Anesthesiology
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Carbon monoxide (CO) is produced by reaction of isoflurane, enflurane, and desflurane in desiccated carbon dioxide absorbents. The inspiratory CO concentration depends on the dryness and identity of the absorbent and anesthetic. The adaptation of existing mathematical models to a rebreathing circuit allows identification of patient factors that predispose to more severe exposures, as identified by carboxyhemoglobin concentration. ⋯ This model predicts that patients with low hemoglobin quantities will have more severe CO exposures based on the attainment of a higher carboxyhemoglobin concentration. This includes patients of small size (pediatric population) and patients with anemia.
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Inhaled prostacyclin and intravenous almitrine have both been shown to improve pulmonary gas exchange in acute lung injury (ALI). This study was performed to investigate a possible additive effect of prostacyclin and almitrine on pulmonary ventilation-perfusion (VA/Q) ratio in ALI compared with inhaled prostacyclin or intravenous almitrine alone. ⋯ The authors conclude that, in this experimental model of ALI, the combination of 25 ng.kg(-1).min(-1) prostacyclin and 1 microg.kg(-1).min(-1) almitrine does not result in an additive improvement of pulmonary gas exchange or VA/Q distribution when compared with prostacyclin or almitrine alone.
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Recent reports suggest that one type of learning, fear conditioning to context, requires more neural processing than a related type, fear conditioning to tone. To determine whether these types of learning were differentially affected by anesthesia, the authors applied isoflurane during the training phases of fear conditioning paradigms for freezing to context and freezing to tone. ⋯ Suppression of fear conditioning to tone required approximately twice the isoflurane concentration that suppressed fear conditioning to context. Thus, the concentration of anesthetic required to suppress learning may depend on the neural substrates of learning. Our results suggest that isoflurane concentrations greater than 0.5 MAC may be needed to suppress both forms of fear conditioning.
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Efficacy of acute normovolemic hemodilution assessed as a function of fraction of blood volume lost.
It has been recommended that intraoperative acute normovolemic hemodilution (ANH) be considered for patients expected to experience surgical blood loss of 20% or more of their blood volume. Previous mathematical analyses have not evaluated the potential efficacy of ANH in terms of fraction of blood volume lost. Since decrease of oxygen-carrying capacity is a function of erythrocyte loss relative to blood volume, the purpose of this analysis was to provide an assessment of ANH applicable to all blood volumes and to determine whether this recommendation is appropriate. ⋯ This analysis suggests that surgical blood loss should be 0.50 or more for ANH to begin to "save" erythrocytes and 0.70 or more of the patient's blood volume for ANH to save 1 unit erythrocytes, for the usual surgical patient with an initial hematocrit of 0.32-0.36 and a transfusion "trigger" hematocrit (the value at which transfusion is initiated) of 0.18-0.21.