Search

Objective: Determine the effects of serial episodes of anoxia in an in vitro peripheral nerve preparation., Methods: The nerve action potential (NAP) from rat sciatic nerve was recorded during 5 cycles of anoxia and reperfusion. Multiple NAP parameters were analyzed as well as stimulus response curves., Results: The amplitude of the NAP declined to half baseline in 865 s on the first cycle of anoxia and recovered to half baseline during recovery in 470 s. These times increased with successive cycles of anoxia. The current required to produce a half maximal NAP showed a variable initial decrease before increasing with anoxia. The paired-pulse response showed a decline at 2-3 ms interstimulus interval during anoxia but was less dependent of interstimulus interval during recovery. NAP amplitude and velocity decrease over successive cycles of anoxia at a rate greater than in the absence of anoxia., Conclusions: The NAP declines slowly when peripheral nerve is exposed to anoxia but returns at least twice as quickly when re-exposed to oxygen. Short periods of anoxia produce long lasting changes in the nerve suggesting greater resistance to anoxia. With serial episodes of anoxia there is gradual NAP amplitude reduction and increase in duration and latency., Significance: Anoxic-preconditioning appears in isolated peripheral nerve., (Copyright © 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Although in-vitro peripheral nerve preparations are useful tools in studying the physiology of axons, their function invariably declines gradually over time. This study investigates the effects of age and temperature on both the in-vitro stability of rat sciatic nerve and the response of the nerve to acute hypoxia. Comparison of the effects of age and temperature in these two models can clarify a possible connection between the hypoxic response and the stability of in-vitro preparations. In in-vitro preparations, the amplitude of the nerve action potential (NAP) declines more rapidly at high temperatures than low temperatures. At high temperatures, the decline in NAP amplitude is faster in nerves taken from younger animals while at low temperatures, the NAP amplitude is the same in both young and old animals. This dependence is similar to that of the time required for the NAP to reach 50% of its baseline value after recovery from hypoxia and the NAP amplitude after a 1.5-h period of hypoxia. It is different from the behavior of the time required for the NAP to drop to 50% of its initial value during hypoxia since the effects of temperature and age on this parameter are independent. This provides evidence of a relationship between the injury caused by hypoxia and the changes that occur after transection. However, since the effect of age on the changes in conduction velocity after transection and after hypoxia are different, the two processes must differ in the response of myelin to the metabolic changes in these conditions., ((c) 2010 Elsevier B.V. All rights reserved.)

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.

Objective: Determine whether EEG findings could be used as an independent prognostic indicator of outcomes in a general patient population., Methods: A large electronic medical record was used to merge the results of EEG studies with the results of medical evaluations including: medications prescribed, medical diagnoses, blood test results, imaging results, and outcomes in 3193 patients. Univariable and multivariable analyses were undertaken to determine whether the EEG had a role in predicting outcomes independent of other factors in a clinic population., Results: Patients with abnormal EEG's had significantly higher mortalities, greater cost of healthcare and more evaluation visits than patients with normal EEG's in every age range independent of the presence other medical conditions. The costs associated with caring for a patient with an abnormal EEG were roughly three times that of a patient with a normal EEG. The risk of death in the multivariable analysis was 3.7 times higher in patients with an abnormal EEG than in patients with a normal EEG., Conclusions: In addition to its traditional diagnostic implications, the EEG may convey information about general level of illness and the cost of caring for patients., Significance: Certain EEG findings may identify high risk patients and thus may open the door to possible interventions.

Background: Although the neurologic status of patients undergoing cardiac operations has been well studied at other times, there are few studies of neurologic status in the immediate postoperative state. This study used standardized nursing neurologic evaluations to describe the sequence of neurologic changes during the first few hours after cardiac operations and the factors that influence them., Methods: In this prospective study, patients arriving in the intensive care unit after cardiac operations were serially assessed using the using the Neurologic Intensive Care Evaluation (NICE) for up to 24 hours postoperatively. The study evaluated the effects on outcome of various preoperative and intraoperative variables, as well as the NICE scores., Results: Recovery of brainstem reflexes occurred at 1.4 +/- 1.4 hours, and the fully alert state occurred at a mean of 5.1 +/- 3.8 hours after admission to the intensive care unit in patients without a new neurologic deficit. Patients with new neurologic deficits or patients discharged to supervised care settings took longer to reach each neurologic milestone. Older patients, patients with more complex surgical procedures, and patients with higher cardiovascular risk factors took longer to become fully alert. The time to reach the highest NICE score was a strong predictor of the duration of intubation but only weakly predicted other outcome variables in a multivariable analysis., Conclusions: Standardized, serial nursing neurologic assessments of postoperative cardiac patients provide insight into the immediate postoperative period and may be a useful tool for early identification of patients at risk for adverse outcomes.

