Which of the following is the most common intrinsic platelet defect?
The most common intrinsic platelet defect is known as storage pool disease. It may involve loss of dense granules (storage sites for adenosine 5'-diphosphate [ADP] , adenosine triphosphate [ATP], Ca2 +, and inorganic phosphate) and α-granules (storage sites for a large number of proteins, some of which are specific to platelets [eg, PF4 and β-thromboglobulin], while others are present in both platelet α -granules and plasma [ eg, fibrinogen, vWF, and albumin] ). Dense granule deficiency is the most prevalent of these. It may be an isolated defect or occur with partial albinism in the Hermansky-Pudlak syndrome. Bleeding is variable; depending on how severe the granule defect is. Bleeding is primarily caused by the decreased release of ADP from these platelets. An isolated defect of the α-granules is known as gray platelet syndrome because of the appearance of the platelets on Wright's stain. Bleeding is usually mild with this syndrome. A few patients have been reported who have decreased numbers ofboth dense and α-granules. These patients have a more severe bleeding disorder. Patients with mild bleeding as a consequence of a form of storage pool disease may have decreased bleeding if given DDAVP. It is likely that the high levels of vWF in the plasma after DDAVP somehow compensate for the intrinsic platelet defect. With more severe bleeding, platelet transfusion is required.
Which finding is not consistent with TTP?
In TTP, large vWF molecules interact with platelets, leading to activation. These large molecules result from inhibition of a metalloproteinase enzyme, ADAMtS13, which cleaves the large von Wille brand factor molecules. TTP is classically characterized by thrombocytopenia, microangiopathic hemolytic anemia, fever, and renal and neurologic signs or symptoms. The finding of schistocytes on a peripheral blood smear aids in the diagnosis. Plasma exchange with replacement of FFP is the treatment for acute TTP. Additionally, rituximab, a monoclonal antibody against the CD20 protein on B lymphocytes has shown promise as an immunomodulatory therapy directed against patients with acquired TTP, of which the majority are autoimmune-mediated.
What is FALSE regarding coagulation during cardiopulmonary bypass (CPB)?
Under normal conditions, homeostasis of the coagulation system is maintained by complex interactions between the endothelium, platelets, and coagulation factors. In patients undergoing cardiopulmonary bypass (CPB), contact with circuit tubing and membranes results in abnormal platelet and clotting factor activation, as well as activation of inflammatory cascades, that ultimately result in excessive fibrinolysis and a combination of both quantitative and qualitative platelet defects. Platelets undergo reversible alterations in morphology and their ability to aggregate, which causes sequestration in the filter, partially degranulated platelets, and platelet fragments. This multifactorial coagulopathy is compounded by the effects of shear stress in the system, induced hypothermia, hemodilution, and anticoagulation.
Following a recent abdominal surgery, your patient is in the ICU with septic shock. Below what level of hemoglobin would a blood transfusion be indicated?
A 1988 National Institutes of Health Consensus Report challenged the dictum that a hemoglobin value of less than 10 g/ dL or a hematocrit level less than 30% indicates a need for preoperative red blood cell (RBC) transfusion. This was verified in a prospective randomized controlled trial in critically ill patients that compared a restrictive transfusion threshold to a more liberal strategy and demonstrated that maintaining hemoglobin levels between 7 and 9 g/dL had no adverse effect on mortality. In fact, patients with APACHE II scores of :s;20 or patients <55 years actually had a lower mortality. Despite these results, change in daily clinical practice has been slow. Critically ill patients still frequently receive transfusions, with the pretransfusion hemoglobin approaching 9 g/dL in a recent large observational study. This outdated approach unnecessarily exposes patients to increased risk and little benefit.
Less than 0.5% of transfusions result in a serious transfusion-related complication.
What is the leading cause of transfusion-related deaths?
Transfusion-related complications are primarily related to blood-induced proinflammatory responses. Transfusion-related events are estimated to occur in approximately 10% of all transfusions, but only less than 0.5% are serious in nature. Transfusion-related deaths, though rare, do occur and are related primarily to transfusion-related acute lung injury (TRALI) (16-22%), ABO hemolytic transfusion reactions (12-15%), and bacterial contamination of platelets (11- 18%).
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