Identification of posttraumatic ischemia and hyperperfusion by determination of the effect of induced arterial hypertension on carbon dioxide reactivity

Post-ischaemic hyperperfusion in traumatic middle cerebral artery dissection detected by arterial spin labelling of magnetic resonance imaging

We report a patient with a traumatic middle cerebral artery dissection, which showed hyperperfusion in the territory supplied by the left middle cerebral artery. A 45-year-old man experienced speech disturbance and motor weakness in his right hemibody on the day following mild head trauma. His symptoms worsened on the fourth day. Magnetic resonance imaging showed narrowing in the left M1 portion of the middle cerebral artery. Angiography showed narrowing and dilatation in the left middle cerebral artery trunk. The lesion was diagnosed as a dissection of the middle cerebral artery. Arterial spin labelling of magnetic resonance imaging and single photon emission computed tomography showed increased cerebral blood flow in the left temporal region compared with the right. The patient was treated conservatively and the symptoms gradually improved. The hyperperfusion observed on arterial spin labelling and single photon emission computed tomography gradually improved and disappeared on the 25th day. This is the first reported case of traumatic middle cerebral artery dissection, which showed post-ischaemic hyperperfusion in the territory of the affected artery. To detect hyperperfusion in the brain, arterial spin labelling is a useful technique.

A study comparing SPECT and MRI in patients with anosmia after traumatic brain injury

PURPOSE

The initial or first clinical presentation of altered sensation of smell is directly linked to the degree of impaired sensitivity. We took the opportunity to examine normal and nonspecific MRI findings in 6 patients with known anosmia after traumatic brain injury with perfusion SPECT brain imaging.

MATERIAL AND METHODS

Patients included those with primary loss of smell after head injury. All patients underwent standard testing by the Taste & Smell Center. Normal or nonspecific near normal brain MRI studies were subsequently referred for SPECT perfusion neuroimaging.

RESULTS

MRI studies were negative in 3 cases. In the remaining studies, one case showed nonspecific white matter change, another low signal in the left frontal gyrus, and the sixth case merely some cortical atrophy. All 6 cases demonstrated lesions on SPECT involving the frontal, temporal, and temporoparietal cortex.

CONCLUSION

This study identified altered blood perfusion pattern in otherwise normal anatomic structures on MRI.

Association between intravascular microthrombosis and cerebral ischemia in traumatic brain injury

OBJECTIVE

To determine the association between traumatic cerebral ischemia and intravascular thrombosis, a common finding after traumatic brain injury (TBI).

METHODS

We reviewed samples of the frontal cortex and hippocampus from individuals who had sustained a fatal TBI. Sections stained with hematoxylin and eosin were reviewed and rated for severity of selective neuronal necrosis (SNN). Because intravascular fibrin microthrombi may lyse within a few days of TBI, we restricted our analysis to patients who had died within 48 hours of injury. Medical records in all cases were reviewed to rule out severe or prolonged hypotension or hypoxemia. Eleven patients with severe or global SNN were compared with 11 patients in whom SNN was mild or absent. Slides adjacent to the hematoxylin and eosin sections were stained with an immunofluorescent antibody to antithrombin III and were reviewed for intravascular microthrombosis. The number of microthrombi on each slide was counted by an investigator blinded to the hematoxylin and eosin findings, and density of intravascular microthrombi was calculated.

RESULTS

Intravascular microthrombi were noted in every section, excluding control (non-TBI) brain tissue. However, the density of microthrombi varied with the degree of SNN. We found a highly significant difference in the mean density of microthrombi between patients with severe SNN (7.74 +/- 3.7/cm(2)) and those with little or no SNN (2.58 +/- 1.0/cm(2)). Furthermore, a good correlation was noted between the location of intravascular microthrombi and that of SNN.

CONCLUSION

These data support a strong link between intravascular microthrombosis and neuronal death after brain trauma in humans and may have important implications for new therapeutic approaches.

