Past tense? Is this no more completely or when you 'used to do them' past tense? What is Pressure Infusion?
In the past it was believed that SBP correlated with perfusion status.
(Some agencies still do, scary thought.)
In order to maintain SBP at about 120mmhg, even on patients still bleeding, we could add pressure to the crystaloid iv bags via anything from squeezing the bag with 2 hands, standing on it, placing the bag under the backboard of a patient on it, using an inflatable device specifically made for it, wrapping a blood pressure cuff around it, or even using a powered device called a rapid infuser.
http://www.smiths-medical.com/catalog/fluid-warming/fast-flow/hardware/level-1-h-1200.html
In our efforts, we poured fluid into people, 16L of NaCl is the most I ever saw on a trauma patient. From the time EMS got to them to when they arrested in the ED. (With a person on the team whose sole task was changing out empty bags)
Anyway, aside from proving we could maintain SBP with water, the outcome was death.
If you are not familiar with the term "bleeding cool-aid" it is because with so much crystaloid going in, the blood coming out of the wounds was so diluted it looked like red or pink cool-aid.
A couple of wars later, knowledge has improved a bit and we now know rapid crystaloid is only indicated in specific cases, like burns.
The rapid infusion of blood products, crystaloid, and medications in various patients is still indicated and useful, but the days of infusing crystaolid in every patient still bleeding trying to maintain SBP is outdated. (though as pointed out, some haven't caught on yet)
There are many practicioners still creeping around who were part of those days. Sometimes, particularly EMS providers, would bleed the air out of the bags "just in case" whenever they inserted an IV and hung fluids.
I am not surpised to hear people still routinely doing it, but aside from specific cases, it is a waste of effort.
Technique wise, those exceptionally skilled could spike a bag, withdraw the spike ever so slightly while simultaneously inverting and squeezing the bag removing the air, maintaining a water seal, and only spilling a few drops of the fluid before returning the spike to the full in position.