Anesthesiology
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Nitrous oxide diffuses easily from blood into air filled spaces. Xenon is also a relatively insoluble gas, like nitrous oxide. Therefore, the authors measured xenon diffusion into obstructed bowel segments during xenon anesthesia and compared this with nitrous oxide and nitrogen diffusion. ⋯ The amount of diffused gas was significantly lower during xenon anesthesia than with nitrous oxide anesthesia but greater than with controls. Blood solubility can therefore be regarded as an important factor influencing gas diffusion into air filled cavities.
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Unexpected awareness is a rare but well-described complication of general anesthesia that has received increased scientific and media attention in the past few years. Transformed electroencephalogram monitors, such as the Bispectral Index monitor, have been advocated as tools to prevent unexpected recall. ⋯ The contention that Bispectral Index monitoring reduces the risk of awareness is unproven, and the cost of using it for this indication is currently unknown.
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The relation between older age and nosocomial infection and mortality in the intensive care unit (ICU) is still a controversial issue. ⋯ In patients referred to a surgical ICU after a surgical procedure, age more than 75 yr by itself does not appear to be a significant predictor of ICU-acquired nosocomial infection or mortality rate during the ICU stay. However, it appears that patients more than 60 yr have a higher incidence of nosocomial infection in ICU.
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The alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype of glutamate receptor mediates fast excitatory neurotransmission in the central nervous system. Many general anesthetics inhibit AMPA receptors in vitro; however, it is not certain if this inhibition contributes to the behavioral properties of these drugs. AMPA receptors lacking the GluR2 subunit are resistant to blockade by barbiturates in vitro. Paradoxically, GluR2 null mutant (-/-) mice are more sensitive to barbiturate-induced loss of the righting reflex (LORR) compared with wild-type (+/+) littermates. To determine if interactions between anesthetics and AMPA receptors account for the increased sensitivity of (-/-) mice, the effects of volatile anesthetics that do not directly inhibit AMPA receptors were examined. ⋯ Direct blockade of AMPA receptors did not account for the increased sensitivity to volatile anesthetics in GluR2 null mutant mice for HPWL or LORR. Thus, the deficiency of GluR2-containing AMPA receptors increases the sensitivity of neuronal circuitry mediating these end points, but not MAC. GluR2-containing receptors do not contribute appreciably to MAC in this mouse model. These results illustrate the difficulties in attributing behavioral responses to drug-receptor interactions in genetically engineered animals.
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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.