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Kirkness CJ, Burr RL, Cain KC, Newell DW, Mitchell PH. Effect of Continuous Display of Cerebral Perfusion Pressure on Outcomes in Patients With Traumatic Brain Injury. Am J Crit Care 2006. [DOI: 10.4037/ajcc2006.15.6.600] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
Abstract
• Background Clinical bedside monitoring systems do not provide prominent displays of data on cerebral perfusion pressure (CPP). Immediate visual feedback would allow more rapid intervention to prevent or minimize suboptimal pressures.
• Objective To evaluate the effect of a highly visible CPP display on immediate and long-term functional outcome in patients with traumatic brain injury.
• Methods A total of 157 patients with traumatic brain injury at a level 1 trauma center who had invasive arterial blood pressure and intracranial pressure monitoring were randomized to beds with or without an additional, prominent continuous CPP display. Primary end points were scores on the Extended Glasgow Outcome Scale (GOSE) and Functional Status Examination (FSE) 6 months after injury. Secondary end points were GOSE scores at discharge and 3 months after injury and FSE score 3 months after injury.
• Results Although GOSE and FSE scores at 6 months were better in the group with the highly visible CPP display, the differences were not significant. Slope of recovery for GOSE and FSE over all follow-up time points did not differ significantly between groups. However, the intervention’s positive effect on odds of survival at hospital discharge was strong and significant. Within a subgroup of more severely injured patients, the intervention group was much less likely than the control group to have CPP deviations.
• Conclusions The presence of a highly visible display of CPP was associated with significantly better odds of survival and overall condition at discharge.
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Affiliation(s)
- Catherine J. Kirkness
- Biobehavioral Nursing and Health Systems (cjk, rlb, phm), Biostatistics and Office for Nursing Research (kcc), University of Washington, Seattle, Wash, and Seattle Neuroscience Institute at Swedish Medical Center, Seattle, Wash (dwn)
| | - Robert L. Burr
- Biobehavioral Nursing and Health Systems (cjk, rlb, phm), Biostatistics and Office for Nursing Research (kcc), University of Washington, Seattle, Wash, and Seattle Neuroscience Institute at Swedish Medical Center, Seattle, Wash (dwn)
| | - Kevin C. Cain
- Biobehavioral Nursing and Health Systems (cjk, rlb, phm), Biostatistics and Office for Nursing Research (kcc), University of Washington, Seattle, Wash, and Seattle Neuroscience Institute at Swedish Medical Center, Seattle, Wash (dwn)
| | - David W. Newell
- Biobehavioral Nursing and Health Systems (cjk, rlb, phm), Biostatistics and Office for Nursing Research (kcc), University of Washington, Seattle, Wash, and Seattle Neuroscience Institute at Swedish Medical Center, Seattle, Wash (dwn)
| | - Pamela H. Mitchell
- Biobehavioral Nursing and Health Systems (cjk, rlb, phm), Biostatistics and Office for Nursing Research (kcc), University of Washington, Seattle, Wash, and Seattle Neuroscience Institute at Swedish Medical Center, Seattle, Wash (dwn)
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152
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Abstract
PURPOSE OF REVIEW To describe the role of O2 positron emission tomography in studies aimed at understanding ischaemia in head injury. It has been difficult to use cerebral blood flow levels to provide a secure definition of cerebral ischaemia in head injury, since primary changes in cerebral metabolism may be responsible for coupled reductions in cerebral blood flow. Further, regional heterogeneity of pathophysiology can confound global measures of adequacy of cerebral oxygen delivery. There is a need for a technique that can provide a comprehensive and quantitative description of cerebral physiology in this setting. RECENT FINDINGS O2 positron emission tomography can image cerebral blood flow, cerebral blood volume, cerebral metabolic rate for oxygen and oxygen extraction fraction, and thus allows a robust and specific definition of true ischaemia. When used in combination with other monitoring tools and imaging modalities, positron emission tomography has also been used to validate and refine bedside monitors of cerebrovascular physiology, study the impact of therapeutic interventions and provide clues to novel pathophysiology. SUMMARY There is a clear role for O2 positron emission tomography in elucidating pathophysiology in head injury. The technique may provide most information when combined with other imaging and monitoring tools.
