Download MBBS Rheumatology Lecture Notes

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Cyanosis Diagnostic Tests

• Arterial Blood Gases

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• PaO2 measures oxygen dissolved in the liquid component of blood (the plasma)
• Oxygen saturation is calculated, not measured
• Carbon monoxide poisoning and methemoglobinemia can have a normal PaO2 yet poorly oxygenated blood
• Cyanosis unresponsive to oxygen -- consider
• Hemoglobinopathy

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• Right to left cardiac shunts (congenital / functional)

Carboxyhemoglobinemia doesn't cause cyanosis (no reduced hemoglobin)

Cyanosis

Methemoglobinemia (1)

• Methemoglobinemia

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• Chemicals: aniline dyes (e.g. shoes), nitrate food additives (e.g. sausage)
• Drugs: lidocaine, sulfonamides, dapsone, benzocaine, Pyridium, nitrates, nitrites, sulfonamides; not at usual exposure levels
• Fe++ (ferrous) iron in Hb becomes oxidized to Fe+++ (ferric) state – hemoglobin is then incapable of carrying O2
• Approximately 1.5gm of Hb need to be in the Fe+++ (ferric) form for cyanosis to develop (chocolate brown blood)

Methemoglobinemia (2)

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• Methemoglobinemia (cont' d)
• Anemic patients require a higher % of Hb being Fe+++ (ferric) to be cyanotic (e.g., 1.5gm/6gm = 25% vs. 1.5gm/15gm = 10% (although may be disproportionately symptomatic)
• Antidote: methylene blue (reduces Fe+++ back to Fe++)
• PaO2 is normal (because ABGs measure oxygen that is dissolved in the plasma – not than attached to Hb)
• Pulse ox misleading (usually 80-85% with metHb) – but reading is likely to be falsely high with significant methemoglobinemia (>15%)

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• Chocolate colored blood = methemoglobinemia

Methemoglobinemia (3)

Amyl nitrite

Aniline derivatives

Butyl nitrite

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Bismuth subnitrite

Dapsone

Lidocaine

Benzocaine

Menthol

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Naphthalene

Phenytoin

NTG

Nitrophenol

Nipride

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Nitrites

Nitrates

Phenacetin

Phenols

Pyridium

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Quinones

Silver nitrate

Sulfonamides

Room deoderizer propellants

Packed Red Cells (PRBC)

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• Shelf life of up to 42 days
• Stays unclotted due to calcium chelation by citrate additive
• Hematocrit 65-80%
• One unit PRBCs increases Hb by 1.5 g/dL
• Human blood volume = 70ml/kg = about 5 liters in 70kg adult

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• Has essentially no platelets / limited clotting factors

Type O = universal donor

Type AB = universal recipient

Packed Cells vs. Whole Blood (1)

• Packed Cells

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• Less volume / less fluid overload
• More RBCs per volume transfused
• Decreased citrate infusion = better coagulation
• Decreased infusion of protein antigens (less autoimmunization)
• Decreased infusion of potassium (from lysed RBCs)

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• Only diluent for RBCs is normal saline
• Calcium in Ringer's lactate causes microclots to form

Packed Cells vs. Whole Blood (2)

Human Whole Blood CPD

Citrate/Phosphate/Dextrose

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Human Whole Blood CPD: Whole blood in collected in 200 mL or 400 mL bag with CPD, an anticoagulant and preservative.

This is for patients who need both red cells and plasma. Irradiated products are also available.

Packed Red Cells MAP (Mannitol/ Adenine/Glucose/Phosphate/Citrate)

Red cells are separated from 200mL or 400mL of whole blood by centrifugation and a preservative, MAP is added. This is the most popular product among red cell products. This is for patients with anemia or dysfunctional red cells.

Massive Blood Transfusion

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• Results in a dilutional coagulopathy since packed cells are deficient in clotting factors and platelets
  • Monitoring of coagulation by lab tests is likely to be impractical in massive transfusions
  • Use of fixed ratios of packed cells, FFP and platelets is now the trend (but the ideal ratio is not known)
• Hypothermia can be a complication -- blood warmer
• Microaggregates from RBC, WBC, platelet debris showered into pulmonary capillary bed causing ARDS -- use 40 micron filter to decrease this risk

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• Citrate toxicity is seen in large volume whole blood transfusions – can result in bleeding and manifestations of hypocalcemia (decreased cardiac pumping power)(QT prolongation)

Immediate Transfusion Reactions (1)

• Acute hemolytic transfusion reactions
• Results from infusion of incompatible RBCs (usually ABO incompatible)
• RBCs are destroyed by antibodies

