Multimodal Monitoring in the Neurological Intensive Care Unit

Evaluation of Morlet Wavelet Analysis for Artifact Detection in Low-Frequency Commercial Near-Infrared Spectroscopy Systems

Regional cerebral oxygen saturation (rSO2), a method of cerebral tissue oxygenation measurement, is recorded using non-invasive near-infrared Spectroscopy (NIRS) devices. A major limitation is that recorded signals often contain artifacts. Manually removing these artifacts is both resource and time consuming. The objective was to evaluate the applicability of using wavelet analysis as an automated method for simple signal loss artifact clearance of rSO2 signals obtained from commercially available devices. A retrospective observational study using existing populations (healthy control (HC), elective spinal surgery patients (SP), and traumatic brain injury patients (TBI)) was conducted. Arterial blood pressure (ABP) and rSO2 data were collected in all patients. Wavelet analysis was determined to be successful in removing simple signal loss artifacts using wavelet coefficients and coherence to detect signal loss artifacts in rSO2 signals. The removal success rates in HC, SP, and TBI populations were 100%, 99.8%, and 99.7%, respectively (though it had limited precision in determining the exact point in time). Thus, wavelet analysis may prove to be useful in a layered approach NIRS signal artifact tool utilizing higher-frequency data; however, future work is needed.

Neurological effects of respiratory dysfunction

The respiratory and the nervous systems are closely interconnected and are maintained in a fine balance. Central mechanisms maintain strict control of ventilation due to the high metabolic demands of brain which depends on a continuous supply of oxygenated blood along with glucose. Moreover, brain perfusion is highly sensitive to changes in the partial pressures of carbon dioxide and oxygen in blood, which in turn depend on respiratory function. Ventilatory control is strictly monitored and regulated by the central nervous system through central and peripheral chemoreceptors, baroreceptors, the cardiovascular system, and the autonomic nervous system. Disruption in this delicate control of respiratory function can have subtle to devastating neurological effects as a result of ensuing hypoxia or hypercapnia. In addition, pulmonary circulation receives entire cardiac output and this may act as a conduit to transmit infections and also for metastasis of malignancies to brain resulting in neurological dysfunction. Furthermore, many neurological paraneoplastic syndromes can have underlying lung malignancies resulting in respiratory dysfunction. It is essential to understand the underlying mechanisms and the resulting manifestations in order to prevent and effectively manage the many neurological effects of respiratory dysfunction. This chapter explores the various neurological effects of respiratory dysfunction with focus on their pathophysiology, etiologies, clinical features and long-term neurological sequelae.

Comparison of Propofol and Sevoflurane on Cerebral Oxygenation Using Juglar Venous Oximetery (SjVo2) in Patients Undergoing Surgery for Traumatic Brain Injury

Background:

Traumatic brain injury (TBI) induces major insult to the normal cerebral physiology. The anesthetic agents may infrequently produce deleterious effects and further aggravate damage to the injured brain. This study was conducted to evaluate the effects of propofol and sevoflurane on cerebral oxygenation, brain relaxation, systemic hemodynamic parameters and levels of interleukin-6 (IL-6) in patients with severe TBI undergoing decompressive craniectomy.

Methods:

A prospective randomized comparative study was conducted on 42 patients undergoing surgery for severe TBI. Patients were randomized into two groups, Group P received propofol and Group S received sevoflurane for maintenance of anesthesia. All patients were induced with fentanyl, propofol, and vecuronium. The effect of these agents on cerebral oxygenation was assessed by jugular venous oxygen saturation (SjVO₂). Hemodynamic changes and quality of intraoperative brain relaxation were also assessed. The serum levels of IL-6 were quantitated using enzyme-linked immunosorbent assay technique.

Results:

SjVO₂ values were comparable and mean arterial pressure (MAP) was found to be significantly lower in Group P as compared to those in Group S (P < 0.05). Brain relaxation scores were comparable between the groups. The level of IL-6 decreased significantly at the end of surgery compared to baseline in patients receiving sevoflurane (P = 0.040).

Conclusions:

Cerebral oxygenation measured by SjVO₂ was comparable when anesthesia was maintained with propofol or sevoflurane. However, significant reduction in MAP by propofol needs attention in patients with severe TBI. The decrease in IL-6 level reflects anti-inflammatory effect and probable neuroprotective potential of propofol and sevoflurane.

