Focal ischemia due to traumatic contusions documented by stable xenon-CT and ultrastructural studies

Regional cerebral blood volume after severe head injury in patients with regional cerebral ischemia

OBJECTIVE

Recent early cerebral blood flow (CBF) studies in cases of severe head injury have revealed ischemia in a substantial number of patients with a variety of computed tomographically demonstrated diagnoses. The underlying derangements causing this early ischemia are unknown, but cerebral blood volume (CBV) measurements might offer some insight into this pathological abnormality.

METHODS

For this purpose, stable xenon-enhanced computed tomography was used for assessment of CBF, and a dynamic computed tomographic imaging technique was used for determining CBV. Based on the occurrence of regional ischemia (CBF < 20 ml/100 g/min), seven patients with varying anatomic lesions revealed by computed tomography were identified for comparison between CBF and CBV in ischemic and nonischemic areas.

RESULTS

Both CBF (15+/-4.3 versus 34+/-11 g/min, P < 0.002) and CBV (2.5+/-1.0 versus 4.9+/-1.9 ml/100 g) exhibited significantly lower values in the ischemic zones than in the nonischemic zones (means+/-standard deviations). Among 26 patients with or without ischemia observed during their initial follow-up studies, which were conducted between Days 2 and 8, all patients showed CBF and CBV values within the low-normal range.

CONCLUSION

These data evidently support the suggestion that compromise of the microvasculature is the cause of early ischemia, rather than vasospasm of the larger conductance vessels.

Head and spinal cord injury

Traumatic brain and spinal cord injuries remain the leading cause of death and disability for individuals under 50 years of age. This article describes common causes of primary and secondary central nervous system injuries. Particular emphasis is placed on the initial evaluation of trauma patients, detection of head and spinal cord injuries, and critical care of these patients. Definitive management of central nervous system injuries and prognosis and long-term management issues are also discussed.

d-Amphetamine attenuates decreased cerebral glucose utilization after unilateral sensorimotor cortex contusion in rats

Unilateral contusion injury to the sensorimotor cortex causes, among other symptoms, a transient contralateral hindlimb hemiparesis in rats. A single i.p. 2 mg/kg dose of d-amphetamine (d-AMPH) 24 h after injury accelerates spontaneous recovery from this particular deficit. The mechanism(s) of spontaneous and d-AMPH enhanced recovery are unknown but alleviation of a neuronal depression has been proposed. This quantitative CMRglu study was designed to determine effects of cortical contusion injury and d-AMPH on CMRglu in cortical and subcortical structures. At 2 days after injury, CMRglu was significantly reduced compared to sham-operated controls only in structures ipsilateral to contusion. Affected structures included the caudate putamen, medial geniculate nucleus, lateral geniculate nucleus and the parietal cortex immediately posterior to injury. By 6 days post-contusion, the hypometabolism partially reversed in all structures. A single low dose of d-AMPH significantly alleviated the post-traumatic CMRglu reduction at 2 days after injury. Importantly, while this alleviation was not significant for any single structure, the main effect of treatment was highly significant. d-AMPH increased CMRglu at 2 days post-injury by 18-33% compared to contused/saline-treated rats. These results suggest that alleviation of neuronal metabolic depression may contribute to spontaneous and d-AMPH enhanced recovery.

Clinical trials in traumatic brain injury. What can we learn from previous studies?

Many compounds have now been tested that were expected to ameliorate the secondary ischemic brain damage after severe head injury. Thus far, none of these have been clearly successful. This review is an attempt to identify factors that could be responsible for some of these failures. Recommendations are made that could help to avoid these pitfalls in the future. The usefulness and criteria for use of animal models for traumatic brain injury to depict human head injury are discussed. Clearly, it has now become widely accepted that mechanism-driven trials, in which individual pathophysiological mechanisms are targeted, are preferable in this heterogeneous patient population. Other factors, such as the effect of brain penetration, safety and tolerability of the compound, and the interface between the pharmaceutical industry and academics are a major influence in the success of these trials. Furthermore, different ways of analyzing trials such as sequential analysis and newer, alternative end points should be considered. Pharmacological agents will never be the "magic bullet" for a process as heterogenous in pathophysiological mechanisms as traumatic brain injury. This does not imply that the role of neuroprotective compounds will not be important in the future. New approaches in developing, conducting and analyzing these expensive clinical trials must be devised in the future.

