Anticoagulation for cardiac surgery Flashcards
(6 cards)
State the dose of Heparin (in IU/kg) used to achieve full anticoagulation for, and the target activated clotting time (ACT) prior to initiation of Cardiopulmonary Bipass
Heparin Dose = 300-400 IU/kg
Activated Clotting Time (ACT) = 3x the baseline or > 480 seconds
NB Baseline ACT needs to be checked, then heparin can be given via a central venous canula. The ACT needs to be checked 3-5 minutes after this and should be rechecked every 15-30 minutes during cardiopulmonary bypass
What is the primary mechanism of action of heparin
It binds to antithrombin III to potentiate it’s inhibitory action on thrombin and factor Xa
Describe the action of Low Molecular Weight Heparins (LMWH)
LMWHs are smaller molecules with greater anti-factor Xa activity and minimal thrombin inhibition (although this latter point does vary according to the type of LMWH) when compared to Heparin
List the Laboratory and point-of-care tests that may be used to determine the effectiveness of heparin anticoagulation in Cardiopulmonary bypass patients, giving an advantage and a disadvantage for each.
Activated Partial Thromboplastin Time (APTT) Lab Test
Pro: Cheap
Con: Slow turnaround time, potentially resulting in less well directed management
Anti-Xa assay Lab Test
Pro: Correlates well with Heparin activity
Con: not widely used for this purpose, poor inter-laboratory correlation, slow
Activated Clotting Time (ACT) Point of Care test
Pro: Rapid Response, Cheap, Familiar
Con: Thrombocytopenia, antiplatelet agents, hypothermia, haemodilution and aprotinin may all prolong ACT so it lacks specificity. ACT also has a poor correlation with anti Xa activity
Heparin Concentration Monitoring, Point of Care Test
Pro: Measuring the heparin concentration once haemodilution has occurred with cardiopulmonary bypass may be more appropriate to direct heparin administration than Activated Clotting Time, which is prolonged by commencing cardiopulmonary bypass. Hence, Higher doses of Heparin would be indicated if using this method
Con: Expensive and not widely used
Thromboelastography (TEG) Point of Care Test
Pro: TEG gives a graphical representation of the ability of the blood to clot. Optionally, heparinase can be added to the test to negate the effect of systemic heparin, thus predicting the patient’s coagulation state after heparin has been reversed, hence, it can guide blood product replacement as well.
Con: cost of the equipment, Training required for interpretation, takes time for clot to evolve.
What are the causes of inadequate anticoagulation after heparin administration
Administration error:
Wrong Drug Administered
Drug not given
Central Line not patent
The central line was not flushed after heparin was given
Pharmacokinetic factors:
Heparin is highly protein-bound so an increase in the presence of plasma proteins reduces the free and therefore active drug or vis versa
Acutely ill patients
Malignancy
Peri or Post Partum
Due to a lack of antithrombin III (which can be treated by administration of FFP):
Drug-induced e.g., recent heparin use
Accelerated consumption e.g., DIC or sepsis
Dilution, e.g., due to cardiopulmonary bypass
Decreased synthesis, e.g., due to liver cirrhosis
Increased excretion i.e., protein-losing states
Familial (genetic) rare 1 in 2 to 20 thousand
What possible adverse reactions are there to protamine
Arterial hypotension / reduced cardiac Output
Pulmonary Vasoconstriction
Anaphylaxis
Unbound protamine inhibits platelet reactivity, adhesion, and aggregation. An excessive dose therefore, promotes bleeding
