Normobaric hyperoxia--induced improvement in cerebral metabolism and reduction in intracranial pressure in patients with severe head injury: a prospective historical cohort-matched study

Cerebral hemodynamic effects of acute hyperoxia and hyperventilation after severe traumatic brain injury

The purpose of this study was to examine the effects of hyperventilation or hyperoxia on cerebral hemodynamic parameters over time in patients with severe traumatic brain injury (TBI). We prospectively studied 186 patients with severe TBI. CO₂ and O₂ reactivity tests were conducted twice a day on days 1-5 and once daily on days 6-10 after injury. During hyperventilation there was a significant decrease in intracranial pressure (ICP), mean arterial pressure (MAP), jugular venous oxygen saturation (Sjvo₂), brain tissue Po₂ (Pbto₂), and flow velocity (FV). During hyperoxia there was an increase in Sjvo₂ and Pbto₂, and a small but consistent decrease in ICP, end-tidal carbon dioxide (etco₂), partial arterial carbon dioxide pressure (Paco₂), and FV. Brain tissue oxygen reactivity during the first 12 h after injury averaged 19.7 ± 3.0%, and slowly decreased over the next 7 days. The autoregulatory index (ARI; normal = 5.3 ± 1.3) averaged 2.2 ± 1.5 on day 1 post-injury, and gradually improved over the 10 days of monitoring. The ARI significantly improved during hyperoxia, by an average of 0.4 ± 1.8 on the left, and by 0.5 ± 1.8 on the right. However, the change in ARI with hyperoxia was much smaller than that observed with hyperventilation. Hyperventilation increased ARI by an average of 1.3 ± 1.9 on the left, and 1.5 ± 2.0 on the right. Pressure autoregulation, as assessed by dynamic testing, was impaired in these head-injured patients. Acute hyperoxia significantly improved pressure autoregulation, although the effect was smaller than that induced by hyperventilation. The very small change in Paco₂ induced by hyperoxia does not appear to explain this finding. Rather, the vasoconstriction induced by acute hyperoxia may allow the cerebral vessels to respond better to transient hypotension. Further studies are needed to define the clinical significance of these observations.

Brain tissue oxygen-directed management and outcome in patients with severe traumatic brain injury

OBJECT

The object of this study was to determine whether brain tissue oxygen (PbtO(2))-based therapy or intracranial pressure (ICP)/cerebral perfusion pressure (CPP)-based therapy is associated with improved patient outcome after severe traumatic brain injury (TBI).

METHODS

Seventy patients with severe TBI (postresuscitation GCS score < or = 8), admitted to a neurosurgical intensive care unit at a university-based Level I trauma center and tertiary care hospital and managed with an ICP and PbtO(2) monitor (mean age 40 +/- 19 years [SD]) were compared with 53 historical controls who received only an ICP monitor (mean age 43 +/- 18 years). Therapy for both patient groups was aimed to maintain ICP < 20 mm Hg and CPP > 60 mm Hg. Patients with PbtO(2) monitors also had therapy to maintain PbtO(2) > 20 mm Hg.

RESULTS

Data were obtained from 12,148 hours of continuous ICP monitoring and 6,816 hours of continuous PbtO(2) monitoring. The mean daily ICP and CPP and the frequency of elevated ICP (> 20 mm Hg) or suboptimal CPP (< 60 mm Hg) episodes were similar in each group. The mortality rate was significantly lower in patients who received PbtO(2)-directed care (25.7%) than in those who received conventional ICP and CPP-based therapy (45.3%, p < 0.05). Overall, 40% of patients receiving ICP/CPP-guided management and 64.3% of those receiving PbtO(2)-guided management had a favorable short-term outcome (p = 0.01). Among patients who received PbtO(2)-directed therapy, mortality was associated with lower mean daily PbtO(2) (p < 0.05), longer durations of compromised brain oxygen (PbtO(2) < 20 mm Hg, p = 0.013) and brain hypoxia (PbtO(2) < 15 mm Hg, p = 0.001), more episodes and a longer cumulative duration of compromised PbtO(2) (p < 0.001), and less successful treatment of compromised PbtO(2) (p = 0.03).

CONCLUSIONS

These results suggest that PbtO(2)-based therapy, particularly when compromised PbtO(2) can be corrected, may be associated with reduced patient mortality and improved patient outcome after severe TBI.

Hyperoxic reperfusion after global cerebral ischemia promotes inflammation and long-term hippocampal neuronal death

In this study we tested the hypothesis that long-term neuropathological outcome is worsened by hyperoxic compared to normoxic reperfusion in a rat global cerebral ischemia model. Adult male rats were anesthetized and subjected to bilateral carotid arterial occlusion plus bleeding hypotension for 10 min. The rats were randomized to one of four protocols: ischemia/normoxia (21% oxygen for 1 h), ischemia/hyperoxia (100% oxygen for 1 h), sham/normoxia, and sham/hyperoxia. Hippocampal CA1 neuronal survival and activation of microglia and astrocytes were measured in the hippocampi of the animals at 7 and 30 days post-ischemia. Morris water maze testing of memory was performed on days 23-30. Compared to normoxic reperfusion, hyperoxic ventilation resulted in a significant decrease in normal-appearing neurons at 7 and 30 days, and increased activation of microglia and astrocytes at 7, but not at 30, days of reperfusion. Behavioral deficits were also observed following hyperoxic, but not normoxic, reperfusion. We conclude that early post-ischemic hyperoxic reperfusion is followed by greater hippocampal neuronal death and cellular inflammatory reactions compared to normoxic reperfusion. The results of these long-term outcome studies, taken together with previously published results from short-term experiments performed with large animals, support the hypothesis that neurological outcome can be improved by avoiding hyperoxic resuscitation after global cerebral ischemia such as that which accompanies cardiac arrest.

The effect of increased inspired fraction of oxygen on brain tissue oxygen tension in children with severe traumatic brain injury

BACKGROUND

This study examines the effect of an increase in the inspired fraction of oxygen (FiO2) on brain tissue oxygen (PbO2) in children with severe traumatic brain injury (TBI).

METHODS

A prospective observational study of patients who underwent PbO2 monitoring and an oxygen challenge test (temporary increase of FiO2 for 15 min) was undertaken. Pre- and post-test values for arterial partial pressure of oxygen (PaO2), PbO2, and arterial oxygen content (CaO2) were examined while controlling for any changes in arterial carbon dioxide tension and cerebral perfusion pressure during the test. Baseline transcranial Doppler studies were done. Outcome was assessed at 6 months.

RESULTS

A total of 43 tests were performed in 28 patients. In 35 tests in 24 patients, the PbO2 monitor was in normal-appearing white matter and in eight tests in four patients, the monitor was in a pericontusional location. When catheters were pericontusional or in normal white matter the baseline PbO2/PaO2 ratio was similar. PaO2 (P < 0.0001) and PbO2 (P < 0.0001) significantly increased when FiO2 was increased. The magnitude of the PbO2 response (PbO2) was correlated with PaO2 (P < 0.0001, R(2) = 0.37) and CaO2 (P = 0.001, R(2) = 0.23). The PbO2/PaO2 ratio (oxygen reactivity) varied between patients, was related to the baseline PbO2 (P = 0.001, r = 0.54) and was inversely related to outcome (P = 0.02, confidence interval 0.03-0.78).

CONCLUSION

Normobaric hyperoxia increases PbO2 in children with severe TBI, but the response is variable. The magnitude of this response is related to the change in PaO2 and the baseline PbO2. A greater response appears to be associated with worse outcome.

A prospective, randomized clinical trial to compare the effect of hyperbaric to normobaric hyperoxia on cerebral metabolism, intracranial pressure, and oxygen toxicity in severe traumatic brain injury

Object

Oxygen delivered in supraphysiological amounts is currently under investigation as a therapy for severe traumatic brain injury (TBI). Hyperoxia can be delivered to the brain under normobaric as well as hyperbaric conditions. In this study the authors directly compare hyperbaric oxygen (HBO2) and normobaric hyperoxia (NBH) treatment effects.