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Affiliation(s)
- David K Menon
- Division of Anaesthesia, University of Cambridge, Honorary Consultant, Neurosciences Critical Care Unit, Addenbrooke's Hospital, Cambridge, UK.
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153
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Nortje J, Gupta AK. The role of tissue oxygen monitoring in patients with acute brain injury. Br J Anaesth 2006; 97:95-106. [PMID: 16751641 DOI: 10.1093/bja/ael137] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Cerebral ischaemia is implicated in poor outcome after brain injury, and is a very common post-mortem finding. The inability of the brain to store metabolic substrates, in the face of high oxygen and glucose requirements, makes it very susceptible to ischaemic damage. The clinical challenge, however, remains the reliable antemortem detection and treatment of ischaemic episodes in the intensive care unit. Outcomes have improved in the traumatic brain injury setting after the introduction of progressive protocol-driven therapy, based, primarily, on the monitoring and control of intracranial pressure, and the maintenance of an adequate cerebral perfusion pressure through manipulation of the mean arterial pressure. With the increasing use of multi-modal monitoring, the complex pathophysiology of the injured brain is slowly being unravelled, emphasizing the heterogeneity of the condition, and the requirement for individualization of therapy to prevent secondary adverse hypoxic cerebral events. Brain tissue oxygen partial pressure (Pb(O2) monitoring is emerging as a clinically useful modality, and this review examines its role in the management of brain injury.
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Affiliation(s)
- J Nortje
- Department of Anaesthesia, University of Cambridge Addenbrooke's Hospital, Cambridge CB2 2QQ, UK.
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154
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Abstract
Raised intracranial pressure (ICP) and low cerebral blood flow (CBF) are associated with ischaemia and poor outcome after brain injury. Therefore, many management protocols target these parameters. This overview summarizes the technical aspects of ICP and CBF monitoring, and their role in the clinical management of brain-injured patients. Furthermore, some applications of these methods in current research are highlighted. ICP is typically measured using probes that are inserted into one of the lateral ventricles or the brain parenchyma. Therapeutic measures used to control ICP have relevant side-effects and continuous monitoring is essential to guide such therapies. ICP is also required to calculate cerebral perfusion pressure which is one of the most important therapeutic targets in brain-injured patients. Several bedside CBF monitoring devices are available. However, most do not measure CBF but rather a parameter that is thought to be proportional to CBF. Frequently used methods include transcranial Doppler which measures blood flow velocity and may be helpful for the diagnosis and monitoring of cerebral vasospasm after subarachnoid haemorrhage or jugular bulb oximetry which gives information on adequacy of CBF in relation to the metabolic demand of the brain. However, there is no clear evidence that incorporating data from CBF monitors into our management strategies improves outcome in brain-injured patients.
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Affiliation(s)
- L A Steiner
- Surgical Intensive Care Unit, Department of Anaesthesia, University Hospital Basel, CH-4031 Basel, Switzerland.
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155
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Pickard JD, Hutchinson PJ, Coles JP, Steiner LA, Johnston AJ, Fryer TD, Coleman MR, Smielewski P, Chatfield DA, Aigbirhio F, Williams GB, Rice K, Clark JC, Salmond CH, Sahakian BJ, Bradley PG, Carpenter TA, Salvador R, Pena A, Gillard JH, Cunningham AS, Piechnik S, Czosnyka M, Menon DK. Imaging of cerebral blood flow and metabolism in brain injury in the ICU. ACTA NEUROCHIRURGICA. SUPPLEMENT 2006; 95:459-64. [PMID: 16463901 DOI: 10.1007/3-211-32318-x_94] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
Abstract
The heterogeneity of the initial insult and subsequent pathophysiology has made both the study of human head injury and design of randomised controlled trials exceptionally difficult. The combination of multimodality bedside monitoring and functional brain imaging positron emission tomography (PET) and magnetic resonance (MR), incorporated within a Neurosciences Critical Care Unit, provides the resource required to study critically ill patients after brain injury from initial ictus through recovery from coma and rehabilitation to final outcome. Methods to define cerebral ischemia in the context of altered cerebral oxidative metabolism have been developed, traditional therapies for intracranial hypertension re-evaluated and bedside monitors cross-validated. New modelling and analytical approaches have been developed.