Bioenergy Crisis in Coronavirus Diseases?

Coronavirus disease (COVID-19) has been declared as a pandemic by the World Health Organization (WHO).[...].

Multimodal Neuromonitoring in Neurocritical Care

Neuromonitoring is important for patients with acute brain injury. The bedside neurologic examination is standard for neurologic monitoring; however, a clinical examination may not reliably detect subtle changes in intracranial physiology. Changes found during neurologic examinations are often late signs. The assessment of multiple physiological variables in real time can provide new clinical insights into treatment decisions. No single monitoring modality is ideal for all patients. Simultaneous assessment of cerebral hemodynamics, oxygenation, and metabolism, such as in multimodal monitoring, allows an innovative approach to individualized patient care.

What lies downstream: Cellular oxygen delivery during hemodialysis

Hemodialysis has been linked to structural and functional damage to vital organs such as the brain and heart, possibly via repetitive intradialytic organ ischemia. There is increasing recognition that tissue ischemia can occur without changes in standard hemodynamic parameters such as blood pressure, leading to interest in more direct assessment of the adequacy of oxygen delivery to tissues. In this article, we discuss our current understanding of what happens to cellular oxygen delivery during hemodialysis: we review the underlying physiology, potential measurement techniques, and the clinical literature to date.

Objective cardiovascular assessment in the neonatal intensive care unit

Traditionally, cardiovascular well-being was essentially based on whether the mean blood pressure was above or below a certain value. However, this singular crude method of assessment provides limited insight into overall cardiovascular well-being. Echocardiography has become increasingly used and incorporated into clinical care. New objective modality assessments of cardiovascular status continue to evolve and are being evaluated and incorporated into clinical care. In this review article, we will discuss some of the recent advances in objective assessment of cardiovascular well-being, including the concept of multimodal monitoring. Sophisticated haemodynamic monitoring systems are being developed, including mechanisms of data acquisition and analysis. Their incorporation into clinical care represents an exciting next stage in the management of the infant with cardiovascular compromise.

Pathophysiological central nervous system changes in a porcine model of acetaminophen-induced acute liver failure

BACKGROUND

Critical care management of patients suffering from acute liver failure (ALF) continues to be challenging. Animal models studying the pathophysiological central nervous system alterations during the course of ALF provide an opportunity to improve diagnostic and therapeutic strategies. The aim of this study was to analyse the course of cerebral oxygenation in addition to conventional neuromonitoring during the course of acetaminophen-induced ALF.

METHODS

ALF was induced by intrajejunal acetaminophen administration in 20 German landrace pigs. All animals underwent invasive hemodynamic and neuromonitoring and were maintained under standardized intensive care support. Neuromonitoring consisted of continuous intraparenchymatous recording of intracranial pressure and brain partial oxygen pressure. Hemodynamic and ventilation parameters were continuously recorded; laboratory parameters were analysed every eight hours. Mean values were compared using the Wilcoxon test.

RESULTS

Acute liver failure occurred in all intoxicated animals after 23±2h, resulting in death due to ALF after further 15±2h. Continuous neuromonitoring was performed in all animals during the whole experiment without observing signs of intracranial haemorrhage. Two hours after manifestation of ALF an increase in brain tissue oxygen (PtiO2) was observed. Brain oxygenation stayed stable until nine hours before death. Intracranial pressure (ICP) remained basically at a plateau level until manifestation of ALF. In the following ten hours a linear and slow increase was observed until five hours before death, followed by a fast and continuous rise in ICP to a final level of 35±1mmHg. Cerebral perfusion pressure (CPP) began to decrease 25h prior to exitus, further decreasing to 18±2mmHg at the end of the experiment. A strong negative linear correlation was found between PtiO2 and ICP (R=0.97). Arterial partial pressure of oxygen (PaO2) below 100mmHg was associated with lower PtiO2 levels. Changes in arterial partial pressure of carbon dioxide (PaC02) did not influence PtiO2 values. Hemoglobin values below 7g/dl were associated with lower PtiO2 values.

CONCLUSIONS

The results of our experiments demonstrate that ICP and PtiO2 measurements indicate impending damage well before serious complications occur and their use should be considered in order to protect endangered brain function in the presence of acetaminophen-induced ALF.