Methods

Sixty-nine patients who had sustained severe TBIs (mean Glasgow Coma Scale Score 5.8) were prospectively randomized to 1 of 3 groups within 24 hours of injury: 1) HBO2, 60 minutes of HBO2 at 1.5 ATA; 2) NBH, 3 hours of 100% fraction of inspired oxygen at 1 ATA; and 3) control, standard care. Treatments occurred once every 24 hours for 3 consecutive days. Brain tissue PO2, microdialysis, and intracranial pressure were continuously monitored. Cerebral blood flow (CBF), arteriovenous differences in oxygen, cerebral metabolic rate of oxygen (CMRO2), CSF lactate and F2-isoprostane concentrations, and bronchial alveolar lavage (BAL) fluid interleukin (IL)–8 and IL-6 assays were obtained pretreatment and 1 and 6 hours posttreatment. Mixed-effects linear modeling was used to statistically test differences among the treatment arms as well as changes from pretreatment to posttreatment.

Results

In comparison with values in the control group, the brain tissue PO2 levels were significantly increased during treatment in both the HBO2 (mean ± SEM, 223 ± 29 mm Hg) and NBH (86 ± 12 mm Hg) groups (p < 0.0001) and following HBO2 until the next treatment session (p = 0.003). Hyperbaric O2 significantly increased CBF and CMRO2 for 6 hours (p ≤ 0.01). Cerebrospinal fluid lactate concentrations decreased posttreatment in both the HBO2 and NBH groups (p < 0.05). The dialysate lactate levels in patients who had received HBO2 decreased for 5 hours posttreatment (p = 0.017). Microdialysis lactate/pyruvate (L/P) ratios were significantly decreased posttreatment in both HBO2 and NBH groups (p < 0.05). Cerebral blood flow, CMRO2, microdialysate lactate, and the L/P ratio had significantly greater improvement when a brain tissue PO2 ≥ 200 mm Hg was achieved during treatment (p < 0.01). Intracranial pressure was significantly lower after HBO2 until the next treatment session (p < 0.001) in comparison with levels in the control group. The treatment effect persisted over all 3 days. No increase was seen in the CSF F2-isoprostane levels, microdialysate glycerol, and BAL inflammatory markers, which were used to monitor potential O2 toxicity.

Conclusions

Hyperbaric O2 has a more robust posttreatment effect than NBH on oxidative cerebral metabolism related to its ability to produce a brain tissue PO2 ≥ 200 mm Hg. However, it appears that O2 treatment for severe TBI is not an all or nothing phenomenon but represents a graduated effect. No signs of pulmonary or cerebral O2 toxicity were present.

Setup accuracy of spine radiosurgery using cone beam computed tomography image guidance in patients with spinal implants

OBJECT

Cone beam computed tomography (CBCT) image guidance technology has been adopted for use in spine radiosurgery. There is concern regarding the ability to safely and accurately perform spine radiosurgery without the use of implanted fiducials for image guidance in postsurgical cases in which titanium instrumentation and/or methylmethacrylate (MMA) has been implanted. In this study the authors prospectively evaluated the accuracy of the patient setup for spine radiosurgery by using CBCT image guidance in the context of orthopedic hardware at the site of disease.

METHODS

The positioning deviations of 31 single-fraction spine radiosurgery treatments in patients with spinal implants were prospectively evaluated using the Elekta Synergy S 6-MV linear accelerator with a beam modulator and CBCT image guidance combined with a robotic couch that allows positioning correction in 3 translational and 3 rotational directions. To measure patient movement, 3 quality-assurance CBCT studies were performed and recorded: before, halfway through, and after radiosurgical treatment. The positioning data and fused images of planning CTs and CBCTs from the treatments were analyzed to determine intrafractional patient movements. From each of 3 CBCTs, 3 translational and 3 rotational coordinates were obtained.

RESULTS

The prescribed dose to the gross tumor volume for the cohort was 12-18 Gy (mean 14 Gy) utilizing 9-14 coplanar intensity-modulated radiation therapy (IMRT) beams (mean 10 beams). At the halfway point of the radiosurgery, the translational variations and standard deviations were 0.6 +/- 0.6, 0.4 +/- 0.4, and 0.5 +/- 0.5 mm in the lateral (X), longitudinal (Y), and anteroposterior (Z) directions, respectively. The magnitude of the 3D vector (X,Y,Z) was 1.1 +/- 0.7 mm. Similarly, the variations immediately after treatment were 0.5 +/- 0.3, 0.4 +/- 0.4, and 0.5 +/- 0.6 mm along the X, Y, and Z directions, respectively. The 3D vector was 1.0 +/- 0.6 mm. The mean rotational angles were 0.3 +/- 0.4, 0.5 +/- 0.6, and 0.3 +/- 0.4 degrees along yaw, roll, and pitch, respectively, at the halfway point and 0.3 +/- 0.4, 0.6 +/- 0.6, and 0.4 +/- 0.5 degrees immediately after treatment.

CONCLUSIONS

Cone beam CT image guidance used for patient setup for spine radiosurgery was highly accurate despite the presence of spinal instrumentation and/or MMA at the level of the target volume. The presence of such spinal implants does not preclude safe treatment via spine radiosurgery in these patients.

The physiology behind direct brain oxygen monitors and practical aspects of their use

INTRODUCTION

Secondary neuronal injury is implicated in poor outcome after acute neurological insults. Outcome can be improved with protocol-driven therapy. These therapies have largely been based on monitoring and control of intracranial pressure and the maintenance of an adequate cerebral perfusion pressure.

DISCUSSION

In recent years, brain tissue oxygen partial pressure (PbtO2) monitoring has emerged as a clinically useful modality and a complement to intracranial pressure monitors. This review examines the physiology of PbtO2 monitors and practical aspects of their use.

Methods of monitoring brain oxygenation

INTRODUCTION

Posttraumatic brain ischemia or hypoxia is a major potential cause of secondary injury that may lead to poor outcome. Avoidance, or amelioration, of this secondary injury depends on early diagnosis and intervention before permanent injury occurs. However, tools to monitor brain oxygenation continuously in the neuro-intensive care unit have been lacking.

DISCUSSION

In recent times, methods of monitoring aspects of brain oxygenation continuously by the bedside have been evaluated in several experimental and clinical series and are potentially changing the way we manage head-injured patients. These monitors have the potential to alert the clinician to possible secondary injury and enable intervention, help interpret pathophysiological changes (e.g., hyperemia causing raised intracranial pressure), monitor interventions (e.g., hyperventilation for increased intracranial pressure), and prognosticate. This review focuses on jugular venous saturation, brain tissue oxygen tension, and near-infrared spectroscopy as practical methods that may have an important role in managing patients with brain injury, with a particular focus on the available evidence in children. However, to use these monitors effectively and to understand the studies in which these monitors are employed, it is important for the clinician to appreciate the technical characteristics of each monitor, as well as respective strengths and limitations of each. It is equally important that the clinician understands relevant aspects of brain oxygen physiology and head trauma pathophysiology to enable correct interpretation of the monitored data and therefore to direct an appropriate therapeutic response that is likely to benefit, not harm, the patient.

