A new technique for measuring fistula flow using venous blood gas oxygen saturation in patients with a central venous catheter

Abstract

Background: Doppler ultrasound (DU) monitoring early after arteriovenous fistula (AVF) creation allows the identification of low blood flow (Qa) requiring prompt revision, but it is costly (needs skilled operators and technical instruments) and is not available in all dialysis units. Therefore alternative first-line methods to measure Qa would be welcomed. We reasoned that once an AVF is created, an increment in central venous oxygen saturation (ScvO2) is predictable and proportional to Qa. Methods: Accordingly, in patients receiving dialysis through a central venous catheter (CVC) in whom an AVF was created, we measured, by means of blood gas analysis, the ScvO2 increment before and after manual compression of the arteriovenous shunt and verified its correlation with DU-measured Qa. Results: We sampled blood gas in 18 patients with CVC and AVF before and after 30 s manual compression of the AVF. ScvO2 averaged 70.5 ± 3% before and 65.2 ± 3% after AVF closure, with an average drop of 5.1 ± 3% (range 1-12). AVF Qa, which was measured within 24 h by means of DU, averaged 635 ± 349 mL/min (range 50-1300) and was strictly and positively correlated with ΔScvO2 (r = 0.954, P < 0.0001). Conclusions: Therefore we suggest that in patients with CVC and a newly created AVF, it is possible to monitor AVF Qa without DU by simply measuring blood gas and ΔScvO2. This technique is simple, cheap, repeatable, non-invasive and operator independent and represents a new useful screening test to detect delayed AVF access maturation deserving prompt DU measurement and surgical revision. It helps to quickly identify patients in urgent need of DU verification and possible surgical revision. Regrettably, it is applicable only in patients with CVC.