This topic has been examined in detail in Question 1 from the first paper of 2006, and briefly in Question 15.1 from the second paper of 2012. Warfarin in general is a favourite of the examiners, but attention is usually focused on its effects on the routine coags panel, or as the mediator of catastrophic bleeding
Reversal of warfarin
One would merely withhold warfarin for a patient with low risk of bleeding.
If the risk of bleeding is high, one would give vitamin K or FFP/prothrombinex.
If bleeding has already occurred, one would resuscitate the patient and also give FFP/prothrombinex.
Warfarin reversal guidelines exist, and may be somehwat individual, according to the local policies. However the general trend is to follow various published consensus statements.
- INR 4.5 – 10.0 and no bleeding: stop warfarin
- INR 4.5 – 10.0 and high risk of bleeding: Vitamin K (1 – 2 mg orally or 0.5 – 1.0 mg iv). The reason for this low dose of Vitamin K is the difficulty of reestablsihing a therapeutic INR after a high dose of Vitamin K; this works on the assumption that you want to remain anticoagulated, albeit at a slightly more sane PT level.
- Immediate reversal: Prothrombinex alone is enough. It contains factors II, IX, X and low levels of factor VII. The dose is 25 – 50 iu/kg. This should usually be enough.
- In contrast to previous guidelines, FFP is no longer recommended as an addition to prothrombinex. There has been a general opinion that FFP contributes factor 7, and therefore to get the full benefit from prothrombinex one should co-transfuse some FFP; however these days this practice is reserved for the most severe of haemorrhages, or bleeding of critical importance (eg. intracranial haemorrhage).
- If the patient is acutely bleeding, the most recent guidelines recommend to use a high dose of Vitamin K - 5-10mg IV. It does not matter what the INR is. Anything less than 3mg is going to be ineffective.
- If the warfarinised patient is bleeding, and the haemorrhage is into a critical organ (eg. brain), one will not only give 5-10mg of Vit K - one will also give prothrombinex 50.0 units/kg, and FFP 150–300mL.
- FFP is generally reserved for situations when the prothrominex is not readily available. The maximum dose is 15ml/kg.