BrainSignals Revisited: Simplifying a Computational Model of Cerebral Physiology

Multimodal monitoring of brain state is important both for the investigation of healthy cerebral physiology and to inform clinical decision making in conditions of injury and disease. Near-infrared spectroscopy is an instrument modality that allows non-invasive measurement of several physiological variables of clinical interest, notably haemoglobin oxygenation and the redox state of the metabolic enzyme cytochrome c oxidase. Interpreting such measurements requires the integration of multiple signals from different sources to try to understand the physiological states giving rise to them. We have previously published several computational models to assist with such interpretation. Like many models in the realm of Systems Biology, these are complex and dependent on many parameters that can be difficult or impossible to measure precisely. Taking one such model, BrainSignals, as a starting point, we have developed several variant models in which specific regions of complexity are substituted with much simpler linear approximations. We demonstrate that model behaviour can be maintained whilst achieving a significant reduction in complexity, provided that the linearity assumptions hold. The simplified models have been tested for applicability with simulated data and experimental data from healthy adults undergoing a hypercapnia challenge, but relevance to different physiological and pathophysiological conditions will require specific testing. In conditions where the simplified models are applicable, their greater efficiency has potential to allow their use at the bedside to help interpret clinical data in near real-time.

Windowed multitaper correlation analysis of multimodal brain monitoring parameters

Although multimodal monitoring sets the standard in daily practice of neurocritical care, problem-oriented analysis tools to interpret the huge amount of data are lacking. Recently a mathematical model was presented that simulates the cerebral perfusion and oxygen supply in case of a severe head trauma, predicting the appearance of distinct correlations between arterial blood pressure and intracranial pressure. In this study we present a set of mathematical tools that reliably detect the predicted correlations in data recorded at a neurocritical care unit. The time resolved correlations will be identified by a windowing technique combined with Fourier-based coherence calculations. The phasing of the data is detected by means of Hilbert phase difference within the above mentioned windows. A statistical testing method is introduced that allows tuning the parameters of the windowing method in such a way that a predefined accuracy is reached. With this method the data of fifteen patients were examined in which we found the predicted correlation in each patient. Additionally it could be shown that the occurrence of a distinct correlation parameter, called scp, represents a predictive value of high quality for the patients outcome.

Technological developments and future perspectives on graphene-based metamaterials: a primer for neurosurgeons

Graphene, a monolayer atomic-scale honeycomb lattice of carbon atoms, has been considered the greatest revolution in metamaterials research in the past 5 years. Its developers were awarded the Nobel Prize in Physics in 2010, and massive funding has been directed to graphene-based experimental research in the last years. For instance, an international scientific collaboration has recently received a €1 billion grant from the European Flagship Initiative, the largest amount of financial resources ever granted for a single research project in the history of modern science. Because of graphene's unique optical, thermal, mechanical, electronic, and quantum properties, the incorporation of graphene-based metamaterials to biomedical applications is expected to lead to major technological breakthroughs in the next few decades. Current frontline research in graphene technology includes the development of high-performance, lightweight, and malleable electronic devices, new optical modulators, ultracapacitors, molecular biodevices, organic photovoltaic cells, lithium-ion microbatteries, frequency multipliers, quantum dots, and integrated circuits, just to mention a few. With such advances, graphene technology is expected to significantly impact several areas of neurosurgery, including neuro-oncology, neurointensive care, neuroregeneration research, peripheral nerve surgery, functional neurosurgery, and spine surgery. In this topic review, the authors provide a basic introduction to the main electrophysical properties of graphene. Additionally, future perspectives of ongoing frontline investigations on this new metamaterial are discussed, with special emphasis on those research fields that are expected to most substantially impact experimental and clinical neurosurgery in the near future.

Physiological monitoring of the severe traumatic brain injury patient in the intensive care unit

Traumatic brain injury (TBI) is a major cause of morbidity and mortality worldwide. Despite encouraging animal research, pharmacological agents and neuroprotectants have disappointed in the clinical environment. Current TBI management therefore is directed towards identification, prevention, and treatment of secondary cerebral insults that are known to exacerbate outcome after injury. This strategy is based on a variety of monitoring techniques that include the neurological examination, imaging, laboratory analysis, and physiological monitoring of the brain and other organ systems used to guide therapeutic interventions. Recent clinical series suggest that TBI management informed by multimodality monitoring is associated with improved patient outcome, in part because care is provided in a patient-specific manner. In this review we discuss physiological monitoring of the brain after TBI and the emerging field of neurocritical care bioinformatics.

