Issues for Surgery
Risk of venous thromboembolism (VTE) if omitted.
Risk of cerebrovascular event (CVA) if omitted.
Risk of bleeding and / or complications of bleeding if continued.
Advice in the Perioperative period
Elective Surgery / Procedures
Perioperative warfarin decision-making should take into account the patient’s underlying thrombotic risk balanced against the bleeding risk associated with the surgery / procedure – see ‘Anticoagulants (Oral) – A General Overview’.
Warfarin may not need to be stopped for the following minor procedures (however it is still recommended that the international normalised ratio (INR) is checked approximately 7 days prior to the procedure to identify patients with a supra-therapeutic INR1): -
For other operations / procedures where anticoagulation is not desirable, follow local pre-existing arrangements with hospital’s anticoagulation service. In the absence of such arrangements check INR 7 days prior to operation / procedure: -
This should allow the INR to fall to 1.5 by day of operation / procedure (this is associated with clotting factor activity levels >40% and essentially normal haemostasis5).
Check INR on admission to ensure safe to proceed with surgery / procedure3.
Bridging with Low Molecular Weight Heparin (LMWH)
The last dose of therapeutic LMWH should be at least 24 hours before surgery3 (see Low Molecular Weight Heparin monograph).
Emergency Surgery / Procedures
Check INR on admission.
If INR therapeutic and surgery can be delayed for 6 to 8 hours give 5mg intravenous vitamin K (phytomenadione) to restore coagulation factors3.
If INR therapeutic and surgery cannot be delayed for sufficient time to allow reversal with vitamin K, anticoagulation can be reversed with prothrombin complex concentrate3 – discuss with Haematologist.
Neuraxial (Spinal / Epidural) Anaesthesia or Lumbar Punctures
Warfarin has a slow onset of action; restart on evening of operation providing adequate haemostasis and Surgeon agrees – either at usual dose1, 3 or two days of double maintenance dose followed by usual dose3.
If a patient has undergone complex surgery and there is a likelihood that the patient may need to return to theatre the Surgeon may decide to delay restarting warfarin for a few days. During this time prophylactic doses of LMWH (or therapeutic dose if high risk of thrombosis e.g. mitral valve replacement) should be considered.
If there are concerns regarding oral absorption post-operatively consider replacing warfarin with therapeutic dose LMWH as clinically appropriate.
Check INR and adjust dose accordingly.
Bridging with LMWH
Consider prophylactic LMWH, commenced a minimum of 2 hours (4 hours for patients with indwelling catheters) post-operatively until therapeutic LMWH can be restarted.
Discontinue LMWH once INR therapeutic.
Interaction(s) with Common Anaesthetic Agents
Interaction(s) with other Common Medicines used in the Perioperative Period
Non-Steroidal Anti-inflammatory Drugs (NSAIDs)
NSAIDs are predicted to increase the risk of bleeding events when given with warfarin; ideally concomitant use should be avoided6, 7.
Low Molecular Weight Heparin (LMWH) / Unfractionated Heparin (UFH)
LMWHs and UFH are predicted to increase the risk of bleeding events when given with warfarin6. If patient ‘bridged’ with LMWH pre-operatively this should be discontinued when INR returns to therapeutic range.
Although the evidence is limited, marked INR increases have been reported with high-dose dexamethasone, prednisolone, or methylprednisolone, however, the significance of this interaction with low doses is not known6, 7. Whilst intraoperative doses should not pose a problem, monitor INR if prolonged administration necessary.
Concomitant administration of warfarin with many antimicrobials causes an increased anticoagulant effect6, 7. Whilst single surgical prophylactic doses should not pose a problem, monitor INR if a course of antimicrobial treatment is required.
Enteral feeds containing vitamin K will reduce the anticoagulant effect of warfarin – monitor INR and adjust warfarin dose accordingly6.
Rationale for Advice
Warfarin has a half‐life of approximately 36 hours and as its effect wears off vitamin K‐dependent procoagulant factors need to be synthesised; therefore, providing INR is in the therapeutic range warfarin needs to be stopped 5 days before elective surgery to ensure haemostasis has returned to normal3.
Bridging with LMWH
When deciding if a patient requires bridging the risk of thrombosis must be weighed against the risk of bleeding - see ‘Anticoagulants (Oral) – A General Overview’. In patients with atrial fibrillation (AF) a randomised controlled trial found that not bridging was non-inferior to perioperative bridging with LMWH for the prevention of arterial thromboembolism and reduced the risk of major bleeding. Therefore, the British Committee for Standards in Haematology only recommend bridging for AF patients at high risk of thrombosis3.
Consider bridging with treatment dose LMWH for the following indications3: -