Continuous monitoring of cerebrovascular pressure reactivity in patients with head injury.

OBJECT: Cerebrovascular pressure reactivity is the ability of cerebral vessels to respond to changes in transmural pressure. A cerebrovascular pressure reactivity index (PRx) can be determined as the moving correlation coefficient between mean intracranial pressure (ICP) and mean arterial blood pressure. METHODS: The authors analyzed a database consisting of 398 patients with head injuries who underwent continuous monitoring of cerebrovascular pressure reactivity. In 298 patients, the PRx was compared with a transcranial Doppler ultrasonography assessment of cerebrovascular autoregulation (the mean index [Mx]), in 17 patients with the PET-assessed static rate of autoregulation, and in 22 patients with the cerebral metabolic rate for O(2). Patient outcome was assessed 6 months after injury. RESULTS: There was a positive and significant association between the PRx and Mx (R(2) = 0.36, p < 0.001) and with the static rate of autoregulation (R(2) = 0.31, p = 0.02). A PRx > 0.35 was associated with a high mortality rate (> 50%). The PRx showed significant deterioration in refractory intracranial hypertension, was correlated with outcome, and was able to differentiate patients with good outcome, moderate disability, severe disability, and death. The graph of PRx compared with cerebral perfusion pressure (CPP) indicated a U-shaped curve, suggesting that too low and too high CPP was associated with a disturbance in pressure reactivity. Such an optimal CPP was confirmed in individual cases and a greater difference between current and optimal CPP was associated with worse outcome (for patients who, on average, were treated below optimal CPP [R(2) = 0.53, p < 0.001] and for patients whose mean CPP was above optimal CPP [R(2) = -0.40, p < 0.05]). Following decompressive craniectomy, pressure reactivity initially worsened (median -0.03 [interquartile range -0.13 to 0.06] to 0.14 [interquartile range 0.12-0.22]; p < 0.01) and improved in the later postoperative course. After therapeutic hypothermia, in 17 (70.8%) of 24 patients in whom rewarming exceeded the brain temperature threshold of 37 degrees C, ICP remained stable, but the average PRx increased to 0.32 (p < 0.0001), indicating significant derangement in cerebrovascular reactivity. CONCLUSIONS: The PRx is a secondary index derived from changes in ICP and arterial blood pressure and can be used as a surrogate marker of cerebrovascular impairment. In view of an autoregulation-guided CPP therapy, a continuous determination of a PRx is feasible, but its value has to be evaluated in a prospective controlled trial.

PET Molecular Imaging of Hypoxia in Ischemic Stroke: An Update.

Hypoxia, a condition of insufficient oxygen availability to support metabolism, occurs when the vascular supply is interrupted, as in stroke. The identification of the hypoxic and viable tissue in stroke as compared with irreversible lesions (necrosis) has relevant implications for the treatment of ischemic stroke. Traditionally, imaging by positron emission tomography (PET), using 15O-based radiotracers, allowed the measurement of perfusion and oxygen extraction in stroke, providing important insights in its pathophysiology. However, these multitracer evaluations are of limited applicability in clinical settings. More recently, specific tracers have been developed, which accumulate with an inverse relationship to oxygen concentration and thus allow visualizing the hypoxic tissue non invasively. These belong to two main groups: nitroimidazoles, and among these the 18F-Fluoroimidazole (18F-FMISO) is the most widely used, and the copper-based tracers, represented mainly by Cu-ATSM. While these tracers have been at first developed and tested in order to image hypoxia in tumors, they have also shown promising results in stroke models and preliminary clinical studies in patients with cardiovascular disorders, allowing the detection of hypoxic tissue and the prediction of the extent of subsequent ischemia and clinical outcome. These tracers have therefore the potential to select an appropriate subgroup of patients who could benefit from a hypoxia-directed treatment and provide prognosis relevant imaging. The molecular imaging of hypoxia made important progress over the last decade and has a potential for integration into the diagnostic and therapeutic workup of patients with ischemic stroke.

Prognostic accuracy of cerebral blood flow measurement by perfusion computed tomography, at the time of emergency room admission, in acute stroke patients.