Effects of ephedrine, dobutamine and dopexamine on cerebral haemodynamics: transcranial Doppler studies in healthy volunteers

BACKGROUND

Sympathomimetic drugs are assumed to have no direct effects on cerebral haemodynamics on the basis of animal experiments; there is little evidence of their direct effects in humans. This study aimed to address this issue.

METHODS

The effects of ephedrine, dobutamine, and dopexamine on cerebral autoregulation, cerebral vascular reactivity to carbon dioxide, estimated cerebral perfusion pressure, and zero flow pressure (ZPF) were studied in 10 healthy volunteers using transcranial Doppler ultrasound. The strength of autoregulation was measured using the transient hyperaemic response test. The reactivity to carbon dioxide was measured as the change in middle cerebral artery flow velocity with a step change in end-tidal carbon dioxide. For the estimated cerebral perfusion pressure and the ZFP, established formulae were used which utilized instantaneous values of arterial pressure and middle cerebral artery flow velocity. Measurements were made at baseline and after i.v. infusion of the study drug to an endpoint of 25% increase in mean arterial pressure (MAP) (ephedrine, dobutamine) or cardiac index (dopexamine).

RESULTS

There was no significant change in the strength of autoregulation (from (mean (SD)) 1.07 (0.16) to 1.07 (0.18); from 1.07 (0.16) to 1.03 (0.19); from 1.04 (0.12) to 1.04 (0.25)), reactivity to carbon dioxide (from 40% (8) to 36 (10); from 37 (12) to 37 (11); from 45 (12) to 43 (11)) with ephedrine, dobutamine, or dopexamine, respectively. Despite a clinically significant increase in MAP with ephedrine and dobutamine and a clinically significant increase in cardiac index with dopexamine, the estimated cerebral perfusion pressure did not change significantly (from 81 (38) to 60 (16) mm Hg with ephedrine; from 67 (22) to 63 (11) mm Hg with dobutamine; from 87 (27) to 79 (17) mm Hg with dopexamine). The ZFP increased significantly with ephedrine (from 29 (10) to 44 (11) mm Hg) and dobutamine (from 35 (14) to 43 (10) mm Hg) but not dopexamine (from 3 (23) to 11 (22) mm Hg).

CONCLUSIONS

Sympathomimetic agents do not significantly change cerebrovascular homeostasis as assessed by the transient hyperaemic response test, reactivity to carbon dioxide and estimated cerebral perfusion pressure.

Neuroprotective effects of an immunosuppressant agent on diffusion/perfusion mismatch in transient focal ischemia

The immunosuppressant FK506 (tacrolimus) exerts potent neuroprotection following focal ischemia in animals; however, the separate effects of FK506 on the ischemic core and penumbra have not been reported. The ischemic penumbra is clinically defined as the difference between a large abnormal area on perfusion-weighted imaging (PWI) and a smaller lesion on diffusion-weighted imaging (DWI). The goal of this study was to determine the effect of FK506 on DWI/PWI match and mismatch areas in transient focal ischemia in rats. Twelve rats were subjected to 1 hr of transient middle cerebral artery (MCA) occlusion, and given an intravenous injection of a placebo (N = 6) or 1 mg/kg FK506 (N = 6) immediately before reperfusion. Magnetic resonance imaging (MRI) was performed during MCA occlusion, and 0.5, 1, and 24 hr after reperfusion. FK506 significantly protected the ischemic brain only in the mismatch cortex where the initial apparent diffusion coefficient (ADC) was normal and there was a mild reduction of cerebral blood flow (CBF). This is the first report to describe the protective effects of FK506 on ischemic penumbra, as measured by DWI/PWI mismatch. The findings provide direct evidence for the utility of DWI/PWI mismatch as a guideline for therapeutic intervention with FK506.

Changes in intracranial pressure and cerebral autoregulation in patients with severe traumatic brain injury

BACKGROUND

Impaired cerebral autoregulation is frequent after severe traumatic head injury. This could result in intracranial pressure fluctuating passively with the mean arterial pressure.

