We're going to kick this week off with a PSA requested by the admins and blood bank — a clarification on the kind of platelets we have and how (and when) to order them, especially as part of a massive transfusion protocol.
First, let's start with a quick review. The most common definition of "massive transfusion" is replacement of one blood volume (approximately 10 units, or 5 liters) within a 24-hour period; but more useful to us in the emergency setting are the alternative definitions of transfusion of >4 units of pRBC within 1 hour, or 50% of blood volume within 3 hours, with foreseeable ongoing need. In this setting, the patient is at risk from the lethal triad of hemorrhagic shock — hypothermia, acidosis, and coagulopathy. Healthcare institutions have developed their own "massive transfusion protocols" as streamlined workflows to expedite delivery/administration of blood products and mitigate the lethal triad.
As we've learned in prior POTDs, in MTPs we transfuse blood products in specific ratios in order to mitigate dilutional coagulopathies — fresh frozen plasma (FFP) provides the fibrinogen, protein C and S, and coagulation factors that are missing in packed RBCs, and platelets are platelets. Sometimes a protocol also calls for cryoprecipitate, which is derived from FFP and contains fibrinogen, factor VIII, factor XIII, and vWF. The "textbook" ratio that you'll hear is a 1:1:1 ratio of pRBCs:FFP:platelets, though some protocols call for a 2:1:1 ratio which has not been found to be inferior.
Here at Maimonides we use the 1:1:1 approach. However, that doesn't mean that we order 4 units of pRBCs, 4 units of FFP, and 4 units of platelets in SCM. Each "unit" of platelets in the 1:1:1 approach refers to a unit of platelets derived from whole blood donation, which yields >55 billion platelets in ~50 mL. However, as technology has advanced, most platelets are now gathered through apheresis — a procedure that removes platelets from blood and returns the remainder to the donors, yielding >300 billion platelets in ~250-300 mL. Thus, our single unit of platelets here is roughly equivalent to 5-6 old-school units of platelets.
As you can see on the ED blood bank request form, we order 1 unit of platelets in each round of MTP to go along with 4 units of pRBCs and 4 units of FFP. A similar ratio can be seen in the pediatric weight-based protocol as well. The indications for MTP here are also stated. For adults: massive bleeding, 10 units in short period with uncontrollable blood loss, ruptured aortic aneurysm, abruption placenta, post-partum bleeding. For peds: massive bleeding, anticipated blood loss of 100% TBV within 24 hours, ongoing hemorrhage of >10% TBV/minute, replacement of >50% TBV within 3 hours.
When you place the order for platelets through the "ED Blood Products Order Set", you can also see that 1 unit (at 200 mL/hr) is the default selection. Leave this at 1 unit for the vast majority of cases including MTP. If you order 4 units here, it'll look like you want to give the patient 20+ standard units of platelets. The blood bank won't actually give you extra units of platelets without question, but it creates confusion in the system.
Outside of massive hemorrhage, there are several indications for administering a platelet transfusion. The list of approved indications is found in the drop-down menu when ordering platelets through the order set, and include:
active bleed on antiplatelet medication with documented platelet dysfunction
platelet count < 20K prior to central line placement
platelet count < 20K prior to bone marrow biopsy/aspiration
platelet count < 20K prior to diagnostic lumbar puncture
platelet count < 10K with or without active bleeding
platelet count < 50K with active bleeding or prior to major surgery
platelet count < 100K prior to neurosurgery or ophthalmic surgery
A single unit of apheresis platelets is expected to increase the platelet count by 30K-60K (per µl) in a 70 kg patient. For most of the above indications, transfusing 1 unit is generally sufficient; if the deficit is wide, a 2nd unit can be ordered after rechecking a platelet count.
There are times when the platelet count is low and platelet transfusion is not indicated. In immune thrombocytopenic purpura, treatment is IVIG + steroids with platelets only recommended prior to procedures/surgery or if there is life-threatening bleeding. Meanwhile, platelet transfusion is contraindicated in thrombotic thrombocytopenic purpura and heparin-induced thrombocytopenia due to increased risk of arterial thrombosis and death, with the exception of cases of life-threatening bleeding.
Further reading on recent guidelines from the Association for the Advancement of Blood & Biotherapies and Pathology and Laboratory Medicine at Henry Ford Health are linked.