Position of probe determines prognostic information of brain tissue PO2 in severe traumatic brain injury

BACKGROUND

Monitoring brain tissue PO2 (PbtO2) is part of multimodality monitoring of patients with traumatic brain injury (TBI). However, PbtO2 measurement is a sampling of only a small area of tissue surrounding the sensor tip.

OBJECTIVE

To examine the effect of catheter location on the relationship between PbtO2 and neurological outcome.

METHODS

A total of 405 patients who had PbtO2 monitoring as part of standard management of severe traumatic brain injury were studied. The relationships between probe location and resulting PbtO2 and outcome were examined.

RESULTS

When the probe was located in normal brain, PbtO2 averaged 30.8 ± 18.2 compared with 25.6 ± 14.8 mm Hg when placed in abnormal brain (P < .001). Factors related to neurological outcome in the best-fit logistic regression model were age, PbtO2 probe position, postresuscitation motor Glasgow Coma Scale score, and PbtO2 trend pattern. Although average PbtO2 was significantly related to outcome in univariate analyses, it was not significant in the final logistic model. However, the interaction between PbtO2 and probe position was statistically significant. When the PbtO2 probe was placed in abnormal brain, the average PbtO2 was higher in those with a favorable outcome, 28.8 ± 12.0 mm Hg, compared with those with an unfavorable outcome, 19.5 ± 13.7 mm Hg (P = .01). PbtO2 and outcome were not related when the probe was placed in normal-appearing brain.

CONCLUSION

These results suggest that the location of the PbtO2 probe determines the PbtO2 values and the relationship of PbtO2 to neurological outcome.

Computerized data analysis of neuromonitoring parameters identifies patients with reduced cerebral compliance as seen on CT

OBJECTIVE

Computer-assisted analysis of neuromonitoring parameters may provide important decision-making support to the neurointensivist. A recently developed mathematical model for the simulation of cerebral autoregulation and brain swelling showed that in the case of an intact autoregulation but diminished cerebral compliance, a negative correlation between arterial blood pressure (ABP) and intracranial pressure (ICP) occurs. The goal of our study was to verify these simulation results in an appropriate patient cohort.

METHODS

Simultaneously measured data (ABP, ICP) of 6 patients (1 female; 5 male) with severe head trauma (n = 5) and stroke (n = 1) were used to calculate time resolved multitaper cross coherence. Further, we calculated the Hilbert phases of both signals, defining a negative correlation in case of a mean Hilbert phase difference greater than 130°. To validate the results, CT scans performed during the critical phases identified were analyzed.

RESULTS

In five out of six datasets we found long lasting events of negative correlation between ABP and ICP. In all patients, corresponding CT scans demonstrated changes in the intracranial compartment characterized by diminished cerebral compliance.

CONCLUSIONS

Our data indicate that complex multidimensional data analysis of neuromonitoring parameters can identify complication-specific data patterns with a high degree of accuracy.

Cerebral blood flow and the injured brain: how should we monitor and manipulate it?

PURPOSE OF REVIEW

Cerebral ischemia plays a major role in the pathophysiology of the injured brain, including traumatic brain injury and subarachnoid hemorrhage, thus improvement in outcome may necessitate monitoring and optimization of cerebral blood flow (CBF). To interpret CBF results in a meaningful way, it may be necessary to quantify cerebral autoregulation as well as cerebral metabolism. This review addresses the recent evidence related to the changes in CBF and its monitoring/management in traumatic brain injury.

RECENT FINDINGS

Recent evidence on the management of patients with traumatic brain injury have focused on the importance of cerebral autoregulation in maintaining perfusion, which necessitates the measurement of CBF. However, adequate CBF measurements alone would not indicate the amount of oxygen delivered to neuronal tissues. Technologic advancements in measurement devices have enabled the assessment of the metabolic state of the cerebral tissue for the purpose of guiding therapy, progress as well as prognostification.

