Continuous monitoring of regional cerebral blood flow during temporary arterial occlusion in aneurysm surgery

Trans-trigeminal transport of masseter-derived neprilysin to hippocampus

OBJECTIVE

To show the possible occurrence of exosomal transport of neprilysin from masseter muscle to hippocampus via trigeminal nerve in the living mouse.

DESIGN

Mouse C2C12 myotube-derived exosomes were labeled with near-infrared (NIR) dye and injected into the masseter muscle to track their fluorescence from masseter muscle to hippocampus via trigeminal nerve. A plasmid vector encoding green fluorescent protein (GFP)-tagged neprilysin (GFP-neprilysin) was transfected into masseter muscle of C57BL/6 J mice. Expression of mRNA and encoded protein of the transgene was identified in masseter muscle, trigeminal nerve and hippocampus by RT-PCR and Western blot, respectively.

RESULTS

Peak of exosomal NIR in masseter muscle at time 0 rapidly reduced at 3 h and 6 h along with the subsequent increases in trigeminal nerve and hippocampus. Expression of GFP-neprilysin mRNA was detected in masseter muscle, but not trigeminal nerve and hippocampus. On the other hand, the corresponding protein of GFP-neprilysin was identified in the three tissues on day 3 after transfection into masseter muscle as a single band on Western blots with anti-GFP and anti-neprilysin antibodies.

CONCLUSION

The appearance of GFP-neprilysin protein in trigeminal nerve and hippocampus without a corresponding mRNA expression indicated the protein's origin from the masseter muscle. Concomitant migration of NIR-exosomes from masseter muscle to hippocampus via trigeminal nerve suggested the possible occurrence of exosomal transport of neprilysin.

Symptomatic and silent cerebral infarction following surgical clipping of unruptured intracranial aneurysms: incidence, risk factors, and clinical outcome

Cerebral infarction (CI) associated with clipping of unruptured intracranial aneurysms (UIAs) has not been completely studied. The role of individual and operative characteristics is not known, and the risk of silent CI has not been well described. To determine the incidence, risk factors, and clinical outcome of postoperative CI, we retrospectively analyzed 388 consecutive patients undergoing clipping of UIAs between January 2012 and December 2015. We reviewed the pre- and postoperative computed tomography (CT) images of each patient. Postoperative CI was defined as a new parenchymal hypodensity in the vascular territory of treated artery. Patient-specific, aneurysm-specific, and operative variables were analyzed as potential risk factors. Functional outcome at discharge was assessed with the modified Rankin Scale (mRS). Postoperative CI was found in 49 (12.6%) patients, 29 of whom manifested neurological deficits. The incidences of symptomatic stroke and silent CI were 7.5 and 5.2%, respectively. Multivariate analysis showed that larger aneurysm size and history of hypertension were significantly associated with CI. Disability (mRS > 2) rate was 42.9% among patients with CI, which was substantially higher than that among patients without (0.9%). In conclusion, the incidence of CI following clipping of UIAs was not low. Larger aneurysm size and history of hypertension were independent risk factors. Postoperative symptomatic stroke correlated with an extremely high risk of disability. Silent CI was seemingly nondisabling, but the possible cognitive consequence is pending.

Monitoring of cerebral blood flow and ischemia in the critically ill

Secondary ischemic injury is common after acute brain injury and can be evaluated with the use of neuromonitoring devices. This manuscript provides guidelines for the use of devices to monitor cerebral blood flow (CBF) in critically ill patients. A Medline search was conducted to address essential pre-specified questions related to the utility of CBF monitoring. Peer-reviewed recommendations were constructed according to the GRADE criteria based upon the available supporting literature. Transcranial Doppler ultrasonography (TCD) and transcranial color-coded duplex sonography (TCCS) are predictive of angiographic vasospasm and delayed ischemic neurological deficits after aneurysmal subarachnoid hemorrhage. TCD and TCCS may be beneficial in identifying vasospasm after traumatic brain injury. TCD and TCCS have shortcomings in identifying some secondary ischemic risks. Implantable thermal diffusion flowmetry (TDF) probes may provide real-time continuous quantitative assessment of ischemic risks. Data are lacking regarding ischemic thresholds for TDF or their correlation with ischemic injury and clinical outcomes.TCD and TCCS can be used to monitor CBF in the neurocritical care unit. Better and more developed methods of continuous CBF monitoring are needed to limit secondary ischemic injury in the neurocritical care unit.

