<prompt> A crisis in a patient with sickle cell disease is most likely to be cause byAlkalosisAcidosisIncreased oxygen concentrationDecreased CO2 concentration  <response>: A crisis in sickle cell disease occurs when deoxygenated HbS precipitates, deforming sickling red blood cells and .blocking capillaries. Variables that increase the proportion ofHbS in the deoxy state tend to increase the probability of a crisis by increasing the extent of sickling. The deoxy form of hemoglobin is favored by a decrease in pH acidosis. An increase in pH alkalosis, increased oxygen concentration, decreased CO2 concentration, and decreased 2,3-bisphosphoglycerate concentration would all favor the oxy form of hemoglobin. 