SUMMARY

Current neurocritical care management strategies are focused on the prevention and limitation of secondary brain injury where neuronal insult continues to evolve during the hours and days after the primary injury. Appropriately chosen multimodal monitoring including CBF and management measures can result in reduction in mortality and morbidity.

Calibration of diffuse correlation spectroscopy with a time-resolved near-infrared technique to yield absolute cerebral blood flow measurements

A primary focus of neurointensive care is the prevention of secondary brain injury, mainly caused by ischemia. A noninvasive bedside technique for continuous monitoring of cerebral blood flow (CBF) could improve patient management by detecting ischemia before brain injury occurs. A promising technique for this purpose is diffuse correlation spectroscopy (DCS) since it can continuously monitor relative perfusion changes in deep tissue. In this study, DCS was combined with a time-resolved near-infrared technique (TR-NIR) that can directly measure CBF using indocyanine green as a flow tracer. With this combination, the TR-NIR technique can be used to convert DCS data into absolute CBF measurements. The agreement between the two techniques was assessed by concurrent measurements of CBF changes in piglets. A strong correlation between CBF changes measured by TR-NIR and changes in the scaled diffusion coefficient measured by DCS was observed (R(2) = 0.93) with a slope of 1.05 ± 0.06 and an intercept of 6.4 ± 4.3% (mean ± standard error).

Cerebral perfusion pressure thresholds for brain tissue hypoxia and metabolic crisis after poor-grade subarachnoid hemorrhage

BACKGROUND AND PURPOSE

To identify a minimally acceptable cerebral perfusion pressure threshold above which the risks of brain tissue hypoxia (BTH) and oxidative metabolic crisis are reduced for patients with subarachnoid hemorrhage (SAH).

METHODS

We studied 30 poor-grade SAH patients who underwent brain multimodality monitoring (3042 hours). Physiological measures were averaged over 60 minutes for each collected microdialysis sample. Metabolic crisis was defined as a lactate/pyruvate ratio>40 with a brain glucose concentration≤0.7 mmol/L. BTH was defined as PbtO2<20 mm Hg. Outcome was assessed at 3 months with the Modified Rankin Scale.

RESULTS

Multivariable analyses adjusting for admission Hunt-Hess grade, intraventricular hemorrhage, systemic glucose, and end-tidal CO2 revealed that cerebral perfusion pressure≤70 mm Hg was significantly associated with an increased risk of BTH (OR, 2.0; 95% CI, 1.2-3.3; P=0.007) and metabolic crisis (OR, 2.1; 95% CI, 1.2-3.7; P=0.007). Death or severe disability at 3 months was significantly associated with metabolic crisis (OR, 5.4; 95% CI, 1.8-16; P=0.002) and BTH (OR, 5.1; 95% CI, 1.2-23; P=0.03) after adjusting for admission Hunt-Hess grade.

CONCLUSIONS

Metabolic crisis and BTH are associated with mortality and poor functional recovery after SAH. Cerebral perfusion pressure levels<70 mm Hg was associated with metabolic crisis and BTH, and may increase the risk of secondary brain injury in poor-grade SAH patients.

Comparison of time-resolved and continuous-wave near-infrared techniques for measuring cerebral blood flow in piglets

A primary focus of neurointensive care is monitoring the injured brain to detect harmful events that can impair cerebral blood flow (CBF), resulting in further injury. Since current noninvasive methods used in the clinic can only assess blood flow indirectly, the goal of this research is to develop an optical technique for measuring absolute CBF. A time-resolved near-infrared (TR-NIR) apparatus is built and CBF is determined by a bolus-tracking method using indocyanine green as an intravascular flow tracer. As a first step in the validation of this technique, CBF is measured in newborn piglets to avoid signal contamination from extracerebral tissue. Measurements are acquired under three conditions: normocapnia, hypercapnia, and following carotid occlusion. For comparison, CBF is concurrently measured by a previously developed continuous-wave NIR method. A strong correlation between CBF measurements from the two techniques is revealed with a slope of 0.79±0.06, an intercept of -2.2±2.5 ml∕100 g∕min, and an R2 of 0.810±0.088. Results demonstrate that TR-NIR can measure CBF with reasonable accuracy and is sensitive to flow changes. The discrepancy between the two methods at higher CBF could be caused by differences in depth sensitivities between continuous-wave and time-resolved measurements.