Intraoperative laser speckle contrast imaging with retrospective motion correction for quantitative assessment of cerebral blood flow

Although multiple intraoperative cerebral blood flow (CBF) monitoring techniques are currently available, a quantitative method that allows for continuous monitoring and that can be easily integrated into the surgical workflow is still needed. Laser speckle contrast imaging (LSCI) is an optical imaging technique with a high spatiotemporal resolution that has been recently demonstrated as feasible and effective for intraoperative monitoring of CBF during neurosurgical procedures. This study demonstrates the impact of retrospective motion correction on the quantitative analysis of intraoperatively acquired LSCI images. LSCI images were acquired through a surgical microscope during brain tumor resection procedures from 10 patients under baseline conditions and after a cortical stimulation in three of those patients. The patient's electrocardiogram (ECG) was recorded during acquisition for postprocess correction of pulsatile artifacts. Automatic image registration was retrospectively performed to correct for tissue motion artifacts, and the performance of rigid and nonrigid transformations was compared. In baseline cases, the original images had [Formula: see text] noise across 16 regions of interest (ROIs). ECG filtering moderately reduced the noise to [Formula: see text], while image registration resulted in a further noise reduction of [Formula: see text]. Combined ECG filtering and image registration significantly reduced the noise to [Formula: see text] ([Formula: see text]). Using the combined motion correction, accuracy and sensitivity to small changes in CBF were improved in cortical stimulation cases. There was also excellent agreement between rigid and nonrigid registration methods (15/16 ROIs with [Formula: see text] difference). Results from this study demonstrate the importance of motion correction for improved visualization of CBF changes in clinical LSCI images.

Intraoperative neurophysiological monitoring of extracranial-intracranial bypass procedures

OBJECT

Intraoperative neurophysiological monitoring (IONM) represents an established tool in neurosurgery to increase patient safety. Its application, however, is controversial. Its use has been described as helpful in avoiding neurological deterioration during intracranial aneurysm surgery. Its impact on extracranial-intracranial (EC-IC) bypass surgery involving parent artery occlusion for the treatment of complex aneurysms has not yet been studied. The authors therefore sought to evaluate the effects of IONM on patient safety, the surgeon's intraoperative strategies, and functional outcome of patients after cerebral bypass surgery. Intraoperative neurophysiological monitoring results were compared with those of intraoperative blood flow monitoring to assess bypass graft perfusion.

METHODS

Compound motor action potentials (CMAPs) were generated using transcranial electrical stimulation in patients undergoing EC-IC bypass surgery. Preoperative and postoperative motor function was analyzed. To assess graft function, intraoperative flowmetry and indocyanine green fluorescence angiography were performed. Special care was taken to compare the relevance of electrophysiological and blood flow monitoring in the detection of critical intraoperative ischemic episodes.

RESULTS

The study included 31 patients with 31 aneurysms and 1 bilateral occlusion of the internal carotid arteries, undergoing 32 EC-IC bypass surgeries in which radial artery or saphenous vein grafts were used. In 11 cases, 15 CMAP events were observed, helping the surgeon to determine the source of deterioration and to react to it: 14 were reversible and only 1 showed no recovery. In all cases, blood flow monitoring showed good perfusion of the bypass grafts. There were no false-negative results in this series. New postoperative motor deficits were transient in 1 case, permanent in 1 case, and not present in all other cases.

CONCLUSIONS

Intraoperative neurophysiological monitoring is a helpful tool for continuous functional monitoring of patients undergoing large-caliber vessel EC-IC bypass surgery. The authors' results suggest that continuous neurophysiological monitoring during EC-IC bypass surgery has relevant advantages over flow-oriented monitoring techniques such as intraoperative flowmetry or indocyanine green-based angiography.

Chronic spinal subdural abscess mimicking an intradural-extramedullary tumor

Spinal subdural abscesses (SSA) are very rare disease. The etiologies of SSA are hematogenous spread, iatrogenic contamination, and local extension. Elevated WBC counts, ESR, and C-reactive protein are usually found in laboratory tests. But they are not sensitive indicators of SSA, especially chronic abscesses patient tend to have a less specific characteristic. We report the case of a healthy man with chronic subdural abscess referred to our hospital as an intradural-extramedullary (IDEM) tumor. The patient presented with voiding difficulty and pain in the back and left leg. In a contrast MRI scan, a rim-enhanced mass-like lesion was seen at the L5/S1 level. But adjacent ill-defined epidural fat enhancement that are unusual imaging manifestation for IDEM tumors was seen. He had no fever and normal WBC, ESR, and CRP. In addition, the patient had no previous infection history or other disease, but he did have an epidural block for back pain at another hospital 2 years previously. So, we repeated the MRI with a high-resolution 3-T scanner. The newly taken MR images in our hospital revealed a clear enlargement of lesion size compared to the previous MRI taken 1 week before in other hospital. We suspected a chronic spinal subdural abscess with recent aggravation and immediately performed surgical evacuation. In the surgical field, tensed dura was observed and pus was identified after opening the abscess capsule. Because chronic spinal subdural abscesses are difficult to diagnose, we could differentiate with IDEM tumor exactly and an exact history taking, contrast MRI are required.

Update on multimodality monitoring

Brain injury is a dynamic process marked by an initial damaging insult followed by a cascade of physical, electrical, and metabolic changes capable of resulting in further patient disability. These subclinical changes should be detected at a time when therapeutic intervention is most efficacious and preemptive. Multimodality monitoring is the practice by which a variety of brain monitors are utilized to deliver care, specific to the needs of the individual patient, in an attempt to minimize secondary injury and long-term disability. Intracranial pressure, continuous electroencephalography, brain tissue oxygen, cerebral microdialysis, cerebral blood flow, and jugular oximetry monitoring have been utilized to direct treatment of the critical ill neurologic and neurosurgical patient. Optimization of monitoring technique and protocol is an ongoing effort of intensivists in the field of neurocritical care.

