Venous thrombo-embolism

Bariatric surgery and venous thrombo-embolism

Bariatric surgery and cancer

Obese patients (BMI >35) have 6 fold increase in VTE risk compared to normal individuals

However there are also great benefits of weight loss and bariatric surgery, which is associated with 40% lower risk of VTE after 10 years

Rates of VTE in the first few weeks after bariatric surgery ranges from 0.4 to 3.4% and for pulmonary embolism it is 0.3 to 2%

  • Over 80% of VTE occurs within the first month

A recent systematic review reported the incidence of VTE to be 0.5%

But PE accounts for nearly 30% of the mortality after bariatric surgery

  • In general higher BMI is associated with VTE risk by 2 to 3 fold
  • Obesity and cancer also increases VTE risk
  • Surgery (endothelial damage, venous stasis) increases the risk

Other causes:

  • Patient risk factors include increasing age, immobility, medications (OCP, HRT), smoking, heart failure, kidney disease
  • Rare inherited thrombophilia (factor 5 Leiden, prothrombin gene mutation, deficiencies of antithrombin, protein C and S)
  • Acquired thrombophilia (polycythaemia PCRV, antiphospholipid syndrome)
In hospital
 
Low molecular weight heparin (LMWH) subcutaneous injection is the agent of choice
*With superior efficacy, ease of administration, cost effective and low risk of bleeding complications compared to unfractionated heparin
*Prophylactic daily dose of 40mg subcutaneous injection is commonly prescribed, 97% of patients reach a steady state after 3 injections (note: for high risk patients twice or three times daily LMWH dosing may be needed)
*LMWH inhibit clotting factor 10a and thrombin

*Blood assay for anti-factor 10a may be done, 4-6 hours after the 3rd dose to monitor the dosing
***0.2 to 0.5 IU/mL is in the prophylactic range
***>0.5 IU/mL  is in the therapeutic range

However routine monitoring with for anti factor 10a is not recommended
 
Caution: statin medications for elevated lipids may potentiate the effects of LMWH

After discharge from hospital
 
There are no standardized protocol for prescribing VTE prophylaxis after discharge from hospital for the high risk patients described above
*If necessary the majority of patients are prescribed low molecular weight heparin
***Treatment courses are usually for 2 weeks, the risk of VTE ranges 0 – 1.4% and bleeding risk 0.1 –  1.6%
*Rivaroxaban and Apixaban has also been prescribed, oral absorption should not be affected after sleeve but ? maybe after gastric bypass
 

ASMBS recommend extended post discharge chemoprophylaxis for very high risk patients (hypercoagulable state, previous DVT/PE, limited mobility)
*LMWH (Enoxaparin injection) or Apixaban (oral tablet direct factor 10a inhibitor) are good options but there are no standardised protocols

Novel or Direct oral anticoagulants
 
Obesity is a well recognized risk factor for thrombogenesis primarily due to chronic inflammation and a pro-coagulant state
*Also co-morbidities such as T2DM and HPT increases the risk
 
Traditionally venous thromboembolism prophylaxis relied on subcutaneous heparin (enoxaparin)
But there are concerns regarding pharmacologic limitation linked to adipose tissue related impact on the drug pharmacodynamics in high BMI patients
 
A systematic review and meta analysis found that
*DOAC demonstrated a low incidence of thrombotic events (0.23%) in bariatric surgery patients supporting their effectiveness in VTE prophylaxis
*Major bleeding events occurred in 0.3 to 1.27% of patients
*This supports the use of DOAC after bariatric surgery
 
 
 
Patients with a high BMI there may be limitations with heparin or enoxaparin that irreversibly inactivates factor 10a
*The distribution of adipose tissue can alter the pharmacokinetics of drugs such as enoxaparin
 
However some claims that enoxaparin is a hydrophilic drug with obesity having little effect on its apparent volume of distribution
*The 1mg/kg dosing may be supra therapeutic
 
DOAC is effective in AF, cancer associated thrombosis, THJ and TKJ surgery
*Dabigatran (Pradaxa)
*Rivaroxaban (Xarelto)
*Apixaban (Eliquis)
*Edoxaban (Savaysa)
*Betrixaban (Bevyxxa)
 
DOCS are categorised into 2 main froups:
*Direct factor 10a inhibitors (Xarelto, Eliquis, Savaysa, Bevyxxa)
*Direct thrombin inhibitors (Pradaxa)
 
DOAC are relevant for individuals for obesity
*Where fat distribution and drug pharmacokinetics are less relevant
*There may be reversal agents for DOAC
*Recent meta analysis demonstrated superiority of DOACS over enoxaparin after high risk surgeries (hip or knee)
*Lower risk of bleeding
*Increased cost effectiveness and enhanced patient comfort
 
Major bleeding are defined as
*Haemoglobin drop by 2g/L (1.24 mmol/L)
*Requiring transfusion 2 or more units
*Haematocrit drop of >9 points
*Haematocrit drop >6 with tachycardia, hypotension
*Requiring radiological or surgical intervention