Antegrade versus retrograde cerebral protection in repair of acute ascending aortic dissection.

The objective of this study was to compare retrograde with antegrade cerebral protection during acute aortic dissection repair using cerebral oximetry measurements. Fifty consecutive acute ascending aortic dissection repairs were analyzed. Cerebral oximetry data were collected for 41 of 50. Eight patients who had antegrade cerebral protection alone and 29 of 41 had retrograde cerebral protection alone. The per cent change in cerebral oximetry values during deep hypothermic circulatory arrest from baseline and from prearrest values was compared for the two groups using Student t test. The per cent change from baseline for the antegrade patients was: right 13.8 per cent and left -2.5 per cent; the per cent change from baseline for retrograde patients was: right 0.8 per cent and left 0.2 per cent (P values 0.216 and 0.725, respectively). The per cent change from the prearrest value for the antegrade patients was: right -12 per cent and left -15 per cent; the per cent change from prearrest for retrograde patients was: right -15 per cent and left -16 per cent (P values 0.514 and 0.956, respectively). No compelling evidence for an advantage to either antegrade or retrograde cerebral perfusion was detected. Further study with a focus on neurologic outcomes is warranted.

American Society of Neurophysiologic Monitoring and American Society of Neuroimaging joint guidelines for transcranial doppler ultrasonic monitoring.

The American Society of Neurophysiologic Monitoring (ASNM) and American Society of Neuroimaging (ASN) Guidelines Committees formed a joint task force and developed guidelines to assist in the use of transcranial Doppler (TCD) monitoring in the surgical and intensive care settings. Specifically, these guidelines: (1) delineate the objectives of TCD monitoring; (2) characterize the responsibilities and behaviors of the sonographer during monitoring; (3) describe methodological and ethical issues uniquely relevant to monitoring. The ASNM and ASN strongly support the positions that (1) acquisition and interpretation of intraoperative TCD ultrasonograms be performed by qualified individuals, (2) service providers define their diagnostic criteria and develop on-going self-validation programs of these performance criteria in their practices. We agree with the guidelines of other professional societies regarding the technical and professional qualifications of individuals responsible for TCD signal acquisition and interpretation (Class III evidence, Type C recommendation). On the basis of current clinical literature and scientific evidence, TCD monitoring is an established monitoring modality for the: (1) assessment of cerebral vasomotor reactivity and autoregulation; (2) documentation of the circle of Willis functional status; (3) identification of cerebral hypo- and hyperperfusion, recanalization and re-occlusion; and (4) detection of cerebral emboli (Class II and III evidence, Type B recommendation).

Guidelines for intraoperative neuromonitoring using raw (analog or digital waveforms) and quantitative electroencephalography: a position statement by the American Society of Neurophysiological Monitoring.

BACKGROUND CONTEXT: Electroencephalography (EEG) is one of the oldest and most commonly utilized modalities for intraoperative neuromonitoring. Historically, interest in the EEG patterns associated with anesthesia is as old as the discovery of the EEG itself. The evolution of its intraoperative use was also expanded to include monitoring for assessing cortical perfusion and oxygenation during a variety of vascular, cardiac, and neurosurgical procedures. Furthermore, a number of quantitative or computer-processed algorithms have also been developed to aid in its visual representation and interpretation. The primary clinical outcomes for which modern EEG technology has made significant intraoperative contributions include: (1) recognizing and/or preventing perioperative ischemic insults, and (2) monitoring of brain function for anesthetic drug administration in order to determine depth of anesthesia (and level of consciousness), including the tailoring of drug levels to achieve a predefined neural effect (e.g., burst suppression). While the accelerated development of microprocessor technologies has fostered an extraordinarily rapid growth in the use of intraoperative EEG, there is still no universal adoption of a monitoring technique(s) or of criteria for its neural end-point(s) by anesthesiologists, surgeons, neurologists, and neurophysiologists. One of the most important limitations to routine intraoperative use of EEG may be the lack of standardization of methods, alarm criteria, and recommendations related to its application. Lastly, refinements in technology and signal processing can be expected to advance the usefulness of the intraoperative EEG for both anesthetic and surgical management of patients. OBJECTIVE: This paper is the position statement of the American Society of Neurophysiological Monitoring. It is the practice guidelines for the intraoperative use of raw (analog and digital) and quantitative EEG. METHODS: The following recommendations are based on trends in the current scientific and clinical literature and meetings, guidelines published by other organizations, expert opinion, and public review by the members of the American Society of Neurophysiological Monitoring. This document may not include all possible methodologies and interpretative criteria, nor do the authors and their sponsor intentionally exclude any new alternatives. RESULTS: The use of the techniques reviewed in these guidelines may reduce perioperative neurological morbidity and mortality. CONCLUSIONS: This position paper summarizes commonly used protocols for recording and interpreting the intraoperative use of EEG. Furthermore, the American Society of Neurophysiological Monitoring recognizes this as primarily an educational service.

