Principles of surgery

Question 1

Screening principles

Answer 1

Wilson’s criteria
- An important problem
- Natural history should be understood
- Early or latent stage
- Acceptable test with low morbidity
- Treatment available
- Facilities for diagnosis and treatment
- An accepted protocol
- Cost effective

Question 2

Clopidogrel info

Answer 2

Binds to P2Y12 ADP receptor on platelets to inghibit activation and aggregation.
Stop 5 days prior to surgery
Do not stop within 12 months of Drug eluting stent or 6 weeks of bare metal cardiac stent.
Discuss with cardio regarding risk profile.
No reversal agent. give platelets

Question 3

Warfarin info

Answer 3

Vit K antagonist, binds to vit K epoxide reductase enzyme and prevents vit K dependent factors 2,7,9,10.
Stop 6 days prior to surgedry with monitoring of INR to achieve INR < 1.5
Reversal:
- Vit K takes 4-6 hours to onset (1-3 hours IV) and 24 hours to work. Check INR 6-12 hours post admin
- Prothrombinex for immediate reversal (discuss with haematologist)

Question 4

Dabigatrin

Answer 4

Direct thrombin (Factor 2a) inhibitor
- Stop 48 hours prior to surgery, or 72 hours if high risk surgery or decreased GFR
- Measure action of dabi by dTCT. If normal (15-20), then it has been totally cleared.
- Reversal agent is idirazicumab (praxibind). 2x 2.5g vials administered 10 mins apart and should work immediately. If APTT and TT measured, should be normal 30 mins later.

Question 5

Rivaroxaban and apixaban

Answer 5

Factor Xa inhibitor
- Stop 48 hours prior to surgery or 72 hours if high risk surgery or GFR low
- No reversal agent. Can give TXA + platelets + prothrombinex after discussion with hematologist. If life-threatening bleeding, can give recombinant Factor VIIa after discussion with a haematologist

Question 6

Ticagrelor

Answer 6

Binds to the P2Y12 ADP receptor on platelets to inhibit platelet activation and aggregation
Stop 5 days prior to surgery
No reversal agent

Question 7

Sutures

Answer 7

Absorbable
- Gut: Purified connective tissue from bovine or ovine intestine. Absorbed rapidly.
- Vicryl: co-polymer polyglactin. 50% at 3 weeks. Absorbed by 10 weeks
- Vicryl rapide: co-polymer polygactin. 50% at 5 days. Lost by 14 days, Absorbed by 6 weeks
- PDS: Polydioxanone. 60% tensile strength at 6 weeks for large calibre. Absorbed by 6 months
- Monocryl: Co-polymer poliglecaprone. Tensile strength 50% at 1 week. Absorption by 15 weeks

Non-absorbable
- Silk: Fibroin organic protein. Gradually encapsulated. Can’t be found in 2 years
- Ethibond: Coated polyester. Gradually encapsulated.
- Ethilon: Nylon. Gradually encapsulated. 20% tensile strength loss per year.
- Prolene: Polypropylene. radually encapsulated

Question 8

Haemostatic adjuncts

Answer 8

Tisseel
- Fibrin tissue sealant
Contains fibrinogen and factor VIII, which when comes in contact with calcium and thrombin, forms a clot. Solution tisseel, patch form is tachosil

Surgicel
- Oxidised cellulose matrix mesh, which acts as a scaffold for activation of coagulation. Can be placed on oozing surfaces eg GB bed, thyroid bed

Floseal
- Topical thrombin and gelatin granules which crosslink to form a hemostatic matrix
- Place on the tissue, cover with a moist gauze and leave for a few minutes.

Gelfoam
- Hydrocolloid derived from porcine collagen.
Provides a scaffold for which clots can form.
Increased infection and granuloma rates compared to surgicel

Tranexamic acid
- Synthetic lysine amino acid, that binds and blocks lysine binding sites on plasminogen, preventing fibrinolysis.