Chapter 12. Anticoagulation, Antiplatelet Medications

Tony P. Tsai, MD

NB: For anticoagulation and neuraxial anesthesia, please see the chapter 119 on safety in regional anesthesia.

Pharmacology:

VKAs block the carboxylation of factors II, VII, IX, and X as well as proteins C and S (coagulation inhibitors)
Equilibrium is reached only after about 5 days as factors have different half-lives
Initial hypercoagulable state as protein C has the shortest half-life

Table 12-1 Indications and Therapeutic Targets of VKAs

Table 12-1 Indications and Therapeutic Targets of VKAs

Indications for target INR of 2.5; range 2–3

Indications for target INR of 3; range 2.5–3.5

Atrial fibrillation (AF)
Rheumatic mitral valve disease and AF or a history of previous systemic embolism
St. Jude Medical aortic bileaflet valve
Bioprosthetic valves: VKA for first 3 months after aortic or mitral valve insertion
AF and a recent CVA or TIA

Tilting disk valves and bileaflet mechanical valves in the mitral position
Caged ball or caged disk valves; give VKA in combination with aspirin, 75–100 mg/day

The following procedures do not warrant VKA discontinuation if INR 2–3:

Cataract surgery without retrobulbar block
EGD without biopsy, colonoscopy without biopsy/polypectomy, ERCP without sphincterotomy
Minor dental procedures
Joint and soft tissue injections and arthrocentesis

For AF, assess thromboembolic risk based on the CHADS2 score (0–6 points).

Table 12-2 CHADS2 Score for Assessment of Thromboembolic Risk

Table 12-2 CHADS2 Score for Assessment of Thromboembolic Risk

CHF

1 point

HTN

1 point

Age >75 years

1 point

History of stroke

2 points

0 points: no indication for chronic anticoagulation; discontinue warfarin 5 days before surgery; do not resume unless other indication
1–2 points: discontinue warfarin 5 days before surgery; resume 5 days after surgery
3 points or more: discontinue warfarin 5 days before surgery; LMWH, or IV UFH relay

For valve replacements:

Discontinue warfarin at least 5 days before elective procedure, or longer if INR >3.0
Assess INR 1–2 days before surgery; if INR >1.5, consider 1–2 mg of oral vitamin K
Reversal for urgent surgery: consider 2.5–5 mg of oral or intravenous vitamin K
Immediate reversal for emergent surgery: consider fresh frozen plasma, prothrombin complex concentrate, or recombinant factor VIIa

Patients at high risk for thromboembolism:

For patients who have a mechanical valve, high risk includes those who have mitral valve prostheses, older aortic valve prostheses, or had a CVA or TIA in the past 6 months
For patients who have atrial fibrillation, high risk includes a CHADS2 score of 5–6, a CVA or TIA within the past 3 months, or rheumatic valvular heart disease
For patients who had a venous thromboembolism (VTE), high risk includes a VTE within the past 3 months, severe thrombophilia
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