The sensor in the venous chamber does not prevent passage of air bubbles during hemodialysis.

We previously showed, in vitro, that micro bubbles pass the air trap without inducing an alarm. The aim was to investigate if micro bubbles bypass the detector during hemodialysis (HD). During HD (40 patients, 47 HD sessions, 231 measurements), an ultrasound detector was fixed just after the venous air trap. Micro bubble size was measured in the range from 5 microm up to >42.5 microm. Blood flow was at a mean 346 mL/min (SD +/- 57). The mean of all micro bubbles per minute, without inducing an alarm, was at start 128 (range 0-769). Measurements revealed the presence of micro bubbles in all of the series and in 90% of the measurements. There was no difference between start and end of the same dialyses. There was a correlation between blood flow and extent of micro bubbles for the smaller sizes and the sum of all bubbles (r > or = 0.29, P < or = 0.026). Micro bubbles passed the air trap without alarming. Most bubbles were approximately 5 microm.