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ANAESTHESIA AND ANTICOAGULANTS. Done by: Dr. Ahmad Alrefaie. Hemostasis. Prevention of blood loss whenever a vessel is severed or ruptured. It is a combination of events that occur due to physical and chemical forces. Achieved by several mechanisms: Vascular spasm.

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ANAESTHESIA AND ANTICOAGULANTS


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anaesthesia and anticoagulants

ANAESTHESIA AND ANTICOAGULANTS

Done by:

Dr. Ahmad Alrefaie

hemostasis
Hemostasis
  • Prevention of blood loss whenever a vessel is severed or ruptured.
  • It is a combination of events that occur due to physical and chemical forces.
  • Achieved by several mechanisms:
  • Vascular spasm.
  • Formation of platelet plug.
  • Formation of blood clot as a result of coagulation.
  • Growth of fibrous tissue.
slide5
The ultimate step in clot formation is conversion of FIBRINOGEN , a soluble plasma protein into FIBRIN , an insoluble thread like molecule.
  • The conversion is catalyzed by the enzyme THROMBENat the site of injury.
  • Thrombin exist in the plasma in the form of an inactive precursor called PROTHROMBIN.
slide6
Prothrombin convert’s into thrombin by FACTOR X, a plasma clotting factor.
  • Factor X present in the blood in inactive form and must be converted into it’s active form by another activated factor, and so on.
why we use anticoagulants
Why we use anticoagulants?
  • Prophylaxis and treatment for deep venous thrombosis (DVT) and pulmonary embolism which are commonly associated with surgical procedures.
  • Mechanical heart valves.
  • Cardiac arrhythmias.
who are patient at risk for dvt
Who are patient at risk for DVT?
  • Major lower limb or pelvic surgery.
  • Trauma patient.
  • Malignancy ( increase the risk 7-fold).
  • Central neuraxial block significantly reduces the incidence of DVT after orthopaedic surgery but additional prophylaxis is necessary to reduce the rate to acceptable levels.
aspirin
Aspirin
  • Also called acytelsalicylic acid.
  • Impair platelet function by inhibiting platelet cyclo-oxygenase (COX).
  • Aspirin inhibits COX irreversibly, Therefore the antiplatelet effect of aspirin persists until a new platelet population is manufactured (at least 7 days).
indications
Indications
  • Local analgesic effect.
  • Antipyretic.
  • Anti-inflammatory.
  • Antiplatelet.
cox 1
COX 1
  • Continuously stimulated by the body.
  • Its concentration in the body remain stable.
  • Creates prostaglandins used for basic house keeping throughout body.
  • Prostaglandins stimulate normal body functions such as stomach mucous production, regulation of gastric acid and kidney water excretion.
cox 2
COX 2
  • Induced ( normally not present in cells).
  • Built only in special cells (A549 lung cells).
  • Used for signaling pain and inflammation.
  • Produces prostaglandins for inflammatory response.
  • Stimulated only as part of immune response.
nsaids
NSAIDs
  • Analgesic, antipyretic and, in higher doses, anti-inflammatory drugs.
  • Impair platelet function by inhibiting platelet cyclo-oxygenase (COX).
  • NSAIDs inhibit COX reversibly.
  • Platelet function returns to normal within 3 days after stopping NSAIDs.
  • It is safe to proceed with central and periphral nerve block in patients taking NSAIDs.
cox 2 inhibitors
COX 2 inhibitors
  • Anti-inflammatory drugs that selectively inhibit COX 2.
  • They do not affect platelet function.
  • It is safe to proceed with central and periphral nerve block in patients taking COX 2 alone.
  • They can potentiate the effect of warfarin by increasing the prothrombin time ( PT ).
clopidogrel
Clopidogrel
  • A thienopyridine derivative.
  • It is a potent antiplatelet agent.
  • It inhibits ADP-induced platelet aggregation and binding between platelets and fibrinogen.
  • The effect is irreversible and platelet function does not return to normal until at least 7 days after stopping the drug.
slide18
It is used in combination with aspirin in patients with acute coronary syndrome.
  • It should be discontinued 7 days before surgery, central neuraxial and peripheral block.
  • If an antiplatelet effect must be maintained, aspirin can be substituted safely.
unfractionated heparin