Recurrent bacterial meningitis accompanied by a spinal intramedullary abscess

Bacterial meningitis is rarely complicated by an intradural spinal abscess, and recurrent meningitis is an uncommon presentation of a spinal intramedullary abscess. Here, we report a 63-year-old patient with recurrent meningitis as the first manifestation of an underlying spinal intramedullary abscess. To the best of our knowledge, no previous report has been issued on recurrent meningitis accompanied by a spinal intramedullary abscess in an adult. In this article, the pathophysiological mechanism of this uncommon entity is discussed and the relevant literature reviewed.

Monitoring techniques for prevention of procedure-related ischemic damage in aneurysm surgery

OBJECTIVE

To describe the application of intraoperative monitoring techniques during aneurysm surgery and to discuss the advantages and limitations of these techniques in prevention of postoperative neurologic deficits.

METHODS

Articles found in the literature through PubMed for the time frame 1980-2011 and the authors' personal files were reviewed.

RESULTS

Various techniques for detection of vascular insufficiency are available, including direct methods to measure cerebral blood flow and indirect methods to evaluate the integrity of neurologic pathways.

CONCLUSIONS

The choice of monitoring modality should be governed by the vessel and by the vascular territory most at risk during the planned procedure with proper awareness of the potential limits related to each technique. Aneurysm surgery monitoring should help to address issues of continuity and provide a morphologic and functional assessment. Although the use of monitoring devices is still not routine in aneurysm surgery and no standards have been established, combining different monitoring techniques is crucial to optimize aneurysm surgery and avoid or minimize complications.

Intracranial hemorrhage surgery on patients on mechanical circulatory support: a case series

BACKGROUND

Cardiac disease is the leading cause of death in the United States and late-stage heart failure is associated with a high level of morbidity and mortality. The ventricular assist devices and extracorporeal membrane oxygenators are the mainstay of mechanical circulatory support devices for the patients with extremely low cardiac output. However, they come at a price of significant risk factors, including intracranial hemorrhage. The incidence of intracranial hemorrhage on extracorporeal membrane oxygenators and on ventricular assist devices is 37% and 13% to 14%, respectively.

METHODS/RESULTS

The cases in this series focus on the risks of ICH and the decompressive craniotomies that were carried out on patients while they were on mechanical circulatory support. The intraoperative anesthetic management for patients on mechanical circulatory support for the noncardiothoracic anesthesiologist is highlighted.

CONCLUSIONS

The results of recent cardiothoracic surgery trials have led to an increase of surgical management instead of medical management in the treatment of heart failure. Although most agree with the immediate reversal of anticoagulation and antiplatelet therapy, there is no standard protocol for restarting anticoagulation or antiplatelet therapy after craniotomy in this population. The standard practices of resuscitation and ACLS including inotropes, vasopressors, and vasodilators (with the exception of chest compressions that can dislodge the devices), can be used as needed. The identification of cardiothoracic surgeons and perfusionists who are available for immediate assistance as and when required during the surgery and transportation is an important factor.

Continuous monitoring of absolute cerebral blood flow by near-infrared spectroscopy during global and focal temporary vessel occlusion

Treatment of intracranial aneurysms by surgical clipping carries a risk of intraoperative ischemia, caused mainly by prolonged temporary occlusion of cerebral arteries. The objective of this study was to develop a near-infrared spectroscopy (NIRS) technique for continuous monitoring of cerebral blood flow (CBF) during surgery. With this approach, cerebral hemodynamics prior to clipping are measured by a bolus-tracking method that uses indocyanine green as an intravascular contrast agent. The baseline hemodynamic measurements are then used to convert the continuous Hb difference (HbD) signal (HbD = oxyhemoglobin - deoxyhemoglobin) acquired during vessel occlusion to units of CBF. To validate the approach, HbD signal changes, along with the corresponding CBF changes, were measured in pigs following occlusion of the common carotid arteries or a middle cerebral artery. For both occlusion models, the predicted CBF change derived from the HbD signal strongly correlated with the measured change in CBF. Linear regression of the predicted and measured CBF changes resulted in a slope of 0.962 (R(2) = 0.909) following carotid occlusion and 0.939 (R(2) = 0.907) following middle cerebral artery occlusion. These results suggest that calibrating the HbD signal by baseline hemodynamic measurements provides a clinically feasible method of monitoring CBF changes during neurosurgery.

Measurement of Cortical Microcirculation During Intracranial Aneurysm Surgery by Combined Laser-Doppler Flowmetry and Photospectrometry

BACKGROUND:

Accidental vessel occlusion is one major risk of intracranial aneurysm surgery potentially causing cerebral ischemia. The intraoperative assessment of cerebral ischemia remains a technological challenge.

OBJECTIVE:

As a novel approach, cortical tissue integrity was monitored using simultaneous measurements of regional capillary-venous cerebral blood flow (rvCBF), oxygen saturation (Srvo2), and hemoglobin amount (rvHb) during aneurysm surgery.

