Journal of clinical monitoring and computing
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J Clin Monit Comput · Jun 2004
The influence of larger subcutaneous blood vessels on pulse oximetry.
Recent studies have renewed interest in reflectance pulse oximetry, specifically for monitoring the patient's forehead. Blood circulation on the forehead immediately above the eyebrow is fed by arteries that branch from the internal carotid artery and lack the vasoconstrictor response present in more peripheral regions. Some investigators question, however, the reliability of monitoring SpO2 on the forehead due to prior reported inaccurate readings with reflectance sensors. The present study evaluates pulse oximetry accuracy when reflectance sensors are placed over potentially pulsing or moving larger arterial vessels, or over more homogeneous microvasculature devoid of larger subcutaneous vessels. METHODS. Ten healthy adult volunteers were fitted with reflectance pulse oximetry sensors and exposed to a controlled desaturation to 70%. Sensors were placed immediately above the left and right eyebrows as well as over the temple. Additionally, numerical modeling was used to simulate light signals and photon migration through a homogeneous tissue bed with an added static or dynamic artery. ⋯ Placement of reflectance pulse oximetry sensors directly over larger cardio-synchronously pulsing or moving vasculature can significantly degrade SpO2 reading accuracy. Reflectance sensors placed low on the forehead directly over the eyebrow and slightly lateral to the iris appear to avoid such vasculature and provide consistent and accurate estimates of SaO2.
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The present paper introduces a new perspective on the classical ensemble averaging which can be useful to analyse the Brainstem Auditory Evoked Potentials (BAEPs). The analysis of the dynamics, related to the BAEP, is performed directly after its acquisition from the electroencephalogram (EEG). ⋯ In order to validate our approach, the proposed technique has been implemented for both simulated and real signals. This approach can also be employed in the context of estimating other evoked potentials and shows rich promise for potential clinical applications in future.
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Direct-current injuries have occurred to anesthetized patients connected to battery-operated medical devices. This study was designed to document the effects of direct current applied to two electrodes on a tissue surrogate (round steak) at room temperature. Direct current from a 9 V source was applied to a pair of stainless steel electrodes (1.6 cm diameter) spaced 4.3 cm center-to-center. ⋯ At the end of each experiment the electrodes were different in appearance. The negative electrode retained its original shiny appearance but the positive electrode was pitted and dull in appearance, reflecting the different chemical reactions at each site. The lesions under the negative electrodes were more severe, indicating that alkali is more damaging than the acid environment that was produced electrolytically.
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J Clin Monit Comput · Jun 2004
N100 auditory potential and electroencephalogram discriminate propofol-induced sedation levels.
In the present study, we evaluated the electroencephalogram (EEG) and auditory N100 potential (N100) before and during propofol-induced sedation. The aim was to test whether using EEG and N100 the level of sedation may be evaluated. ⋯ Our findings suggest that the combined use of EEG and N100 may help to differentiate the propofol-induced sedation levels, and thus be a useful compliment to clinical sedation scales.
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J Clin Monit Comput · Jun 2004
Facilitated assessment of unconsciousness from morphologic changes in the bilateral posterior tibial nerve cortical somatosensory evoked potential under total intravenous propofol anesthesia during spine surgery.
To describe a unique morphologic feature of the bilateral posterior tibial nerve cortical somatosensory evoked potential, the S-wave, which varies systematically with propofol infusion rate and which appears to be useful in guiding adequate propofol concentration levels during spine surgery. ⋯ The bilateral posterior tibial nerve cortical somatosensory evoked potential changes its morphology in predictable fashion with decreased depth of propofol anesthesia, allowing for anticipation of imminent anesthetic "lightening." It serves as a useful cross-check to Bispectral Index (BIS) or other "level of consciousness" EEG-based algorithms for monitoring depth of propofol anesthesia during prolonged corrective spine surgery.