The wound drain I mentioned yesterday was a Bellovac Drain although I am sure there are other drains out there that do the same thing. This drain is inserted whilst the patient is still on the operating table. The idea is to drain the haematoma from the wound site. This is effectively just pooled blood and it is in question weather or not draining this blood does much. This blood is no longer part of the circulating volume and this isnt supplying any tissue. Once the blood is drained into the bag a nurse can just replace the bag and hook the blood filled back up to a standard IV for transfusion. Obviously you require a certain amount of blood before its worth replacing the bag, anything less than 120ml and it will probably get lost in the IV tubing.
In my opinion this is one of the greatest recent achievements of medical science. I am still in awe of the fact we can reinfuse a patients own blood from a wound drain.
Sometime a patient wont bleed enough to warrent transfusion, this largely depends on the operation and the surgeon involved. Total Knee Replacements always bleed well. However for those who dislike transfusions there are other options for boosting your circulating volume. First off you hang a bag of saline just to keep the volume in the vessels high, and then you can administer a drug called erythropoietin. The athletes among you might refer to this as Epo. Its a drug designed to increase the rate at which the body produces red blood cells. This is of particular interest to athletes as the mood red blood cells you have circulating, the more haemoglobin, which means more oxygen, which means the muscles are better fed during periods of heavy exercise.