Journal of clinical monitoring
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This study describes the results from a series of human experiments demonstrating the ability to measure arterial hemoglobin oxygen saturation (SaO2) from the forearm and calf using a reflectance pulse oximeter sensor. A special optical reflectance sensor that includes a heating element was interfaced to a temperature controller and a commercial Data-scope ACCUSAT pulse oximeter that was adapted for this study to perform as a reflectance pulse oximeter. The reflectance pulse oximeter sensor was evaluated in a group of 10 healthy adult volunteers during steady-state hypoxia. ⋯ The equations for the best-fitted linear regression lines between the percent reflectance, SpO2(r), and transmittance, SpO2(t), values in the range between 73 and 100% were SpO2(r) = -7.06 + 1.09 SpO2(t) for the forearm (n = 91, r = 0.95) and SpO2(r) = 7.78 + 0.93 SpO2(t) for the calf (n = 93, r = 0.88). The regression analysis of the forearm data revealed a mean +/- SD error of 2.47 +/- 1.66% (SaO2 = 90-100%), 2.35 +/- 2.45% (SaO2 = 80-89%), and 2.42 +/- 1.20% (SaO2 = 70-79%). The corresponding regression analysis of the calf data revealed a mean +/- SD error of 3.36 +/- 3.06% (SaO2 = 90-100%), 3.45 +/- 4.12% (SaO2 = 80-89%), and 2.97 +/- 2.75% (SaO2 = 70-79%).(ABSTRACT TRUNCATED AT 250 WORDS)
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Comparative Study
The relative accuracies of two automated noninvasive arterial pressure measurement devices.
We compared the accuracies of two types of noninvasive blood pressure devices. Thirty-two patients requiring an intraarterial catheter for anesthetic management underwent simultaneous monitoring with Dinamap 1846SX and Ohmeda Finapres 3700 devices. For the first 10 minutes of recording, new Dinamap determinations were performed every 60 seconds; subsequent recordings were made at 3-minute intervals. ⋯ We conclude that continuous Finapres readings and new Dinamap determinations are equally accurate for diastolic and mean arterial pressures. The accuracy of Finapres appears to be slightly superior for systolic pressure. The intermittent sampling of oscillometric devices compromises their performance relative to the Finapres in many, but not all, cases.
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We modified a Bain circuit by placing the circuit into the Y piece of a standard carbon dioxide absorber circle, connecting the fresh gas hose on the anesthetic machine to the Bain's fresh gas inlet, and occluding the circle's fresh gas inlet. This circle-modified Bain breathing circuit was studied to evaluate whether it reduces fresh gas flow requirements. The Bain and modified Bain steady states were analyzed by mechanical and computer modeling. ⋯ The circle-modified Bain greatly reduced retention of carbon dioxide. For example, with 1-liter tidal volumes, 10-liter minute volumes (10 breaths per minute), and a 2.1 L/min fresh gas flow, the steady-state end-tidal carbon dioxide values of the Bain and modified Bain were 9.3 and 4.6%, respectively, in the physical model (carbon dioxide inflow of 230 ml/min). Results from the mechanical model helped validate the computer model.
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The esophageal stethoscope has evolved into a device for both acoustic and core temperature monitoring. To test whether routine placement according to acoustic criteria results in placement of the core temperature sensor in the region of contiguity between the esophagus and the heart, we determined the depth of placement electrocardiographically. All patients were undergoing nonthoracic elective operations requiring general anesthesia and tracheal intubation. ⋯ In the remaining patients, measured discrepancies ranged up to 13.5 cm. We conclude that the prevailing stethoscope design, with a thermistor at the tip, below the acoustic window, does not ensure placement of the thermistor within the optimal region for monitoring of core temperature. A modification in design that would take advantage of the reliability of electrocardiographic positioning is suggested.