EBME Forums Forums Maintenance Technical Assistance ECG interference in Haemofiltration

Has anyone encountered problems with ECG monitoring whilst the patient is receiving haemofiltration? If so how did you overcome the problem? What are the contraindications?

Any input would be appreciated

yes. it is due to static.
one way of solving the problem is to use a little anti-static spray on the blood pump rotor.
It has been suggested that the problem could be down to the flow of the blood through the tubing, but if this was the case you also see the same problem in dialysis unit, but im not sure if many are connected to an ECG.
hope that helps some, I think Jan at Telford did a paper on this subject, dont know if it was ever finished.

If you find any thing else out i would like to know.
Scott

Hi Ironman,

What haemofiltration system are you using? What monitoring do you have?

We have Gambro Prisma machine with GE monitoring and have had no complaints of interference.

I can imagine the power supply causing some sort of interference when it drives the pumps.

Cheers

Rob

Infusion of electrolytes can cause small electrical currents to be generated, that can be observed on ECG monitoring, plus you have blood in tubing that encloses a relatively large area (for picking up interference) thus significant, i.e. measureable, potentials may occur across the heamofiltration circuit I suppose. Probably not this but it's a known problem that can occur.

Hi all,

We have Gambro Primsa and GE Solar monitoring in our ICU and have had this problem and still continue to get it quite often, we can however get rid of it 90% of the time and get a perfectly good trace with diagnostic filtering set.

We have found that if low impedance electrodes are used and the positions of right and left are moved slightly closer together and the reference electrode is positioned as close as possible to the access site, (not stuck on top of the dressing as I’ve seen a few times, following a call for a poor trace!) the trace is almost as good as with no CVVH running. Prior to this the skin is prepared by cleaning with an alcohol wipe following a slight abrasion with a tongue depressor.

Hope this helps
Matt

That's sounds like good practical advice - as Matt says, If you put surface electrodes closer together then the amplitude of ECG complexes tends to reduce (because the surface potentials tend to be smaller as distance between electrodes across the chest reduce and when the line between electrodes is anything other than the direction of depolarisation RA-LL - from base to apex of the heart - that's why LDII gives a bigger complex - it's along the long axis of the heart and in the direction of electrical depolaristion) so I guess visible interference will reduce as well (even if SNR does not increase). I think it's the filtering that really does the trick.

The thing that really improves CMRR, thus improves the differential gain relative to the 50Hz common mode interference that's present on all electrodes, is to get a really good low impedance contact with the patients skin. Any imbalance in the resistance "looking" into the leads that are used to measure a particular lead selection will reduce the CMRR or ability to reject common-mode noise, i.e. mains, which is present on all leads and the patient.

As an aside can I just comment about the Solars with anything more that diagnostic levels of filtering filtering set? I noticed a few years ago (and it mentions this in the manual) that if filtering is set to "severe", i.e. for ESU use in theatre, that the ECG complex can become so heavily distorted in the time domain it doesn't look like the trace should with monitoring or diagnostic filtering. Just thought I'd mention this for the sake of those who need to do look at the characteristics in the waveform (without distortion) on poorly patients on 3/5 lead monitoring. Heavy filtering is not suitable in all circumstances).

Good point about the filtering on the Solars, the number of times in CVVH applications I have been called to poor traces only to find the filter set to "maximum", as stated this setting changes the ECG morphology so much its nearly pointless monitoring at all, as we all know good preperation goes a long way to getting a good trace, start with the basic things first!

An anesthetist told me of the CM5 lead positioning pattern that he used in theatres when there was a lot of electrical interference from diathermy etc
It stands for Common-Mediastinum-V5 The leads are placed in a straight line with one active on the medicastinum and the other in the V5 position. This effectively looks down the length of the heart giving the largest trace. The Common is placed in line with these to give the greatest CMRR.
Simple but effective.
Robert

Good stuff - our haemofiltration equipment is contract managed so i cant really mention names or question the reliabilty of the equipment here: but yes we are using the GE solar monitor where the problem is prevalent -hit the nail on the head there cheers Matt/MR.Ling.

Matt Could you just expand on the "diagnostic filtering set"??

Right got ya Filter setting on the Solar Monitor set to "Diagnostic".