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Affiliation(s)
- J D Pickard
- Wolfson Brain Imaging Centre, University of Cambridge, Addenbrookes Hospital, Cambridge, UK.
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156
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Adamides AA, Winter CD, Lewis PM, Cooper DJ, Kossmann T, Rosenfeld JV. CURRENT CONTROVERSIES IN THE MANAGEMENT OF PATIENTS WITH SEVERE TRAUMATIC BRAIN INJURY. ANZ J Surg 2006; 76:163-74. [PMID: 16626360 DOI: 10.1111/j.1445-2197.2006.03674.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
BACKGROUND Traumatic brain injury is a major cause of mortality and morbidity, particularly among young men. The efficacy and safety of most of the interventions used in the management of patients with traumatic brain injury remain unproven. Examples include the 'cerebral perfusion pressure-targeted' and 'volume-targeted' management strategies for optimizing cerebrovascular haemodynamics and specific interventions, such as hyperventilation, osmotherapy, cerebrospinal fluid drainage, barbiturates, decompressive craniectomy, therapeutic hypothermia, normobaric hyperoxia and hyperbaric oxygen therapy. METHODS A review of the literature was performed to examine the evidence base behind each intervention. RESULTS There is no class I evidence to support the routine use of any of the therapies examined. CONCLUSION Well-designed, large, randomized controlled trials are needed to determine therapies that are safe and effective from those that are ineffective or harmful.
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157
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Abstract
PURPOSE OF REVIEW In this article we aim to review the recent literature concerning the management of traumatic brain injury patients, summarize the main findings, and discuss the impact of these findings on clinical practice. RECENT FINDINGS Several authors have focused on the development of more reliable and informative tools to predict outcome in traumatic brain injury as well as refining the definition of cerebral ischemia in last year's literature. The validity of the current cerebral perfusion pressure management guidelines has also come under scrutiny. It appears that a one size fits all therapy is not a suitable approach for traumatic brain injury patients. An individualized approach, depending on the integrity of pressure autoregulation mechanisms, would be more advisable. Clinical trials investigating brain protective treatments in head injured patients have been disappointing so far. Increasing the homogeneity of patients entering brain protective studies might be an answer. Finally, the use of hyperoxia as well as factors contributing to secondary brain injury such as the occurrence of hyperthermia, with or without an infectious process, have been assessed in head injury patients. SUMMARY The key term for the management of traumatic brain injury patients in the early twenty-first century will clearly be 'individualized therapy'. The search of an ideal cerebral perfusion pressure target that would fit every head-injured patients is a utopia. More energy should be focused on the development of reliable tools for outcome prediction and outcome assessment for traumatic brain injured patients. That, and a better targeting of patients entering brain protective trials, should increase the likelihood of demonstrating a significant salvaging effect of a particular treatment in humans.
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Affiliation(s)
- François Girard
- Department of Anesthesiology, CHUM, Notre-Dame Hospital, Montreal, Canada.
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158
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Abstract
PURPOSE OF REVIEW This article reviews recent advances in multimodality monitoring of patients following severe head injury during the period of 2004-2005. RECENT FINDINGS Whilst intracranial pressure measurement remains the cornerstone of neuromonitoring, analysis of the intracranial pressure waveform provides additional information, which may help guide treatment and predict outcome. Non-invasive detection of intracranial hypertension and assessment of cerebral perfusion pressure and autoregulation is the focus of ongoing research. Although jugular venous saturation monitoring remains a useful method for detecting global hypoperfusion its sensitivity to regional ischaemia is low. Brain tissue oxygen monitoring overcomes this deficiency and sheds new light on the pathophysiology of cerebral ischaemia following brain injury. Further studies are required to define ischaemic thresholds and their association with outcome. Extracellular brain pH has been recently linked to outcome and further studies are required to establish the role of pH regulation. Monitoring of brain metabolism using a cerebral microdialysis continues to develop its niche in clinical neuromonitoring, although it currently remains a research tool. SUMMARY Multimodality neuromonitoring plays an important role in managing patients with severe head injury. It helps guide treatment, provides prognostic information and explores the pathophysiology of evolving brain injury.
