Journal of clinical monitoring
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The accuracy of two commercially available pulse oximeters (the Ohmeda Biox 3700, software version "J," and the Nellcor N-100) in detecting low levels of arterial hemoglobin oxygen saturation (SaO2) was evaluated in 10 dogs in which hypoxia was induced by stopping the fresh gas flow into the anesthesia machine circle system. Measurements made in vivo with the pulse oximeters, with detectors placed on the tongue, were compared with measurements made in vitro using an IL 282 CO-Oximeter as SaO2 decreased toward zero. Measurements from the two oximeters correlated poorly over the range from 0 to 100% SaO2 (r = 0.69). ⋯ The correlation with the CO-Oximeter was similar for both the Ohmeda and the Nellcor pulse oximeters at an SaO2 of 80% or more. However, when SaO2 was less than 80%, measurements by pulse oximetry correlated less well with CO-Oximeter measurements (r = 0.62, slope = 0.64, and y intercept = 21.0 for Nellcor; r = 0.71, slope = 0.67, and y intercept = 32.4 for Ohmeda). When SaO2 was less than 60%, both oximeters inaccurately indicated the co-oximetry values (r = 0.36 and y intercept = 26.1 for the Nellcor; r = 0.48 and y intercept = 33.2 for the Ohmeda).(ABSTRACT TRUNCATED AT 250 WORDS)
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This study compares two noninvasive techniques for monitoring the partial pressure of carbon dioxide (PCO2) in 24 anesthetized adult patients. End-tidal PCO2 (PetCO2) and transcutaneous PCO2 (PtcCO2) were simultaneously monitored and compared with arterial PCO2 (PaCO2) determined by intermittent analysis of arterial blood samples. PETCO2 and PtcCO2 values were compared with PaCO2 values corrected to patient body temperature (PaCO2T) and PaCO2 values determined at a temperature of 37 degrees C (PaCO2). ⋯ Temperature correction of the arterial values (PaCO2T) slightly improved the correlation, with respect to PETCO2, but it had the opposite effect for PtcCO2. In this study, the chief distinction between these two noninvasive monitors was that PETCO2 had a large negative bias, whereas PtcCO2 had a small bias. We conclude from these data that PtcCO2 may be used to estimate PaCO2 with an accuracy similar to that of PETCO2 in anesthetized patients.
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Tidal volume (VT) delivered by mechanical ventilation during anesthesia may be influenced by factors related not only to the patient and the breathing circuit, but also to the interaction between the anesthesia machine and the anesthesia ventilator. To characterize this interaction, we studied in a test lung the effect of fresh-gas-flow (FGF) (0.25, 2.5, 5, and 10 L/min), inspiratory-to-expiratory time ratio (I:E) (1:1, 1:2, and 1:3), and ventilatory frequency (8, 12, and 16 breaths/min) at fixed ventilator bellows excursions of 300, 600, and 900 ml. The influence of these variables was also estimated mathematically for a pediatric situation: a bellows excursion of 50 ml at 20 and 30 breaths/min. ⋯ Thus it is possible in the pediatric situation to increase the delivered VT by sixfold without changing the ventilator bellows excursion. The magnitude of the changes was slightly larger for the VT settings for adult patients because of the slower respiratory rate. This VT augmentation can be predicted by the product of FGF (ml/s) and inspiratory time (seconds).(ABSTRACT TRUNCATED AT 250 WORDS)
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A healthy patient who was undergoing cystoscopy suddenly showed a rapid increase in heart rate on a pulse oximeter. The cause was determined to be incident light from the light source for the cystoscope.