independent outcome. Our threshold values for young children are likely to be important in the identification of patients who might benefit from new treatments such as surgical decompression.

Severe head injury in childhood is associated with considerable mortality and morbidity. In this study we determined age-related differences in the relationship between outcome and intracranial pressure (ICP) and cerebral perfusion pressure (CPP) in the first 6 h of monitoring in a large cohort of head-injured children.

Head injury is a major cause of death and disability in children. Despite advances in resuscitation, emergency care, intensive care monitoring, and clinical practices, there are few data demonstrating the predictive value of certain physiological variables regarding outcome in this patient population. Mean arterial blood pressure (MABP), intracranial pressure (ICP), and cerebral perfusion pressure (CPP = MABP − ICP) are routinely monitored in patients in many neurological intensive care units throughout the world, but there is little evidence indicating that advances in care have been matched with corresponding improvements in outcome. Nonetheless, there is evidence that hypotension immediately following head injury is predictive of early death, and many patients with these features die with clinical signs of brain herniation caused by intracranial hypertension. Furthermore, available data indicate that a minimal and a mean CPP measured during intensive care are good predictors of outcome in survivors, but a target threshold to improve outcome has yet to be defined. Some medical management strategies can have detrimental effects, and there is now a good case for undertaking a controlled trial of immediate or delayed craniectomy. Independent outcome in children following severe head injury is associated with higher levels of CPP. The ability to tolerate different levels of CPP may be related to age, and therefore any such surgical trial would need a carefully defined protocol so that the potential benefit of such a treatment is maximized.

Object. Intracranial pressure (ICP) and cerebral perfusion pressure (CPP) are frequently monitored in severely head injured patients. To establish which one (ICP or CPP) is more predictive of outcome and to examine whether there are significant threshold levels in the determination of outcome, receiver—operating characteristic (ROC) curves were used to analyze data in a large series of head-injured patients. Methods. Data were obtained from a total of 291 severely head injured patients (207 adults and 84 children). Outcome was categorized as either independent (good recovery or moderate disability) or poor (severely disabled, vegetative, or dead) by using the Glasgow Outcome Scale; patients were also grouped according to the Marshall computerized tomography scan classification. Conclusions. The maximum value of a 2-minute rolling average of ICP readings (defined as ICP_max) and the minimum value of the CPP readings (CPP_min) were then used to calculate the sensitivity and specificity of the ROC curves over a range of values. Using ROC curves, a threshold value for CPP_min of 55 mm Hg and for ICP_max of 35 mm Hg appear to be the best predictors in adults. For children the levels appear to be 43 to 45 mm Hg for CPP_min and 35 mm Hg for ICP_max. Higher levels of CPP_min seem important in adults with mass lesions. These CPP thresholds (45 mm Hg for children and 55 mm Hg for adults) are lower than previously predicted and may be clinically important, especially in children, in whom a lower blood pressure level is normal. Also, CPP management at higher levels may be more important in adults with mass lesions. A larger observational series would improve the accuracy of these predictions.