Emergency Surgery or Urgent Surgery.
The choice of treatment is dependent on the urgency of the surgery.
For immediate surgery
· Stop Warfarin
· Administer vitamin K 3 to 5 mg i.v.
· Prothrombinex-VF dose based on weight and the target INR for surgery (see table below)
· Repeat INR measurement immediately prior to surgery.
If surgery can be delayed for 12 to 24 hrs Prothrombinex-VF may not be necessary.
Vitamin K
Intravenous vitamin K will reverse the effects of warfarin more rapidly than oral administration. When used to reverse an elevated INR, intravenous vitamin K achieves a significant correction within 6 to 8 hours where as oral medication takes 10 to 16 hours. In one series of patients with an elevated INR (mean INR greater 5.0), intravenous vitamin K corrected the INR to <2.0 in 44% of patients by 12 hrs where as oral vitamin K only corrected 14% over the same time period1.
The required dose of vitamin K remains unclear. A dose of 1mg intravenously appears to achieve correction to an INR of 1.4 or less more effectively than a dose less than 1mg. It is unclear if a higher dose actually achieves more rapid correction. In one study where patients received a fixed intravenous dose of 3mg, 94% of patients achieved an INR < 1.5 within 18hrs. The ACCP guidelines recommend higher doses of 5mg or 10mg for patients with an INR >10.0 but do not have clear advice for patients prior to emergency surgery. The disadvantage of higher doses of warfarin is that there can be a delay in re-establishing a therapeutic INR in patients after surgery.
The conclusion from these studies is that a vitamin K dose of between 1mg and 5mg is appropriate in most circumstances and intravenous administration should be used if a rapid response is required. The risk of anaphylaxis from intravenous vitamin K appears to be extremely low.
Suggested dose of Prothrombinex-VF to reverse Warfarin according to the initial
and target INR
|
Initial INR |
|||
Target INR |
1.5 – 2.5 |
2.6 – 3.5 |
3.6 – 10.0 |
>10.0 |
0.9 – 1.3 |
30 IU/kg |
35 IU/kg |
50 IU/kg |
50 IU/kg |
1.4 – 2.0 |
15 IU/kg |
25 IU/kg |
30 IU/kg |
40 IU/kg |
Tran HA, Chunilal SD, Harper PL, et
al. An update of consensus guidelines for warfarin reversal. Med J Aust 2013;
198 (4): 198-199. © Copyright 2013
The Medical Journal of Australia -
reproduced with permission.