Old dogma die hard. One of them is not heating platelets when giving transfusions. This breaks up the flow of transfusions and makes the process somewhat erratic. But the platelets are obviously heated when entering the body – the extra few, fever-like degrees of a fluid warmer can hardly matter. So many ignore this guideline, and just heat. But the question often surfaces, and sometimes brings a slight unease to the trauma team.

Platelet recommendations
Happily, someone else have been annoyed by the don’t-heat-the-platelets strategy, and have already done some research. The recommendation of not warming platelets seem to stem from fear of platelet activation, and cemented by fluid warmer manufaturers’ operator’s manual, where platelets are not recommended to be warmed – because they haven’t done the testing required to get FDA approval. But it’s hard to find any clinical evidence opposing platelt warming. Miller’s says blood warmers can reduce the number of platelets reaching the circualtion, as platelets may be activated and bind to surfaces of the infusion set/warmer.

Secondly, we will look briefly at another platelet dogma: not pressurising platelet bags. But first: the platelet warming:

The study
The Konig study in Anaesthesia and Analgesia used 10 units of three-day old platelets, and the researchers drew control samples from the bags, before running them through a fluid warmer (the Ranger system was used). This device will, like most fluid warmers, warm up to 42 degrees and is approved from PRBC and plasma. Both the control and the warmed platelets were tested using TEG and platelet aggregometry (PAP-4, but similar to Multiplate).

The Konig study recognises that small differences cannot be found with this small sample, but it was impractical to use 300 packs of platelets to get the necessary power needed for small differences.

This study found no significant differences in the PLT aggregation tests or in the TEG max amplitudes between the room temperated control platelets and the warmed platelets that held a temperature of 38 degrees C +/- 2 degrees, so, up to 40 degrees C.

There was up to a 5% difference in platelet function between control and warmed samples, but the intertest variability was quite large in both the control and warmed platelets.

But do platelets crack under pressure?
The other dogma is that platelets cannot be infused by using rapid infuesers or pneumatic pressure on the platelet bag. Not many studies to be found here, but the one from Thrombosis Research listed below this post, looked at both warming and pressure, then measuring platelet function using platelet aggreometry, and found no difference to the control plasma. But this study also used just 10 bags of platelets and measured in vitro platelet function.

There’s also another study from Transfusion 2010 looking at pressurising platelets, finding no significan functional degradation. This study used TEG and flow cytometry for platelet function assessment, where platelet aggreometry would be considered the gold standard. And again, this was an in vitro study.

There seems to be no major harm to platelet function by fluid warming during infusion of platelets, nor pressurising the infusion bag. The evidence is limited, but no major harm has been found, nor can major harm be deducted by the physiology of warming or pressurising transfusions of platelets, apart from a possible loss of some platelets through activation. So, any degradation seems to be minor, of less impact than time degradation from storing – and without real clinical implications. But the evidence is limited.

I would adopt a strategy in massive bleeeds where platelets are transfused pressurised and warmed as the rest of the blood components. This may differ from more defensive approaches adopted by many centres and guidelines. It can be useful to discuss these strategies.

Stored platelet functionality is not decreased after warming with a fluid warmer, Anesth Analg, 2013.

Pressure-aided transfusion of platelets: does it affect the platelets?, Transfusion, 2010.

Response of platelet concentrates to pressure and temperature changes without impairment of the in vitro function, Thrombosis Research, 2015.

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