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.

A novel lab-on-a-tube for multimodality neuromonitoring of patients with traumatic brain injury (TBI)

A novel lab-on-a-tube integrated with spirally-rolled pressure, temperature, oxygen and glucose microsensors is described for multimodal neuromonitoring of patients with traumatic brain injury. In addition to measuring various crucial parameters in real-time continuous formats, the newly developed device also works as an intraventricular catheter to lower the elevated intracranial pressure by draining cerebrospinal fluid.

Toward real-time continuous brain glucose and oxygen monitoring with a smart catheter

Oxygen and glucose biosensors have been designed, fabricated, characterized and optimized for real-time continuous monitoring on a new smart catheter for use in patients with traumatic brain injury (TBI). Oxygen sensors with three-electrode configuration were designed to achieve zero net oxygen consumption. Glucose sensors were based on the use of platinum nanoparticle-enhanced electrodes that were modified with polycation and glucose oxidase immobilized by chitosan matrix. An iridium oxide electrode was developed to work as a biocompatible reference electrode with enhanced durability and stability in the biological solutions. A study of the effect of temperature on oxygen sensor performance, and both temperature and oxygen effects on glucose sensor performance were accomplished to enhance their operative stability and provide useful information for in vivo applications. A new methodology for automatic correction of the temperature and oxygen dependence of biosensor outputs is demonstrated through programmed LabView software. In vitro experiments in both physiological and pathophysiological ranges (oxygen: 0-60 mmHg; glucose: 0.1-10 mM; temperature: 25-40 degrees C) with clinical samples of cerebrospinal fluid obtained from TBI patients have demonstrated stable measurements with enhanced accuracy, indicating the feasibility of the sensors for a real-time continuous in vivo monitoring.

RESUSCITATION AND CRITICAL CARE OF POOR-GRADE SUBARACHNOID HEMORRHAGE

AS OUTCOMES HAVE improved for patients with aneurysmal subarachnoid hemorrhage, most mortality and morbidity that occur today are the result of severe diffuse brain injury in poor-grade patients. The premise of this review is that aggressive emergency cardiopulmonary and neurological resuscitation, coupled with early aneurysm repair and advanced multimodality monitoring in a specialized neurocritical care unit, offers the best approach for achieving further improvements in subarachnoid hemorrhage outcomes. Emergency care should focus on control of elevated intracranial pressure, optimization of cerebral perfusion and oxygenation, and medical and surgical therapy to prevent rebleeding. In the postoperative period, advanced monitoring techniques such as continuous electroencephalography, brain tissue oxygen monitoring, and microdialysis can detect harmful secondary insults, and may eventually be used as end points for goal-directed therapy, with the aim of creating an optimal physiological environment for the comatose injured brain. As part of this paradigm shift, it is essential that aggressive surgical and medical support be linked to compassionate end-of-life care. As neurosurgeons become confident that comfort care can be implemented in a straightforward fashion after a failed trial of early maximal intervention, the usual justification for withholding treatment (survival with neurological devastation) becomes less relevant, and lives may be saved as more patients recover beyond expectations.

Perioperative uses of transcranial perfusion monitoring

Transcranial perfusion monitoring provides early warning of impending brain ischemia and may be used to guide management of cerebral perfusion and oxygenation. The monitoring options include measurement of intracranial and cerebral perfusion pressures, assessment of cerebral blood flow, and assessment of the adequacy of perfusion by measurement of cerebral oxygenation and brain tissue biochemistry. Some monitoring techniques are well established, whereas others are relatively new to the clinical arena and their indications are still being evaluated. Currently available monitoring techniques are reviewed and their appropriateness and application to the perioperative period is discussed.

Real-time monitoring of mitochondrial NADH and microcirculatory blood flow in the spinal cord

STUDY DESIGN

We developed a real-time, in vivo monitoring system for the evaluation of spinal cord viability in rats during spinal cord ischemia.

OBJECTIVE

The aim of the present study was to apply a real-time multiparametric monitoring system in a rat spinal cord model exposed to ischemia or mechanical compression.

SUMMARY OF BACKGROUND DATA

The evaluation of spinal cord integrity during spine surgeries is highly important, as it enhances the potential to prevent secondary irreversible damage to the spinal cord tissue. Mitochondrial NADH redox state is the most sensitive parameter for tissue oxygenation state and, together with microcirculatory blood flow, can estimate the metabolic status of the spinal cord tissue.

