RECIRCULATION, UREA DISEQUILIBRIUM, AND DIALYSIS EFFICIENCY - PERIPHERAL ARTERIOVENOUS VERSUS CENTRAL VENOVENOUS VASCULAR ACCESS

When accurate, non-urea-based methods of measuring recirculation are u sed, recirculation is usually absent in arteriovenous (AV) accesses, W hen urea-based methods are used to measure recirculation in AV accesse s, falsely elevated recirculation rates are common, These errors are d ue to AV and venovenous disequilibrium (peripheral vein method), delay ed systemic sampling (two-needle methods), and errors in urea measurem ent (all methods), The literature suggests that recirculation in centr al venovenous (CV) catheters is approximately 5%, The methods used for these determinations have all been urea based, However, there are few theoretical problems in using urea-based measurements for measuring r ecirculation in this setting, making it more likely that these values are accurate. When hemodialysis via CV and AV accesses are compared, e quilibrated Kt/V values differ significantly for the same single-pool Kt/V when 15-second postdialysis blood urea nitrogen values are used f or modeling, but differ minimally when 2-minute postdialysis samples a re used, The impact of transient retrograde blood flow in the superior vena cava on recirculation and whether dialysis efficiency is influen ced by the exact site of CV catheter placement (superior vena cava v r ight atrium) is uncertain. (C) 1997 by the National Kidney Foundation, Inc.