Journal of clinical monitoring
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Comparative Study
Forehead pulse oximetry compared with finger pulse oximetry and arterial blood gas measurement.
Usual monitoring sites for pulse oximetry involve the fingers, toes, ear lobe, and nasal septum. This study examined the performance of a forehead sensor compared with a finger sensor for the pulse oximeter and arterial blood gas (ABG) analysis. Ten healthy adult volunteers and 22 ventilator-dependent patients were studied. ⋯ The forehead pulse oximeter sensor works well on healthy, well-oxygenated volunteers. Difficulty was experienced when applying and using the sensor on critically ill patients. The reliability of the forehead pulse oximeter sensor has not been established at low saturations.
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Functional residual capacity as a noninvasive indicator of optimal positive end-expiratory pressure.
We hypothesized that functional residual capacity (FRC) could be used as a noninvasive indicator of "optimal" positive end-expiratory pressure (PEEP), the level of PEEP that results in venous admixture below 15% with an inspired oxygen fraction less than 0.5. We compared several variables for PEEP optimization--oxygen transport, total respiratory system compliance, FRC-based compliance, mixed venous oxygen saturation, end-tidal to arterial carbon dioxide tension difference, and arterial oxygen saturation--by producing four different PEEP levels, 0, 5, 10 and 15 cm H2O, in 24 mongrel dogs in which pulmonary injury was produced. The data were regressed versus PEEP by using analysis of variance for regression. ⋯ Total respiratory system compliance (F1,23 = 66.6; P less than 0.0001) and mixed venous oxygen saturation (F1,23 = 12.2; P less than 0.002) had a quadratic relationship with respect to PEEP with a peak at 5 cm H2O. FRC-based compliance did not have a significant relationship to PEEP. The maximum values of total respiratory system compliance, FRC-based compliance, mixed venous oxygen saturation, and oxygen transport did not occur at PEEP levels that corresponded to a venous admixture below 15% ("optimal" PEEP).(ABSTRACT TRUNCATED AT 250 WORDS)
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The process of monitoring carbon dioxide in the respired gas is described. The physical principle employed in many capnometers is nondispersive infrared absorption: An infrared light beam is projected through a gas sample and the intensity of transmitted light is measured. ⋯ The value of the data displayed, once derived, is based on the knowledge that carbon dioxide is an end product of the metabolism of oxygen-consuming organisms. The data can be a useful indicator of metabolic, circulatory, and ventilatory processes.
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We evaluated a new combined sensor for monitoring transcutaneous carbon dioxide tension (PtcCO2) and oxygen tension (PtcO2) in 20 critically ill newborn infants. Arterial oxygen tension (PaO2) ranged from 16 to 126 torr and arterial carbon dioxide tension (PaCO2) from 14 to 72 torr. Linear correlation analysis (100 paired values) of PtcO2 versus PaO2 showed an r value of 0.75 with a regression equation of PtcO2 = 8.59 + 0.905 (PaO2), while PtcCO2 versus PaCO2 revealed a correlation coefficient of r = 0.89 with an equation of PtcCO2 = 2.53 + 1.06 (PaCO2). ⋯ The transcutaneous sensor detected 83% of hypoxia (PaO2 less than 45 torr), 75% of hyperoxia (PaO2 greater than 90 torr), 45% of hypocapnia (PaCO2 less than 35 torr), and 96% of hypercapnia (PaCO2 greater than 45 torr). We conclude that the reliability of the combined transcutaneous PO2 and PCO2 monitor in sick neonates is good for detecting hypercapnia, fair for hypoxia and hyperoxia, but poor for hypocapnia. It is an improvement in that it spares available skin surface and requires less handling, but it appears to be slightly less accurate than the single electrodes.