Normobaric hyperoxia therapy for traumatic brain injury and stroke: a review

Traumatic brain injury (TBI) and acute ischaemic stroke are major causes of mortality and morbidity and there is an urgent demand for new neuroprotective strategies following the translational failure of neuroprotective drug trials. Oxygen therapy--especially normobaric, may offer a simple and effective therapeutic strategy which we review in this paper. Firstly we review mechanisms underlying the therapeutic effects of hyperoxia (both normobaric and hyperbaric) including mitochondrial rescue, stabilisation of intracranial pressure, attenuation of cortical spreading depression and inducing favourable endothelial-leukocyte interactions, all effects of which are postulated to decrease secondary injury. Next we survey studies using hyperbaric oxygen therapy for TBI and stroke, which formed the basis for early studies on normobaric hyperoxia. Thirdly, we present clinical studies of the efficacy of normobaric hyperoxia on TBI and stroke, emphasising their safety, efficacy and practicality. Finally we consider safety concerns and side effects, particularly pulmonary pathology, respiratory failure and theoretical risks in paediatric patients. A neuroprotective role of normobaric hyperoxia is extremely promising and further studies are warranted.

Mitochondrial damage: a target for new therapeutic horizons

Traumatic brain injury (TBI) represents a leading cause of death and morbidity, as well as a considerable social and economical burden in western countries, and has thus emerged as a formidable therapeutic challenge. Yet despite tremendous efforts enlightening the mechanisms of neuronal death, hopes for the "magic bullet" have been repeatedly deceived, and TBI management has remained focused on the control of increased intracranial pressure. Indeed, impairment of cerebral metabolism is traditionally attributed to impaired oxygen delivery mediated by reduced cerebral perfusion in the swollen cerebral parenchyma. Although intuitively appealing, this hypothesis is not entirely supported by physiological facts and does not take into consideration mitochondrial dysfunction that has been repeatedly reported in both human and animal TBI. Although the nature and origin of the events leading to mitochondrial damage may be different, most share a permeabilization of mitochondrial membrane, which therefore may represent a logical target for new therapeutic strategies. Therefore, the proteins mediating these events may represent promising targets for new TBI therapies. Furthermore, mimicking anti-apoptotic proteins, such as Bcl-2 or XIAP, or inhibiting mitochondrial pro-apoptotic proteins, such as Smac/DIABLO, Omi/HTRA2, and ARTS (septin 4 isoform 2) may represent useful novel therapeutic strategies. This review focuses on mechanisms of the mitochondrial membrane permeabilization and its consequences and discusses the current and possible future therapeutic implications of this key event of neuronal death.

Use of magnesium in traumatic brain injury

Depletion of magnesium is observed in animal brain and in human blood after brain injury. Treatment with magnesium attenuates the pathological and behavioral changes in rats with brain injury; however, the therapeutic effect of magnesium has not been consistently observed in humans with traumatic brain injury (TBI). Secondary brain insults are observed in patients with brain injury, which adversely affect clinical outcome. Systemic administration studies in rats have shown that magnesium enters the brain; however, inducing hypermagnesemia in humans did not concomitantly increase magnesium levels in the CSF. We hypothesize that the neuroprotective effects of magnesium in TBI patients could be observed by increasing its brain bioavailability with mannitol. Here, we review the role of magnesium in brain injury, preclinical studies in brain injury, clinical safety and efficacy studies in TBI patients, brain bioavailability studies in rat, and pharmacokinetic studies in humans with brain injury. Neurodegeneration after brain injury involves multiple biochemical pathways. Treatment with a single agent has often resulted in poor efficacy at a safe dose or toxicity at a therapeutic dose. A successful neuroprotective therapy needs to be aimed at homeostatic control of these pathways with multiple agents. Other pharmacological agents, such as dexanabinol and progesterone, and physiological interventions, with hypothermia and hyperoxia, have been studied for the treatment of brain injury. Treatment with magnesium and hypothermia has shown favorable outcome in rats with cerebral ischemia. We conclude that coadministration of magnesium and mannitol with pharmacological and physiological agents could be an effective neuroprotective regimen for the treatment of TBI.

Stereotactic spine radiosurgery for intradural and intramedullary metastasis

Object

Stereotactic radiosurgery (SRS) has become an important treatment alternative to surgery for a variety of spinal lesions. However, the use of SRS in the management of intradural intramedullary (IDIM) metastasis remains controversial. The aim of this study was to determine the clinical efficacy and safety of SRS for treatment of IDIM metastasis.

Methods

Nine patients with 11 IDIM metastases treated with SRS at Henry Ford Hospital were retrospectively reviewed. The mean age at presentation was 50 years, with a range of 14–71 years. There were 4 intradural extramedullary and 7 intramedullary lesions. The radiosurgery procedure used techniques of image-guided and intensitymodulated radiation. The mean treatment dose was 13.8 Gy, with a range of 10–16 Gy. All patients had clinical follow-up (except in 1 lesion), with an emphasis on initial symptoms and ambulatory status, and 8 patients (9 lesions) had imaging studies. The median follow-up duration was 10 months.

Results

The presenting symptoms were improved in 8 (80%) of 10 evaluable lesions, unchanged in 1 case, and worsened in 1 case. Radiographic responses were seen as follows: complete response in 2 (22%) of 9; partial response in 3 (33%) of 9; stable disease in 3 (33%) of 9; and progressive disease in 1 (11%) of 9. After radiosurgery, 7 patients (78%) remained ambulatory until the last follow-up visit. The overall median survival time after SRS was 8 months, with a range of 2–19 months. No radiation toxicity was detected clinically during the follow-up period.

Conclusions

Despite the fact that this was a small series of patients with IDIM metastasis who had limited treatment options, SRS appears to be an effective and safe method of treating patients with these lesions.

Complete percutaneous treatment of vertebral body tumors causing spinal canal compromise using a transpedicular cavitation, cement augmentation, and radiosurgical technique

Object

Patients with symptomatic pathological compression fractures require spinal stabilization surgery for mechanical back pain control and radiation therapy for the underlying malignant process. Spinal radiosurgery provides excellent long-term radiographic control for vertebral metastases. Percutaneous cement augmentation using polymethylmethacrylate (PMMA) may be contraindicated in lesions with spinal canal compromise due to the risk of displacement of tumor resulting in spinal cord or cauda equina injury. However, there is also significant morbidity associated with open corpectomy procedures in patients with metastatic cancer, especially in those who subsequently require adjuvant radiotherapy. This study evaluated a treatment paradigm for malignant vertebral compression fractures consisting of transpedicular coblation corpectomy combined with closed fracture reduction and fixation, followed by spinal radiosurgery.

Methods

Eleven patients (6 men and 5 women, mean age 58 years) with symptomatic vertebral body metastatic tumors associated with moderate spinal canal compromise were included in this study (8 thoracic levels, 3 lumbar levels). Primary histologies included 4 lung, 2 breast, 2 renal, and 1 each of thyroid, bladder, and hepatocellular carcinomas. All patients underwent percutaneous transpedicular coblation corpectomy immediately followed by balloon kyphoplasty through the same 8-gauge cannula under fluoroscopic guidance. Patients subsequently underwent radiosurgery to the affected vertebral body (mean time to treatment 14 days). Postoperatively, patients were assessed for pain reduction and neurological morbidity.

Results

There were no complications associated with any part of the procedure. Adequate cement augmentation within the vertebral body was achieved in all cases. The mean radiosurgical tumor dose was 19 Gy covering the entire vertebral body. The procedure provided long-term pain improvement and radiographic tumor control in all patients (follow-up range 7–44 months). No patient later required open surgery. No radiation-induced toxicity or new neurological deficit occurred during the follow-up period.

Conclusions

This treatment paradigm for pathological fractures of percutaneous transpedicular corpectomy combined with cement augmentation followed by radiosurgery was found to be safe and clinically effective. This technique combines minimally invasive procedures that avoid the morbidity associated with open surgery while providing spinal canal decompression and immediate fracture stabilization, and then administering a single-fraction tumoricidal radiation dose.