METHODS:

Fifteen patients scheduled for aneurysm surgery of the anterior and posterior circulation were included. A fiber optic probe was placed on the cortex associated with the distal branch of the aneurysmatic vessel. Blinded measurements by combined laser-Doppler flowmetry (rvCBF) and photospectrometry (Srvo2, rvHb) were performed before and after surgical clipping or trapping of the aneurysm. Data were correlated with postoperative imaging and neurological outcome.

RESULTS:

Cortical measurements could be successfully performed in all patients. Significant increase (>25% change from baseline) or decrease (<25% change from baseline) of rvCBF, Srvo2, and rvHb was detectable in 33 to 46% of patients after surgical intervention. Severe decrease (>50% change from baseline) of all parameters or solitary of rvCBF was correlated to reduced cerebral perfusion and neurological deficits in 2 patients.

CONCLUSION:

Combined laser-Doppler flowmetry and photospectrometry provides real-time information on cortical microcirculation. Intraoperative alterations of parameters (rvCBF, Srvo2, rvHb) might reflect changes of cerebral tissue integrity during intracranial aneurysm surgery.

Incorporating a parenchymal thermal diffusion cerebral blood flow probe in bedside assessment of cerebral autoregulation and vasoreactivity in patients with severe traumatic brain injury

OBJECT

Cerebral autoregulation may be altered after traumatic brain injury (TBI). Recent evidence suggests that patients' autoregulatory status following severe TBI may influence cerebral perfusion pressure management. The authors evaluated the utility of incorporating a recently upgraded parenchymal thermal diffusion probe for the measurement of cerebral blood flow (CBF) in the neurointensive care unit for assessing cerebral autoregulation and vasoreactivity at bedside.

METHODS

The authors evaluated 20 patients with severe TBI admitted to San Francisco General Hospital who underwent advanced neuromonitoring. Patients had a parenchymal thermal diffusion probe placed for continuous bedside monitoring of local CBF ((loc)CBF) in addition to the standard intracranial pressure and brain tissue oxygen tension (P(bt)O(2)) monitoring. The CBF probes were placed in the white matter using a separate cranial bolt. A pressure challenge, whereby mean arterial pressure (MAP) was increased by about 10 mm Hg, was performed in all patients to assess autoregulation. Cerebral CO(2) vasoreactivity was assessed with a hyperventilation challenge. Local cerebral vascular resistance ((loc)CVR) was calculated by dividing cerebral perfusion pressure by (loc)CBF. Local cerebral vascular resistance normalized to baseline ((loc)CVR(normalized)) was also calculated for the MAP and hyperventilation challenges.

RESULTS

In all cases, bedside measurement of (loc)CBF using a cranial bolt in patients with severe TBI resulted in correct placement in the white matter with a low rate of complications. Mean (loc)CBF decreased substantially with hyperventilation challenge (-7 ± 8 ml/100 g/min, p = 0.0002) and increased slightly with MAP challenge (1 ± 7 ml/100 g/min, p = 0.17). Measurements of (loc)CBF following MAP and hyperventilation challenges can be used to calculate (loc)CVR. In 83% of cases, (loc)CVR increased during a hyperventilation challenge (mean change +3.5 ± 3.8 mm Hg/ml/100 g/min, p = 0.0002), indicating preserved cerebral CO(2) vasoreactivity. In contrast, we observed a more variable response of (loc)CVR to MAP challenge, with increased (loc)CVR in only 53% of cases during a MAP challenge (mean change -0.17 ± 3.9 mm Hg/ml/100 g/min, p = 0.64) indicating that in many cases autoregulation was impaired following severe TBI.

CONCLUSIONS

Use of the Hemedex thermal diffusion probe appears to be a safe and feasible method that enables continuous monitoring of CBF at the bedside. Cerebral autoregulation and CO(2) vasoreactivity can be assessed in patients with severe TBI using the CBF probe by calculating (loc)CVR in response to MAP and hyperventilation challenges. Determining whether CVR increases or decreases with a MAP challenge ((loc)CVR(normalized)) may be a simple provocative test to determine patients' autoregulatory status following severe TBI and helping to optimize CPP management.

Practical aspects of bedside cerebral hemodynamics monitoring in pediatric TBI

INTRODUCTION

Disturbances in cerebral hemodynamics may have a profound influence on secondary injury after traumatic brain injury (TBI), and many therapies in the neurocritical care unit may adversely affect cerebral blood flow. However, the clinician is often unaware of this when it occurs because practical methods for monitoring cerebral hemodynamics by the bedside have been lacking. Current imaging studies only provide a snapshot of the brain at one point in time, giving limited information about a dynamic condition.

DISCUSSION

This review will focus on key pathophysiological concepts required to understand changes in cerebral hemodynamics after TBI and the principles, potential benefits, and limitations of currently available bedside monitoring techniques, including transcranial Doppler, autoregulation, and local/regional cerebral blood flow.

