Isoflurane

Their interaction with hemoglobin and its affinity for oxygen, best described by the oxygen dissociation curve (ODC), has already been investigated, with ...

A right shift of the ODC on the other hand, can increase the amount of O2 released in the tissues, although a reduced absorption of oxygen in the lungs must be considered. As a potential cause, red blood cell shrinkage, resulting in an increase in 2,3-DPG levels was ruled out as the right shift of the ODC was also observed in red blood cells where shrinkage was prevented. A total of 22 subjects (11 female; 11 male) were included in the study. This increase was linked to a right shift of the ODC and a lower affinity for oxygen. Prior to the study, stability of inhaled anesthetics in the gas sampling bags was confirmed by preparation of a defined gas mixture and repeated measurements over 24 h using the above-mentioned gas monitor. In the clinical setting the potency and dosage of inhaled anesthetics are often described by the Minimum Alveolar Concentration (MAC), which expresses the concentration at sea level where 50% of the volunteers did not show purposeful movement after a surgical stimulus 6. Overall, the effects of various inhaled anesthetics on the ODC and the influence of differing dosages is not well established and for some anesthetics even contradictory. The ODC is best described by two main parameters: the p50, representing the partial pressure of O2 at 50% Hb-O2 saturation, and the Hill Coefficient (HC), representing the maximum steepness of the curve in the logarithmic Hill plot 3. Blood samples were either exposed to control or to three different concentrations of desflurane, isoflurane or sevoflurane prior to and during measurements (low, medium and high corresponding to MAC 0.5, MAC 1.0 and MAC 2.0). With increasing concentrations from control to medium, desflurane and isoflurane significantly decreased Hb-O2 affinity by shifting the ODC to the right (p = 0.016 and p < 0.001) but sevoflurane showed no effects. also showed a right shift of the ODC not only for nitrous oxide but also for isoflurane 11, 12, while for sevoflurane no effects were found 13. In intensive care medicine inhaled anesthetics are used for sedation, particularly in the context of distinct tolerance or tachyphylaxis to intravenous sedatives, severe bronchospasms and epilepsy refractory to regular treatment or as anesthetic preconditioning 5. When further increasing concentrations from medium to high, all three inhaled anesthetics shifted the ODC back to the left (p < 0.001). Comparing only controls to high concentrations, a significant increase in Hb-O2 affinity for desflurane (p = 0.005) and sevoflurane (p < 0.001) was detected.