Background: Measurements of auto and cross covariance functions are frequently used to investigate neural systems. In interpreting this data, it is commonly assumed that the largest contribution to the recordings comes from sources near the electrode. However, the potential recorded at an electrode represents the superimposition of the potentials generated by large numbers of active neural structures. This creates situations under which the measured auto and cross covariance functions are dominated by the activity in structures far from the electrode and in which the distance dependence of the cross-covariance function differs significantly from that describing the activity in the actual neural structures., Methods: Direct application of electrostatics to calculate the theoretical auto and cross covariance functions that would be recorded from electrodes immersed in a large volume filled with active neural structures with specific statistical properties., Results: It is demonstrated that the potentials recorded from a monopolar electrode surrounded by dipole sources in a uniform medium are predominantly due to activity in neural structures far from the electrode when neuronal correlations drop more slowly than 1/r3 or when the size of the neural system is much smaller than a known correlation distance. Recordings from quadrupolar sources are strongly dependent on distant neurons when correlations drop more slowly than 1/r or the size of the system is much smaller than the correlation distance. Differences between bipolar and monopolar recordings are discussed. It is also demonstrated that the cross covariance of the recorded in two spatially separated electrodes declines as a power-law function of the distance between them even when the electrical activity from different neuronal structures is uncorrelated., Conclusion: When extracellular electrophysiologic recordings are made from systems containing large numbers of neural structures, it is important to interpret measured auto and cross covariance functions cautiously in light of the long range nature of the electric fields. Using recording electrodes that are bipolar or quadrupolar minimizes or eliminates these effects and hence these electrodes are preferred when electrical recordings are made for the purpose of auto and cross correlation analysis of local electrical activity.

Objective. There are two objectives of this study. The first is to understand how practitioners of differing backgrounds approach the process of interpreting intra-operative neurophysiologic monitoring. The second is to understand whether the experience and educational background of practitioners influences the degree of agreement in their interpretations. Methods. A survey was distributed at the 2004 American Society of Neurophysiological Monitoring meeting. A total of 92 responses were obtained. The effect that various characteristics of the respondents including their experience, degree, certification and role in monitoring had on a number of outcome measures was assessed. These outcome measures included the probability that the surgeon responded to a warning, the chance that the patient would wake without a deficit after a warning was delivered, and the degree to which respondents agreed on interpretations of SSEP traces. Results. It was found that surgeons were more likely to respond to warnings issued by a monitrist with a higher degree of experience. Respondents with higher levels of experience, certification level, and degree level were more likely to agree on interpretations of evoked potential tracings. Overall, however, the degree of agreement between respondents was at most moderate. Respondents with higher levels of experience and training were more likely to provide correct answers to a subset of traces that were designed to reflect a classic pattern of change. Conclusions. This study indicates the need for additional studies on the criteria for providing warnings during IOM and the characteristics of monitrists that influence their interpretations.

The American Society of Neurophysiological Monitoring (ASNM) is developing position statements aimed at assisting practitioners and others in making decisions regarding neurophysiological monitoring practice. This paper describes the procedures used in drafting these documents.

The response to transcranial electrical stimulation of the brain is an important means of assessing motor pathways in the anesthetized patient. The purposes of this study were to elucidate the pattern of axonal excitation produced by transcranial stimulation and to demonstrate how this pattern is affected by changes in the conductivity or geometry of the skull-CSF-brain complex. To this end, analytic solutions to the problem of electrodes placed on a three shell spherical model were obtained under constant current conditions. The potentials, currents and fields generated were computed and the "activating function" was computed for an idealized set of radially organized axons in order to estimate the degree of membrane depolarization produced by stimulation. The degree to which electromagnetic/radiation effects change these solutions was also estimated. The pattern of stimulation was only slightly dependent on the conductivity and the thickness of the CSF layer. Axons very close to the anode were stimulated with lowest threshold at the brain surface. Axons further away were stimulated with higher thresholds and the point of maximum stimulation moved nearer the center of the sphere. Near the cathode, stimulation was maximal about 5-7 degrees away from the edge of the electrode but the peak magnitude of the activating function was generally 20 times lower than over the anode.

Somatosensory evoked potentials are widely used in spine surgery to prevent injury to the spinal cord. However, their application in cardiac and major vascular surgery is largely unappreciated. This paper will review the unique stresses placed on peripheral nerves, spinal cord, and brain during these operations. In addition, the potential benefits of peri-operative somatosensory evoked potentials monitoring are described in detail.