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• Fever, chills, low back pain, breathlessness, burning at infusion site
• May progress to hypotension, bleeding, respiratory failure, ATN

Immediate Transfusion Reactions (2)

• Acute hemolytic transfusion reactions (cont' d)
• Treatment

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• Stop transfusion
• Hydration to promote brisk diuresis
• Symptomatic
• Lab
• Free hemoglobinemia and hemoglobinuria

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• Haptoglobin (binds to free hemoglobin) is decreased
• Coombs testing of pre- and post-transfusion blood ( a test for globulin antibodies on the surface of RBCs)

Immediate Transfusion Reactions (3)

• Febrile nonhemolytic transfusion reaction
• Most common transfusion reaction

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• Fever and chills
• Due to interaction between recipient and donor non-RBC components
• May be hard to distinguish from early acute hemolytic reaction
• Must stop transfusion and r/o hemolysis

Immediate Transfusion Reactions (4)

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• Allergic transfusion reactions
• Range from minor to anaphylaxis
• Due to plasma protein incompatibilities
• Erythema, urticaria, pruritus, bronchospasm, vasomotor instability
• Reaction severity is not dose-related

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• Discontinuation of transfusion is not always required

Delayed Transfusion Reactions (1)

• Infections
• Overall risk of acquiring a viral, bacterial, or parasitic infection is 1:500
• Risk of hepatitis B is 1:200,000

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• Risk of hepatitis C or HIV is 1:2,000,000
• Risk of West Nile virus and Creutzfeldt-Jakob disease is unknown
• Chlamydia transmission is common
• Delayed hemolytic reaction
• Antigen-antibody reaction 7-10 days after transfusion

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• Other transfusion-related risks
• Volume overload
• Hypothermia

Delayed Transfusion Reactions (2)

• Other transfusion-related risks

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• Noncardiogenic pulmonary edema
• Pulmonary edema secondary to incompatibility of passively transferred leukocyte antibodies
• Electrolyte imbalance
• Hyperkalemia from lysed RBCs
• Low calcium from excess citrate causing chelation (causes prolonged QT)

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• Hypokalemia from citrate being metabolized to bicarbonate and resultant plasma alkalosis

Platelets

• Five day storage life
• 1 unit of platelets derived from one unit of whole blood will raise the recipients platelet count by 10,000
• A platelet pheresis pack contains about six units of platelets and is derived from a single donor

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• Give ABO compatible platelets whenever possible (a small amount of RBCs contaminates platelet packs)

Platelet Disorders (1)

• Nonpalpable purpura – think low or dysfunctional platelets
• Palpable purpura – think angiopathy / vasculitis
• Causes of dysfunctional platelets (increases the bleeding time / platelet function test):

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• Aspirin (for the life of the platelet)
• NSAIDS (only as long as in the blood stream)
• Ticlopidine (Ticlid) / clopidogrel (Plavix)
• Other drugs less commonly (penicillin / cephalosporins / calcium channel blockers / propranolol / nitroglycerin / antihistamines / others

Platelet Disorders (2)

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• Causes of low platelet counts (increases the bleeding time / platelet function test)
• Decreased platelet production
• Aplastic anemia / viral infections / drugs (ethanol, thiazides, estrogens, chemotherapy drugs, heparin)
• Increased platelet destruction
• ITP / TTP / HUS / DIC / viruses / drugs (heparin)

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• Splenic sequestration (trapping of RBCs)
• Hypersplenism (enlarged, overactive spleen [rapidly and prematurely destroying RBCs])
• Hypothermia
• Platelet loss
• Bleeding / hemodialysis

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Immune Thrombocytopenic Purpura (1)

• Can be primary where the immune trigger is unknown (called by some idiopathic thrombocytopenic purpura – but is still immune in nature)
• Can be secondary – immune stimulus is known (the vast minority of cases)
• Pediatric version
• Peak age, 5 y/o, both sexes equally

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• Sudden onset of petechiae or purpura several weeks after an infectious illness
• Most cases resolve within six months
• Generally do well without treatment

Immune Thrombocytopenic Purpura (2)

• Adult version

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• Insidious onset / chronic duration / mostly women
• Genetic propensity in certain families
• Diagnosis largely via exclusion from other causes of thrombocytopenia
• Generally no other findings except petechiae and purpura – CBC normal except for low platelets
• Platelet count >50,000 usually found incidentally

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• 50,000-30,000 = excess bruising with minor trauma
• 30,000-10,000 = spontaneous petechiae and bruising
• < 10,000 = spontaneous visceral hemorrhage

