Journal of clinical monitoring
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Current forms of brain monitoring, such as electroencephalography (EEG), have had limited clinical utility. The EEG records spontaneous cerebrocortical activity and thus is an indirect indicator of metabolic demand and, to a lesser extent, an indicator of mismatch of supply versus demand. Ischemia modulates EEG activity in ways that can usually be detected, but EEG patterns can be similarly modulated by many other factors, including temperature and pharmacologic manipulation. ⋯ We compared estimators of changes in microcirculatory blood volume using reflection at two wavelengths: 366 nm and 585 nm, the wavelengths for maximum and isobestic absorption. The results of the studies were as follows: (1) during transient hypoxia, NADH and local hemoglobin saturation signals changed in concert with arterial pulse oximetry, with changes in NADH lagging behind changes in saturation by an average of 5.3 seconds; (2) after hypocapnic ventilation to a mean PaCO2 of 20.2 +/- 0.8 mm Hg, NADH increased by 11.5 +/- 8.7% (as compared with maximal change during anoxia), local hemoglobin saturation decreased by 7.7 +/- 6.4%, and local blood volume decreased by 12.5 +/- 13%, while arterial SpO2 was unchanged; (3) our two measures of local blood volume were closely correlated during carbon dioxide perturbations, but poorly correlated during hypoxic perturbation; and (4) NADH fluorescence provided a more rapid, sensitive indicator of oxygen deprivation than did the EEG. During transient hypoxia, EEG changes occurred 57.4 +/- 10.4 seconds after the onset of decline in local hemoglobin saturation, after NADH had completed 50% of its maximal increase.
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Two patients are described in whom double-lumen endotracheal tube malplacement and its ventilatory consequences were not detected by infrared capnography. Problems were suspected on auscultation, and the malplacement was diagnosed by means of bronchospirometry. We conclude that bronchospirometry helps detect problems with endotracheal intubation.
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The introduction of the variable-pitch feature on pulse oximeters in 1983 by the Nellcor Corporation (Hayward, CA) allowed users to rapidly detect changes in oxygen saturation by listening for changes in the pitch of the tones emitted by the pulse oximeter. A few individuals have reported that they have been unable to detect a change in pitch when oxygen saturation changes. To these individuals, the variable-pitch feature of these pulse oximeters has not been beneficial. ⋯ The pitches were recorded onto a tape player and played for 75 volunteer subjects unfamiliar with the pitches of a variable-pitch pulse oximeter. Of our sample, 67% were able to detect a single change in pitch corresponding to a 1% fall in oxygen saturation, and 11% of the population could not detect a change in pitch until there was a change in pitch with every beat. We suggested four alternative designs that may prove beneficial to this group of individuals.
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Randomized Controlled Trial Comparative Study Clinical Trial
Radial artery cannulation: a comparison of 15.2- and 4.45-cm catheters.
Eighty-nine patients were studied prospectively to compare the incidence of postdecannulation arterial thrombosis and ischemic complications associated with percutaneous insertion of two different radial artery catheters. Patients scheduled for peripheral vascular surgery were randomized to receive a 15.2-cm (6 in, Argon Medical Corp.) or 4.45-cm (1.75 in, Arrow International, Inc.) 20-gauge, Teflon catheter. Extremity blood flow was evaluated prior to cannulation and again after decannulation with the modified Allen's test, pulse-volume plethysmography, and Doppler ultrasound. ⋯ Of the 8 patients with positive modified Allen's test who underwent radial artery cannulation, one suffered arterial occlusion. Radial artery cannulation with a 15.2-cm catheter was associated with a lower incidence of postdecannulation radial artery thrombosis than cannulation with the 4.45-cm catheter. Radial artery cannulation with longer catheters (greater than 5.0 cm) appears to be a safe practice.