OBJECTIVE

This study examines the influence of autoregulation on the amplitude and direction of changes in intracranial pressure in patients with severe head injuries during the management of cerebral perfusion pressure.

DESIGN

Prospective study.

SETTING

Neurosurgical intensive care unit

PATIENTS

A total of 42 patients with severe head injuries.

INTERVENTIONS

Continuous recording of cerebral blood flow velocity, intracranial pressure, and mean arterial pressure during the start or change of continuous norepinephrine infusion.

MEASUREMENTS AND MAIN RESULTS

Cerebrovascular resistance was calculated from the cerebral perfusion pressure and middle cerebral artery blood flow velocity. The strength of autoregulation index was calculated as the ratio of the percentage of change in cerebrovascular resistance by the percentage of change in cerebral perfusion pressure before and after 121 changes in mean arterial pressure at constant ventilation between day 1 and day 18 after trauma. The strength of autoregulation index varied widely, indicating either preserved or severely perturbed autoregulation during hypotensive or hypertensive challenge in patients with or without intracranial hypertension at the basal state (strength of autoregulation index, 0.51 +/- 0.32 to 0.71 +/- 0.25). The change in intracranial pressure varied linearly with the strength of autoregulation index. There was a clinically significant change in intracranial pressure (> or =5 mm Hg) in the same direction as the change in mean arterial pressure in five tracings of three patients. This was caused by the mean arterial pressure dropping below the identified lower limit of autoregulation in three tracings for two patients. It seemed to be caused by a loss of cerebral autoregulation in the remaining two tracings for one patient.

CONCLUSION

Cerebral perfusion pressure-oriented therapy can be a safe way to reduce intracranial pressure, whatever the status of autoregulation, in almost all patients with severe head injuries.

[The usefulness of transcranial Doppler ultrasonography in the early phase of head injury]

OBJECTIVES

1) To know the transcranial Doppler (TCD) patterns in the early phase of the severe and moderate head injury and its prognostic implications. 2) To ascertain the TCD measurements concordance among different operators.

MATERIAL AND METHODS

A prospective observational study in 275 consecutive intensive care unit patients with severe or moderate head injury was designed. Within 12 hrs. of the traumatic event a TCD study was done and a second one within the first 24 hrs. All patients were managed following a protocol made with the aim of promoting the early evacuation of the intracranial space occupying mass, preventing delayed brain damage and keeping the intracranial pressure (ICP) < 20 mm Hg and the cerebral perfusion pressure (CPP) > 60 mm Hg. The patient outcome was categorized with the Glasgow Outcome Score (GOS) at the discharge of the ICU. The mean velocity (MV) and the pulsatily index (PI) were measured in both middle cerebral arteries (MCA) and in the intracranial part of the internal carotid arteries in order to calculate the Lindegaard index. The presence of hypoperfusion, hyperaemia, vasospasm and cerebral circulatory arrest was registered. The presence of high intracranial pressure (HICP), the ICP peak and mode, the lowest CPP, the CPP mode, the minor medium arterial pressure (MAP) and the MAP mode were also recorded. A concordance analysis was made to ascertain the validity of the TCD data obtained by different operators.

RESULTS

The concordance analysis among observers showed a kappa index of 0.7863 (p < 0.0001). The median stay in ICU was 7 days (Q1-Q3 of 3-15 days). The intra-ICU mortality was 20.72% (57/275) and the 53.44% of patients (147/275) showed favourable outcome (GOS 4-5) at the discharge of the ICU. The initial TCD showed a MV decreased and a PI increased in the MCA. Eighty of the e 275 patients showed a normal haemodynamic pattern whereas the pattern was abnormal in the remaining 195, degrees the hypoperfusion pattern predominated overall (181/275, 61.87%). HIPO was registered in 123 patients (58.01) an not in 89 (41.99%). A statistic significant correlation was found between the HICP and the DTC data. The early hypoperfusion pattern was related with a higher incidence of HICP (p > 0.05). The decrease in the MV and the increase in the PI were significantly associated with a higher mortality and a worse functional outcome (except for the MV within the first day). The PI was high within the first 24 h in the group of patients who died but was normalised among the survivals group.