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Affiliation(s)
- Ivan Timofeev
- Department of Neurosurgery, Addenbrooke's Hospital, Cambridge, UK
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159
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Cunningham AS, Salvador R, Coles JP, Chatfield DA, Bradley PG, Johnston AJ, Steiner LA, Fryer TD, Aigbirhio FI, Smielewski P, Williams GB, Carpenter TA, Gillard JH, Pickard JD, Menon DK. Physiological thresholds for irreversible tissue damage in contusional regions following traumatic brain injury. Brain 2005; 128:1931-42. [PMID: 15888537 DOI: 10.1093/brain/awh536] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Cerebral ischaemia appears to be an important mechanism of secondary neuronal injury in traumatic brain injury (TBI) and is an important predictor of outcome. To date, the thresholds of cerebral blood flow (CBF) and cerebral oxygen utilization (CMRO(2)) for irreversible tissue damage used in TBI studies have been adopted from experimental and clinical ischaemic stroke studies. Identification of irreversibly damaged tissue in the acute phase following TBI could have considerable therapeutic and prognostic implications. However, it is questionable whether stroke thresholds are applicable to TBI. Therefore, the aim of this study was to determine physiological thresholds for the development of irreversible tissue damage in contusional and pericontusional regions in TBI, and to determine the ability of such thresholds to accurately differentiate irreversibly damaged tissue. This study involved 14 patients with structural abnormalities on late-stage MRI, all of whom had been studied with (15)O PET within 72 h of TBI. Lesion regions of interest (ROI) and non-lesion ROIs were constructed on late-stage MRIs and applied to co-registered PET maps of CBF, CMRO(2) and oxygen extraction fraction (OEF). From the entire population of voxels in non-lesion ROIs, we determined thresholds for the development of irreversible tissue damage as the lower limit of the 95% confidence interval for CBF, CMRO(2) and OEF. To test the ability of a physiological variable to differentiate lesion and non-lesion tissue, we constructed probability curves, demonstrating the ability of a physiological variable to predict lesion and non-lesion outcomes. The lower limits of the 95% confidence interval for CBF, CMRO(2) and OEF in non-lesion tissue were 15.0 ml/100 ml/min, 36.7 mumol/100 ml/min and 25.9% respectively. Voxels below these values were significantly more frequent in lesion tissue (all P < 0.005, Mann-Whitney U-test). However, a significant proportion of lesion voxels had values above these thresholds, so that definition of the full extent of irreversible tissue damage would not be possible based upon single physiological thresholds. We conclude that, in TBI, the threshold of CBF below which irreversible tissue damage consistently occurs differs from the classical CBF threshold for stroke (where similar methodology is used to define such thresholds). The CMRO(2) threshold is comparable to that reported in the stroke literature. At a voxel-based level, however (and in common with ischaemic stroke), the extent of irreversible tissue damage cannot be accurately predicted by early abnormalities of any single physiological variable.