The purpose of this study was to determine the prognostic accuracy of perfusion computed tomography (CT), performed at the time of emergency room admission, in acute stroke patients. Accuracy was determined by comparison of perfusion CT with delayed magnetic resonance (MR) and by monitoring the evolution of each patient's clinical condition. Twenty-two acute stroke patients underwent perfusion CT covering four contiguous 10mm slices on admission, as well as delayed MR, performed after a median interval of 3 days after emergency room admission. Eight were treated with thrombolytic agents. Infarct size on the admission perfusion CT was compared with that on the delayed diffusion-weighted (DWI)-MR, chosen as the gold standard. Delayed magnetic resonance angiography and perfusion-weighted MR were used to detect recanalization. A potential recuperation ratio, defined as PRR = penumbra size/(penumbra size + infarct size) on the admission perfusion CT, was compared with the evolution in each patient's clinical condition, defined by the National Institutes of Health Stroke Scale (NIHSS). In the 8 cases with arterial recanalization, the size of the cerebral infarct on the delayed DWI-MR was larger than or equal to that of the infarct on the admission perfusion CT, but smaller than or equal to that of the ischemic lesion on the admission perfusion CT; and the observed improvement in the NIHSS correlated with the PRR (correlation coefficient = 0.833). In the 14 cases with persistent arterial occlusion, infarct size on the delayed DWI-MR correlated with ischemic lesion size on the admission perfusion CT (r = 0.958). In all 22 patients, the admission NIHSS correlated with the size of the ischemic area on the admission perfusion CT (r = 0.627). Based on these findings, we conclude that perfusion CT allows the accurate prediction of the final infarct size and the evaluation of clinical prognosis for acute stroke patients at the time of emergency evaluation. It may also provide information about the extent of the penumbra. Perfusion CT could therefore be a valuable tool in the early management of acute stroke patients.

The effects of sevoflurane and halothane anesthesia on cerebral blood flow velocity in children.

We compared cerebral blood flow velocity during anesthesia with sevoflurane and halothane in 23 children admitted for elective surgery (age, 0.4-9.7 yr; median age, 1.9 yr; ASA physical status I-II). Inhaled induction was performed in a randomized sequence with sevoflurane or halothane. Under steady-state conditions, cerebral blood flow velocity (systolic [V(s)], mean [V(mn)], and diastolic [VD]) were measured by a blinded investigator using transcranial pulsed Doppler ultrasonography. The anesthetic was then changed. CBFV measurements were repeated after washout of the first anesthetic and after steady-state of the second (equivalent minimal alveolar concentration to first anesthetic). The resistance index was calculated. VD and V(mn) were significantly lower during sevoflurane (V(mn) 1.35 m/s) than during halothane (V(mn) 1.50 m/s; P = 0.001), whereas V(s) was unchanged. The resistance index was lower during halothane (P < 0.001). Our results indicate lower vessel resistance and higher mean velocity during halothane than during sevoflurane. IMPLICATIONS: The mean cerebral blood flow velocity is significantly decreased in children during inhaled anesthesia with sevoflurane than during halothane. This might be relevant for the choice of anesthetic in children with risk of increased intracranial pressure, neurosurgery, or craniofacial osteotomies.

Intratracheal suctioning in sick preterm infants: prevention of intracranial hypertension and cerebral hypoperfusion by muscle paralysis.

In a prospective nonrandomized study, using each baby as his or her own control, we compared intracranial pressure (anterior fontanel pressure as measured with the Digilab pneumotonometer), cerebral perfusion pressure, BP, heart rate, transcutaneous Po2, and transcutaneous Pco2 before, during, and after endotracheal suctioning, with and without muscle paralysis, in 28 critically ill preterm infants with respiratory distress syndrome. With suctioning, there was a small but significant increase in intracranial pressure in paralyzed patients (from 13.7 [mean] +/- 4.4 mm Hg [SD] to 15.8 +/- 5.2 mm Hg) but a significantly larger (P less than .001) increase when they were not paralyzed (from 12.5 +/- 3.6 to 28.5 +/- 8.3 mm Hg). Suctioning led to a slight increase in BP with (from 45.3 +/- 9.1 to 48.0 +/- 8.7 mm Hg) and without muscle paralysis (from 45.1 +/- 9.4 to 50.0 +/- 11.7 mm Hg); but there was no significant difference between the two groups. The cerebral perfusion pressure in paralyzed infants did not show any significant change before, during, and after suctioning (31.5 +/- 9.1 mm Hg before v 32.0 +/- 8.7 mm Hg during suctioning), but without muscle paralysis cerebral perfusion pressure decreased (P less than .001) from 32.8 +/- 9.7 to 21.3 +/- 13.1 mm Hg. Suctioning induced a slight decrease in mean heart rate and transcutaneous Po2, but pancuronium did not alter these changes. There was no statistical difference in transcutaneous Pco2 before, during, and after suctioning with and without muscle paralysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic treatment of hypertensive patients with converting enzyme inhibitors.

