Surgical hemostasis

Question 1

How long does it take for a clot to form?

Answer 1

30 seconds for initial platelet aggregation, 2-3 minutes for the clot to become cross-linked with a fibrin matrix

Question 2

What are the potential disadvantages with the use of abdominal counterpressure for the treatment of abdominal hemorrhage?

Answer 2

Increased intraabdominal, intrathoracic and intracranial pressures.

Question 3

What are potential methods to facilitate blood flow reduction to aid in hemostasis?

Answer 3

1. Pressure/tamponade
2. Topical vasoconstrictors (epinephrine, adrenaline, ephedrine)
3. Distant control of blood flow

Question 4

What vessels are able to be permanently ligated in the dog and cat?

Answer 4

Question 5

What arteries and veins can be occluded on a temporary basis during surgery if required?

Answer 5

Question 6

What are they suggested temporary ligation times for vessels if required during surgery?

Answer 6

Question 7

What has been shown to result with high tourniquet pressures in humans?

Answer 7

Nerve demyelination and neurologic deficits for up to 6 months post-operative

Question 8

What is the ideal cuff pressure of a tourniquet?

Answer 8

100 mm Hg above systolic blood pressure

Question 9

What is the safe duration of tourniquet application in animals?

Answer 9

Not determined. Most recommend a maximum of 1.5 - 2 hours which corresponds to the point at which muscle ATP stores are depleted. Mitochondrial damage has been experimentally demonstrated after 1 hour.

Question 10

What are the systemic responses to tourniquet application in humans?

Answer 10

Increased circulating blood volume, hypertension and hypercoagulopathy. Following removal transient hypotension, hypercapnia, increased ICP, pulmonary thromboembolism and increased fibrinolysis.

Question 11

What are the three categories of hemostatic agents?

Answer 11

1. Mechanical
2. Active
3. Hemostatic sealants

Question 12

List commonly used mechanical hemostatic agents in companion animal surgery.

Answer 12

Gelatins, collagens, oxidized cellulose, polysaccharide spheres, wax

Question 13

How long does it take for gelatins, collagens, oxidized cellulose and polysaccharide spheres to be resorbed?

Answer 13

Gelatins: 5-weeks secondary to granulomatous inflammation
Collagens: 8-10 weeks by fibroblast remodelling
Oxidized cellulose: 2-6 weeks
Polysaccharide spheres: rapidly metabolized in 24-48 hours by endogenous amylases

Question 14

What is the mechanism of action of gelatin on hemostasis?

Answer 14

Product swells and provides a matrix for fibrin strand formation

Question 15

What is the mechanism of action of collagen on hemostasis?

Answer 15

Mechanical action and enhances platelet aggregation

Question 16

What is the mechanism of action of cellulose on hemostasis?

Answer 16

Forms a dense gelatinized clot on contact with the blood independent of the coagulation pathway

Question 17

What effect does the acidic nature of cellulose have on hemostasis?

Answer 17

Inactivates thrombin decreasing its hemostatic properties. However, it does create a bactericidal effect

Question 18

How much swelling occurs of polysaccharide spheres occurs with blood contact?

Answer 18

500%

Question 19

What is the mechanism of action of bone wax on hemostasis?

Answer 19

Mechanical obstruction of bleeding and subsequent clot formation

Question 20

Name two active hemostatic agents

Answer 20

Thrombin, alginate

Question 21

What are the three forms of thrombin available for use in hemostasis?

Answer 21

Human, recombinant, bovine

Question 22

What is the mechanism of action of thrombin in surgical hemostasis?

Answer 22

Utilizes the clotting cascade converting endogenous fibrinogen to fibrin. May be ineffective in the face of consumptive coagulopathy

Question 23

What is the mechanism of action of alginate in surgical hemostasis?

Answer 23

Alginate is a seaweed derived protein that is combined with calcium ions. On contact with blood the calcium is released and stimulates clotting

Question 24

Can alginate be used as a surgical hemostatic agent in body cavities?

Answer 24

No - causes a foreign body reaction

Question 25

What are two examples of hemostatic sealants?

Answer 25

Fibrin combination sealants and synthetic sealants (polyethylene glycol polymers or albumin)

Question 26

What is the main difference between hemostatic sealants and mechanical or active hemostatic agents?

Answer 26

Hemostatic sealants do not rely on the patients clotting ability (e.g. fibrin combination sealants contain both thrombin and fibrinogen)

Question 27

What are the two main groups of antifibrinolytics?

Answer 27

Serine protease inhibitors (aprotinin), lysine analogues (tranexamic acid, epsilon aminocaproic acid)

Question 28

Are lysine analogues helpful in maintaining hemostasis when coagulation factors are depleted or in the face of coagulopathy?

Answer 28

No - because they only prevent fibrinolysis (stabilize the clot), they do no effect platelet numbers or normal coagulation times

Question 29

What are the main side effects of desmopressin administration?

Answer 29

Hyponatremia and water retention (as is a vasopressin analogue so acts as an antidiuretic)

Question 30

What are the two primary hemostatic polymers/minerals for use in emergency situations?

Answer 30

Zeolite: Crystalline mineral compound with a high surface area. May be exothermic. Should be washed from wound as will create FB reaction.

Chitosan: Carbohydrate made from chitin (from shrimp shells). Not exothermic. Is metabolized into glucosamine leaving no residue.

Both these substances work by dehydrating blood and concentrating platelets and clotting factors.