Near-infrared spectroscopy as a guide for an intermittent cerebral perfusion strategy during neonatal circulatory arrest.

In view of the existing controversy concerning the best perfusion technique during deep hypothermic circulatory arrest (DHCA) for neonatal heart operations, we examined intraoperative rSO2 to help define an optimal interval for an intermittent antegrade cerebral perfusion (IACP) strategy. Records of patients undergoing stage 1 palliation (S1P) and repair of total anomalous pulmonary venous return (rTAPVR) from 1996 to 2004 were reviewed. A total of 16 patients were identified (11 S1P, 5 rTAPVR) with complete data and long periods of DHCA. A decline in rSO2 of either 20% or below a value of 50 was considered significant. The rSO2 for all patients was evaluated after 5, 10, 15, and 20 minutes of DHCA for significant cerebral desaturation. The average rSO2 at the start of DHCA ranged from 45 to 89 for S1P and 35-86 for rTAPVR. Significant cerebral desaturation was observed in 25%-31% of patients after 5 minutes; 42%-44% of patients after 10 minutes; 58%-69% after 15 minutes; and 75%-83% after 20 minutes. Each neonate has a unique baseline cerebral saturation. Also, the response to DHCA varies among subjects as the rate of decrease of rSO2 was not uniform. Universally applying the same interval after which to perfuse the brain permits significant cerebral desaturation in a large percentage of patients. Cerebral oximetry may provide a guide for developing an individualized cerebral perfusion strategy.

Alternative surgical strategy for the treatment of a mycotic aortic arch aneurysm.

We report the case of a 69-year-old man who presented with a symptomatic mycotic aneurysm of the aortic arch. Diagnosis was confirmed by positron emission tomography and by blood cultures positive for Salmonella species. A complete resection of the aortic arch process was performed via left thoracotomy using a cryopreserved aortic homograft and normothermic left heart bypass. The left-sided cerebral vessels were clamped, and adequacy of collateral left brain flow and oxygenation was confirmed by neurophysiologic monitoring. Using this less-invasive operative strategy, we avoided the risks inherent to deep hypothermic circulatory arrest and the use of prosthetic materials.

Cerebral oximetry improves detection of sickle cell patients at risk for nocturnal cerebral hypoxia.

We previously used cerebral oximetry to identify low cerebral venous oxygen saturation in waking children with sickle cell disease (SCD). Because arterial oxyhemoglobin desaturation is common during sleep in SCD patients, this study compared both waking and sleeping systemic arterial and cerebral venous oxygenation dynamics in children with and without SCD. Seventeen African-American (AA) children with homozygous SCD [8 (4-15) years; 29% male; normal transcranial Doppler velocities] were compared with a control cohort (CON) comprised of six healthy AA children [9 (4-16) years, 33% male]. Standard all-night polysomnographic recordings were performed, including measurement of arterial oxygen saturation by pulse oximetry (SpO(2)). Regional cerebral oxygen saturation (rSO(2)) was measured non-invasively with cerebral oximetry. Intra-cohort comparisons examined the influence of sleep on SpO(2) and rSO(2) in the subjects. Inter-cohort comparisons of SpO(2), rSO(2,) and the rSO(2)/SpO(2) ratio assessed the impact of SCD on systemic and cerebral oxygenation during wakefulness and sleep. Cohort differences in SpO(2) were not statistically significant in either wakefulness or sleep. However, only in the SCD cohort was the magnitude of SpO(2) change statistically significant (P = 0.002). In contrast, both waking and sleep rSO(2) cohort median values did differ significantly [awake: CON 76 (67-86) vs. SCD 62 (58-71), P = 0.01; sleep: CON 65 (60-77) vs. SCD 55 (48-61), P = 0.01)]. The waking rSO(2)/SpO(2) ratio was also significantly lower in the SCD group [CON 0.78 (0.68-0.88) vs. SCD of 0.66 (0.61-0.72); P = 0.015]. During sleep, the ratio was also significantly lower in the SCD group [CON 0.71 (0.66-0.81) vs. SCD 0.59 (0.52-0.65); P = 0.011]. Our findings suggest that SCD patients may be at increased risk of cerebral hypoxia during both wakefulness and sleep.