Cerebral arteriovenous oxygen difference: a predictor of cerebral infarction and outcome in patients with severe head injury

Jugular bulb oxygen monitoring can be used to estimate the adequacy of cerebral blood flow to support cerebral metabolism after severe head injury. In the present study, the authors studied the cerebral arteriovenous oxygen difference (AVDO[2]) before and after treatment in 32 head-injured patients (Glasgow Coma Scale scores < or = 8) to examine the relationships among AVDO and cerebral perfusion pressure (CPP), delayed cerebral infarction, and outcome. Fifteen patients (Group A) underwent craniotomy for hematoma evacuation and 17 (Group B) received mannitol for sustained intracranial hypertension (intracranial pressure > 20 mm Hg, > 10 minutes). Radiographic evidence of delayed cerebral infarction was observed in 14 patients. Overall, 17 patients died or were severely disabled. Cerebral AVDO(2) was elevated before craniotomy or mannitol administration; the mean AVDO(2) for all patients before treatment was 8.6 +/- 1.8 vol%. Following craniotomy or mannitol administration, the AVDO(2) decreased in 27 patients and increased in five patients (mean AVDO(2) 6.2 +/- 2.1 vol% in all patients; 6 +/- 1.9 vol% in Group A; and 6.4 +/- 2.4 vol% in Group B). The mean CPP was 75 +/- 9.8 mm Hg and no relationship with AVDO(2) was demonstrated. Before treatment, the AVDO(2) was not associated with delayed cerebral infarction or outcome. By contrast, a limited improvement in elevated AVDO(2) after craniotomy or mannitol administration was significantly associated with delayed cerebral infarction (Group A: p < 0.001; Group B: p < 0.01). Similarly, a limited improvement in elevated AVDO(2) after treatment was significantly associated with an unfavorable outcome (Group A: p < 0.01; Group B: p < 0.001). In conclusion, these findings strongly indicate that, despite adequate cerebral perfusion, limited improvement in elevated cerebral AVDO(2) after treatment consisting of either craniotomy or mannitol administration may be used to help predict delayed cerebral infarction and poor outcome after traumatic brain injury.

Characterization of cerebral hemodynamic phases following severe head trauma: hypoperfusion, hyperemia, and vasospasm

The extent and timing of posttraumatic cerebral hemodynamic disturbances have significant implications for the monitoring and treatment of patients with head injury. This prospective study of cerebral blood flow (CBF) (measured using 133Xe clearance) and transcranial Doppler (TCD) measurements in 125 patients with severe head trauma has defined three distinct hemodynamic phases during the first 2 weeks after injury. The phases are further characterized by measurements of cerebral arteriovenous oxygen difference (AVDO[2]) and cerebral metabolic rate of oxygen (CMRO[2]). Phase I (hypoperfusion phase) occurs on the day of injury (Day 0) and is defined by a low CBF calculated from cerebral clearance curves integrated to 15 minutes (mean CBF 32.3 +/- 2 ml/100 g/minute), normal middle cerebral artery (MCA) velocity (mean V[MCA] 56.7 +/- 2.9 cm/second), normal hemispheric index ([HI], mean HI 1.67 +/- 0.11), and normal AVDO(2) (mean AVDO[2] 5.4 +/- 0.5 vol%). The CMRO, is approximately 50% of normal (mean CMRO(2) 1.77 +/- 0.18 ml/100 g/minute) during this phase and remains depressed during the second and third phases. In Phase II (hyperemia phase, Days 1-3), CBF increases (46.8 +/- 3 ml/100 g/minute), AVDO(2) falls (3.8 +/- 0.1 vol%), V(MCA) rises (86 +/- 3.7 cm/second), and the HI remains less than 3 (2.41 +/- 0.1). In Phase III (vasospasm phase, Days 4-15), there is a fall in CBF (35.7 +/- 3.8 ml/100 g/minute), a further increase in V(MCA) (96.7 +/- 6.3 cm/second), and a pronounced rise in the HI (2.87 +/- 0.22). This is the first study in which CBF, metabolic, and TCD measurements are combined to define the characteristics and time courses of, and to suggest etiological factors for, the distinct cerebral hemodynamic phases that occur after severe craniocerebral trauma. This research is consistent with and builds on the findings of previous investigations and may provide a useful temporal framework for the organization of existing knowledge regarding posttraumatic cerebrovascular and metabolic pathophysiology.

