We have had three occurrences of air being spotted down steam of the pump (Graseby 500) towards the end of blood infusions recently. The pumps are being used by experienced, trained staff who have had competency based training on the product.
The staff ensured that the air was not injected however their confidence has been knocked.

The bubbles have been between 3 and 12mm long in a standard blood set (not I believe enough to be dangerous but still worrying) with one infusion having 4 separate bubbles.

The giving sets on close inspection show many small bubbles above the pump typically smaller than 0.5mm diameter and the same below the pump but up to 2mm diameter; these bubbles are not apparent when the infusion starts. Watching the small bubbles during an infusion showed them slowly getting larger but not moving down the set. (sizes of bubbles at end of infusion)

The infusions are typically of around 250ml infused over two hours twenty minutes, so infusion rates around 100ml an hour.

The incidents have occurred with different pumps, bloods and batches of giving set.

I have tested these pumps to Graseby’s Checklist and found no problems; they have also been tested by a third party; I could not get air to go past the first blister and its air detection system, Graseby are also investigating this.

The blood is coming down immediately after matching so will still be relatively cold.

Does anyone know what is causing this problem?
What is a safe level of air to be injected into a vein? (Yes I have read the Infusion Pump Technical Article).

Lee

Hi Lee

I'm making the obvious assumption, that you're using the appropriate blood giving set.

Is this just a recent occurance or have you been troubled with it for some time?

I know blood outgasses when it is warmed, hence the need for an air trap on blood warming sets, but I'd be surprised it could happen as the blood is warming up to room temperature.

I've just spoken to our ICU staff and they have had no problems with blood and air in line, unlike some other fluids they put through.

Is this noticed at the beginning or latter part of the infusion?

I have a feeling that your pumps are OK but you've got problems outside your control.

Sorry not to be much help but I would be looking at the blood / admin lines myself as a next stage.

Good luck and keep us informed

Brian

Hi Brian

Yes they are Graseby Blood sets.

The first occurrence was in February then two this month. We have two other departments running bloods who have not noticed any problems.

The problem is noticed at the end of the infusion.

Lee

Must be out gassing in the line between the pump and patient Lee. I can't see any other reason.

Does the tubing become warm for any reason, radiators, sunlight ??

The fact that you get a few small bubbles above the pump in the short section of tubing whilst the larger quantity collects in the longer section would tend to support this view, also that the effect is cumulative and most noticable and the end of infusion.

You've got yourself a good one there mate!

Brian

Hi All,
Could it be cavitation causing air to be drawn into the blood due to too low a resevoir level in the chamber?
Did come acros this many, many years ago..........
Regards

Ed Bennett
Southwest Medical Ltd

Two factors that I would look at:- 1) Bag height 2) It's getting hot (as Brian mentions)!

Brian
You are right it has certainly got me thinking. The patients normally sit near some large windows I will sort out some monitoring to see if problems occur with higher temperatures or strong sunlight.

Ed
If I understand you correctly I would expect to see air above the pump.

Geoff
The patients sit in comfortable chairs, whilst the pumps are mounted on pole stands at a comfortable height for the nurses to operate(so at or just above the patients head height)with the bags hanging from loops that are 6 foot from the ground.

Lee

Hi Lee,
In your original post you said "The giving sets on close inspection show many small bubbles above the pump typically smaller than 0.5mm diameter and the same below the pump but up to 2mm diameter". The bubbles above the pump is what put me in mind of cavitation. If there really is no air bubbles above the pump then it can only be getting in at or around the pump head or being generated therin?
Will be watching with interest................

Ed Bennett
Southwest Medical Ltd

Hi, we dont use pumps at all primarily because the peristaltic pump part damages the blood cells as it forces them through.(unless transfusing paeds of course)
we use gravity sets and we dont warm the blood unless giving it to a hypothermic patient.
we dont have problems with air bubbles.
why dont you contact one of the transfusin specialist nurses, there is one at almost every hospital.

Hi Quinny

Small point, Graseby 500's don't use peristaltic action, they have a couple of small pistons which pump the fluid through compressable chambers in the giving set. Hence the cells don't get crushed - bit like using a series of sequenced syringe drivers!

Interestingly, Alaris have use peristaltic acion with their pumps and sell dedicated sets for blood delivery. Anyone able to provide a reasoning behind that? Is it the fact that the percentage of cells damaged is insignificant?? I know our BT service insist that all blood is delivered via pumps unless in an emergency.

Brian