Effect of nitrous oxide use on long-term neurologic and neuropsychological outcome in patients who received temporary proximal artery occlusion during cerebral aneurysm clipping surgery

BACKGROUND

The authors explored the relationship between nitrous oxide use and neurologic and neuropsychological outcome in a population of patients likely to experience intraoperative cerebral ischemia: those who had temporary cerebral arterial occlusion during aneurysm clipping surgery.

METHODS

A post hoc analysis of a subset of the data from the Intraoperative Hypothermia for Aneurysm Surgery Trial was conducted. Only subjects who had temporary arterial occlusion during surgery were included in the analysis. Metrics of short-term and long-term (i.e., 3 months after surgery) outcome were evaluated via both univariate and multivariate logistic regression analysis. An odds ratio (OR) greater than 1.0 denotes a worse outcome in patients receiving nitrous oxide.

RESULTS

The authors evaluated 441 patients, of which 199 received nitrous oxide. Patients receiving nitrous oxide had a greater risk of delayed ischemic neurologic deficits (i.e., the clinical manifestation of vasospasm) (OR, 1.78, 95% confidence interval [CI], 1.08-2.95; P = 0.025). However, at 3 months after surgery, there was no difference in any metric of gross neurologic outcome: Glasgow Outcome Score (OR, 0.67; CI, 0.44-1.03; P = 0.065), Rankin Score (OR, 0.74; CI, 0.47-1.16; P = 0.192), National Institutes of Health Stroke Scale (OR, 1.02; CI, 0.66-1.56; P = 0.937), or Barthel Index (OR, 0.69; CI, 0.38-1.25; P = 0.22). The risk of impairment on at least one test of neuropsychological function was reduced in those who received nitrous oxide (OR, 0.56; CI, 0.36-0.89; P = 0.013).

CONCLUSION

In this patient population, use of nitrous oxide was associated with an increased risk for the development of delayed ischemic neurologic deficits; however, there was no evidence of detriment to long-term gross neurologic or neuropsychological outcome.

Symptomatic and Silent Ischemia Associated With Microsurgical Clipping of Intracranial Aneurysms

Background and Purpose— Silent ischemic events are known to occur during diagnostic and interventional endovascular procedures between 10% and 69% of the time. The occurrence of silent and symptomatic ischemic events in the surgically treated population is not known, although atherosclerotic changes of intracranial vessels or within the aneurysms wall or neck area are seen often during surgery.

Methods— Patients with unruptured and ruptured intracranial aneurysms treated by microsurgical clipping were prospectively evaluated with MRI using diffusion-weighted imaging sequences before and within 24 hours after surgery. Patients were evaluated clinically before and after surgery. During surgery, the overall and maximal time of temporary occlusion as well as the total number of temporary and finally applied clips was noted. Diffusion-weighted images were analyzed with determination and characterization of diffusion-weighted imaging abnormalities.

Results— Thirty-six patients with 51 aneurysms were included. One symptomatic and 5 silent ischemic lesions were found in 5 patients. This represents a risk of silent ischemia of 9.8% per treated aneurysm and a risk of symptomatic stroke of 2%. The most significant risk factor in increasing order was: age ( P <0.05), presence of thrombus ( P <0.05), number of final clips applied ( P <0.05), number of temporary clips used ( P <0.01), total time of temporary clip occlusion ( P <0.001), and maximal time of temporary occlusion ( P <0.001).

Conclusions— The risk of silent and symptomatic ischemic events during microsurgical clipping of intracranial aneurysms seems to be low. Microsurgical clipping is safe and should continue to be strongly considered as a treatment option.

A new technique allowing prolonged temporary cerebral artery occlusion

OBJECT

Clipping of complex cerebral aneurysms often requires temporary vessel occlusion. The risk of stroke, however, increases exponentially with occlusion time. The authors hypothesized that prolonged temporary occlusion might be tolerated if the occluded vessels were perfused with cold physiological saline solution (CPSS). A low-flow perfusion rate would permit surgical manipulation of an aneurysm distal to the occlusion.

METHODS

To test this hypothesis, the authors temporarily occluded the middle cerebral artery (MCA) with an endovascular catheter in 6 rats. Three animals, the treatment group, were perfused with 5-ml CPSS/hour through the occluding endovascular catheter into the MCA, and the other 3 served as an ischemic control group. In both groups, the catheter was removed after 90 minutes of occlusion. The brain temperature was monitored with a stereotactically placed probe in the caudate-putamen in 2 separate experimental groups (11 animals).

RESULTS

Magnetic resonance imaging perfusion scanning during vessel occlusion confirmed similar reduction of cerebral blood flow during MCA occlusion in both the simple-occlusion and perfusion-occlusion groups. Magnetic resonance imaging diffusion scans performed 24 hours after temporary occlusion revealed infarcts in the ischemic control group of 138.3 +/- 28.0 mm(3) versus 9.9 +/- 9.9 mm(3) in the cold saline group (p < 0.005). A focal cooling effect during perfusion with CPSS was demonstrated (p < 0.05).

CONCLUSIONS

Prolonged temporary cerebral vessel occlusion can be tolerated using superselective CPSS perfusion through an occluding endovascular catheter into the ischemic territory. This technique could possibly be applied in neurosurgery practice to the management of complex intracranial aneurysms.