Immune Thrombocytopenic Purpura (3)

• Thresholds for treatment

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• A platelet count of 20-30,000
• Active bleeding with a 30-50,000 count
• Treatment:
• Suppress the immune response first with prednisone (50-75% remission rate by 3 weeks)
• High-dose RhoGAM (anti-D immune globulin) is efficacious (can only be given to Rh+ patients)
  • Is more efficacious and more expensive than steroids

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  • Causes spleen to destroy antibody-coated Rh+ red cells and destroy less platelets
• Can also give IV immune globulin (not as effective and can have adverse side effects)

Immune Thrombocytopenic Purpura (4)

• Fear of intracranial bleeding usually prompts treatment (major cause of mortality due to ITP – especially in the elderly)

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• After suppressing the immune system about 2-3 times the calculated number of platelets need to be given to get the count over 50,000
• Generally, in adults, one platelet pack will raise the platelet count by 10,000
• Splenectomy is the ultimate treatment for those not responding or having relapses
  • Is not always effective (about 70% effective)
  • Accessory spleens may be the cause of lack of success
  • Predisposes the patient to serious bacterial infections (need all manner of immunizations)

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Tests of Hemostasis (1)

• Bleeding time
• Has been replaced with the lab-performed "Platelet Function Test"
• Measures platelet function

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• Prolonged by uremia, NSAIDs, ASA, von Willebrand's
• Not reliable for predicting risk of bleeding.

Tests of Hemostasis (2)

• Prothrombin time (PT)
• Measures extrinsic pathway (tissue factor) and common pathway (prothrombin ? thrombin ? fibrinogen ? fibrin)

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• Reported as INR (INR=PTtest/PTnormal)
• Prolonged PT (possibly also prolonged aPTT due to effects on final common pathway)
• Warfarin (Coumadin)
• Liver disease
• Vitamin K deficiency

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• DIC

Tests of Hemostasis (3)

• Activated partial thromboplastin time (aPTT)
• Measures intrinsic system and common pathway
• Prolonged aPTT

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• Heparin
• Hemophilia
• von Willebrand's disease
• Lupus anticoagulant

Tests of Hemostasis (4)

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• Platelet count
• Decreased production: viral infections, marrow infiltration, drugs (worst = heparin [a major complication of this drug], gold, sulfa antibiotics, quinine, quinidine, chronic alcohol use)
• Increased destruction: viral infections, ITP, TTP, DIC, HUS, heparin, protamine, splenic sequestration, uremia, hemorrhage

The Coagulation Cascade

Intrinsic Pathway

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(Measured by Partial Thromboplastin Time)

Blood Trauma

Exposed Collagen

Kallikrein

XII

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XIIIa

High molecular weight Kininogen,

Platelet phospholipid

Prekallikrein

XI

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? XIa

Ca++

IXa

(Hemophilia B) IX

(Hemophilia A

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VIII

von Willebrand's Disease)

Common Pathway

Ca++, platelet phospholipid,

thrombin

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Prothrombin (II)

XIII |

XIIIa

Extrinsic Pathway

(Measured by Prothrombin Time)

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Tissue Trauma

Releases

Tissue Thromboplastin

(includes phospholipids and lipoproteins)

VIIa

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Xa

Prothrombin Activator

?Thrombin (IIa)

Fibrinogen

Fibrin Monomer

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Fibrin Threads

(clot)

Disseminated Intravascular Coagulation (DIC) (1)

• Also known as “consumptive coagulopathy” is an extrinsic pathway problem (vs dilutional)
• Most commonly caused by liberation of tissue activating factor ? small fibrin and blood clots deposited in the microcirculation (consume clotting factors; can cause tissue hypoxemia) ? fibrinolysis ? fibrin degradation products and d-dimer

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• Causes: meningococcemia (most extreme form of DIC), trauma (especially head), sepsis, retained products of conception

Disseminated Intravascular Coagulation (DIC) (2)

• Signs
• Bleeding
• Thrombosis

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• Purpura fulminans
• Gangrene
• Multisystem organ failure
• Lab Findings
• Prolonged PT, aPTT (+/-)

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• Low platelet count
• Low fibrinogen level (but may be normal yet DIC is present / In one study only 28% of DIC patients had a low fibrinogen – 22% in another study)
• Elevated FDPs and d-dimer (combo was 91% sensitive / 94% specific in one study
• Fragmented RBCs

Disseminated Intravascular Coagulation (DIC) (3)

