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.

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 ICPmax) and the minimum value of the CPP readings (CPPmin) 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 CPPmin of 55 mm Hg and for ICPmax 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 CPPmin and 35 mm Hg for ICPmax. Higher levels of CPPmin 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.

The cause and incidence of secondary insults in severely head-injured adults and children.

The cause and incidence of reductions in cerebral perfusion pressure, and rises in intracranial pressure have been examined in a series of patients with severe head injury defined as an initial Glasgow Coma Sum of less than or equal to 8. Two-hundred-and-seven adults (aged over 16 years) and 84 children admitted to Newcastle General Hospital, who had intracranial pressure monitoring as part of their routine management, were studied. Intracranial pressure (ICP), arterial pressure and cerebral perfusion pressure (CPP) were sampled and recorded every 2 min. Patients' CT findings were classified into distinct groups using the method described by Marshall. Secondary insults were defined using the Edinburgh University Secondary Insult Grades (EUSIG) and the incidence and cause (raised ICP, reduced CPP or a combination of the two) was established. Outcome was assessed at 6 months using the Glasgow Outcome Scale. In the majority of adults with head injury it is the combination of reduced arterial pressure and raised ICP that contributes to the reduction in cerebral perfusion pressure. This was not the case for Diffuse Injury Type I. In children similar characteristics were found across each of the CT classifications. The vast majority of falls in CPP down to 60 mmHg were caused by reduced arterial pressure. Reductions below 50 mmHg were almost always due to a combination of both reduced arterial pressure and raised ICP. The results in adults were similar, but not identical, to those of the paediatric cases. Diffuse Injury Type I stood out from all the other categories as the only one where reductions in perfusion pressure were almost exclusively due to reductions in arterial pressure and not to increases in ICP. The management of these patients should ensure the adequacy of perfusion pressure by maintaining arterial pressure at a satisfactory level. These results suggest that vigilant monitoring of both intracranial pressure and arterial pressure is required to lower the incidence of secondary insults.

Audit of head injury management in the Northern Region. Northern Regional Head Injury Group.

Head injury is a major cause of mortality and morbidity in the UK and is more prevalent among children and young adults. However, certain factors that contribute to deaths and brain damage can be audited. This article describes an audit of head injury management conducted by the Northern Regional Head Injury Group.