Pressure reactivity as a guide in the treatment of cerebral perfusion pressure in patients with brain trauma

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Object. The aim of this study was to compare the effects of two different treatment protocols on physiological characteristics and outcome in patients with brain trauma. One protocol was primarily oriented toward reducing intracranial pressure (ICP), and the other primarily on maintaining cerebral perfusion pressure (CPP).

Methods. A series of 67 patients in Uppsala were treated according to a protocol aimed at keeping ICP less than 20 mm Hg and, as a secondary target, CPP at approximately 60 mm Hg. Another series of 64 patients in Edinburgh were treated according to a protocol aimed primarily at maintaining CPP greater than 70 mm Hg and, secondarily, ICP less than 25 mm Hg for the first 24 hours and 30 mm Hg subsequently.

The ICP and CPP insults were assessed as the percentage of monitoring time that ICP was greater than or equal to 20 mm Hg and CPP less than 60 mm Hg, respectively. Pressure reactivity in each patient was assessed based on the slope of the regression line relating mean arterial blood pressure (MABP) to ICP. Outcome was analyzed at 6 months according to the Glasgow Outcome Scale (GOS).

The prognostic value of secondary insults and pressure reactivity was determined using linear methods and a neural network. In patients treated according to the CPP-oriented protocol, even short durations of CPP insults were strong predictors of death. In patients treated according to the ICP-oriented protocol, even long durations of CPP insult—mostly in the range of 50 to 60 mm Hg—were significant predictors of favorable outcome (GOS Score 4 or 5). Among those who had undergone ICP-oriented treatment, pressure-passive patients (MABP/ICP slope ≥ 0.13) had a better outcome. Among those who had undergone CPP-oriented treatment, the more pressure-active (MABP/ICP slope < 0.13) patients had a better outcome.

Conclusions. Based on data from this study, the authors concluded that ICP-oriented therapy should be used in patients whose slope of the MABP/ICP regression line is at least 0.13, that is, in pressure-passive patients. If the slope is less than 0.13, then hypertensive CPP therapy is likely to produce a better outcome.

Article Information

Address reprint requests to: Tim Howells, Ph.D., Department of Neurosurgery, University Hospital, 751 85 Uppsala, Sweden. email: timothy.howells@lul.se.

© AANS, except where prohibited by US copyright law.

Headings

Figures

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    Bar graphs demonstrating the distribution of ICP and CPP insults in patients from Edinburgh and Uppsala. The vertical axis represents the number of patients in each range, for example, the number of patients with an ICP of at least 20 mm Hg between 0 and 10% of the monitoring time. There was no statistically significant difference in the distribution of ICP insults, but the difference in the distribution of CPP insults was significant (p < 0.001).

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    Graphs showing the probability of a favorable outcome (GOS Score 4 or 5) as a function of the percentage of monitoring time that a patient experienced a CPP less than 60 mm Hg. In the patients in Edinburgh, longer durations of CPP insult were strongly associated with death; in those in Uppsala, however, longer durations of CPP insult were prognostic of favorable outcome.

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    Bar graphs demonstrating CPP values in the patient groups in Uppsala and Edinburgh who experienced CPP insults for more than 10% of the monitoring time. In the patients in Edinburgh, the insults often occurred in the most severe range, with a CPP less than 40 mm Hg 59% of the time. This was not true in the patients in the Uppsala group. N = number of patients.

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    Bar graphs indicating the nature of the ICP insults in two Uppsala patient groups: those with CPP insult less than 10% of the time (left) and those with CPP insult more than or equal to 10% of the time (right). The patients with more CPP insult had a signifi- cantly better outcome than those with less insult, despite the fact that they had also experienced more ICP insult.

  • View in gallery

    Scatterplots of ICP graphed against MABP in the Uppsala and Edinburgh patient groups. Each point represents the mean ICP and MABP values recorded for a patient over the course of 1 hour. Data were excluded when ICP was greater than 40 mm Hg. Regression lines were calculated by minimizing the sum-squared distance from the line.

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    Graphs demonstrating the probability of a favorable outcome as a function of the slope of MABP/ICP. Pressure-active patients (negative slope) in Edinburgh had a better outcome, whereas pressure-passive patients (positive slope) in Uppsala had a better outcome. Dotted lines represent boundaries of 90% confidence region; solid line represents a maximum likelihood estimate of probability.

  • View in gallery

    Graph of curves featured in Fig. 6. We estimated that the optimal point at which to switch from one treatment strategy to the other in a given patient is at an MABP/ICP trend with a slope of approximately 0.13. This result corresponds to a patient in whom an increase of 15 mm Hg in MABP leads to an increase of 2 mm Hg in ICP. Solid line represents Uppsala; dotted line represents Edinburgh.

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