METHODS

We applied the Tissue Vitality Monitoring System (TVMS) that includes optical fibers for the simultaneous monitoring of the spinal cord blood flow (SCBF) using laser Doppler flowmetry, and the mitochondrial NADH fluorescence using the fluorometric technique. Additionally, systemic arterial blood pressure was measured. Two models involving the interruption of the spinal blood flow were tested: the occlusion of the abdominal aorta (ischemia) and spine mechanical compression.

RESULTS

The results clearly demonstrated the link between the level of ischemia and the viability state of the spinal tissue. When SCBF decreased, in both experimental models, mitochondrial NADH was elevated, while reperfusion was associated with NADH oxidation. Nevertheless, during the recovery phase, even though SCBF significantly increased (became hyperemic), no further oxidation of NADH was observed.

CONCLUSION

The monitoring of the mitochondrial function together with SCBF by the TVMS reflects the viability of the spinal cord tissue and, together with the conventional monitoring techniques, may help to evaluate the spine conditions, especially under surgical procedures involving the deterioration of the spinal cord blood supply.

Laboratory testing of the Pressio intracranial pressure monitor

OBJECTIVE

The Sophysa Pressio (Sophysa Ltd., Orsay, France) is a new intracranial pressure monitoring system. This study aimed to evaluate its accuracy and compare it with the popular Codman intracranial pressure transducer (Codman/Johnson & Johnson, Raynham, MA) in vitro.

METHODS

A computerized rig was used to test the Pressio and Codman transducers simultaneously. Properties that were tested included drift over 7 days, the effect of temperature on drift, frequency response, the accuracy of measurement of static and pulsatile pressures, and connectivity of the system.

RESULTS

Long-term (7 d) relative zero drift was less than 0.05 mmHg. The temperature drift was low (0.3 mmHg/207C). Absolute static accuracy was better than 0.5 mmHg over the range of 0 to 100 mmHg. Pulse waveform accuracy, relative to the Codman transducer, was better than 0.2 mmHg over the range of 1 to 20 mmHg. The frequency bandwidth of the Pressio transducer was 22 Hz. The Pressio monitor can transmit data directly to an external computer without the use of a pressure bridge amplifier.

CONCLUSION

The new Pressio transducer proved to be accurate for measuring static and dynamic pressure during in vitro evaluation.

Hypothermia effects on neurovascular coupling and cerebral metabolic rate of oxygen

Neuronal activation is accompanied by a local increase in cerebral blood flow (CBF) and in cerebral metabolic rate of oxygen (CMRO(2)), caused by neurovascular and neurometabolic coupling. Hypothermia is used as a neuroprotective approach in surgical patients and therapeutically after cardiac arrest or stroke. The effect of hypothermia on neurovascular coupling is of interest for evaluating brain function in these patients, but has not been determined so far. It is not clear whether functional hyperaemia actually operates at subnormal temperatures. In addition, decreasing brain temperature reduces spontaneous CMRO(2) following a known quantitative relationship (Q(10)). Q(10) determination may serve to validate a recently introduced CMRO(2) measurement approach relying on optical measurements of CBF and hemoglobin concentration. We applied this method to investigate hypothermia in a functional study of the somatosensory cortex. Anesthetized Wistar rats underwent surgical implantation of a closed cranial window. Using laser Doppler flowmetry and optical spectroscopy, relative changes in CBF and hemoglobin concentration were measured continuously. At the same time, an electroencephalogram (EEG) was recorded from the measurement site. By the application of ice packs, whole-body hypothermia was induced, followed by rewarming. Spontaneous EEG, CBF and CMRO(2) were measured, interleaved by blocks of electrical forepaw stimulation. The Q(10) obtained from spontaneous CMRO(2) changes of 4.4 (95% confidence interval 3.7-5.1) was close to published values, indicating the reliability of the CMRO(2) measurement. Lowering brain temperature decreased functional changes of CBF and CMRO(2) as well as amplitudes of somatosensory evoked potentials (SEP) to the same degree. In conclusion, neurovascular and neurometabolic coupling is preserved during hypothermia.

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.

