ANAESTHESIA AND ANTICOAGULANTS

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ANAESTHESIA AND ANTICOAGULANTS

• Done by
• Dr. Ahmad Alrefaie

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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.

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• 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
  THROMBEN at the site of injury.
• Thrombin exist in the plasma in the form of an
  inactive precursor called PROTHROMBIN.

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• Prothrombin converts into thrombin by FACTOR X,
  a plasma clotting factor.
• Factor X present in the blood in inactive form
  and must be converted into its active form by
  another activated factor, and so on.

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Anticoagulants
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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.

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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.

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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).

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Indications

• Local analgesic effect.
• Antipyretic.
• Anti-inflammatory.
• Antiplatelet.

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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.

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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.

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• It is safe to proceed with central and periphral
  nerve block in patients taking Aspirin.

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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.

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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 ).

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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.

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• 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.

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Unfractionated heparin

• Indications
• Thromboprophylaxis.
• Therapeutic anticoagulation.
• Subcutaneous thromboprophylactic doses are seldom
  associated with bleeding complications.

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• 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.
  

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• 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.

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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.

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• 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.

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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.

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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.

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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.

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• 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.

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• Unfractionated heparin is preferable to LMWH
  because it may be monitored more easily and
  reversal titrated more accurately.

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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.

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• Unfractionated heparin
• Thromboprophylaxis dose stop 4 hours before or gt
  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.

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• 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.

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• 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

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