Evaluation of a bedside monitor of regional CBF as a measure of CO2 reactivity in neurosurgical intensive care patients

OBJECTIVE

Mild hyperventilation remains a key element in the management of elevated intracranial pressure. However, a harmful effect of hyperventilation on the development or deterioration of ischemic lesions has been shown in patients after severe head trauma. The objective of this study was to investigate the clinical feasibility and reliability of continuous monitoring of regional cerebral blood flow (rCBF) during mild hyperventilation using a thermodiffusion probe. CO2 reactivity was calculated. The measurement of the partial pressure of oxygen (PtiO2) in the cerebral tissue served as a reference parameter.

METHODS

An intraparenchymal intracranial pressure sensor, a multiparameter probe for determining the partial pressure of cerebral gases (pHti, PtiO2, PtiCO2), and a thermodiffusion probe for measuring rCBF were used in 10 intensive care patients. All patients were analgosedated and received pressure-controlled mechanical ventilation. Controlled mild hyperventilation was carried out on 2 consecutive days. CO2 reactivity was determined in relation to both CBF and PtiO2.

RESULTS

Controlled hyperventilation resulted in a rCBF reduction from 30+/-3 mL/100 g/min to 25+/-2.4 mL/100 g/min (-17%; P<0.05) on the first day of examination and 31+/-3.6 mL/100 g/min to 22+/-4.9 mL/100 g/min (-29%; P<0.05) on the second day. Likewise, mild hyperventilation resulted in a reduction of regional cerebral tissue oxygen partial pressure from 20+/-2.9 mm Hg to 15+/-4 (-25%; P<0.05) on the first day and 20+/-3.1 mm Hg to 14+/-1.5 mm Hg (-30%; P<0.05) on the second.

CONCLUSIONS

Continuous monitoring of regional CBF, using an intraparenchymally placed thermodiffusion probe, seems to be a simple and safe bedside technique. The promise of reliably monitoring and interpreting additional parameters such as PtiO2 and PtiCO2 warrants further investigation.

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.

Pyogenic intradural abscess: a case report

STUDY DESIGN

A case report of pyogenic intradural abscess is described.

OBJECTIVES

The rarity of the presentation and its successful management are discussed.

SUMMARY OF BACKGROUND DATA

Intradural abscesses are exceptionally rare.

METHOD

The abscess was drained by performing a posterior midline lumbar durotomy, and intravenous antibiotics were initiated.

RESULT

At the 1 year follow-up, the patient has made significant neurologic recovery.

CONCLUSION

Intradural pyogenic abscess secondary to chronic pyogenic spondylodiscitis is a rare manifestation. MRI is a vital component in diagnosis, which revealed key pathologic features within the dural sac as well as in the vertebral column. An emergency decompression and appropriate antibiotic regimen is the solution for a favorable outcome.

A new technique for the mapping of oxygen tension on the brain surface

Most measurements of oxygen tension (PO(2)) in the brain have been performed using oxygen microelectrodes. However, the insertion of microelectrodes into the brain per se causes cortical injury and hence could lead to erroneous PO(2) measurements. The recently developed "quenching lifetime method" requires the injection of fluorescent chemicals into the blood circulation. To address this issue, we tested the feasibility of our O(2)-sensitive fluorescent membrane technique in the rat brain, and visualized the spatial distribution of PO(2) on the brain surface as epifluorescent microscopic patterns. An O(2)-quenching fluorescence dye, tris (1,10-phenanthroline) Ru(2+), was immobilized in a highly gas-permeable, thin silicone-rubber film formed on a microscope coverslip. Unlike the original method, which was intended for transparent rat mesenteric tissue, any change in the redox state in the brain tissue will influence the optical measurement of PO(2). Thus, in the present study, the O(2)-sensing membrane was further coated with a thin opaque silicone-rubber to minimize this type of influence. This new method enabled us to visualize the PO(2) gradient on the rat brain without causing cortical injuries. In an ischemia/reperfusion model using Pulsinelli's four-vessel occlusion rats, the changes in the PO(2) were highly heterogeneous during the ischemic period and this heterogeneity, both temporal and spatial, was higher in the off-arteriolar area than in the peri-arteriolar area.

Future of brain support: multimodality monitoring

Multimodality monitoring of cerebral physiology encompasses the application of different monitoring techniques and integration of several measured physiological and biochemical variables into the assessment of brain metabolism, structure, perfusion and oxygenation status, in addition to clinical evaluation. 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 electroencephalography. Multimodality monitoring enables the immediate detection and prevention of acute neurological events, as well as appropriate intervention based on a patient’s individual disease state in the neurocritical care unit. Simultaneous real-time analysis of cerebral physiological, metabolic and cardiovascular parameters has broadened knowledge regarding complex brain pathophysiology and cerebral hemodynamics. Integration of this information allows for a more precise diagnosis and optimization of management of patients with brain injury.