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• Treatment of DIC
• Treat the precipitating problem
• If primarily bleeding manifestations, follow the prothrombin (best single test in this setting)
• Give FFP replacement (10-15ml/kg) if the prothrombin time is prolonged plus vitamin K and folate
• May give platelets if needed as well

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• If primarily thrombosis, consider low-dose heparin infusion

Thrombotic Thrombocytopenic Purpura (TTP)

• Similar to DIC
• Five clinical features:
• Severe decrease in platelets

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• Severe microangiopathic hemolytic anemia with red cell fragmentation
• Transient neuro deficits
• Renal failure
• Fever
• Systemic endothelial cell damage leads to release of von Willebrand factor and consumption thrombocytopenia--small thrombi occlude arterials in heart, lung, kidney, pancreas, adrenals leading to end organ ischemia

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• Causes = idiopathic, drug-induced, pregnancy, infection
• Treatment: steroids, plasmapheresis, FFP
• Avoid platelet transfusion (can aggravate thrombosis)

HUS / TTP / DIC

*MAHA = microangiopathic hemolytic anemia

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Heparin

• Inhibits clotting factor activity
• Doesn't cross placenta (even LMWH doesn't)
• Complications: bleeding, decreased platelets (aggregation / splenic sequestration / antibody formation [can immediately reduce platelets if previous exposure to heparin, otherwise takes 6-10 days to occur])

Reversed with protamine sulfate

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(1mg reverses 100 units)

Low Molecular Weight Heparin

• At least as efficacious as standard heparin
• Doesn't cross placenta
• Short chains derived from standard heparin

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• Once or twice daily dosing
• Less likely to cause thrombocytopenia
• Reliable dose/response curve = no monitoring
• Does not affect the aPTT
• Each LMWH product is produced differently and has different doses and frequency of dosing

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Warfarin (1)

• Inhibits liver synthesis of vitamin K-dependent clotting factors (II, VII, IX, and X)
• Monitored by PT (INR)
• Over-anticoagulation will also cause prolonged aPTT because both the PT and aPTT measure the function of the final common coagulation pathway
• Multiple drugs (particularly oral antibiotics – inhibit gut bacteria needed for vitamin K production) can increase the effects of warfarin

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Warfarin (2)

• Treatment of warfarin-induced over anticoagulation depends on the urgency of the clinical situation:
• Stop the drug (2.5 day half-life)
• Parenteral vitamin K (takes 12-24 hours)
• IV may be associated with anaphylactic reactions – IM safer

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• May last up to 2 weeks making reanticoagulation problematic
• Fresh frozen plasma (10-15ml/kg, may result in fluid overload, requires defrosting, may require significant time for infusion)

Warfarin (3)

• Treatment of warfarin-induced over anticoagulation depends on the urgency of the clinical situation:
• Prothrombin complex concentrates

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• Concentrates of II, VII, IX and X
• No defrosting required, small volume injected IV (30ml)
• Works immediately and is advised by the American College of Chest Physicians in their 2008 guidelines* and the British Committee for Standards in Haematology
• Very costly
• *The ACCP statement regarding the urgent reversal of warfarin anticoagulation: “Although fresh frozen plasma can be given in this situation, immediate and full correction can only be achieved by the use of factor concentrates because of the amount of FFP required to fully correct the INR is considerable and may take hours to infuse."

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Newer Anticoagulants

Direct Thrombin Inhibitors

• Attributes of both direct thrombin inhibitors and Xa inhibitors - oral dosing / predictable effects / fewer food and drug interactions / shorter plasma half-life / improved efficacy-safety ratio / once or twice a day dosing
• Primary indication – non-valvular atrial fibrillation to prevent strokes
• Direct thrombin inhibitors

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• Dabigatran (Pradaxa) / 80% excreted by the kidneys
• Thrombin is a component of the final common pathway of the clotting cascade
• A aPPT more than twice the upper limit of normal suggests excess bleeding risk
• An INR cannot be used to assess bleeding risk

Newer Anticoagulants

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Factor Xa Inhibitors

• Factor Xa inhibitors
• Rivararoxiban (Xarelto) / 35% renal excretion
• Apixaban (Eliquis) / 37% renal excretion
• Edoxaban (Lixiana) / 50% renal excretion

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• Xa is a component of the final common pathway of the clotting cascade
• aPTT tests are not appropriate for factor Xa inhibitor assessment
• An INR cannot be used, but a prolonged PT may indicate excess risk but direct quantitation is not reliable

Bleeding and Newer Anticoagulants

• Maximum effect on coagulation tests occur about 3 hours after ingestion – therefore it is important to know when the drug was taken

