High postdialysis urea rebound can predict intradialytic increase in intraocular pressure in dialysis patients with lowered intradialytic hemoconcentration

Background: Intradialytic (ID) decrease in intraocular pressure (IOP) parallel to ultrafiltration-induced hemo-concentration has been recently reported. However, exacerbation of glaucoma in hemodialysis (HD) patients during HD sessions is occasionally observed. Postdialysis urea rebound (PDUR) is induced by the lag in urea removal from the cells to urea removal from the extracellular fluid, which when increased can result in ID drag of water to intracellular compartment. It is our hypothesis that similar lag in urea removal from ocular compartments may also be reflected by PDUR, and may induce drag of water into ocular compartments counteracting the effect of hemoconcentration. Our assumption was, therefore, that PDUR might predict ID increase in IOP. Methods: IOP, serum urea and hematocrit levels were measured at the start, end and 1 h postdialysis, in 19 chronic HD patients with normal IOP. Results: PDUR was positively correlated with mean (both eyes) ID changes in IOP (MIDIOP) (r = 0.5, p = 0.03) and % MIDIOP (r = 0.55, p = 0.02). ID increase in IOP was observed only in the 7 patients with relatively higher PDUR (≥9 mg%), who had also a relatively lower % ID change in Hct (<8%). MIDIOP was negatively correlated with % ID changes in Hct (r = -0.65, p = 0.03) in the 12 patients with PDUR ≥9 mg, and positively correlated with PDUR (r = 0.57, p = 0.03) in the 14 patients with % ID change in Hct <8%. Conclusion: High PDUR may predict susceptibility to ID increase in IOP in patients with lowered ID hemoconcentration.