Hyperbaric oxygenation alleviates MCAO-induced brain injury and reduces hydroxyl radical formation and glutamate release

The present study examined the effect of hyperbaric oxygen (HBO) on the formation of 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-dihydroxybenzoic acid (2,5-DHBA), the products of salicylate trapping of hydroxyl free radicals, and glutamate release in the striatum during acute ischemia and reperfusion. Non-HBO rats (n = 8) were subjected to 1-h ischemia. Study rats (n = 8) were treated with HBO at 2.8 ATA for 1 h during ischemia. Artificial CSF solution containing 5 mM sodium salicylate was perfused at 1 microl/min. Samples were continuously collected at 15 min intervals and the levels of 2,3-DHBA, 2,5-DHBA, and glutamate were analyzed. The lesion volume was determined by TTC stain. Occlusion of the middle cerebral artery induced a significant increase in the levels of 2,3-DHBA and 2,5-DHBA. A peak of approximately two and fourfold of baseline levels was reached at 45 min and was maintained at elevated levels during reperfusion. The level of glutamate increased approximately two times at 30 min during ischemia, continued to increase, and reached approximately three times baseline level during reperfusion. HBO significantly alleviated brain injury associated with decreased levels of 2,3-DHBA, 2,5-DHBA and glutamate. This study suggests that the decreased glutamate release and the reduced formation of hydroxyl free radicals might contribute to the neuroprotective effect of HBO.

Radiotherapy and radiosurgery for metastatic spine disease: what are the options, indications, and outcomes?

STUDY DESIGN

Systematic literature review.

OBJECTIVE

To determine the options, indications, and outcomes for conventional radiotherapy and radiosurgery for metastatic spine disease.

METHODS

Three research questions were determined through a consensus among a multidisciplinary panel of spine oncology experts. A systematic review of the literature was conducted regarding radiotherapy and radiosurgery for metastatic spine disease using PubMed, Embase, the Cochrane Evidence Based Medicine Database, and a review of bibliographies of reviewed articles.

RESEARCH QUESTIONS

1. What are the clinical outcomes of the current indications for conventional radiotherapy alone and stereotactic radiosurgery for metastatic spine disease? 2. What are the current dose recommendations and fractionation schedules for conventional spine radiotherapy and stereotactic radiosurgery for metastatic spine disease? 3. What are the current known patterns of failure and complications after conventional spine radiation and stereotactic radiosurgery for metastatic spine disease?

RESULTS

For conventional radiotherapy, the initial literature search yielded a total of 531 potentially relevant abstracts. Each of these abstracts was reviewed for relevance, and 62 were selected for in-depth review. Forty-nine studies met all the inclusion criteria. References from the articles included in the analysis and review articles were also examined for potential inclusion in the study. For conventional radiotherapy, 3 randomized trials (high-quality evidence), 4 prospective studies (moderate-quality evidence), and over 40 nonprospective data sets (low- or very-low-quality evidence) that included over 5000 patients in the literature were included in this review. Drawing from the same databases, a systematic search for radiosurgery yielded 195 abstracts, of which 29 met all inclusion criteria. They all represented single-institution reports (low- or very-low-quality data). No randomized data are available for spine radiosurgery.

CONCLUSION

A systematic review of the available evidence suggests that conventional radiotherapy is safe and effective with good symptomatic response and local control, particularly for radiosensitive histologies. A strong recommendation can be made with moderate quality evidence that conventional fractionated radiotherapy is an appropriate initial therapy option for patients with spine metastases in cases in which no relative contraindication exists. A systematic review of the available evidence suggests that radiosurgery is safe and provides an incremental benefit over conventional radiotherapy with more durable symptomatic response and local control independent of histology, even in the setting of prior fractionated radiotherapy. A strong recommendation can be made with low-quality evidence that radiosurgery should be considered over conventional fractionated radiotherapy for the treatment of solid tumor spine metastases in the setting of oligometastatic disease and/or radioresistant histology.

Neurologic outcomes with cerebral oxygen monitoring in traumatic brain injury

BACKGROUND

Optimizing cerebral oxygenation is advocated to improve outcome in head-injured patients. The purpose of this study was to compare outcomes in brain-injured patients treated with 2 types of monitors.

METHODS

Patients with traumatic brain injury and a Glasgow Coma Scale score<8 were identified on admission. A polarographic cerebral oxygen/pressure monitor (Licox) or fiberoptic intracranial pressure monitor (Camino) was inserted. An evidence-based algorithm for treatment was implemented. Elements from the prehospital and emergency department records and the first 10 days of intensive care unit (ICU) care were collected. Glasgow Outcome Scores (GOS) were determined every 3 months after discharge.

RESULTS

Over a 3-year period, 145 patients were entered into the study; 81 patients in the Licox group and 64 patients in the Camino group. Mortality, hospital length of stay, and ICU length of stay were equivalent in the 2 groups. More patients in the Licox group achieved a moderate/recovered GOS at 3 months than in the Camino Group (79% vs 61%; P = .09).

CONCLUSION

Three-month GOS revealed a clinically meaningful 18% benefit in patients undergoing cerebral oxygen monitoring and optimization. Six-month outcomes were also better. Unfortunately, these important differences did not reach significance. Continued study of the benefits of cerebral oxygen monitoring is warranted.

Brain tissue oxygen tension monitoring in pediatric severe traumatic brain injury. Part 1: Relationship with outcome

INTRODUCTION

Intracranial pressure (ICP) monitoring and cerebral perfusion pressure (CPP) management are the current standards to guide care of severe traumatic brain injury (TBI). However, brain hypoxia and secondary brain injury can occur despite optimal ICP and CPP. In this study, we used brain tissue oxygen tension (PbtO(2)) monitoring to examine the association between multiple patient factors, including PbtO(2), and outcome in pediatric severe TBI.

MATERIALS AND METHODS

In this prospective observational study, 52 children (less than 15 years) with severe TBI were managed with continuous PbtO(2) and ICP monitoring. The relationships between outcome [Glasgow Outcome Score (GOS) and Pediatric Cerebral Performance Category Scale] and clinical, radiologic, treatment, and physiological variables, including PbtO(2), were examined using multiple logistic regression analysis.

RESULTS

Outcome was favorable in 40 patients (77%) and unfavorable (mortality, 9.6%; n = 5) in 12 (23%). In univariate analysis, the following variables had a significant association with unfavorable outcome: initial GCS, computed tomography classification, ICP(peak), mICP(24), mICP, CPP(low), CPP(<40), pupil reactivity, PbtO(2)(low), PbtO(2) < 5 mmHg, PbtO(2) < 10 mmHg, mPbtO(2)(24), and time-severity product. PbtO(2) parameters had the strongest independent association with poor outcome in multiple regression analysis. In particular, when PbtO(2) was <5 mmHg for >1 h, the adjusted OR for poor outcome was 27.4 (95% confidence interval, 1.9-391). No variables apart from PbtO(2) were independently associated with mortality when controlled for PbtO(2).

CONCLUSION

Reduced PbtO(2) is shown to be an independent factor associated with poor outcome in pediatric severe TBI in the largest study to date. It appears to have a stronger association with outcome than conventionally evaluated measures.

Brain tissue oxygen tension monitoring in pediatric severe traumatic brain injury. Part 2: Relationship with clinical, physiological, and treatment factors

INTRODUCTION

Brain tissue oxygen tension (PbtO(2)) monitoring is used increasingly in adult severe traumatic brain injury (TBI) management. Several factors are known to influence PbtO(2) in adults, but the variables that affect PbtO(2) in pediatric TBI are not well described. This study examines the relationships between PbtO(2) and (1) physiological markers of potential secondary insults commonly used in pediatric TBI, in particular intracranial pressure (ICP), cerebral perfusion pressure (CPP), and systemic hypoxia, and (2) other clinical factors and treatment received that may influence PbtO(2).