CONCLUSIONS

Early TCD detects a cerebral hypoperfusion status in the severe and moderate head injury that may imply therapeutic considerations. This hypoperfusion strongly correlates with the severity of the injury, the incidence of HICP and the functional outcome at the ICU discharge. In experienced hands, TCD measurements are reliable when done by different operators.

Middle cerebral artery flow velocity correlates with common carotid artery volume flow rate after CO2 inhalation

Cerebral vasoreactivity can be studied with transcranial Doppler (TCD) by monitoring CO2-induced middle cerebral artery (MCA) velocity changes. Expected MCA mean velocity (Vm) changes due to changes in end-expiratory CO2 (EE-CO2) are established, but reactivity of common carotid artery (CCA) volume flow rate (VFR) has not been extensively reported. The authors assess the relationship between MCA Vm, CCA VFR, and EE-CO2. Ten normal individuals without cerebrovascular disease and with CCA diameters of more than 3.0 mm were studied. CCA VFR was obtained by Color Velocity Imaging Quantification and Ipsilateral MCA Vm by standard TCD methods. Each side was studied before, during, and after inhalation of 5% CO2. EE-CO2, blood pressure, and pulse rate were monitored. Four women and 6 men with mean age of 36 years were included. Significant correlations between MCA Vm and EE-CO2, CCA VFR and EE-CO2, and MCA Vm and CCA VFR were found. MCA Vm and CCA VFR increased 5.2% and 4.3% per mm Hg increase in EE-CO2, respectively. MCA Vm increased 0.3 cm/s for each ml/min increase in CCA VFR. In normal individuals, there is a direct correlation between MCA Vm, CCA VFR, and EE-CO2. Measurement of CCA VFR changes during CO2 inhalation may be an alternative method to estimate cerebral vasoreactivity when the MCA velocity cannot be obtained because of inadequate acoustic temporal windows.

Delayed, transient neurological deterioration after mild head injury--case report

A 16-year-old boy presented with delayed, transient neurological deterioration 18 days after mild head injury. Left hemiparesis and left homonymous hemianopsia appeared after right frontal contusional and mild subdural hematomas subsided. Neuroimaging examinations including cerebral angiography, magnetic resonance imaging, and single photon emission computed tomography showed vasodilation and hyperemia in the right cerebral hemisphere. The present case is not typical of acute "juvenile head trauma syndrome," but may represent a possible pathophysiology of the delayed type of transient neurological deterioration after mild head injury.

Monitoring neurologic patients in intensive care

The brain is sensitive to changes in substrate delivery. In neurologically critically ill patients (e.g., those with head injury, subarachnoid hemorrhage, or stroke), interruption of this supply causes ischemic brain damage and thus impairs the outcome. To prevent, detect, and treat these ischemic events as soon as possible, the cerebral blood flow is continuously monitored, its coupling or not with the consumption of oxygen and so forth, and the detected derangements of normal physiology. Intracranial pressure and cerebral perfusion pressure are two parameters that often reflect ischemic events, and thus it is mandatory to continuously measure them. To better assess cerebral hemodynamics, jugular bulb oxymetry and brain pressure tissue oxygen monitoring are two neuromonitoring techniques that allow for a better understanding of the balance between oxygen supply and consumption, and therefore are useful in directing therapy. Transcranial Doppler ultrasonography is a noninvasive technique with the same purpose but with less clinical relevance. The new neuromonitoring technique, microdialysis, is useful for understanding the mechanisms involved in brain ischemia. However, it is clear that the physician who interprets the measurements given by devices and the clinical data (e.g., temperature, glycemia) is still the cornerstone in the management of neurologically critically ill patients.

