Air Bubbles Pass the Security System of the Dialysis Device Without Alarming

Abstract

During hemodialysis microembolic findings have been noted after the venous chamber (subclavian vein). The aim of this study was to evaluate if air could pass the venous chamber and, if so, if it passes the safety-system detector for air-infusion without triggering an alarm. Various in vitro dialysis settings were performed using regular dialysis devices. A dextran fluid was used instead of blood to avoid the risk of development of emboli. Optical visualization as well as recirculation and collection of eventual air into an intermediate bag were investigated. In addition, a specifically designed ultrasound monitor was placed after the venous air trap to measure the presence of eventual microbubbles. Speed of dialysis fluid was changed, as was the level of the fluid in the air trap. Thereby a fluid level was considered "high" if it was close to the top of the air trap and "low" if it was around the mid part of the air trap. By optical vision microbubbles were seen at the bottom of the air trap and could pass the air trap towards the venous line without alarming. During recirculation several mL of air were collected in an intermediate bag after the venous line. Ultrasound monitoring exhibited the presence of microbubbles of the size of approximately 5 microm upwards passing to the venous line in all runs performed. Amount of bubbles differed between devices and in general an increased fluid speed correlated significantly with the increased counts of microbubbles/min. No alarming of the detector occurred. A more concentrated fluid allowed higher counts/min when flow was increased to 600 mL/min. Data revealed that air passes the safety-sensor in the air trap without alarming. The presence of air increased in general with fluid speed and a lower fluid level in the air trap. Differences were present between devices. If this affects the patients has to be elucidated.

Two‐Dimensional Computational Analysis of Microbubbles in Hemodialysis

“…1), with a range of flow rates that correspond to those investigated by Jonsson et al (5). 1), with a range of flow rates that correspond to those investigated by Jonsson et al (5).…”

“…In the present analysis, blood is modeled as an incompressible, homogenous, and Newtonian fluid with a density of 1050 kg/m 3 and viscosity of 0.003 kg/ms. 1) in a Lagrangian frame has been implemented to track the bubbles; this is suitable for the low concentration (a volume fraction less than 10%) of bubbles inside the air trap (1,5). ANSYS Fluent 13 software (Canonsburg, PA, USA) was used to solve the finite volume approximation of the Navier-Stokes equations.…”

Multidisciplinary Evaluation for Severity of Hazards Applied to Hemodialysis Devices

“…In particular, they could explain the high pulmonary morbidity that affects long-term patients, even if clinical confirmation is pending. In fact, air detectors in current HD devices are not designed to prevent infusion of microbubbles (19,20). In accordance with the rationales given by Polaschegg (21), we considered as NS the long-term effect of this hazardous situation.…”

Pulsatility Produced by the Hemodialysis Roller Pump as Measured by Doppler Ultrasound

“…There have been several cases which report the presence of air emboli or microbubbles within the extracorporeal circuit (1)(2)(3)(4)(5)(6). All hemodialysis circuits contain an air trap on the venous side to measure venous pressures and to prevent large air bubbles from entering the patient.…”

“…Microbubbles in the range of 5-42.5 μm have been shown to pass through the venous air trap without activating the alarm and enter the blood stream (1,2,5,7). In addition, preliminary computational simulations have shown the inefficiency of the venous air trap in trapping bubbles smaller than 200 μm (7).…”