Contemporary Management of Aneurysmal Subarachnoid Hemorrhage in Germany: Results of a Survey among 100 Neurosurgical Departments

OBJECTIVE

To assess the status quo of clinical management in patients with ruptured intracranial aneurysms in Germany. In addition to preferences in vascular treatment (i.e., surgical versus endovascular), the choice of diagnostics and treatment options in the pre- and postprocedural phase is emphasized.

METHODS

A standardized questionnaire was used in a postal survey. Participants were representatives of neurosurgical departments in Germany (n = 130, total number of departments). Comparisons between groups of respondents were tested using chi statistics (Fisher's exact test, two-sided).

RESULTS

The overall response rate was 77% (n = 100). Preoperative assessment is standard by computed tomography and conventional angiography. Currently, endovascular treatment options are available in 71% of all responding centers. On the basis of self estimates it is projected that 63% of all ruptured aneurysms are treated surgically, whereas 37% are treated endovascularly. For anterior circulation aneurysms, a significantly higher number of respondents commit to routine or frequent use of surgical techniques compared with endovascular treatment options (93 versus 52%, P < or = 0.05). In contrast, for posterior circulation aneurysms, endovascular treatment is preferred (24 versus 94%, P < or = 0.05). Acute posthemorrhagic hydrocephalus is treated by external ventricular drainage routinely (97%). Doppler sonography, monitoring of cerebral perfusion pressure, and electrophysiology are used by a significant number of respondents. Specific treatment of subarachnoid hemorrhage (SAH) patients includes calcium antagonists (70%), glucocorticosteroids (35%), and hemorheologic agents (30%).

CONCLUSION

In Germany, aneurysmal subarachnoid hemorrhage remains a disease in which standardization of clinical management is highest in preoperative diagnostics, intensive care unit monitoring, and postoperative treatment. With respect to currently published guidelines for subarachnoid hemorrhage treatment, compliance is moderate. Preferred treatment for anterior circulation aneurysms is predominantly surgical, whereas endovascular treatment options are preferentially used in aneurysms of the posterior circulation. This survey serves as a basis to analyze future developments in the management of subarachnoid hemorrhage more effectively and as an aid in finding a consensus in treatment both nationally and internationally.

Clampage vasculaire temporaire

In many situations, temporary artery occlusion is an integral component of aneurysm surgery. The use of temporary clip may allow safer and easier aneurysmal dissection and clipping. Several points, concerning the duration and overall risks of temporary occlusion and the method of choice for cerebral function monitoring have to be discussed.

MATERIAL AND METHODS

Non exhaustive review of neurosurgical literature.

DISCUSSION

Temporary clip application decreases the risk of intraoperative aneurysmal rupture. The analysis of data published in the literature showed that several questions remain open concerning the optimal method of neuroprotection and cerebral function monitoring, as well as the limit of occlusion duration. Other clinical trials are needed to assess the efficacy and safety of this technique.

Multimodal Monitoring in the Neurological Intensive Care Unit

BACKGROUND

Neurocritical care is a specialty that focuses on the critical care management of patients with catastrophic neurologic diseases. Brain ischemia and hypoxia are often central causes of brain damage in these patients. Until recently, the only methods widely accepted for monitoring in the neurological intensive care unit have been intracranial pressure and cerebral perfusion pressure monitoring. Recent developments in technology have resulted in several new monitoring techniques that can provide the neurointensivist with information, at the cellular level, that can help guide management.

REVIEW SUMMARY

The brain requires a continuous blood-borne supply of oxygen and glucose for normal metabolism. Ischemia occurs when supply is insufficient to meet the metabolic demand. Cerebral blood flow can now be directly monitored using laser Doppler or thermal diffusion techniques. Transcranial cerebral oximetry can estimate regional cerebral oxygen saturation, although the reliability is questionable. Jugular bulb oximetry can provide a global assessment of oxygen delivery, and consumption and brain tissue oxygen tension monitoring can provide a focal measurement of cerebral oxygenation. Intracerebral microdialysis can provide information about glucose metabolism and the overall health of the neuron.

CONCLUSIONS

New monitoring techniques can provide the neurointensivist with crucial information about brain physiology and metabolism. Combining these techniques ("multimodal monitoring") can produce a more accurate overall picture. This approach, along with new computer systems for integrating data at the bedside, may change the way patients with brain injury are monitored and treated in the future.

[Intraoperative detection of ischemic brain hypoxia using oxygen tissue pressure microprobes]

OBJECTIVE AND IMPORTANCE

Detection of intraoperative ischemic events could lead to the resolution of their cause and to the prevention of the definitive establishment of a postoperative infarct. We want to illustrate the possibilities that intraoperative monitoring of oxygen tissue pressure (PtiO2) in critical areas during a neurosurgical vascular procedure offers, enhancing its reliability and immediacy in obtaining information about tissue oxygenation status as a marker of ischemia in the vascular territory at risk.

CLINICAL PRESENTATION

We report the case of a 32 year-old male with a deep arteriovenous malformation (AVM) localised in the insular region. The patient had been previously treated with radiosurgery without achieving a satisfactory result.