Multimodal monitoring in the ICU: When could it be useful?

In the neurointensive care unit, neurologic monitoring is depended upon to signal the onset of neurologic decline. Many monitoring techniques such as intracranial pressure monitoring, cerebral perfusion pressure measurement, jugular venous oxygen saturation, transcranial Doppler ultrasound and continuous electroencephalogram are commonly practiced. Newer methods of monitoring include quantitative EEG, direct cerebral blood flow measurements, cerebral microdialysis, brain tissue oxygenation and cerebral near-infrared spectroscopy. When used in combination, as in multimodal monitoring, the goal is to overcome some of the disadvantages of each technique and to achieve a higher degree of accuracy in detecting secondary brain insults. However, such a large amount of data can be generated that such combinations have to be chosen carefully, or the monitoring data will not be able to be acted upon quickly enough to be of benefit to the patient.

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

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

Perioperative uses of transcranial perfusion monitoring

Transcranial perfusion monitoring provides early warning of impending brain ischemia and may be used to guide management of cerebral perfusion and oxygenation. The monitoring options include measurement of intracranial and cerebral perfusion pressures, assessment of cerebral blood flow, and assessment of the adequacy of perfusion by measurement of cerebral oxygenation and brain tissue biochemistry. Some monitoring techniques are well established, whereas others are relatively new to the clinical arena and their indications are still being evaluated. Currently available monitoring techniques are reviewed and their appropriateness and application to the perioperative period is discussed.

Monitoring cerebral oxygenation in traumatic brain injury

Ischemia is a common problem after traumatic brain injury (TBI) that eludes detection with standard monitoring. In this review we will discuss four available techniques (SjVO2, PET, NIRS and PbrO2) to monitor cerebral oxygenation. We present technical data including strengths and weaknesses of these systems, information from clinical studies and formulate a vision for the future.

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.

Applications of transcranial Doppler in the ICU: a review

OBJECTIVE

Transcranial Doppler (TCD) ultrasonography is a technique that uses a hand-held Doppler transducer (placed on the surface of the cranial skin) to measure the velocity and pulsatility of blood flow within the intracranial and the extracranial arteries. This review critically evaluates the evidence for the use of TCD in the critical care population.

DISCUSSION

TCD has been frequently employed for the clinical evaluation of cerebral vasospasm following subarachnoid haemorrhage (SAH). To a lesser degree, TCD has also been used to evaluate cerebral autoregulatory capacity, monitor cerebral circulation during cardiopulmonary bypass and carotid endarterectomies and to diagnose brain death. Technological advances such as M mode, colour Doppler and three-dimensional power Doppler ultrasonography have extended the scope of TCD to include other non-critical care applications including assessment of cerebral emboli, functional TCD and the management of sickle cell disease.

CONCLUSIONS

Despite publications suggesting concordance between TCD velocity measurements and cerebral blood flow there are few randomized controlled studies demonstrating an improved outcome with the use of TCD monitoring in neurocritical care. Newer developments in this technology include venous Doppler, functional Doppler and use of ultrasound contrast agents.

Monitoring of head injured patients

PURPOSE OF REVIEW

This article reviews recent advances in multimodality monitoring of patients following severe head injury during the period of 2004-2005.

RECENT FINDINGS

Whilst intracranial pressure measurement remains the cornerstone of neuromonitoring, analysis of the intracranial pressure waveform provides additional information, which may help guide treatment and predict outcome. Non-invasive detection of intracranial hypertension and assessment of cerebral perfusion pressure and autoregulation is the focus of ongoing research. Although jugular venous saturation monitoring remains a useful method for detecting global hypoperfusion its sensitivity to regional ischaemia is low. Brain tissue oxygen monitoring overcomes this deficiency and sheds new light on the pathophysiology of cerebral ischaemia following brain injury. Further studies are required to define ischaemic thresholds and their association with outcome. Extracellular brain pH has been recently linked to outcome and further studies are required to establish the role of pH regulation. Monitoring of brain metabolism using a cerebral microdialysis continues to develop its niche in clinical neuromonitoring, although it currently remains a research tool.

SUMMARY

Multimodality neuromonitoring plays an important role in managing patients with severe head injury. It helps guide treatment, provides prognostic information and explores the pathophysiology of evolving brain injury.