Journal of clinical monitoring
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When we ask, what renders essential a particular monitoring approach during routine anesthesia for a healthy patient, perplexing questions, rather than satisfying answers, are raised. I have examined these questions with the help of three lenses that focus on the relationship between the outcome of anesthesia and the detection, and thus correction, of abnormalities during anesthesia. The first lens looks at whether the monitoring modalities accepted by anesthesiologists as "minimal" and "essential" have been scientifically proven to affect outcome from routine anesthesia. ⋯ The third lens looks at whether there are nonclinical influences on monitoring practice. This lens views the gap between recognizing monitoring possibilities and adopting them clinically; it also views geographic differences in monitoring, as well as social pressures exerted through legal proceedings. Finally, currently recognized essential monitors such as blood pressure measurement, electrocardiography, and oxygen analysis are mentioned, and candidates for inclusion in the list of essential monitors, such as oximeters, capnographs, and the automated record, are discussed.
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Development of the flow-directed pulmonary artery catheter in combination with reflective fiberoptic oximetry techniques allows the clinician to continuously measure mixed venous oxygen saturation (SvO2). A brief review of the determinants of oxygen balance, the Fick principle, and the technology of continuous SvO2 monitoring is preliminary to a debate between two clinicians on the usefulness of SvO2 monitoring. One clinician highly recommends use of the flow-directed pulmonary artery catheter in patients who require pulmonary artery catheterization. ⋯ Major mistakes in patient management could follow from overreliance upon either absolute SvO2 measurements or analysis of trends over time. Use of the SvO2 monitor has not been proven cost-effective and may actually increase monitoring costs. Both clinicians agree that continuous SvO2 monitoring is valuable in many clinical circumstances, provided the limitations of the measurement are understood.
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To confirm the clinical applicability of a commercial pulse oximeter, we compared arterial hemoglobin saturation values determined by in-vitro oximetry and pulse oximetry in 15 critically ill children. One hundred ninety-two paired hemoglobin saturations were determined by both noninvasive pulse oximetry and direct measurement of arterial blood samples. ⋯ Pulse oximetry was found to be safe and less cumbersome than other methods of monitoring arterial oxygen content. Overall, pulse oximetry was precise and provided a clinically satisfactory noninvasive method for continuously monitoring arterial hemoglobin saturation in critically ill children.
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The natural frequencies, damping coefficients, and accuracies of umbilical artery catheters were determined. The damping coefficients for the 3.5, 5.0, and 8.0 French catheters were 0.40 +/- 0.04 (mean +/- SD), 0.42 +/- 0.05, and 0.19 +/- 0.02, respectively. ⋯ Measurements obtained with 3.5 and 8.0 French catheters were within 6% of the reference pressure at all pressures and rates tested. With the 5.0 French catheter, however, error greater than 10% from the reference pressure occurred when the rate was 200 pulses per minute or greater and the applied maximum pressure was 100 mm Hg or more.