MATERIALS AND METHODS

In this prospective observational study, 52 children (mean age, 6.5 +/- 3.4 years; range, 9 months to 14 years old) with severe TBI and a median post-resuscitation Glasgow Coma Score (GCS) of 5 were managed with continuous PbtO(2) monitoring. The relationships between PbtO(2) parameters (Pbt)(2)(low), PbtO(2) < 5, PbtO(2) < 10, and mPbtAO(2)(24)) and clinical, physiological, and treatment factors were explored using time-linked data and Spearman's correlation coefficients.

RESULTS

No clinical, physiological, or treatment variable was significantly associated with all PbtO(2) parameters, but individual associations were found with initial GCS (PbtO(2) < 5, p = 0.0113), admission Pediatric Trauma Score (PbtO(2) < 10, 0.0175), mICP > 20 (mPbtO(2)(24), p = 0.0377), CPP(low) (PbtO(2)(low), p = 0.0065), CPP < 40 (PbtO(2)(low), p = 0.0269; PbtO(2) < 5, p = 0.0212), P(a)O(2) < 60 (mPbtO(2)(24), p = 0.0037), S(a)O(2) < 90 (PbtO(2)(low), p = 0.0438), and use of inotropes during ICU care (PbtO(2)(low), p = 0.0276; PbtO(2) < 10, p = 0.0277; p = mPbtO(2)(24)).

CONCLUSION

Delivery of oxygen to the brain is important to limit secondary neuronal injury after severe TBI. Our data show that PbtO(2) is poorly predicted by clinical and physiological factors commonly measured in the pediatric ICU. Multimodality monitoring may be needed to detect all secondary cerebral insults in pediatric TBI.

Mitochondrial mechanisms of cell death and neuroprotection in pediatric ischemic and traumatic brain injury

There are several forms of acute pediatric brain injury, including neonatal asphyxia, pediatric cardiac arrest with global ischemia, and head trauma, that result in devastating, lifelong neurologic impairment. The only clinical intervention that appears neuroprotective is hypothermia initiated soon after the initial injury. Evidence indicates that oxidative stress, mitochondrial dysfunction, and impaired cerebral energy metabolism contribute to the brain cell death that is responsible for much of the poor neurologic outcome from these events. Recent results obtained from both in vitro and animal models of neuronal death in the immature brain point toward several molecular mechanisms that are either induced or promoted by oxidative modification of macromolecules, including consumption of cytosolic and mitochondrial NAD(+) by poly-ADP ribose polymerase, opening of the mitochondrial inner membrane permeability transition pore, and inactivation of key, rate-limiting metabolic enzymes, e.g., the pyruvate dehydrogenase complex. In addition, the relative abundance of pro-apoptotic proteins in immature brains and neurons, and particularly within their mitochondria, predisposes these cells to the intrinsic, mitochondrial pathway of apoptosis, mediated by Bax- or Bak-triggered release of proteins into the cytosol through the mitochondrial outer membrane. Based on these pathways of cell dysfunction and death, several approaches toward neuroprotection are being investigated that show promise toward clinical translation. These strategies include minimizing oxidative stress by avoiding unnecessary hyperoxia, promoting aerobic energy metabolism by repletion of NAD(+) and by providing alternative oxidative fuels, e.g., ketone bodies, directly interfering with apoptotic pathways at the mitochondrial level, and pharmacologic induction of antioxidant and anti-inflammatory gene expression.

Lactate and glucose as energy substrates and their role in traumatic brain injury and therapy

Traumatic brain injury is a leading cause of disability and mortality worldwide, but no new pharmacological treatments are clinically available. A key pathophysiological development in the understanding of traumatic brain injury is the energy crisis derived from decreased cerebral blood flow, increased energy demand and mitochondrial dysfunction. Although still controversial, new findings suggest that brain cells try to cope in these conditions by metabolizing lactate as an energy substrate ‘on-demand’ in lieu of glucose. Experimental and clinical data suggest that lactate, at least when exogenously administered, is transported from astrocytes to neurons for neuronal utilization, essentially bypassing the slow, catabolizing glycolysis process to quickly and efficiently produce ATP. Treatment strategies using systemically applied lactate have proved to be protective in various experimental traumatic brain injury studies. However, lactate has the potential to elevate oxygen consumption to high levels and, therefore, could potentially impose a danger for tissue-at-risk with low cerebral blood flow. The present review outlines the experimental basis of lactate in energy metabolism under physiological and pathophysiological conditions and presents arguments for lactate as a new therapeutical tool in human head injury.

Bench-to-bedside review: oxygen as a drug

Oxygen is one of the most commonly used therapeutic agents. Injudicious use of oxygen at high partial pressures (hyperoxia) for unproven indications, its known toxic potential, and the acknowledged roles of reactive oxygen species in tissue injury led to skepticism regarding its use. A large body of data indicates that hyperoxia exerts an extensive profile of physiologic and pharmacologic effects that improve tissue oxygenation, exert anti-inflammatory and antibacterial effects, and augment tissue repair mechanisms. These data set the rationale for the use of hyperoxia in a list of clinical conditions characterized by tissue hypoxia, infection, and consequential impaired tissue repair. Data on regional hemodynamic effects of hyperoxia and recent compelling evidence on its anti-inflammatory actions incited a surge of interest in the potential therapeutic effects of hyperoxia in myocardial revascularization and protection, in traumatic and nontraumatic ischemicanoxic brain insults, and in prevention of surgical site infections and in alleviation of septic and nonseptic local and systemic inflammatory responses. Although the margin of safety between effective and potentially toxic doses of oxygen is relatively narrow, the ability to carefully control its dose, meticulous adherence to currently accepted therapeutic protocols, and individually tailored treatment regimens make it a cost-effective safe drug.

Physiologic and functional outcome correlates of brain tissue hypoxia in traumatic brain injury

OBJECTIVE

Assess the prevalence of brain tissue hypoxia in patients with severe traumatic brain injuries (TBI), and to characterize the relationship between brain tissue hypoxia and functional outcome.

DESIGN

Retrospective review of severe TBI patients.

SETTING

Intensive care unit of a level I trauma center.

PATIENTS

Twenty-seven patients with severe TBI requiring intracranial pressure (ICP) monitoring. Median age was 22 yrs, and a majority (63%) had traumatic subarachnoid hemorrhage.

INTERVENTIONS

Hourly assessments of ICP, brain tissue oxygen, mean arterial pressure, fraction of inspired oxygen (FiO2), partial pressure of arterial carbon dioxide (PaCO2), and hemoglobin concentration (hemoglobin) were recorded. Outcome was assessed 6-9 months postinjury.

MEASUREMENTS AND MAIN RESULTS

Mean (SD) ICP and BTpO2 were 13.7 (6.6) cm H2O and 30.8 (13.6) mm Hg. A total of 13.5% (379) of the BTpO2 values recorded were < 20 mm Hg, only 86 of which were associated with ICP > or = 20 cm H2O. This prevalence was comparable with episodes of ICP elevations above 20 cm H2O (14.1%, 397). Hypoxic episodes were more common when cerebral perfusion pressure was below 60 mm Hg (relative risk = 3.0, p < 0.0001). We did not find an association in hypoxic risk and hemoglobin in the range of 7-12 g/dL or PaCO2 in the range of 25-40 mm Hg. Subjects with hourly episodes (epochs) of hypoxia > 20% of the time had poorer scores on outcome measures compared with those with fewer hypoxic epochs.

CONCLUSIONS

Hypoxic episodes are common after severe TBI, and most are independent of ICP elevations. Most episodes of hypoxia occur while cerebral perfusion pressure and mean arterial pressure are within the accepted target range. There is no clear association between PaCO2 and hemoglobin with BTpO2. The young age and high prevalence of traumatic subarachnoid hemorrhage in this cohort may limit its generalizability. Increased frequency of hypoxic episodes is associated with poor functional outcome.

