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HAEMATOLOGY (ANAEMIA (Transfusion targets - TRICC study (NEJM 1999 -…
HAEMATOLOGY
ANAEMIA
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Haemolysis
Congenital
G6PD, sickle cell, spherocytosis
Acquired
Immune mediated
MAHA - ITP, TTP, DIC, haemolytic uraemia syndrome
TTP - ADAMTS13 - usually responsible for breakdown of vWF - low ADAMTS13 means TTP (vWF accumulates and prothrombotic state occurs, planet adhesion causes mechanical shearing to rbcs and MAHA). Plasmapheresis and steroids.
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Non-immune mediated
Mechanical destruction - extra-corporeal circuits, IABP, VAD, infection (clostridium perfrinigens), drug induced
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anaemia of inflammation - Inflammation -> cytokines (IL6) -> increased hepcidin -> decreased iron release from bone marrow, decreased iron release from macrophages, decreased absorption of iron -> suppressed erythopoeisis
Transfusion targets - TRICC study (NEJM 1999 - liberal (100) vs. restrictive (70g/L) - worse outcomes in liberal group - NB - underpowered and before leucodepleted blood. TRISS study 2014 NEJM - no difference on outcomes for 70 vs 90. Less transfusions in 70 group.
Sepsis - 70g/L as per TRISS - aiming for higher Hb as per Rivers not bourne out by ARISE/PROMISE/PROCESS trials
Post elective cardiac surgery - >90 as per Murphy et al NEJM 2015 - slightly increased mortality in restrictive group
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TRALI - non-cariogenic pulmonary oedema following transfusion of blood products. Typically associated with platelets and FFP - much less common in PRBC with leucodepleted blood. Results from capillary leak due to white cell antibodies antibodies and granulocytes OR cytokines in lung parenchyma. Can lead to ARDS. 1 in 5000 transfusions.
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Thrombocytopaenia
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Bone marrow suppression - ETOH, Linezolid, Bactrim, chemotherapy, myelofibrosis, neoplasm, viral infection
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IMMUNE SYSTEM FUNCTION
Innate immune system - responds to infection/stress with acute phase response - release of inflammatory mediators, decrease in Hb/iron and albumin (through redistribution. one of main components is fibrinogen (raised ESR). Also involves natural Killer cells, alternative complement pathway and some macrophages. Neutrophils are most numerous white cells - phagocytes that migrate out of capillaries in acute inflammation. Segment more the older they get, preferentially phagocytose sugars and work less well in the presence of sugars.
Adaptive immune system - specificity (MHC antigen presentation), memory (cell surface receptors on lymphocytes - memory B cells), amplification (cytokines and CD4 cells) and diversity (cytokines).
Class 1 MHC - present on surface of most cells. Present fragments of intracellular organisms (e.g. viruses) on cell surface. Activated cytotoxic T cells (CD8) then initiate cell death to kill virus.
Class 2 MHC - present on macrophages and monocytes - present fragments of phagocytksed micro-organisms to CD4 (helper T cells) and B cells. Activation of CD4 cells leads to release of a wide range of cytokines with effects on numerous other cell types including B cells (therefore central player in amplification and diversity responses.
Viral infection - CD8, Intracellular infection - CD4, Encapsulated bacteria - opsonising antibody response, other bacteria e.g. Neisseria - complement activating response
Encapsulated bacteria (HiB, Strep. Pneumo., Neisseria men., Group B strep., Kleb. Pneumonia. Salmonella) are covered by a polysaccharide capsule - the negative charge and smoothness make primary phagocytosis difficult therefore opsonisation becomes more important. Asplenia/complement deficiencies make infection more likely.
Immunodeficiency - antibody deficiency, complement deficiency, cell mediated deficiency, phagocyte dysfunction and combined immunodeficiency.
Primary antibody deficiency disorders and acquired (asplenism, B cell CLL, lymphoma and multiple myeloma all result in decreased antibody function.
Cellular immune deficiency - Di-George syndrome (congenital lack of thymus).Acquired - HIV, Hodgkins and T cell lymphomas, immunosuppression for transplants. Usually result in re-activation of indolent infection.
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Disorders of phagocytosis - increased propensity to bacterial (esp. Staph. Aureus) and fungal infection (aspergillus.candida). Primary disorders are rare acquired is primarily neutropenia (drug therapy, aplastic anaemia, cytotoxic chemotherapy)
Combined immune deficiency - SCID, post haemopoietic stem cell transplantation and CRITICAL ILLNESS (
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