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• Plasma abundance of the drugs may block the effects of newly administered clotting factors
• Time is the most important antidote in the setting of non-life-threatening bleeding due to the relatively short elimination half lives of these drugs
• Normalization of hemostasis is about 12-24 hours with the Xa inhibitors and the direct thrombin inhibitors (assuming normal renal function in DTI patients) (consider dialysis with DTIs)
• Local hemostatic measures / fluid replacement / RBCs if needed / FFP as a volume expander (doesn't reverse these drugs)
• Consider tranexamic acid and desmopressin (transports Factor 8 and simulates release of von Willebrand factor)

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• If life-threatening bleeding, consider adding prothrombin complex concentrate (PCC) (no clinical evidence of its efficacy) and activated factor VIla

Sickle Cell Anemia

• A genetically based chronic hemolytic anemia
• Baseline hemoglobin = 6-9 g/dL
• 5-15% reticulocyte count

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• Cardiac and respiratory dysfunction is common
• Routinely icteric
• Splenomegaly ? splenic infarction ? autosplenectomy

Sickle Cell Anemia

Sickle Cell Vasoocclusive Crisis (1)

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• Cause: sludging of sickled RBCs causing microcirculation obstruction, ? viscosity, ischemic pain, infarction
• Precipitants: infection / cold exposure / dehydration / high altitude / exertion – common theme, increased need for cellular oxygenation / trigger is unknown in more than half of the cases
• Manifestations
• Musculoskeletal pain: most common presentation (arm, leg, low back)
• Abdominal pain: second most common presentation / diffuse, no peritoneal signs, poorly localized, rather sudden in onset

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What are the consequences of RBC sickling?

Sickle Cell Vasoocclusive Crisis (2)

• Acute chest syndrome
• The leading cause of sickler death and 2nd most common cause of hospitalization (pain is first) / most cases less than 21 years old
• Clinical syndrome:

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• New pulmonary infiltrate involving at least one complete lung segment (usually lower lobes)
• Chest pain
• Fever (more than 38.5C)
• Concomitant tachypnea, wheezing or cough
• In about half the cases the initial cause for admission is a reason other than acute chest syndrome (mostly with vaso-occlusive pain crisis)

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• In these cases, the syndrome develops on average 2.5 days into the hospitalization

Sickle Cell Vasoocclusive Crisis (3)

• Acute chest syndrome etiology
• Most common causes:
• Pulmonary infections (usually chlamydia / mycoplasma)

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• Pulmonary infarctions
• Fat embolism
• Can be a combination of the above
• Heavy emphasis on empiric treatment
• Oxygen (hypoxemia out of proportion to CXR findings is the rule)(also is noted in PCP pneumonia)

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• Antibiotics (always include a macrolide)
• Mechanical ventilation (13% in one large study)
• Incentive spirometry
• Pain management
• Bronchodilator therapy (even if not wheezing)

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• Transfusions (especially if at high risk)

Sickle Cell Vasoocclusive Crisis (4)

• CNS crisis: painless, cerebral infarction in children / hemorrhage in adults
• Other CNS problems: TIAs, strokes, seizures, paresthesias
• Renal crisis: infarction, hematuria, flank pain, papillary necrosis

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• Hand-Foot Syndrome: in first two years of age, swelling of hands or feet due to avascular necrosis due to vasoocclusion - may be first sign of sickle cell disease
• Priapism – exchange transfusion / corporal epi and aspiration

Hematologic Sickle Cell Crisis

• Splenic sequestration
• 2nd most common cause of death in SCD children (infections are first, mostly pulmonary)

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• Sickled blood blocks splenic outflow = hypovolemic shock, painful hepatosplenomegaly
• Treat with RBCs and exchange transfusion
• Aplastic crisis
• Failure of bone marrow erythropoiesis
• Reticulocyte count low

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• Precipitants: infection, ? folate
• Usually self-limited

Infectious Sickle Cell Crisis

• Infection is the leading cause of death
• Especially in children under 5

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• Have functional asplenia as a predisposer to infection

Prone to infection by encapsulated organisms e.g. Pneumococcus

Also prone to Salmonella (bone infection),

H. influenzae, Staph, E. coli and Mycoplasma

Also watch for influenza and parvovirus

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• Need immunizations to decrease risk of preventable infections
• Low threshold for antibiotics if infection suspected

Treatment of Sickle Cell Crisis

• Hydration
• Analgesics

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• Oxygen
• Transfusions if indicated
• Emergent exchange transfusion for serious sickle crisis (CNS infarction, sequestration)
• Antibiotics if indicated

Malaria (1)

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