Journal of clinical monitoring and computing
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J Clin Monit Comput · Dec 2009
Comparative StudyMixed-muscle electrode placement ("jumping" muscles) may produce false-negative results when using transcranial motor evoked potentials to detect an isolated nerve root injury in a porcine model.
Placing EMG electrode pairs that span several muscles is sometimes used to enhance the efficacy of electromyographic recordings. This technique, often referred to as "jumping," has not been studied when using Motor Evoked Potentials (TcMEP) for detecting isolated spinal nerve root injury during spine surgery. ⋯ Mixed-myotomal recording electrodes did not consistently increase baseline TcMEP amplitude. The decrease in amplitude after ligation was both smaller and more variable in the "jumped" TA-GAS electrodes. Thus, this technique may allow someone relying on TcMEP monitoring to miss an otherwise detectable isolated nerve root injury (i.e., have a false-negative result).
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J Clin Monit Comput · Dec 2009
Practice GuidelineGuidelines for intraoperative neuromonitoring using raw (analog or digital waveforms) and quantitative electroencephalography: a position statement by the American Society of Neurophysiological Monitoring.
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. ⋯ 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.
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Monitoring of aortic blood flow, conducting large portions of the cardiac output (CO), allows conclusions on the global hemodynamic status of patients. For this purpose, transesophageal Doppler (TED) devices have been developed, which interrogate the descending aorta and calculate aortic blood flow velocity using the Doppler principle. The recorded velocity-time curve can be used to estimate CO as well other advanced hemodynamic parameters such as preload, afterload and myocardial contractility. ⋯ However, several assumptions are needed to translate the measured Doppler frequency shift to hemo- dynamic variables and discrepancies between the assumed and the actual condition may introduce a considerable risk for erroneous calculations. A correct interpretation of the displayed parameters requires profound knowledge on the technical basis of this method as well as its technical limitations. Our review focuses on these technical aspects which the clinician should be familiar with to allow proper use of TED monitoring devices.
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The Systolic pressure variation (SPV) is known to be a sensitive indicator of hypovolemia. However, the SPV may be elevated due to other reasons, such as changes in lung compliance or tidal volumes. Using the SPV to monitor the hemodynamic status of patients in the prone position may, therefore, be problematic due to possible effects of increased abdominal pressure on both venous return and lung compliance. The purpose of this study is to examine whether or not the SPV changes significantly when placing the patient in the prone position. ⋯ This study is important because it shows for the first time that the SPV does not change significantly in the prone position, and may therefore continue to be used as an indicator of the volume status. It also would appear to indicate that our methods for protecting the chest and abdomen in the prone position are effective.
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J Clin Monit Comput · Oct 2009
Clinical TrialA novel electronic algorithm for detecting potentially insufficient anesthesia: implications for the prevention of intraoperative awareness.
A recent clinical trial compared a minimum alveolar concentration (MAC)-based protocol to an electroencephalography (EEG)-based protocol for the prevention of intraoperative awareness. One limitation of this study design is that MAC-based protocols are not sensitive to the use of intravenous agents, while EEG-based protocols are. Our objective was to develop a MAC alert that incorporates intravenous agents. ⋯ Our novel electronic alerting system incorporates both age-adjusted MAC and intravenous anesthesia, and triggers with a higher frequency in cases of awareness. These data suggest the potential for our system to alert clinicians to insufficient anesthesia.