A prospective analysis of intraoperative electromyographic monitoring of posterior cervical screw fixation.

OBJECTIVE: This is a prospective study of 26 patients undergoing posterior cervical spine instrumentation with lateral mass or pedicle screws to determine the correlation between intraoperative screw stimulation thresholds and the position of posterior cervical lateral mass and pedicle screws. METHODS: One hundred forty-seven posterior cervical screws (122 lateral mass screws and 25 C7 pedicle screws) in 26 patients were electrically stimulated intraoperatively and stimulation thresholds recorded. Computed tomography (CT) scans were taken postoperatively and were evaluated independently to assess screw position. Electromyographic (EMG) thresholds and CT data were compared to assess the accuracy of the EMG screw stimulation technique in detecting screw malposition. RESULTS: Intraoperative electrical stimulation was accurate in verifying screw position. A stimulation threshold of 15 mA provided a 99% positive predictive value (89% sensitivity, 87% specificity) that the screw was within the lateral mass or pedicle. Stimulation values of 10-15 mA provided a 13% predictive value (66% sensitivity, 90% specificity) that the screw was within the lateral mass or pedicle. A stimulation value of <10 mA provided a 100% predictive value that the screw was malpositioned (70% sensitivity, 100% specificity). CONCLUSIONS: Intraoperative evoked EMG monitoring is a valuable tool in posterior cervical instrumentation using lateral mass and pedicle screws. Stimulation thresholds in this study correlated with screw position. Stimulation values of >15 mA reliably predict acceptable screw position. Values between 10 and 15 mA are generally associated with acceptable screw position, although exploration is recommended. Values below 10 mA are associated with screw malposition and warrant exploration, repositioning, and possible removal.

Protective effect of neuromonitoring during cardiac surgery.

This study was a retrospective examination of the influence of multimodality neuromonitoring on the incidence of serious brain injury associated with a common type of adult cardiac surgery, coronary artery bypass grafting (CABG). Multichannel EEG, cerebral oximetry, and transcranial Doppler ultrasound were used to detect and correct imbalances in cerebral perfusion and oxygenation. Imbalances were detected in 59% of the cases and successfully corrected in all but 2%. In the absence of neuromonitoring, the expected incidence of serious brain injury is 6.1%. With neuromonitoring, the actual observed incidence was 3.0% (P = 0.03). The apparent improvement can be attributed primarily to a reduction in the number of nonembolic diffuse injuries.

Cerebral oximetry for cardiac and vascular surgery.

The technology of transcranial near-infrared spectroscopy (NIRS) for the measurement of cerebral oxygen balance was introduced 25 years ago. Until very recently, there has been only occasional interest in its use during surgical monitoring. Now, however, substantial technologic advances and numerous clinical studies have, at least partly, succeeded in overcoming long-standing and widespread misunderstanding and skepticism regarding its value. Our goals are to clarify common misconceptions about near-infrared spectroscopy and acquaint the reader with the substantial literature that now supports cerebral oximetric monitoring in cardiac and major vascular surgery.

Assessment of cerebral tissue oxygenation in patients with sickle cell disease: effect of transfusion therapy.

This study used spatially resolved transcranial near-infrared spectroscopy (NIRS) to compare brain tissue oxygenation in sickle cell disease (SCD) patients with that of healthy children. In addition, NIRS was used to measure the dynamic response of cerebral oxygen balance to erythrocytapheresis. Transcranial NIRS measurements were obtained from 25 children with SCD who were not receiving transfusion or hydroxyurea therapy (NT-SCD). These patients were divided into two subgroups, those with mild (n = 10) or severe (n = 15) SCD symptoms. In addition, NIRS measurements were performed in 16 SCD patients with severe disease maintained on long-term erythrocytapheresis (T-SCD) and in 35 control children. The lowest mean brain tissue oxygen saturation occurred in the NT-SCD subgroup with severe symptoms (48 +/- 9%; P < 0.001 vs. control). NT-SCD patients with mild symptoms had higher saturation (62 +/- 8%; P < 0.001 vs. control), while the highest appeared in the control group (72 +/- 7%). In T-SCD patients, however, brain tissue oxygen saturations were higher than severely symptomatic NT-SCD children and similar to mildly symptomatic NT-SCD children (65 +/- 7%). Non-invasive measurements of brain tissue oxygenation with NIRS revealed that abnormal oxygen saturation levels in SCD patients correlated with the severity of their clinical manifestations. Additionally, cerebral oxygen balance seems to be favorably affected by erythro-cytapheresis.