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Affiliation(s)
- A S Cunningham
- Division of Anaesthesia, Department of Medicine, University of Cambridge, Cambridge, UK
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160
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Coles J. Regional is Chaemia following Acute Head Injury. J Intensive Care Soc 2005. [DOI: 10.1177/175114370500600116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- J.P. Coles
- The Division of Anaesthesia, University of Cambridge, Box 93, Addenbrooke's Hospital, Cambridge CB2 2QQ, UK
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161
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Abstract
PURPOSE OF REVIEW This review on traumatic brain injury consolidates the substantial current literature available on the pathophysiology, mechanisms, developments, and their subsequent effects on outcome. In particular, it tries to conceptualize why our greatly improved understanding of pathophysiology and neurobiology in traumatic brain injury has not translated into clear outcome improvements. RECENT FINDINGS Early cerebral ischaemia has been characterized further, with ischaemic brain volume correlating with 6-month outcome. The Brain Trauma Foundation has revised perfusion pressure targets, and there are additional data on the outcome impact of brain tissue oxygen response and asymmetric patterns of cerebral autoregulation. Mechanistic studies have highlighted the role of inflammation and introduced concepts such as therapeutic vaccination and immune modulation. Experimental neurogenesis and repair strategies show promise. Despite continuing gains in knowledge, the experimental successes have not yet translated to the clinic. Indeed, several major articles have attempted to understand the clinical failure of highly promising strategies such as hypothermia, and set out the framework for further studies (e.g. addressing decompressive craniectomy). High-dose mannitol has shown promise in poor grade patients, while hypertonic saline has shown better intracranial pressure control. Negative results may be the consequence of ineffective therapies. However, there is a gathering body of work that highlights the outcome impact of subtle neurocognitive changes, which may not be quantified adequately by outcome measures used in previous trials. Such knowledge has also informed improved definition of mild traumatic brain injury, and allowed validation of management guidelines. SUMMARY The evidence base for current therapies in this heterogeneous patient group is being refined, with greater emphasis on long-term functional outcomes. Improved monitoring techniques emphasize the need for individualization of therapeutic interventions.
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Affiliation(s)
- Jurgens Nortje
- Department of Anaesthesia, University of Cambridge, Cambridge CB2 2QQ, UK
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162
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Johnston AJ, Steiner LA, Coles JP, Chatfield DA, Fryer TD, Smielewski P, Hutchinson PJ, O'Connell MT, Al-Rawi PG, Aigbirihio FI, Clark JC, Pickard JD, Gupta AK, Menon DK. Effect of cerebral perfusion pressure augmentation on regional oxygenation and metabolism after head injury*. Crit Care Med 2005; 33:189-95; discussion 255-7. [PMID: 15644668 DOI: 10.1097/01.ccm.0000149837.09225.bd] [Citation(s) in RCA: 130] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
OBJECTIVE In this study we have used O positron emission tomography, brain tissue oxygen monitoring, and cerebral microdialysis to assess the effects of cerebral perfusion pressure augmentation on regional physiology and metabolism in the setting of traumatic brain injury. DESIGN Prospective interventional study. SETTING Neurosciences critical care unit of a university hospital. PATIENTS Eleven acutely head-injured patients requiring norepinephrine to maintain cerebral perfusion pressure. INTERVENTIONS Using positron emission tomography, we have quantified the response to an increase in cerebral perfusion pressure in a region of interest around a brain tissue oxygen sensor (Neurotrend) and microdialysis catheter. Oxygen extraction fraction and cerebral blood flow were measured with positron emission tomography at a cerebral perfusion pressure of approximately 70 mm Hg and approximately 90 mm Hg using norepinephrine to control cerebral perfusion pressure. All other aspects of physiology were kept stable. MEASUREMENTS AND MAIN RESULTS Cerebral perfusion pressure augmentation resulted in a significant increase in brain tissue oxygen (17 +/- 8 vs. 22 +/- 8 mm Hg; 2.2 +/- 1.0 vs. 2.9 +/- 1.0 kPa, p < .001) and cerebral blood flow (27.5 +/- 5.1 vs. 29.7 +/- 6.0 mL/100 mL/min, p < .05) and a significant decrease in oxygen extraction fraction (33.4 +/- 5.9 vs. 30.3 +/- 4.6 %, p < .05). There were no significant changes in any of the microdialysis variables (glucose, lactate, pyruvate, lactate/pyruvate ratio, glycerol). There was a significant linear relationship between brain tissue oxygen and oxygen extraction fraction (r = .21, p < .05); the brain tissue oxygen value associated with an oxygen extraction fraction of 40% (the mean value for oxygen extraction fraction in normal controls) was 14 mm Hg (1.8 kPa). The cerebral perfusion pressure intervention resulted in a greater percentage increase in brain tissue oxygen than the percentage decrease in oxygen extraction fraction; this suggests that the oxygen gradients between the vascular and tissue compartments were reduced by the cerebral perfusion pressure intervention. CONCLUSIONS Cerebral perfusion pressure augmentation significantly increased levels of brain tissue oxygen and significantly reduced regional oxygen extraction fraction. However, these changes did not translate into predictable changes in regional chemistry. Our results suggest that the ischemic level of brain tissue oxygen may lie at a level below 14 mm Hg (1.8 kPa); however, the data do not allow us to be more specific.