Unfractionated heparin
  • Indications:
  • Thromboprophylaxis.
  • Therapeutic anticoagulation.
  • Subcutaneous thromboprophylactic doses are seldom associated with bleeding complications.
slide20
Central and periphral block in thromboprophylaxis dose: the dose should be stoped 4 hours before or more than one hour after the procedures.
  • Catheter should be removed 2-4 hours after the last dose.
  • In therapeutic dose: activated partial thromboplastin time (APTT) should be normal before attempting a block or removing a catheter.
slide21
Patients who have been receiving unfractionated heparin for more than 4 days should have a platelet count, because the incidence of heparin-induced thrombocytopenia is about 3%.
lmwhs
LMWHs
  • Indications:
  • Thromboprophylaxis.
  • Therapeutic anticoagulation.
  • Have longer half-lives than unfractionated heparin, which allows once daily administration.
  • They have anti-Xa activity.
  • There is no monitoring test for routine use.
slide23
Central and periphral block in thromboprophylaxis dose: the dose should be stoped 12 hours before the block or catheter removal.
  • The first dose is given within 6 hours of surgery or 2 hours after the block.
  • In therapeutic dose: it takes about 24 hours for coagulation to return to normal. Therefore, an interval of 24 hours should elapse before attempting block.
fondaparinux
Fondaparinux
  • Indications: for thromboprophylaxis.
  • It is a synthetic pentasaccharide, which has potent anti-Xa activity.
  • It has a longer elimination half-life than LMWH ( 17 hours in young patients and 21 hours in healthy elderly patients ).
  • It is administered 6 hours after surgery.
  • An interval of at least 24 hours should elapse before removal of neuraxial or peripheral nerve catheters.
warfarin
Warfarin
  • Indications:
  • Thromboprophylaxis in AF.
  • Post prosthetic heart valve replacement.
  • Treatment of DVT or PE.
  • Central and periphral block: INR ≤ 1.5, this normally takes about 4 days after stoping warfarin.
  • If a LMWH or unfractionated heparin has been administered in place of warfarin, the recommended intervals discussed above should be observed before performing any block.
anticoagulants perioperatively
Anticoagulants perioperatively
  • Warfarin should be stopped 2-4 days preoperatively, and the PT time monitored daily (INR ≤ 1.5).
  • If INR prolonged:
  • Administer vitamin K.
  • Fresh frozen plasma.
  • It is often appropriate to start an alternative anticoagulant, such as LMWH or unfractionated heparin, until warfarin is re-established and the INR is back in the therapeutic range postoperatively.
slide27
After minor surgery: warfarin may be restarted on the first postoperative day.
  • After major surgery: an infusion of unfractionated heparin may be used to maintain anticoagulation ( with control by APTT ) until warfarin therapy is restarted.
  • Unfractionated heparin is reversed rapidly with protamine 1 mg for every 100 units of heparin.
slide28
Unfractionated heparin is preferable to LMWH because it may be monitored more easily and reversal titrated more accurately.
summary
Summary
  • Aspirin and NSAIDs: No contraindication.
  • Clopidogrel: Stop 7 days before surgery, central and peripheral block.
  • Warfarin: INR ≤ 1.5. After minor surgery: start on the first postoperative day. After major surgery: an infusion of unfractionated heparin may be used to maintain anticoagulation.
slide30
Unfractionated heparin:
  • Thromboprophylaxis dose: stop 4 hours before or > than one hour after the procedures. Catheter should be removed 2-4 hours after the last dose.
  • Therapeutic dose: (APTT) should be normal before attempting a block or removing a catheter.
slide31
LMWH:
  • Thromboprophylaxis dose: the dose should be stoped 12 hours before the block or catheter removal. The first dose is given within 6 hours of surgery or 2 hours after the block.
  • Therapeutic dose: the dose should be stoped 24 hours before the block.
slide32
Fondaparinux: Start 6 hours after surgery. Stop 24 hours before removal of neuraxial or peripheral nerve catheters.

REFERENCE:

  • AnaesthesiaUK
  • Europian Journal of Anaesthesiology2007
  • Medical Physiology, Guyton
  • Fundamentals of Physiology
  • Text book of Anaesthesia, Aitkenhead