INTERVENTION

AVM removal was performed through a transylvian transinsular approach. PtiO2 was monitorised at the temporal pole (reference area) and at the posterior temporal region (risk area). Both probes maintained close tissue oxygenation levels until the last stage of the AVM resection when, during the coagulation of a supposed afferent vessel, a brisk fall of the oxygen tissue pressure in the posterior temporal region was detected. An ischemic infarct in this area was observed postoperatively.

CONCLUSIONS

PtiO2 monitoring has a high reliability in the detection of intraoperative tissue hypoxia. Data obtained could lead to early identification of these events and, whatever possible, to resolve this situation preventing the definitive establishment of an ischemic infarct.

Regional cerebral blood flow monitoring in the diagnosis of delayed ischemia following aneurysmal subarachnoid hemorrhage

OBJECT

The goal of this study was to evaluate regional cerebral blood flow (rCBF) monitoring, performed using thermal-diffusion (TD) flowmetry, as a novel means for the bedside diagnosis of symptomatic vasospasm.

METHODS

Fourteen patients with high-grade subarachnoid hemorrhage (SAH) who underwent early clip placement for anterior circulation aneurysms were prospectively entered into the study. Thermal-diffusion microprobes were implanted into the white matter of vascular territories that were deemed at risk for developing symptomatic vasospasm. Data on arterial blood pressure, intracranial pressure, cerebral perfusion pressure, rCBF measurement obtained using a TD probe (TD-rCBF), cerebrovascular resistance (CVR), and blood flow velocities were collected at the patient's bedside. The diagnosis of symptomatic vasospasm was based on the manifestation of a delayed ischemic neurological deficit and/or a reduced territorial level of CBF as assessed using stable Xe-enhanced computerized tomography (CT) scanning in combination with vasospasm demonstrated by angiography. Bedside monitoring of TD-rCBF and CVR allowed the detection of symptomatic vasospasm. In the 10 patients with vasospasm the TD-rCBF decreased from 21 +/- 4 to 9 +/- 1 ml/100 g/min (mean +/- standard error of the mean), whereas in the four other patients the TD-rCBF value remained unchanged (mean TD-rCBF = 25 +/- 4 compared with 21 +/- 4 m/100 g/min). A comparison of the results of TD-rCBF and Xe-enhanced CT studies, as well as the calculation of sensitivities, specificities, predictive values, and likelihood ratios, identified a TD-rCBF value of 15 ml/100 g/min as a reliable cutoff for the diagnosis of symptomatic vasospasm. In addition, TD flowmetry was characterized by a more favorable diagnostic reliability than transcranial Doppler ultrasonography.

CONCLUSIONS

Thermal-diffusion flowmetry represents a promising method for the bedside monitoring of patients with SAH to detect symptomatic vasospasm. This is of major clinical interest for patients with high-grade SAH, who often cannot be assessed neurologically.

Monitoring of brain tissue oxygenation during aneurysm surgery: prediction of procedure-related ischemic events

OBJECT

The aim of this study was to evaluate the feasibility of monitoring brain tissue oxygenation (PO2) during aneurysm surgery for the detection of procedure-related ischemia.

METHODS

Between 1997 and 1998, PO2 was monitored prospectively in a cohort of 40 patients (42 recordings) during aneurysm surgery in the anterior circulation within the vascular territory of the aneurysm-bearing artery. The position of the probe used to measure oxygenation levels was verified on computerized tomography (CT) scanning on the 1st postoperative day. Because of the mislocation of one probe and the malfunction of another, data from only 38 patients (40 recordings) were suitable for analysis. Relative changes from baseline to absolute nadir values of intraoperative PO2 were correlated with simultaneously recorded somatosensory evoked potentials (SSEPs), and cardiovascular and ventilatory parameters. The frequency of ischemic events was evaluated with the aid of CT on the 1st postoperative day as a substitute parameter for intraoperative ischemia. Clinical outcome was evaluated 30 days postoperatively based on the Glasgow Outcome Scale. Except for three, all patients underwent surgery for treatment of a symptomatic aneurysm. Mean baseline PO2 was 23.9 mm Hg (range 2-67.2 mm Hg) before clip application. A relative decrease in PO2 (20% decrease in value compared with baseline) occurred in 12 patients and was a sensitive indicator for the risk of ischemia during temporary arterial occlusion, but was less predictive of nonocclusive ischemia (sensitivity 0.5; positive predictive value [PPV] 0.42; p > 0.05). Results of receiver operating characteristic analysis demonstrated a postclipping PO2 nadir of 15 mm Hg as a dichotomizing threshold for the prediction of ischemia. This threshold rendered an improved sensitivity (0.9) and PPV (0.56) for procedure-related ischemia (p = 0.0003). The results of utility analysis revealed this monitoring parameter to be clinically diagnostic. Only PO2 monitoring, and not SSEP at the tibial nerve, was predictive of ischemia within the anterior cerebral artery territory.

CONCLUSIONS

Using 15 mm Hg as a dichotomizing threshold, intraoperative PO2 monitoring enables one to identify patients at risk for procedure-related ischemia during aneurysm surgery and surpasses SSEP monitoring. This newly defined threshold based on intraoperative PO2 monitoring provides a basis for studies on treatments for procedure-related ischemia during aneurysm surgery.