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  • Author or Editor: Geoffrey T. Manley x
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Guy Rosenthal, Rene O. Sanchez-Mejia, Nicolas Phan, J. Claude Hemphill III, Christine Martin and Geoffrey T. Manley

Object

Cerebral autoregulation may be altered after traumatic brain injury (TBI). Recent evidence suggests that patients' autoregulatory status following severe TBI may influence cerebral perfusion pressure management. The authors evaluated the utility of incorporating a recently upgraded parenchymal thermal diffusion probe for the measurement of cerebral blood flow (CBF) in the neurointensive care unit for assessing cerebral autoregulation and vasoreactivity at bedside.

Methods

The authors evaluated 20 patients with severe TBI admitted to San Francisco General Hospital who underwent advanced neuromonitoring. Patients had a parenchymal thermal diffusion probe placed for continuous bedside monitoring of local CBF (locCBF) in addition to the standard intracranial pressure and brain tissue oxygen tension (PbtO2) monitoring. The CBF probes were placed in the white matter using a separate cranial bolt. A pressure challenge, whereby mean arterial pressure (MAP) was increased by about 10 mm Hg, was performed in all patients to assess autoregulation. Cerebral CO2 vasoreactivity was assessed with a hyperventilation challenge. Local cerebral vascular resistance (locCVR) was calculated by dividing cerebral perfusion pressure by locCBF. Local cerebral vascular resistance normalized to baseline (locCVRnormalized) was also calculated for the MAP and hyperventilation challenges.

Results

In all cases, bedside measurement of locCBF using a cranial bolt in patients with severe TBI resulted in correct placement in the white matter with a low rate of complications. Mean locCBF decreased substantially with hyperventilation challenge (−7 ± 8 ml/100 g/min, p = 0.0002) and increased slightly with MAP challenge (1 ± 7 ml/100 g/min, p = 0.17). Measurements of locCBF following MAP and hyperventilation challenges can be used to calculate locCVR. In 83% of cases, locCVR increased during a hyperventilation challenge (mean change +3.5 ± 3.8 mm Hg/ml/100 g/min, p = 0.0002), indicating preserved cerebral CO2 vasoreactivity. In contrast, we observed a more variable response of locCVR to MAP challenge, with increased locCVR in only 53% of cases during a MAP challenge (mean change −0.17 ± 3.9 mm Hg/ml/100 g/min, p = 0.64) indicating that in many cases autoregulation was impaired following severe TBI.

Conclusions

Use of the Hemedex thermal diffusion probe appears to be a safe and feasible method that enables continuous monitoring of CBF at the bedside. Cerebral autoregulation and CO2 vasoreactivity can be assessed in patients with severe TBI using the CBF probe by calculating locCVR in response to MAP and hyperventilation challenges. Determining whether CVR increases or decreases with a MAP challenge (locCVRnormalized) may be a simple provocative test to determine patients' autoregulatory status following severe TBI and helping to optimize CPP management.

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Guy Rosenthal, J. Claude Hemphill III, Marco Sorani, Christine Martin, Diane Morabito, Michele Meeker, Vincent Wang and Geoffrey T. Manley

Object

Previous studies have demonstrated that periods of low brain tissue oxygen tension (PbtO2) are associated with poor outcome after head trauma but have primarily focused on cerebral and hemodynamic factors as causes of low PbtO2. The purpose of this study was to investigate the influence of lung function on PbtO2 with an oxygen challenge (increase in fraction of inspired oxygen [FiO2] concentration to 1.0).

Methods

This prospective observational cohort study was performed in the neurointensive care unit of the Level 1 trauma center at San Francisco General Hospital. Thirty-seven patients with severe traumatic brain injury (TBI) undergoing brain tissue oxygen monitoring as part of regular care underwent an oxygen challenge, consisting of an increase in FiO2 concentration from baseline to 1.0 for 20 minutes. Partial pressure of arterial oxygen (PaO2), PbtO2, and the ratio of PaO2 to FiO2 (the PF ratio) were determined before and after oxygen challenge.

Results

Patients with higher PF ratios achieved greater PbtO2 during oxygen challenge than those with a low PF ratio because they achieved a higher PaO2 after an oxygen challenge. Lung function, specifically the PF ratio, is a major determinant of the maximal PbtO2 attained during an oxygen challenge.

Conclusions

Given that patients with TBI are at risk for pulmonary complications such as pneumonia, severe atelectasis, and adult respiratory distress syndrome, lung function must be considered when interpreting brain tissue oxygenation.

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Oral Presentations

2010 AANS Annual Meeting Philadelphia, Pennsylvania May 1–5, 2010