Secondary reduction in the apparent diffusion coefficient of water, increase in cerebral blood volume, and delayed neuronal death after middle cerebral artery occlusion and early reperfusion in the rat

It has been reported recently that very delayed damage can occur as a result of focal cerebral ischemia induced by vascular occlusion of short duration. With use of diffusion-, T2-, and contrast-enhanced dynamic magnetic resonance imaging (MRI) techniques, the occlusion time dependence together with the temporal profile for this delayed response in a rat model of transient focal cortical ischemia have been established. The distal branch of the middle cerebral artery was occluded for 20, 30, 45, or 90 minutes. Twenty minutes of vascular occlusion with reperfusion exhibited no significant mean change in either the apparent diffusion coefficient of water (ADC) or the T2 relaxation time at 6, 24, 48, or 72 hours after reperfusion (P = 0.97 and 0.70, respectively). Ninety minutes of ischemia caused dramatic tissue injury at 6 hours, as indicated by an increase in T2 relaxation times to 135% of the contralateral values (P < 0.01). However, at intermediate periods of ischemia (30 to 45 minutes), complete reversal of the ADC was seen at 6 hours after reperfusion but was followed by a secondary decline over time, such that a 25% reduction in tissue ADC was seen at 24 as compared with 6 hours (P < 0.02). This secondary response was accompanied by an increase in cerebral blood volume (CBV), as shown by contrast-enhanced dynamic MRI (120% of contralateral values; P < 0.001), an increase in T2 relaxation time (132%; P < 0.01), together with clear morphological signs of cell death. By day 18, the mean volume of missing cortical tissue measured with high-resolution MRI in animals occluded for 30 and 45 minutes was 50% smaller than that in 90-minute occluded animals (P < 0.005). These data show that ultimate infarct size is reduced after early reperfusion and is occlusion time dependent. The early tissue recovery that is seen with intermediate occlusion times can be followed by cell death, which has a delayed onset and is accompanied by an increase in CBV.

Changes in cerebral blood flow during PaCO2 variations in patients with severe closed head injury: comparison between the Fick and transcranial Doppler methods

OBJECT

The aim of this study was to reassess whether middle cerebral artery blood flow velocity (MCAv) variations measured by transcranial Doppler ultrasonography during acute PaCO2 manipulation adequately reflect cerebral blood flow (CBF) changes in patients with severe closed head injury.

METHODS

The study was performed by comparing MCAv variations to changes in CBF as assessed by measurements of the difference in the arteriovenous content in oxygen (AVDO2). The authors initiated 35 CO2 challenges in 12 patients with severe closed head injury during the acute stage. By simultaneous recording of systemic and cerebral hemodynamic parameters, 105 AVDO2 measurements were obtained. Patients were stratified into two groups, "high" and "low," with respect to whether their resting values of MCAv were greater than 100 cm/second during moderate hyperventilation. Four patients displayed an elevated MCAv, which was related to vasospasm in three cases and to hyperemia in one case. The PaCO2 and intracranial pressure levels were not different between the two groups. The slope of the regression line between 1 divided by the change in (delta)AVDO2 and deltaMCAv was not different from identity in the low group (1/deltaAVDO2 = 1.08 x deltaMCAv - 0.07, r = 0.93, p < 0.001) and significantly differed (p < 0.05) from the slope of the high group (1/deltaAVDO2 = 1.46 x deltaMCAv - 0.4, r = 0.83, p < 0.001).

CONCLUSIONS

In patients with severe closed head injury, MCAv variations adequately reflect CBF changes as assessed by AVDO2 measurements in the absence of a baseline increase in MCAv. These observations indicate that both moderate variations in PaCO2 and variations in cerebral perfusion pressure do not act noticeably on the diameter of the MCA. The divergence from the expected relationship in the high group seems to be due to the heterogeneity of CO2-induced changes in cerebrovascular resistance between differing arterial territories.