It is widely accepted that pharmacologic reduction of the blood pressure of hypertensive patients reduces the risk of at least some of the major cardiovascular complications (1-5). All major studies were carried out before orally active converting enzyme inhibitors had become available. In other words, very effective antihypertensive drugs have been around for quite some time and have already proven their efficacy. Therefore, the considerable enthusiasm that has developed during the very recent years for the new converting enzyme inhibitors should be evaluated in the light of previously available antihypertensive drugs, the more so, as drugs cheaper than converting enzyme inhibiting agents are presently available. Thus, the increased expense when using this new class of antihypertensive compounds should be justified by a therapeutic gain. When evaluating a class of antihypertensive drugs such as converting enzyme inhibitors, there are basically three main considerations: What is their efficacy in long-term use? This includes the effect on blood pressure, on heart, on hemodynamics, and on blood flow distribution. What are the metabolic effects? What is the effect on sodium and potassium excretion? How are the serum lipids affected by its use? Are there any untoward effects related either to the chemical structure of the compound per se or rather to the approach? In particular, are there any central effects of the drug which can cause discomfort to the patient? The following discussion has the principal aim to review these aspects with chronic use of oral converting enzyme inhibiting agents without, however, even attempting to provide an exhaustive review of the subject.

Perfusion computed tomography-guided subacute endovascular reperfusion in a patient with carotid occlusion.

Most patients with symptomatic internal carotid artery occlusion have a single minor or major hemispheric stroke. A minority of patients have ipsilateral retinal ischemia, recurrent strokes, or transient ischemic attacks. Whereas spontaneous carotid recanalization is rare, acute surgical recanalization has been attempted, with mixed results. Recently, acute endovascular recanalization has been performed and described as feasible and relatively safe. We describe a patient with symptom recurrence related to hemodynamic factors after occlusion of the carotid artery who was successfully treated 14 days after symptom onset.

Total aortic arch stenting--hemodynamical impact of carotid artery perfusion.

The aim of this experimental study is to evaluate the feasibility and the outcome of total endovascular stent implantation in the aortic arch. Indications for this operation-technique would be acute or chronic dissection of the aortic arch (non-A-non-B dissection) or type B dissection with retrograde extension. Four pigs were canulated via the distal abdominal aorta and a retrograde placement of a Djumbodis arch stent (4-9 cm) was controlled by using intravascular ultrasound and intracardiac ultrasound by the inferior cava vein and under radioscopic control. Cerebral perfusion, by using a flow meter placed on one prepared carotid artery, were controlled before, immediate post-procedural (<1 min), and in the early follow-up after aortic arch stent implantation. During the implantation process, especially during balloon inflation and deflation, mean carotid perfusion decreases slightly. A reactive increase of carotid perfusion after stent placements indicates transitory cerebral hypo-perfusion. Non-covered aortic arch stent implantation is technically feasible and could be a potential treatment option in otherwise inoperable arch dissections. The time required for balloon inflation and deflation causes an important risk of cerebral ischemia. The latter can be reduced by transaxillary perfusion.

Controlled contrast transcranial Doppler and arterial blood gas analysis to quantify shunt through patent foramen ovale.

BACKGROUND AND PURPOSE: A right-to-left shunt can be identified by contrast transcranial Doppler ultrasonography (c-TCD) at rest and/or after a Valsalva maneuver (VM) or by arterial blood gas (ABG) measurement. We assessed the influence of controlled strain pressures and durations during VM on the right-to-left passage of microbubbles, on which depends the shunt classification by c-TCD, and correlated it with the right-to-left shunt evaluation by ABG measurements in stroke patients with patent foramen ovale (PFO). METHODS: We evaluated 40 stroke patients with transesophageal echocardiography-documented PFO. The microbubbles were recorded with TCD at rest and after 4 different VM conditions with controlled duration and target strain pressures (duration in seconds and pressure in cm H2O, respectively): V5-20, V10-20, V5-40, and V10-40. The ABG analysis was performed after pure oxygen breathing in 34 patients, and the shunt was calculated as percentage of cardiac output. RESULTS: Among all VM conditions, V5-40 and V10-40 yielded the greatest median number of microbubbles (84 and 95, respectively; P&lt;0.01). A significantly larger number of microbubbles were detected in V5-40 than in V5-20 (P&lt;0.001) and in V10-40 than in V10-20 (P&lt;0.01). ABG was not sensitive enough to detect a shunt in 31 patients. CONCLUSIONS: The increase of VM expiratory pressure magnifies the number of microbubbles irrespective of the strain duration. Because the right-to-left shunt classification in PFO is based on the number of microbubbles, a controlled VM pressure is advised for a reproducible shunt assessment. The ABG measurement is not sensitive enough for shunt assessment in stroke patients with PFO.

Using 80 kVp versus 120 kVp in perfusion CT measurement of regional cerebral blood flow.