Brain oxygen tension and outcome in patients with aneurysmal subarachnoid hemorrhage

Object

Poor outcome is common after aneurysmal subarachnoid hemorrhage (SAH). Clinical studies suggest that cerebral hypoxia after traumatic brain injury is associated with poor outcome. In this study we examined the relationship between brain oxygen tension (PbtO2) and death after aneurysmal SAH.

Methods

Forty-six patients, including 34 women and 12 men (Glasgow Coma Scale Score ≤ 8 and median age 58.5 years) who underwent PbtO2 monitoring were studied prospectively during a 2-year period in a neurosurgical intensive care unit at a University Level I Trauma Center. Brain oxygen tension, intracranial pressure (ICP), mean arterial pressure, cerebral perfusion pressure (CPP), and brain temperature were continuously monitored, and treatment was directed toward ICP, CPP, and PbtO2 targets. The relationship between PbtO2 and 1-month survival was examined.

Results

Data were available from 5424 hours of PbtO2 monitoring. For the entire cohort the mean ICP, CPP, and PbtO2 were 13.85 ± 2.40, 84.05 ± 3.41, and 30.79 ± 1.91 mm Hg, respectively. Twenty-five patients died (54%). The mean daily PbtO2 was higher in survivors than nonsurvivors (33.94 ± 2.74 vs 28.14 ± 2.59 mm Hg; p = 0.05). In addition, survivors had significantly shorter episodes of compromised PbtO2 (defined as 15–25 mm Hg) than nonsurvivors (125.85 ± 15.44 vs 271.14 ± 55.23 minutes; p < 0.01). Intracranial pressure was similar in survivors and nonsurvivors. In contrast, the average CPP was significantly lower in nonsurvivors than survivors (76.96 ± 5.50 vs 92.49 ± 2.75 mm Hg; p = 0.01). When PbtO2 was stratified according to CPP level, survivors had higher PbtO2 levels. Following logistic regression, the number of episodes of compromised PbtO2 (odds ratio 1.1, 95% confidence interval 1.003–1.2) and number of episodes of cerebral hypoxia (< 15 mm Hg; odds ratio 1.3, 95% confidence interval 1.0–1.7) were more frequent in those who died.

Conclusions

Patient deaths after SAH may be associated with a lower mean PbtO2 and longer periods of compromised cerebral oxygenation than in survivors. This knowledge may be used to help direct therapy.

Oxygen therapy in stroke: past, present, and future

Oxygen is frequently administered to patients with suspected stroke. However, the role of oxygen therapy in ischemic stroke remains controversial in light of the failure of three clinical trials of hyperbaric oxygen therapy to show efficacy, and the fear of exacerbating oxygen free radical injury. The previous trials had several shortcomings, perhaps because they were designed on basis of anecdotal case reports and little preclinical data. Most animal studies concerning oxygen therapy in stroke have been conducted over the last 6 years. Emerging data suggests that hyperbaric and even normobaric oxygen therapy can be effective if used appropriately, and raises the tantalizing possibility that hyperoxia can be used to extend the narrow therapeutic time window for stroke thrombolysis. This article reviews the history, rationale, mechanisms of action and adverse effects of hyperoxia, the key results of previous hyperoxia studies, and the potential role of oxygen therapy in contemporary stroke treatment.

Increase in cerebral aerobic metabolism by normobaric hyperoxia after traumatic brain injury

OBJECT

Traumatic brain injury (TBI) is associated with depressed aerobic metabolism and mitochondrial dysfunction. Normobaric hyperoxia (NBH) has been suggested as a treatment for TBI, but studies in humans have produced equivocal results. In this study the authors used brain tissue O(2) tension measurement, cerebral microdialysis, and near-infrared spectroscopy to study the effects of NBH after TBI. They investigated the effects on cellular and mitochondrial redox states measured by the brain tissue lactate/pyruvate ratio (LPR) and the change in oxidized cytochrome c oxidase (CCO) concentration, respectively.

METHODS

The authors studied 8 adults with TBI within the first 48 hours postinjury. Inspired oxygen percentage at normobaric pressure was increased from baseline to 60% for 60 minutes and then to 100% for 60 minutes before being returned to baseline for 30 minutes.

RESULTS

The results are presented as the median with the interquartile range in parentheses. During the 100% inspired oxygen percentage phase, brain tissue O2 tension increased by 7.2 kPa (range 4.5-9.6 kPa) (p < 0.0001), microdialysate lactate concentration decreased by 0.26 mmol/L (range 0.0-0.45 mmol/L) (p = 0.01), microdialysate LPR decreased by 1.6 (range 1.0-2.3) (p = 0.02), and change in oxidized CCO concentration increased by 0.21 mumol/L (0.13-0.38 micromol/L) (p = 0.0003). There were no significant changes in intracranial pressure or arterial or microdialysate glucose concentration. The change in oxidized CCO concentration correlated with changes in brain tissue O(2) tension (r(s)= 0.57, p = 0.005) and in LPR (r(s)= -0.53, p = 0.006).

CONCLUSIONS

The authors have demonstrated oxidation in cerebral cellular and mitochondrial redox states during NBH in adults with TBI. These findings are consistent with increased aerobic metabolism and suggest that NBH has the potential to improve outcome after TBI. Further studies are warranted.

Brain metabolic and hemodynamic effects of cyclosporin A after human severe traumatic brain injury: a microdialysis study

BACKGROUND

Mitochondrial dysfunction is a major limiting factor in neuronal recovery following traumatic brain injury. Cyclosporin A (CsA) has been recently proposed for use in the early phase after severe head injury, for its ability to preserve mitochondrial bioenergetic state, potentially exerting a neuroprotective effect. The aim of this study was, therefore, to evaluate the effect of CsA on brain energy metabolism, as measured by cerebral microdialysis, and on cerebral hemodynamics, in a group of severely head injured patients.

METHODS

Fifty adult patients with a severe head injury were enrolled in this randomized, double-blind, placebo-controlled study. Patients received 5 mg/kg of CsA over 24 h, or placebo, within 12 h of the injury. A microdialysis probe was placed in all patients, who were managed according to standard protocols for the treatment of severe head injury.

FINDINGS

The most robust result of this study was that, over most of the monitoring period, brain dialysate glucose was significantly higher in the CsA treated patients than in placebo. Both lactate and pyruvate were also significantly higher in the CsA group. Glutamate concentration and lactate/pyruvate ratio were significantly higher in the placebo group than in CsA treated patients, respectively 1 to 2 days, and 2 to 3 days after the end of the 24-h drug infusion. The administration of CsA was also associated with a significant increase in mean arterial pressure (MAP) and cerebral perfusion pressure (CPP).

CONCLUSIONS

The administration of CsA in the early phase after head injury resulted in significantly higher extracellular fluid glucose and pyruvate, which may be evidence of a beneficial effect. The early administration of CsA was also associated with a significant increase in MAP and CPP and such a potentially beneficial hemodynamic effect might contribute to a neuroprotective effect.

Review of spinal radiosurgery: a minimally invasive approach for the treatment of spinal and paraspinal metastases

Intracranial radiosurgery has been proved effective for the treatment of brain metastasis. The treatment of paraspinal and spinal metastasis with spinal radiosurgery represents a natural extension of the principles of intracranial radiosurgery. However, spinal radiosurgery is a far more complicated process than intracranial radiosurgery. Larger treatment volumes, numerous organs at risk, and the inability to utilize rigid, frame-based immobilization all contribute to the substantially more complex process of spinal radiosurgery.

Beyond the convenience of a shorter duration of treatment for the patient, spinal radiosurgery affords a greater biological equivalent dose to a metastatic lesion than conventional radiotherapy fractionation schemes. This appears to translate into a high rate of tumor control and fast pain relief for patients. The minimally invasive nature of this approach is consistent with trends in open spinal surgery and helps to maintain or improve a patient's quality of life. Spinal radiosurgery has expanded the neurosurgical treatment armamentarium for patients with spinal and paraspinal metastasis.

