EBME Forums Forums Maintenance Technical Assistance Haemodiafiltration and ECG monitoring

We keep experiencing difficulties with ECG monitoring (gross noise and interference) when patients on ICU are undergoing haemodiafiltration.

It happens with a range of different monitoring equipment, Kontron, Propaq, Fukuda Denshi etc, adjusting monitoring settings filters etc does not resolve the problem.

Does anyone know exactly what the underlying cause is, it seems to relate somehow to the peristaltic pumps ?do they cause potential differences within the blood resulting in current flow and surface potentials on the patient.

If anyone knows of a solution or ways of mimising the problem please let me know.

Paul
I've never heard of anything like this. Are you sure the haemodiafiltration unit is not faulty?
I doubt whether the filtration causes enough of change in physiological signals to cause this kind of interference.
I would suspect something like an insulation failure on the pump mechanisms which could give rise to electromagnetic noise - this is more likely. Check to see if the interference is there when the pumps are not activated , and when the machine is not activated. Is the insulation breaking down due to heat/spillages etc. I would go down this road first until you are sure the insulation resistances, and leakage currents are within expected norms. Also check that earth connections (leakage paths) from the motors are good.
hope this helps.

We had this problem for several years. Apparently it is due to the pump in the haemofiltration machine causing static interference directly into the bloodstream and this being picked up on the ECG. We found it could be reduced by using antistatic spray on the pump tubing.

We had exactly the same problem on our Spacelabs Monitors - but the interference was worst on the pressure waveform where you would get very large, very sharp spikes, which couldn't possibly have been real pressure variations. When the filtration unit had been running for a bit, you could sometimes watch the spikes gradually reduce and then dissappear. But sometime they didn't - and we couldn't get rid of them with earth straps or by moving the machine. The interference was definately being picked up from the patient and not direct in the monitor, because if you disconnected the patient, you lost the inteference !
No one suggested static as a cause - but that sounds very plausible.

If static was the cause, and it was'nt electrical faults. It would suggest that the materials being used i.e. the rollers, and tubing should be conductive?

Check whether you have a proper earthing in the ICU. Due to some earth loop this type of ECG interferance can occur.We had this problem.

We had a similar experience in our ITU some months ago. The haemofiltration unit caused severe disruption to the ECG trace on a Marquette monitor. Turning the haemofiltration unit off and then on again cured the problem and we've had no further reports since. Consequently, we weren't able to find the cause of the problem.

Eukeka (I hope) I have just received a copy of an ECRI Health Devices report, March-April 1991-Vol.20,Nos.3-4.
This contains a description of artifactual noise associated with infusion pumps and haemodialysis machine pumps, the article contains the following explanation "ECG artifact is caused by the cyclic pinching and releasing of the polyvinyl chloride (PVC) tubing (or possibly other plastic parts) in the pump, which can generate electricity through piezoelectric or static electricity effects. The resulting electrical signal flows into the patient through the fluid in the tubing and may be picked up through the ECG electrodes. The currents associated with this signal pose no electrical safety risk".
The article goes on to recommend the use of good quality electrodes, proper skin preparation, monitoring lead selection etc.

Hope this is useful to you, thanks for your comments.

It might "pose no electrical safety risk", but if it seriously interfers with the intensive monitoring being done, it must surely create a risk ? We found that when the problem was really bad, the staff in ICU had to switch the alarms off - or at least set them at silly limits.
I assume you are a member of ECRI, Paul, to be receiving copies of these reports - or is someone in our hospital filtering them out before they get to me I wonder!

I agree knowing of a possible cause does not solve the problem, and we have similar experience of unusable alarms and disruption of the ECG waveform such that it would be impossible to see fine VF or event developing VT.

We are now putting in place a monitoring and response process to try and identify the circumstances, patient, environment, equipment operation, use of monitor elecytrodes etc, which I hope will enable us to understand better and find out whether or not spraying pumps with anti-static cleaner or other interventions resolve the problem.

Unfortunately we do not have ECRI membership, as the Trust will not pay the fee, you all know how the NHS works!!