Perfusion CT studies of regional cerebral blood flow (rCBF), involving sequential acquisition of cerebral CT sections during IV contrast material administration, have classically been reported to be achieved at 120 kVp. We hypothesized that using 80 kVp should result in the same image quality while significantly lowering the patient's radiation dose, and we evaluated this assumption. In five patients undergoing cerebral CT survey, one section level was imaged at 120 kVp and 80 kVp, before and after IV administration of iodinated contrast material. These four cerebral CT sections obtained in each patient were analyzed with special interest to contrast, noise, and radiation dose. Contrast enhancement at 80 kVp is significantly increased (P < .001), as well as contrast between gray matter and white matter after contrast enhancement (P < .001). Mean noise at 80 kVp is not statistically different (P = .042). Finally, performance of perfusion CT studies at 80 kVp, keeping mAs constant, lowers the radiation dose by a factor of 2.8. We, thus, conclude that 80 kVp acquisition of perfusion CT studies of rCBF will result in increased contrast enhancement and should improve rCBF analysis, with a reduced patient's irradiation.

Surgical management of hemorrhage from rupture of the aortic arch.

BACKGROUND: Control of hemorrhage in patients with active bleeding from rupture of the aortic arch is difficult, because of the location of the bleeding and the impossibility of cross-clamping the aorta without interfering with cerebral perfusion. A precise and swift plan of management helped us salvage some patients and prompted us to review our experience. METHODS: Six patients with active bleeding of the aortic arch in the mediastinum and pericardial cavity (5 patients) or left pleural cavity (1 patient), treated between 1992 and 1996, were reviewed. Bleeding was reduced by keeping the mediastinum under local tension (3 patients) or by applying compression on the bleeding site (2 patients), or both (1 patient) while circulatory support, retransfusion of aspirated blood, and hypothermia were established. The diseased aortic arch was replaced during deep hypothermic circulatory arrest, which ranged from 25 to 40 minutes. In 3 patients, the brain was further protected by retrograde (2 patients) or antegrade (1 patient) cerebral perfusion. RESULTS: Hemorrhage from the aortic arch was controlled in all patients. Two patients died postoperatively, one of respiratory failure and the other of abdominal sepsis. Recovery of neurologic function was assessed and complete in all patients. The 4 survivors are well 8 to 49 months after operation. CONCLUSIONS: An approach relying on local tamponade to reduce bleeding, rapid establishment of circulatory support and hypothermia, retransfusion of aspirated blood, and swift repair of the aortic arch under circulatory arrest allows salvage of patients with active bleeding from an aortic arch rupture.

The history and role of long duration stimulation in fMRI.

During the past 20 years, BOLD fMRI has developed towards a central and fundamental tool in neuroscience. It has been shown that the BOLD response provides an indicator of neuronal activity in the brain. Consequently, for an accurate interpretation of findings in BOLD MRI experiments and to draw meaningful conclusions about the temporal evolution of neural events, a deep understanding of the nature of the BOLD contrast has become of essential importance. Since the dynamics of the major direct determinants of the BOLD signal (CBF, CBV and CMRO(2)) range between seconds and minutes, long duration stimulation was an early key strategy needed to study and understand the BOLD characteristics. This paper summarizes and discusses the thoughts and rationales of the long duration stimulation studies.

Postoperative management of adult central neurosurgical patients: systemic and neuro-monitoring.

Postoperative neurosurgical patients are at risk of developing complications. Systemic and neuro-monitoring are used to identify patients who deteriorate in order to treat the underlying cause and minimize the impact on outcome. Hypotension and hypoxia are likely to be the most frequent insults and can be detected easily with blood pressure monitoring and pulse oximetry. Repeated clinical examination, however, is probably the most important monitor in the postoperative setting. Clinical scores such as the Glasgow Coma Score and the more recently introduced FOUR Score are important tools to standardize the clinical assessment. Intracranial pressure monitoring, cerebral blood flow monitoring, electroencephalography, and brain imaging are often used postoperatively. Despite the numerous publications on this topic only few studies address the impact of postoperative monitoring on outcome. Accordingly, in most patients the decision on which monitors are to be used must be based on the patient's presentation and clinical judgment.

Blood pressure treatment in acute ischemic stroke: a review of studies and recommendations.

PURPOSE OF REVIEW: Elevated blood pressure (BP) is frequent in patients with acute ischemic stroke. Pathophysiological data support its usefulness to maintain adequate perfusion of the ischemic penumba. This review article aims to summarize the available evidence from clinical studies that examined the prognostic role of BP during the acute phase of ischemic stroke and intervention studies that assessed the efficacy of active BP alteration. RECENT FINDINGS: We found 34 observational studies (33,470 patients), with results being inconsistent among the studies; most studies reported a negative association between increased levels of BP and clinical outcome, whereas a few studies showed clinical improvement with higher BP levels, clinical deterioration with decreased BP, or no association at all. Similarly, the conclusions drawn by the 18 intervention studies included in this review (1637 patients) were also heterogeneous. Very recent clinical data suggest a possible beneficial effect of early treatment with some antihypertensives on late clinical outcome. SUMMARY: Observational and interventional studies of management of acute poststroke hypertension yield conflicting results. We discuss different explanations that may account for this and discuss the current guidelines and pathophysiological considerations for the management of acute poststroke hypertension.