Contamination of microbubbles of air may occur at all investigated measurement points during hemodialysis.

Microbubbles (MBs) of air occur in the hemodialysis (HD) extracorporeal circuit and may enter the bloodlines of the patient. The aim of the present study was to investigate possible sites of contamination. Seventeen patients performed 20 HD (Baxter AK200S  = 5 and Artis  = 15) and 930 ultrasound measurements of MBs/min (Hatteland CMD10 device). Detection ranges were diameters between 2.5 and 50 µm. Hemodiafiltration with postdilution (HDF-post) was performed in 14 dialyses, predilution (HDF-pre) in 1 dialysis, and HD using hemocontrol (HDhc) in 5 dialyses. Measurement points were M1-after the blood access, M2-before the dialyzer, M3-after the dialyzer, and M4-after the venous chamber. At each point, 10 measures of MBs were performed. MB contamination of the blood was larger at all points when the access was an arteriovenous fistula compared to a central dialysis catheter ( < 0.001). MB levels with the AK200 versus the Artis were lower at M1, higher at M2 ( ⩽ 0.005), and were similar at M3 and M4. HDF-pre had fewer MBs than HDF-post, whereas HDhc had more MBs than HDF-post ( < 0.001). An increase of MBs was seen at M2 during an internal "Autotest." No air alarms were induced during dialyses. MBs were detected in the extra corporeal circuit at all points investigated. The venous chambers used did not significantly reduce contamination. The detected MBs did not induce air alarms when the blood returned to the patient.