Here’s a fun ICU puzzle: what is causing this crazy spiking pattern on the ECG waveform of both an intra-aortic balloon pump & ICU monitor?
A #MedEd 🧵 on an important clinical artifact, medical pumps, & the triboelectric effect.
We’ll need to go back 2500 years to understand the cool physics behind this important effect! #FOAMed #FOAMcc #PhysicsInTheICU
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Before we get to the cool physics behind this important clinical artifact, what device could attached to the patient that’s causing these crazy spikes on the EKG channels?
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The answer is: CRRT machine
In fact, any machine that uses a *ROLLER pump* can cause this artifact. (see the example below)
A roller pump squeezes tubing to generate flow. But it can also generate an electrical artifact that can interfere with many medical devices!
But why?
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In order to understand this phenomenon, we need to understand the triboelectric effect:
If you rub two different non-conductive materials on each other, electrons can accumulate electrons. This is the primary cause of static electricity.
For example rubbing a balloon against fur 👇
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Triboelectricity was discovered around ~600 BCE, when the Greek philosopher/scientist Thales of Miletus demonstrated that rubbing amber with cloth caused the amber to attract lightweight particles. This was the discovery of charge.
The word triboelectic comes from Greek tríbō (meaning “to rub”) & ḗlektron (meaning “amber”).
In fact, thats where we get the modern word "electricity";
It's named after the amber used by Thales to describe the triboelectric effect!
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Whenever your have friction between two dissimilar insulators you can get triboelectric charging, where electrons accumulate on one surface.
That's what's going on in roller the pump of our dialysis machine: with each rotation, the roller is rubbing against the PVC tubing. This accumulates an electric charge which is periodically discharged into the patient through the blood in the tubing!
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Other types of pumps don't have this problem. For example ECMO machines used in the ICU typically use a centrifugal pump (not a roller pump).
There are a couple advantages of this & one is no accumulation of static electricity! ⚡️
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But this artifact isn't just cool physics, it can cause real problems for several essential life support devices in the ICU.
For example, the roller pump on a CRRT machine can interfere with the EKG triggering on an intra-aortic balloon pump (IABP), just link in our case.
Here's a similar case report:
https://journals.lww.com/asaiojournal/Fulltext/2000/01000/Abnormal_Electrical_Stimulus_of_an_Intra_Aortic.31.aspx
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in four patients requiring both systems. The patients had acute renal failure in the face of multi-organ failure and were dependant upon the balloon pump for pressure support. Electrical interference created by the roller pump action of the CVVHD system was identified by the balloon pump as cardiac in origin, and it responded by inflation and deflation. As the blood pump rate was reduced, the interference reduced to the point of complete cessation when the blood pump was shut down. Whereas one patient transiently had a significant drop of mean arterial pressure (from 70 ± 4 to 40 ± 2 mm Hg) the other observed occurrences had no clinically significant sequelae. Electrocardiogram (ECG) tracings identified the abnormal stimulus and systematic review identified as potential sources for the creation of this interference static electricity buildup, piezoelectric properties of the polyvinyl chloride tubing, and, possibly but less likely, radiofrequency interference. A newer generation ECG cable and advanced cardiac rhythm recognition software (CardioSync) have been introduced with the Datascope System 98, and the ECG interference, although still occasionally present, does not cause erratic inflation and deflation of the intra-aortic balloon pump. Interference between different electrical support systems may occur, and we suggest that the systems be tested for compatibility before combined use and that older equipment be more rigorously tested for potential clinically significant interference....
The same artifact caused by roller pumps can also interfere with EEGs, causing an irregular 5-11 Hz spiking pattern.
Don't be fooled, it's not a seizure. It's a Roller pump artifact!
https://pubmed.ncbi.nlm.nih.gov/19715185/
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We describe an electrical EEG artifact seen during continuous renal replacement therapy (CRRT). This artifact was spiky waves that disappeared with grounding of the CRRT device allowing accurate interpretation of the EEG tracing.
@medicine there’s always trade-offs.
Several pros: Peristaltic/Roller pumps are simpler & don’t touch the liquid. Flow rate is linearly proportional to the rotation rate & thus easy to control/measure. It has less potential for hemolysis.
On the other hand roller pumps can generate very high pressures that can burst tubing. They can also wear out tubing. They may have triboelectric charging.
The Optimal pump depends on the application.
@nick I have inside information but could it be.... STATIC ELECTRICITY? :)
This is a wonderful example as
to the importance of getting all the signals into one place so that you can capture x-system influence/anomalies #allthedata
Nick Mark, MD 
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Aaron Nelson, MD MBS FAAP FAAN
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