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Affiliation(s)
- Andrew J Johnston
- University Department of Anaesthetics, Addenbrooke's Hospital, Cambridge, UK
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163
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Chan MTV, Ng SCP, Lam JMK, Poon WS, Gin T. Re-defining the ischemic threshold for jugular venous oxygen saturation--a microdialysis study in patients with severe head injury. ACTA NEUROCHIRURGICA. SUPPLEMENT 2005; 95:63-6. [PMID: 16463822 DOI: 10.1007/3-211-32318-x_14] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Neurological change is more likely to occur when jugular venous oxygen saturation (SjvO2) is less than 50%. However, the value indicating cellular damage has not been clearly defined. We determined the critical SjvO2 value below which intracerebral extracellular metabolic abnormalities occurred in 25 patients with severe head injury. All patients received standard treatment with normoventilation and maintenance of intracranial pressure < 20 mmHg. SjvO2 was measured from the dominant jugular bulb using a calibrated fibreoptic catheter. Intracerebral metabolic monitoring was performed by collecting perfusate from a microdialysis probe placed in the frontal lobe anterior to the intracranial catheter. Excitotoxin (glutamate) and other extracellular metabolites (lactate, glucose and glycerol) were measured frequently using enzymatic and colorimetric methods. We observed biphasic relationships between SjvO2 and all intracerebral metabolites. Analysis of variance showed that there were rapid increases in glutamate, glycerol and lactate when SjvO2 dropped below 40, 43 and 45% respectively. Extracellular glucose decreased when SjvO2 dropped below 42%. Our findings suggested that the ischemic threshold for SjvO2 in patients with severe head injury is 45%, below which secondary brain damage occurred.
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Affiliation(s)
- M T V Chan
- Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Prince of Wales Hospital, Hong Kong, China.
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164
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Marshall RS. The functional relevance of cerebral hemodynamics: why blood flow matters to the injured and recovering brain. Curr Opin Neurol 2004; 17:705-9. [PMID: 15542979 DOI: 10.1097/00019052-200412000-00010] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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165
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Affiliation(s)
- David S Warner
- Departments of *Anesthesiology, †Neurobiology, and ‡Surgery, Duke University Medical Center, Durham, North Carolina
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166
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Coles JP, Steiner LA, Johnston AJ, Fryer TD, Coleman MR, Smieleweski P, Chatfield DA, Aigbirhio F, Williams GB, Boniface S, Rice K, Clark JC, Pickard JD, Menon DK. Does induced hypertension reduce cerebral ischaemia within the traumatized human brain? ACTA ACUST UNITED AC 2004; 127:2479-90. [PMID: 15456706 DOI: 10.1093/brain/awh268] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Recent changes in published guidelines for the management of patients with severe head injury are based on data showing that aggressive maintenance of cerebral perfusion pressure (CPP) can worsen outcome due to extracranial complications of therapy. However, it remains unclear whether CPP augmentation could reduce cerebral ischaemia, a finding which might prompt the search for CPP augmentation protocols that avoid these extracranial complications. We studied 10 healthy volunteers and 20 patients within 6 days of closed head injury. All subjects underwent imaging of cerebral blood flow (CBF), blood volume (CBV), oxygen metabolism (CMRO2) and oxygen extraction fraction (OEF) using 15O PET. In addition, for patients, the EEG power ratio index (PRI), burst suppression ratio and somatosensory evoked potentials (SEP) were obtained and CPP was increased from 68 +/- 4 to 90 +/- 4 mmHg using an infusion of norepinephrine and measurements were repeated. Following elevation