Perioperative Anticoagulation

Note: also discuss with your local cardiologist.

Elective Surgery

    Warfarinised Patients
    Long term LMWH Therapy
    Aspirin Therapy
   
Acute Surgery

Risks of stopping anticoagulation

Heparin Infusion
Low Molecular Weight Heparin


WARFARIN
Management depends on the reason for which the patient is anticoagulated:
    Heart Valve
    Atrial Fibrillation
    Recent VTE, DVT or PE

Heart Valve

Overall, the embolic risk for these patients, without anticoagulation, is 8%/year.
Surgery does not increase the risk.

Mechanical Valves
Patients with mechanical valves can be divided into a low and high risk group
    High risk:
    Previous embolic event (especially <3/12 ago)
    Ball cage valve (Starr-Edwards)
    MVR and AVR
    MVR alone, unless a modern type bileaflet or tilting valve was used
        Stop warfarin 4/7 pre-op (patient at home)  
        Admit 2/7 pre-op and start heparin infusion when INR <2.0
        Stop heparin 6h pre-op
        Check INR/APPT 1h pre-op
        Post-op restart heparin at 12hrs if no evidence of bleeding.  Consider delaying to 24hrs if bleeding risk outweighs thromboembolic risk.
        Restart warfarin on evening of first post-op day using previous dose.
        Stop heparin when INR>2.0

    Low risk:
    Modern bileaflet (
St Jude Medical, Sorin Bicarbon, Carbomedics) or tilting valve (Bjork-Shiley, Medtronic Hall)
    No previous embolic event
        Stop warfarin 4/7 pre-op
        Give clexane if possible
        Check INR on admission
        Recommence warfarin post-op on evening of surgery, using previous dose, unless INR <1.2 in which case give initial 10mg then return to usual dose.        

   
   
Tissue Valves (Carpentier-Edwards, Tissue Med (Aspire), Hancock II)
These patients are only on warfarin for 3/12 after insertion thus delay elective surgery until warfarin is discontinued.

Atrial Fibrillation

Risk of embolisation is 7%/year wthout anticoagulation and up to 12% in patients who have had a previous embolus.
Surgery does not increase the risk.

Stop warfarin 4/7 pre-op
Give clexane if possible
Check INR on admission
Restart warfarin post-op on evening of surgery using usual dose

If previous embolic event:
Add LMWH prophylaxis post-op until INR >2.0 (unless high bleeding risk)

Recent VTE, DVT or PE

Thrombosis >6/12 ago
Patients on long-term anticoagulation because of previous multiple events, an underlying thrombophilia or another risk factor such as malignancy have a risk of recurrence at surgery of 0.5-5%.
    Stop warfarin 4/7 pre-op
    Restart warfarin on the post-op evening of surgery using usual dose
    LMWH prophylaxis post-op until INR >2.0


Thrombosis <6/12 ago

In the first month, each day without anticoagulation is associated with a 1.0% absolute increase in the risk of recurrence.  
The risk of recurrence occurring at surgery within 3/12 of embolic event without prophylaxis may approach 50%.
    Avoid surgery within 3/12 and preferably 6/12 of embolic event

If it is not possible to postpone surgery:
    VTE <1/12 ago     
        IV heparin should be given before and after the procedure while the INR is <2.0.  
        Stop IV heparin 6hrs before surgery
     
    VTE >1/12 and <3/12 ago
        Preoperative IV heparin is not justified unless there are additional risk factors for recurrent VTE e.g. hospitalisation for acute illness.
        Post-op IV heparin is recommended until warfarin therapy is resumed and INR >2.0.
   
     VTE >3/12
    
    Pre-op IV heparin not recommended
         Post-op prophylaxis with LMWH and compression stockings until INR >2.0.  IV heparin is an acceptable alternative.


ACUTE SURGERY
Check INR and aim to correct to <1.5 before surgery

FFP
12-15ml/kg drops a high INR immediately.
The effect lasts only a few hours.

Vitamin K
Takes 6-8 hours to drop the INR, thus may be used if surgery can be delayed 12 to 24 hours.  
If INR >3.0 give 1mg of Vit K
If INR >8.0 give 2mg of Vit K
The effect of vitamin K can linger for many hours making the re-establishment of anticoagulation difficult, thus FFP is preferred to Vit K.


INR
Surgery is safely performed at INR <1.5
Anaesthetists require INR <1.4 for spinal/epidural


Therapeutic ranges
2-3
    An INR in this range typically takes 4 days to fall to 1.5 or less.
    After restarting warfarin it usually takes 3 days for the INR to reach >2.0


LONG TERM LMWH THERAPY

Discuss management of these patients with physician/haematologist.  It is not safe practice to assume that LMWH in these patients can be  stopped the evening before surgery.  It may need to be discontinued 3-4 days pre-op.


ASPIRIN THERAPY

If on aspirin for primary prophylaxis:
    Stop 4/7 pre-op
    Restart post-op on morning of the first day after surgery

If patient has had a previous arterial thrombotic event:
    Either:
    Continue peri-operatively
    Or:
    Stop the aspirin if the surgical bleeding risk is considered to be significantly increased for the particular type of surgery
RISKS

HEPARIN INFUSION
Heparin is given as an initial loading bolus followed by an infusion adjusted to maintain the APTT at a therapeutic level.  APTT values vary according to the laboratory, requiring normalised data to be established for each hospital.  

The therapeutic level for a prophylactic heparin infusion is 2 - 2.5x the normal APTT.  (This is a lower level than that required for treatment of a DVT or PE).
At Nelson Hospital a normal APTT is 26-36s thus the required therapeutic level is 50-70s.  (Laboratory testing, not bedside testing).
Initial Bolus Loading Dose
5 000 units of heparin diluted in 5mL of normal saline as a slow IV push over 1-2 mins.

Infusion
25 000 units of heparin in 45ml of normal saline (making a total volume of 50mls) - generates a  solution of 500 units/ml.

Infusion is commenced immediately following the bolus at 1 000 units/hr (2ml/hr).  

The APTT is measured at 6 hourly intervals until therapeutic and stable, then daily measures (usually each morning) for duration of heparin therapy.

The infusion is adjusted according to the following table:

APTT
BOLUS THERAPY (units heparin)
STOP INFUSION
RATE CHANGE (units/hr)
VOLUME CHANGE (ml/hr)
NEXT APTT
<40
3000
0 min
increase 150 u/hr
increase 0.3ml/hr
6 hours
40-49
nil
0 min
increase 100 u/hr
increase 0.2 ml/hr
6 hours
50-75
nil
0 min
no change
no change
next am
76-100
nil
0 min
decrease 100 u/hr
decrease 0.2ml/hr
6 hours
101-130
nil
30 min
decrease 150 u/hr
decrease 0.3ml/hr
6 hours
>130
nil
60 min
decrease 200 u/hr
decrease 0.4ml/hr
6 hours

Low Molecular Weight Heparin may be considered as an alternative to IV heparin.


LOW MOLECULAR WEIGHT HEPARIN
Low molecular weight heparin is convenient as it can be given as an outpatient and is widely used as an alternative to IV heparin.  There are currently no RCTs to support its use, however initial reviews do suggest a favourable comparison.  

Treatment doses of LMWH are required, i.e. 1.5mg/kg od

In severe renal impairment (<30ml/min) this should be adjusted to 1mg/kg od

REFERENCES



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