Brain tissue oxygen tension is more indicative of oxygen diffusion than oxygen delivery and metabolism in patients with traumatic brain injury

OBJECTIVES

Despite the growing clinical use of brain tissue oxygen monitoring, the specific determinants of low brain tissue oxygen tension (P(bt)O2) following severe traumatic brain injury (TBI) remain poorly defined. The objective of this study was to evaluate whether P(bt)O2 more closely reflects variables related to cerebral oxygen diffusion or reflects cerebral oxygen delivery and metabolism.

DESIGN

Prospective observational study.

SETTING

Level I trauma center.

PATIENTS

Fourteen TBI patients with advanced neuromonitoring underwent an oxygen challenge (increase in FiO2 to 1.0) to assess tissue oxygen reactivity, pressure challenge (increase in mean arterial pressure) to assess autoregulation, and CO2 challenge (hyperventilation) to assess cerebral vasoreactivity.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

P(bt)O2 was measured directly with a parenchymal probe in the least-injured hemisphere. Local cerebral blood flow (CBF) was measured with a parenchymal thermal diffusion probe. Cerebral venous blood gases were drawn from a jugular bulb venous catheter. We performed 119 measurements of PaO2, arterial oxygen content (CaO2), jugular bulb venous oxygen tension (PVO2), venous oxygen content (CVO2), arteriovenous oxygen content difference (AVDO2), and local cerebral metabolic rate of oxygen (locCMRO2). In multivariable analysis adjusting for various variables of cerebral oxygen delivery and metabolism, the only statistically significant relationship was that between P(bt)O2 and the product of CBF and cerebral arteriovenous oxygen tension difference (AVTO2), suggesting a strong association between brain tissue oxygen tension and diffusion of dissolved plasma oxygen across the blood-brain barrier.

CONCLUSIONS

Measurements of P(bt)O2 represent the product of CBF and the cerebral AVTO2 rather than a direct measurement of total oxygen delivery or cerebral oxygen metabolism. This improved understanding of the cerebral physiology of P(bt)O2 should enhance the clinical utility of brain tissue oxygen monitoring in patients with TBI.

NICEM consensus on neurological monitoring in acute neurological disease

This manuscript summarises the consensus on neuromonitoring in neuro-intensive care promoted and organised by the Neuro-Intensive Care and Emergency Medicine (NICEM) Section of the European Society of Intensive Care Medicine (ESICM). It is expected that continuous monitoring using multi-modal techniques will help to overcome the limitations of each individual method and will provide a better diagnosis. More specific treatment can then be applied; however, it remains to be determined which combination of parameters is optimal. The questions discussed and addressed in this manuscript are: (1) Who should have ICP monitoring and for how long? (2) What ICP technologies are available and what are their relative advantages/disadvantages? (3) Should CPP monitoring and autoregulation testing be used? (4) When should brain tissue oxygen tension (PbrO(2)) be monitored? (5) Should structurally normal or abnormal tissue be monitored with PbrO(2)? (6) Should microdialysis be considered in complex cases? It is hoped that this document will prove useful to clinicians working in NICU and also to those developing specialist NICU services within their hospital practice.

Hyperoxia: good or bad for the injured brain?

PURPOSE OF REVIEW

For decades it was assumed that cerebral ischemia was a major cause of secondary brain injury in traumatic brain injury, and management focused on improving cerebral perfusion and blood flow. Following the observation of mitochondrial dysfunction in traumatic brain injury and the widespread use of brain tissue oxygen tension (P(br)O(2) monitoring, however, recent work has focused on the use of hyperoxia to reduce the impact of traumatic brain injury.

RECENT FINDINGS

Previous work on normobaric hyperoxia utilized very indirect measures of cerebral oxygen metabolism (intracranial pressure, brain oxygen tension and microdialysis) as outcome variables. Interpretation of these measures is controversial, making it difficult to determine the impact of hyperoxia. A recent study, however, utilized positron emission tomography to study the impact of hyperoxia on patients with acute severe traumatic brain injury and found no improvement on cerebral metabolic rate for oxygen with this intervention.

SUMMARY

Despite suggestive data from microdialysis studies, direct measurement of the ability of the brain to utilize oxygen indicates that hyperoxia does not increase oxygen utilization. This, combined with the real risk of oxygen toxicity, suggests that routine clinical use is not appropriate at this time and should await appropriate prospective outcome studies.

Normoxic ventilatory resuscitation following controlled cortical impact reduces peroxynitrite-mediated protein nitration in the hippocampus

OBJECTIVES

Ventilatory resuscitation with 100% O2 after severe traumatic brain injury (TBI) raises concerns about the increased production of reactive oxygen species (ROS). The product of peroxynitrite-meditated tyrosine residue nitration, 3-nitrotyrosine (3-NT), is a marker for oxidative damage to proteins. The authors hypothesized that posttraumatic resuscitation with hyperoxia (100% fraction of inspired oxygen [FiO2] concentration) results in increased ROS-induced damage to proteins compared with resuscitation using normoxia (21% FiO2 concentration).

METHODS

Male Sprague-Dawley rats underwent controlled cortical impact (CCI) injury and resuscitation with either normoxic or hyperoxic ventilation for 1 hour (5 rats per group). Twenty-four hours after injury, rat hippocampi were evaluated using 3-NT immunostaining. In a second experiment, animals similarly underwent CCI injury and normoxic or hyperoxic ventilation for 1 hour (4 rats per group). One week after injury, neuronal counts were performed after neuronal nuclei immunostaining.

RESULTS

The 3-NT staining was significantly increased in the hippocampi of the hyperoxic group. The normoxic group showed a 51.0% reduction of staining in the CA1 region compared with the hyperoxic group and a 50.8% reduction in the CA3 region (p < 0.05, both regions). There was no significant difference in staining between the injured normoxic group and sham-operated control groups. In the delayed analysis of neuronal survival (neuronal counts), there was no significant difference between the hyperoxic and normoxic groups.

CONCLUSIONS

In this clinically relevant model of TBI, normoxic resuscitation significantly reduced oxidative damage to proteins compared with hyperoxic resuscitation. Neuronal counts showed no benefit from hyperoxic resuscitation. These findings indicate that hyperoxic ventilation in the early stages after severe TBI may exacerbate oxidative damage to proteins.

Multimodality monitoring in neurocritical care

Multimodality monitoring of cerebral physiology encompasses the application of different monitoring techniques and integration of several measured physiologic and biochemical variables into assessment of brain metabolism, structure, perfusion, and oxygenation status. Novel monitoring techniques include transcranial Doppler ultrasonography, neuroimaging, intracranial pressure, cerebral perfusion, and cerebral blood flow monitors, brain tissue oxygen tension monitoring, microdialysis, evoked potentials, and continuous electroencephalogram. Multimodality monitoring enables immediate detection and prevention of acute neurologic injury as well as appropriate intervention based on patients' individual disease states in the neurocritical care unit. Real-time analysis of cerebral physiologic, metabolic, and cardiovascular parameters simultaneously has broadened knowledge about complex brain pathophysiology and cerebral hemodynamics. Integration of this information allows for more precise diagnosis and optimization of management of patients with brain injury.

Effect of hyperoxia on regional oxygenation and metabolism after severe traumatic brain injury: preliminary findings

OBJECTIVE

To determine the effect of normobaric hyperoxia on cerebral metabolism in patients with severe traumatic brain injury.

DESIGN

Prospective clinical investigation.

SETTING

Neurosciences critical care unit of a university hospital.

PATIENTS

Eleven patients with severe traumatic brain injury.

INTERVENTIONS

Cerebral microdialysis, brain tissue oximetry (PbO2), and oxygen-15 positron emission tomography (15O-PET) were undertaken at normoxia and repeated at hyperoxia (FiO2 increase of between 0.35 and 0.50).

