Microchannel occlusion depends on fluid admixture final sodium and tonicity. The average number of sRBCs occluding microchannels was dependent on final sodium concentrations and tonicities of the fluid admixtures. Data represent results from a total of 8857 sRBCs analyzed from 4 patient samples (N = 5 conditions per sample; N = 20 total experiments; N = 300-500 red cells/experiment; N = 28 microchannels/experiment; N = 560 total microchannels). Boxes and bars represent mean ± standard error of the mean.