New neurophysiology and central nervous system dysfunction.

PURPOSE OF REVIEW: The goal of this article is to summarize very recent technologic advances in neurophysiologic monitoring and to illustrate their potential benefit to critical care medicine. RECENT FINDINGS: Simplified, computer-processed electroencephalography devices now permit cost-effective, long-term critical care monitoring. They may be used alone to objectively assess sedation or coma level. In addition, these monitors serve as screening tools for more detailed electrophysiologic characterization of cortical dysfunction resulting from seizures, ischemia, or hypoxia. Somatosensory potentials broaden these capabilities to the entire neuraxis, whereas long-latency auditory evoked potentials facilitate measurement of changes in vigilance and cognition. Motor evoked potentials offer a sensitive and reliable method to determine the function of descending motor pathways in uncooperative or unresponsive patients. They may also yield a new measure of cortical excitability. New developments with transcranial Doppler ultrasonography promise noninvasive measures of cerebral perfusion pressure and particulate embolization. Near-infrared spectroscopy appears to enable noninvasive measurement of regional tissue oxygenation in both the brain and spinal cord. SUMMARY: When used together, these continuous measures of synaptic function, cerebral perfusion, and oxygenation give the clinician a vast amount of otherwise unobtainable information regarding the functional status of the central nervous system.

Multi-modality neurophysiologic monitoring for cardiac surgery.

BACKGROUND: A high percentage of patients who undergo cardiac surgery experience persistent cognitive decline. The costs to insurers from brain injury associated with cardiac surgery is enormous. Furthermore, the same processes that injure the brain also appear to cause dysfunction of other vital organs. Therefore, there are great clinical and economic incentives to improve brain protection during cardiac surgery. This article discusses the methods of monitoring neurophysiologic function during heart surgery, including electroencephalography (EEG), near-infrared spectroscopy (NIRS), transcranial doppler (TCD) ultrasound, and cerebral oximetry, and analyzes the effectiveness of multi-modality neuromonitoring. METHODS: Neurophysiologic studies have implicated hypoperfusion and dysoxygenation as major causative factors for brain injury during cardiac surgery. Since these functional disturbances are often detectable and correctable, there is a new impetus to examine the role of neurophysiologic monitoring in brain protection. We have used a retrospective, single-surgeon case-control study to examine the influence on outcome following myocardial revascularization of multi-modality neuromonitoring, with modalities that include 4-channel EEG, bilateral cerebral oximetry, and single channel TCD. RESULTS: The majority of noteworthy functional disturbances detected by neuromonitoring can be corrected by simple adjustments in perfusion, oxygenation, or anesthetic administration. In more recalcitrant cases, pharmacological neuroprotection has proven effective. In addition to the substantial reductions in length of hospital stay, costs, and neurologic complications, the results of neuromonitoring suggest a possible benefit to other vital organ systems. Future studies of neuromonitoring efficacy should not overlook these important accessory benefits. CONCLUSION: This study provides the clearest evidence to date that multi-modality neuromonitoring for cardiac surgery is safe, clinically beneficial, and cost-effective. Although neuromonitoring involves negligible risk and modest costs, it's benefits for patient outcome and cost control are substantial.

Monitoring Seizure Duration During Electroconvulsive Therapy.

Three alternative monitoring methods for assessing the duration of seizures during electroconvulsive therapy were studied. The mean integrated amplitude of the electroencephalogram, facial muscle electromyogram, and "cuff method" were compared with the reference single-channel unprocessed electroencephalogram in 78 sessions with 17 patients. The measures of seizure duration differed significantly (p < 0.001). The mean integrated electroence phalographic amplitude differences were small and an artifact of the sampling procedure. Larger, but clinically unimportant, discrepancies were obtained with the facial electromyogram amplitude. In contrast, there were marked differences between the electroencephalogram and the "cuff method," which suggest that the latter technique may be of limited usefulness.