MEASUREMENTS AND MAIN RESULTS

Established models were used to image cerebral blood flow, blood volume, oxygen metabolism, and oxygen extraction fraction. Physiology was characterized in a focal region of interest (surrounding the microdialysis catheter) and correlated with microdialysis and oximetry. Physiology was also characterized in a global region of interest (including the whole brain), and a physiologic region of interest (defined using a critical cerebral metabolic rate of oxygen threshold). Hyperoxia increased mean +/- sd PbO2 from 28 +/- 21 mm Hg to 57 +/- 47 mm Hg (p = .015). Microdialysate lactate and pyruvate were unchanged, but the lactate/pyruvate ratio showed a statistically significant reduction across the study population (34.1 +/- 9.5 vs. 32.5 +/- 9.0, p = .018). However, the magnitude of reduction was small, and its clinical significance doubtful. The focal region of interest and global 15O-PET variables were unchanged. "At-risk" tissue defined by the physiologic region of interest, however, showed a universal increase in cerebral metabolic rate of oxygen from a median (interquartile range) of 23 (22-25) micromol x 100 mL(-1) x min(-1) to 30 (28-36) micromol x 100 mL(-1) x min(-1) (p < .01).

CONCLUSIONS

In severe traumatic brain injury, hyperoxia increases PbO2 with a variable effect on lactate and lactate/pyruvate ratio. Microdialysis does not, however, predict the universal increases in cerebral metabolic rate of oxygen in at-risk tissue, which imply preferential metabolic benefit with hyperoxia.

Brain tissue oxygen tension response to induced hyperoxia reduced in hypoperfused brain

Object

Increasing PaO2 can increase brain tissue PO2 (PbtO2). Nevertheless, the small increase in arterial O2 content induced by hyperoxia does not increase O2 delivery much, especially when cerebral blood flow (CBF) is low, and the effectiveness of hyperoxia as a therapeutic intervention remains controversial. The purpose of this study was to examine the role of regional (r)CBF at the site of the PO2 probe in determining the response of PbtO2 to induced hyperoxia.

Methods

The authors measured PaO2 and PbtO2 at baseline normoxic conditions and after increasing inspired O2 concentration to 100% on 111 occasions in 83 patients with severe traumatic brain injury in whom a stable xenon–enhanced computed tomography measurement of CBF was available. The O2 reactivity was calculated as the change in PbtO2 × 100/change in PaO2.

Results

The O2 reactivity was significantly different (p < 0.001) at the 5 levels of rCBF (<10, 11–15, 16–20, 21–40, and > 40 ml/100 g/min). When rCBF was < 20 ml/100 g/min, the increase in PbtO2 induced by hyperoxia was very small compared with the increase that occurred when rCBF was > 20 ml/100 g/min.

Conclusions

Although the level of CBF is probably only one of the factors that determines the PbtO2 response to hyperoxia, it is apparent from these results that the areas of the brain that would most likely benefit from improved oxygenation are the areas that are the least likely to have increased PbtO2.

The role of lung function in brain tissue oxygenation following traumatic brain injury

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.

Monitoring brain tissue oxymetry: Will it change management of critically ill neurologic patients?

Based on the assumption that brain ischemia and hypoxia are central causes of brain damage, the maintenance of an adequate tissue oxygenation is a primary objective in the field of neurocritical care. Thus, monitoring brain tissue oxymetry, allowing the possibility to discriminate between normal and critically impaired tissue oxygenation, is recognized as an essential part of the management of the neurological critically ill patient. The clinical usefulness of this neuromonitoring tool in the area of neurosciences (traumatic brain injury, aneurysm surgery, arteriovenous malformation resection, brain tumors) is discussed. Monitoring brain tissue oxymetry not only allows the detection of impending cerebral ischemia, thus providing the clinician with essential information for the management and correction of harmful intracerebral events, but it also helps in understanding the pathophysiology of neuro-injury. It can also be used as a "surrogate end point" to evaluate putative therapies, targeting therapy towards improved cerebral oxygenation. As brain tissue oxygenation correlates closely with outcome, several outcome categories have been differentiated, aiding in predicting prognosis after injury. The rationale for monitoring brain tissue oxygenation is to provide essential information about oxygen supply and utilization in this specific tissue bed, thus reducing secondary brain damage and improving neurological outcome.

Phase I/II study of stereotactic body radiotherapy for spinal metastasis and its pattern of failure

OBJECT

The authors report data concerning the safety, effectiveness, and patterns of failure obtained in a Phase I/II study of stereotactic body radiotherapy (SBRT) for spinal metastatic tumors.

METHODS

Sixty-three cancer patients underwent near-simultaneous computed tomography-guided SBRT. Spinal magnetic resonance imaging was conducted at baseline and at each follow-up visit. The National Cancer Institute Common Toxicity Criteria 2.0 assessments were used to evaluate toxicity.

RESULTS

The median tumor volume of 74 spinal metastatic lesions was 37.4 cm3 (range 1.6-358 cm3). No neuropathy or myelopathy was observed during a median follow-up period of 21.3 months (range 0.9-49.6 months). The actuarial 1-year tumor progression-free incidence was 84% for all tumors. Pattern-of-failure analysis showed two primary mechanisms of failure: 1) recurrence in the bone adjacent to the site of previous treatment, and 2) recurrence in the epidural space adjacent to the spinal cord. Grade 3 or 4 toxicities were limited to acute Grade 3 nausea, vomiting, and diarrhea (one case); Grade 3 dysphagia and trismus (one case); and Grade 3 noncardiac chest pain (one case). There was no subacute or late Grade 3 or 4 toxicity.

CONCLUSIONS

Analysis of the data obtained in the present study supports the safety and effectiveness of SBRT in cases of spinal metastatic cancer. The authors consider it prudent to routinely treat the pedicles and posterior elements using a wide bone margin posterior to the diseased vertebrae because of the possible direct extension into these structures. For patients without a history of radiotherapy, more liberal spinal cord dose constraints than those used in this study could be applied to help reduce failures in the epidural space.

Effect of lactate therapy upon cognitive deficits after traumatic brain injury in the rat

BACKGROUND

In previous studies, it has been shown that intravenous lactate therapy can improve brain neurochemistry, adenosine triphosphate (ATP) generation and outcome after traumatic brain injury (TBI) in rats. In this study, we examined: (1) four L-lactate concentrations to determine the optimal therapeutic dose post TBI in terms of cognitive function; (2) ATP production after TBI for the L-lactate concentration found to be the optimal dose; (3) the possible production of lactic acidosis with the highest L-lactate concentration tested.

METHODS

Thirty minutes following a fluid percussion injury (FPI) over the left cerebral hemisphere, the animals received an intravenous infusion of 10, 28, 100, or 280 mM L-lactate (n = 10 for each group) for 3 h at a rate of 0.65 ml/h. Shams and control injured animals received a saline infusion. At 11-15 days post injury, cognitive deficits were examined using the Morris Water Maze (MWM) test. Three groups of rats were used for ATP analysis: shams, injured + saline infusion, and injury + the optimal lactate dose as determined by the MWM (n = 4/group). Additionally, a group receiving 280 mM L-lactate (n = 5) and one receiving a saline infusion (n = 3) were monitored for arterial blood variables and blood pressures.

FINDINGS

In the MWM test, only the 100 mM L-lactate-treated injured animals showed a significant reduction in cognitive deficits when compared to saline-treated injured animals (p <or= 0.05). In the ATP study, injured animals without treatment had a 53% reduction in ATP level in the ipsilateral cortex, while animals with 100 mM lactate treatment had a 28% reduction. (p <or= 0.05). No lactic acidosis was induced by the intravenous infusion of 280 mM L-lactate.

CONCLUSIONS

This study indicates that the intravenous infusion of 100 mM L-lactate provided the optimal concentration of the substrate to ameliorate cognitive impairment, probably via the regeneration of ATP following TBI in rats.