Cerebral arteriovenous oxygen difference: a predictor of cerebral infarction and outcome in patients with severe head injury

Jugular bulb oxygen monitoring can be used to estimate the adequacy of cerebral blood flow to support cerebral metabolism after severe head injury. In the present study, the authors studied the cerebral arteriovenous oxygen difference (AVDO2) before and after treatment in 32 head-injured patients (Glasgow Coma Scale scores ¾ 8) to examine the relationships among AVDO2 and cerebral perfusion pressure (CPP), delayed cerebral infarction, and outcome. Fifteen patients (Group A) underwent craniotomy for hematoma evacuation and 17 (Group B) received mannitol for sustained intracranial hypertension (intracranial pressure > 20 mm Hg, > 10 minutes). Radiographic evidence of delayed cerebral infarction was observed in 14 patients. Overall, 17 patients died or were severely disabled. Cerebral AVDO2 was elevated before craniotomy or mannitol administration; the mean AVDO2 for all patients before treatment was 8.6 ± 1.8 vol%. Following craniotomy or mannitol administration, the AVDO2 decreased in 27 patients and increased in five patients (mean AVDO2 6.2 ± 2.1 vol% in all patients; 6 ± 1.9 vol% in Group A; and 6.4 ± 2.4 vol% in Group B). The mean CPP was 75 ± 9.8 mm Hg and no relationship with AVDO2 was demonstrated. Before treatment, the AVDO2 was not associated with delayed cerebral infarction or outcome. By contrast, a limited improvement in elevated AVDO2 after craniotomy or mannitol administration was significantly associated with delayed cerebral infarction (Group A: p < 0.001; Group B: p < 0.01). Similarly, a limited improvement in elevated AVDO2 after treatment was significantly associated with an unfavorable outcome (Group A: p < 0.01; Group B: p < 0.001). In conclusion, these findings strongly indicate that, despite adequate cerebral perfusion, limited improvement in elevated cerebral AVDO2 after treatment consisting of either craniotomy or mannitol administration may be used to help predict delayed cerebral infarction and poor outcome after traumatic brain injury.

Characterization of cerebral hemodynamic phases following severe head trauma: hypoperfusion, hyperemia, and vasospasm

The extent and timing of posttraumatic cerebral hemodynamic disturbances have significant implications for the monitoring and treatment of patients with head injury. This prospective study of cerebral blood flow (CBF) (measured using 133Xe clearance) and transcranial Doppler (TCD) measurements in 125 patients with severe head trauma has defined three distinct hemodynamic phases during the first 2 weeks after injury. The phases are further characterized by measurements of cerebral arteriovenous oxygen difference (AVDO2) and cerebral metabolic rate of oxygen (CMRO2). Phase I (hypoperfusion phase) occurs on the day of injury (Day 0) and is defined by a low CBF15 calculated from cerebral clearance curves integrated to 15 minutes (mean CBF15 32.3 ± 2 ml/100 g/minute), normal middle cerebral artery (MCA) velocity (mean VMCA 56.7 ± 2.9 cm/second), normal hemispheric index (mean HI 1.67 ± 0.11), and normal AVDO2 (mean AVDO2 5.4 ± 0.5 vol%). The CMRO2 is approximately 50% of normal (mean CMRO2 1.77 ± 0.18 ml/100 g/minute) during this phase and remains depressed during the second and third phases. In Phase II (hyperemia phase, Days 1-3), CBF increases (46.8 ± 3 ml/100 g/minute), AVDO2 falls (3.8 ± 0.1 vol%), VMCA velocity rises (86 ± 3.7 cm/second), and the HI remains less than 3 (2.41 ± 0.1). In Phase III (vasospasm phase, Days 4-15), there is a fall in CBF (35.7 ± 3.8 ml/100 g/minute), a further increase in VMCA (96.7 ± 6.3 cm/second), and a pronounced rise in the HI (2.87 ± 0.22).

This is the first study in which CBF, metabolic, and TCD measurements are combined to define the characteristics and time courses of, and to suggest etiological factors for, the distinct cerebral hemodynamic phases that occur after severe craniocerebral trauma. This research is consistent with and builds on the findings of previous investigations and may provide a useful temporal framework for the organization of existing knowledge regarding posttraumatic cerebrovascular and metabolic pathophysiology.