Differences between constant current and constant voltage nerve stimulation are controversial. To elucidate this controversy, exact solutions are found for the electrical potential and current of a conducting electrode of finite size placed near a boundary of altered conductivity. Substantial differences in the effects of a finite and a point stimulator are predicted. This was strongly dependent on the stimulator-boundary distance, the conductivity of the media, and the curvature of the boundary. The difference between constant voltage and constant current stimulation was smaller than the effects of changes in medium conductivity and electrode distance. A poorly conducting boundary layer surrounding the stimulator minimized these differences.

A case of an older patient with the Angelman syndrome due to a deletion at the 15q11-q13 region is presented. The patient demonstrated generalized prolonged myoclonus severe enough to produce temperatures of 41.4 degrees C and CPK elevations to 7281 U/l. This myoclonus was unresponsive to benztropine, clonazepam and worsened with bromocriptine. It resolved with sleep induced by either lorazepam or diphenhydramine and during treatment with reserpine. Once discharged from the hospital and treated with reserpine, there were much less frequent recurrences of the myoclonus that responded well to concomitant treatment with clonazepam. Later attempts to reduce the reserpine resulted in worsening of the myoclonus. Older patients with Angelman syndrome may display a wide variety of neurologic syndromes. This severe myoclonus in this patient worsened with dopamine agonist treatment and initially improved with dopamine depletion therapy while in the long-term responding best to a combination of clonazepam and reserpine.

Background: Neurocognitive changes are common after cardiac operations. The acute post-operative period is a critical time when significant neurologic changes may be detected and appropriate therapy initiated promptly. Formal neuropsychologic testing in this situation however is impractical so other means of early detection are required. The goal of this preliminary study was to determine whether simple, standardized, serial nursing neurologic evaluations using the Neurologic Intensive Care Evaluation (NICE) could be helpful in screening patients for neurologic injury in the immediate post-operative period., Material/methods: Details of the intra-operative and post-operative anesthetic management were obtained during report and nurses subsequently scored acute post-operative patients in the CTSICU using the NICE every half hour for the first five hours. Finally, a chart review was performed to determine the neurologic outcome of the patients., Results: The time to achieve the lower NICE scores which reflect mainly brainstem function was the same whereas the time to achieve NICE scores>4 was prolonged in patients with neurocognitive dysfunction. The effect of intra-operative factors on the times to achieve NICE scores was different for the higher and lower scores. The times to reach NICE scores correlated with outcome variables including the time in ICU and time of intubation., Conclusions: Standardized, serial nursing neurologic assessments of post-operative cardiac patients may be a useful tool for early identification of patients with neurologic injury. They may also provide useful information complementing the data obtained from detailed neuropsychologic testing on the neurologic effects of cardiac operations.

Monitoring the vagus nerve and the recurrent laryngeal nerve during surgical procedures may reduce the probability of significant nerve injury. As such, a number of methods to monitor these nerves have been devised including placing electrodes directly into the vocal cords or recording from surface electrodes. In direct comparison, monitoring the identical muscles, bipolar hookwire electrodes displayed approximately one order of magnitude greater amplitude, of both spontaneously occurring and evoked electrical activity than double wire endotracheal tube electrodes. The enhanced sensitivity of the hookwire electrodes, despite the technical difficulties with placement, suggests their use when maximum sensitivity is required.

Background: Hypothermia is used clinically to prevent neurologic injury but the degree of protection which it affords at various levels of the nervous system in humans is difficult to establish., Material/methods: The temporal changes in EEG amplitude and somatosensory evoked potential (SEP) amplitudes in a patient experiencing acute normothermic hypoxemia, a patient experiencing acute circulatory arrest at moderate hypothermia and a collection of patients undergoing deep hypothermic circulatory arrest were analyzed to determine the rate at which changes occur during acute lack of oxygen delivery at various temperatures., Results: In each case, it was found that more rostrally generated potentials disappeared more quickly than more peripheral potentials. All potentials decayed more slowly during acute normothermic hypoxemia than during circulatory arrest. During circulatory arrest at 14.4 degrees C, the amplitude of the Erb's point, N13 and N18 potentials in the SEP took 5 times longer to drop to 50% of their value at the onset of ischemia than with circulatory arrest at 30.9 degrees C., Conclusions: The longer times to disappearance of the SEP potentials during deep hypothermia compared to moderate hypothermia was consistent with the predicted 3.5-6.5 fold reduction in metabolic activity at deep hypothermia compared to moderate hypothermia. The prolonged time to disappearance of the SEP during normothermic hypoxemia demonstrates that even with reduced oxygen delivery the continued delivery of metabolic substrate can be critical to neural function.