of CPP, CBF and CBV were increased and CMRO2 and OEF were reduced (P < 0.001 for all comparisons). Regions with a reduction in CMRO2 were associated with the greatest reduction in OEF (r2 = 0.3; P < 0.0001). Although CPP elevation produced a significant fall in the ischaemic brain volume (IBV) (from 15 +/- 16 to 5 +/- 4 ml; P < 0.01) and improved flow metabolism coupling, the IBV was small and clinically insignificant in the majority of these patients. However, the reduction in IBV was directly related to the baseline IBV (r2 = 0.97; P < 0.001) and patients with large baseline IBV showed substantial and clinically significant reductions. CPP augmentation increased the EEG PRI (5.0 +/- 1.5 versus 4.3 +/- 1.4, P < 0.01), implying an overall decrease in neural activity, but these changes did not correlate with the reduction in CMRO2 and there was no change in SEP cortical amplitude (N20-P27). These data provide support for recent changes in recommended CPP levels for head injury management across populations of patients with significant head injury. However, they do not provide guidance on whether the intervention may be more appropriate at earlier stages after injury, or in patients selected because of high baseline IBV. It also remains unclear whether CPP values below 65 mmHg can be safely used in this population. Clarification of the significance of a reduction in CMRO2 and neuronal electrical function will require further study.
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167
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Menon DK, Coles JP, Gupta AK, Fryer TD, Smielewski P, Chatfield DA, Aigbirhio F, Skepper JN, Minhas PS, Hutchinson PJ, Carpenter TA, Clark JC, Pickard JD. Diffusion limited oxygen delivery following head injury*. Crit Care Med 2004; 32:1384-90. [PMID: 15187523 DOI: 10.1097/01.ccm.0000127777.16609.08] [Citation(s) in RCA: 235] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVE To use a range of techniques to explore diffusion limitation as a mechanism of cellular hypoxia in the setting of head injury. DESIGN A prospective interventional study. SETTING A specialist neurocritical care unit. PATIENTS Thirteen patients within 7 days of closed head injury underwent imaging studies. Tissue for ultrastructural studies was obtained from a cohort of seven patients who required surgery. INTERVENTIONS Cerebral tissue PO2 (PtO2) was obtained using a multiple-variable sensor, and images of oxygen extraction fraction (OEF), derived from positron emission tomography, were used to calculate cerebral venous PO2 (PvO2). These data were used to derive the PvO2-PtO2 gradient in a region of interest around the sensor, which provided a measure of the efficiency of microvascular oxygen delivery. Measurements were repeated after PaCO2 was reduced from 37 +/- 3 to 29 +/- 3 torr (4.9 +/- 0.4 to 3.9 +/- 0.4 kPa) to assess the ability of the microvasculature to increase oxygen unloading during hypocapnia-induced hypoperfusion. Pericontusional tissue was submitted to electron microscopy to illustrate the structural correlates of physiologic findings. MEASUREMENTS AND MAIN RESULTS Tissue regions with hypoxic levels of PtO2 (<10 torr) had similar levels of PvO2 compared with nonhypoxic areas and hence displayed larger PvO2-PtO2 gradients (27 +/- 2 vs. 9 +/- 8 torr, p <.001). Despite similar cerebral blood flow reductions with hyperventilation, hypoxic regions achieved significantly smaller OEF increases compared with normoxic regions (7 +/- 5 vs. 16 +/- 6 %, p <.05). Pericontusional tissue showed varying degrees of endothelial swelling, microvascular collapse, and perivascular edema. CONCLUSIONS Increased diffusion barriers may reduce cellular oxygen delivery following head injury and attenuate the ability of the brain to increase oxygen extraction in response to hypoperfusion. Global or regional OEF underestimates tissue hypoxia due to such mechanisms.
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Affiliation(s)
- David K Menon
- Division of Anaesthesia, and the Wolfson Brain Imaging Centre, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK.
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