Cerebral blood flow and vasoresponsivity within and around cerebral contusions

There is increasing evidence that regional ischemia plays a major role in secondary brain injury. Although the cortex underlying subdural hematomas seems particularly vulnerable to ischemia, little is known about the adequacy of cerebral blood flow (CBF) or the vasoresponsivity within the vascular bed of contusions. The authors used the xenon-enhanced computerized tomography (CT) CBF technique to define the CBF and vasoresponsivity of contusions, pericontusional parenchyma, and the remainder of the brain 24 to 48 hours after severe closed head injury in 10 patients: six patients with one contusion and four with two contusions, defined as mixed or high-density lesions on CT scanning. The CBF within the contusions (29.3 +/- 16.4 ml/100 g/minute, mean +/- standard deviation) was significantly lower than both that found in the adjacent 1-cm perimeter of normal-appearing tissue (42.5 +/- 15.8 ml/100 g/minute) and the mean global CBF (52.5 +/- 17.5 ml/100 g/minute) (p < 0.004, repeated-measures analysis of variance). A subset of seven patients (10 contusions) also underwent a second Xe-CT CBF study during mild hyperventilation (a PaCO2 of 24-32 mm Hg). In only two of these 10 contusions was vasoresponsivity less than 1% (range 0%-7.6%); in the rim of normal-appearing pericontusional tissue, it was 0.4% to 9.1%. The authors conclude that CBF within intracerebral contusions is highly variable and is often above 18 ml/100 g/minute, the reported threshold for irreversible ischemia. Intracontusional CBF is significantly reduced relative to surrounding brain parenchyma, and CO2 vasoresponsivity is usually present. In the contusion and the surrounding parenchyma, vasoresponsivity may be nearly three times normal, suggesting hypersensitivity to hyperventilation therapy. Given this possible hypersensitivity and relative hypoperfusion within and around cerebral contusions, these lesions are particularly vulnerable to secondary injury such as that which may be caused by hypotension or aggressive hyperventilation.

Focal cerebral hyperemia after focal head injury in humans: a benign phenomenon?

To assess the relationship between posttraumatic cerebral hyperemia and focal cerebral damage, the authors performed cerebral blood flow mapping studies by single-photon emission computerized tomography (SPECT) in 53 patients within 3 weeks of brain injury. Focal zones of hyperemia were present in 38% of patients. Hyperemia was correlated with clinical features and early computerized tomography (CT) and magnetic resonance (MR) imaging performed within 48 hours of the SPECT study and late CT and MR studies at 3 months. The hyperemia was observed primarily in structurally normal brain tissue (both gray and white matter), as revealed by CT and MR imaging, immediately adjacent to intraparenchymal or extracerebral focal lesions; it persisted for up to 10 days, but was never seen within the edematous pericontusional zones. The percentage of patients in the hyperemic group having brief (< 30 minutes) or no loss of consciousness was significantly higher than in the nonhyperemic group (twice as high, p < 0.05). Other clinical parameters were not significantly more common in the hyperemic group. The mortality of patients with focal hyperemia was lower than that of individuals without it, and the outcome of survivors with hyperemia was slightly better than patients without hyperemia. These results differ from the literature, which suggests that global post-traumatic hyperemia is primarily an acute, malignant phenomenon associated with increased intracranial pressure, profound unconsciousness, and poor outcome. The current results agree with more recent studies which show that posttraumatic hyperemia may occur across a wide spectrum of head injury severity and may be associated with favorable outcome.

The effect of the glycine site-specific N-methyl-D-aspartate antagonist ACEA1021 on ischemic brain damage caused by acute subdural hematoma in the rat

Acute subdural hematoma (SDH) complicates about 20% of severely head-injured patients, and death and severe disability frequently result, yet over half of these patients may have been conscious, at some time after injury, implying secondary mechanisms of brain damage. Drugs that block the "excitotoxic" effects of glutamate at the N-methyl-D-aspartate (NMDA) receptor have generally been effective in reducing ischemic brain damage associated with SDH in animal models, yet these agents all appear to be associated with major behavioral side effects, in conscious patients, at neuroprotective doses. We therefore evaluated the effects of treatment with a novel antagonist for the glycine binding site of the NMDA receptor (ACEA1021) upon ischemic brain damage, in the rat SDH model. ACEA1021 may be free of psychomotor effects, and may thus permit high dose therapy in conscious trauma and stroke patients. SDH was produced by the slow injection of 0.4 mL autologous blood into the subdural space overlying the parietal cortex. brain damage was assessed histologically at 8 coronal planes, in animals sacrificed 4 h after induction of hematoma. Both pre- and posttreatment with ACEA1021 significantly reduced hemispheric ischemic damage produced by SDH. The magnitude of neuroprotection with this compound (26 to 39% reduction in infarct size) is similar to other NMDA antagonists, and the robust posttreatment effect implies that human studies with this compound should be performed in head injured patients, subject to completion of toxicology testing.