Surgical hemostasis Flashcards
How long does it take for a clot to form?
30 seconds for initial platelet aggregation, 2-3 minutes for the clot to become cross-linked with a fibrin matrix
What are the potential disadvantages with the use of abdominal counterpressure for the treatment of abdominal hemorrhage?
Increased intraabdominal, intrathoracic and intracranial pressures.
What are potential methods to facilitate blood flow reduction to aid in hemostasis?
- Pressure/tamponade
- Topical vasoconstrictors (epinephrine, adrenaline, ephedrine)
- Distant control of blood flow
What vessels are able to be permanently ligated in the dog and cat?
What arteries and veins can be occluded on a temporary basis during surgery if required?
What are they suggested temporary ligation times for vessels if required during surgery?
What has been shown to result with high tourniquet pressures in humans?
Nerve demyelination and neurologic deficits for up to 6 months post-operative
What is the ideal cuff pressure of a tourniquet?
100 mm Hg above systolic blood pressure
What is the safe duration of tourniquet application in animals?
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.
What are the systemic responses to tourniquet application in humans?
Increased circulating blood volume, hypertension and hypercoagulopathy. Following removal transient hypotension, hypercapnia, increased ICP, pulmonary thromboembolism and increased fibrinolysis.
What are the three categories of hemostatic agents?
- Mechanical
- Active
- Hemostatic sealants
List commonly used mechanical hemostatic agents in companion animal surgery.
Gelatins, collagens, oxidized cellulose, polysaccharide spheres, wax
How long does it take for gelatins, collagens, oxidized cellulose and polysaccharide spheres to be resorbed?
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
What is the mechanism of action of gelatin on hemostasis?
Product swells and provides a matrix for fibrin strand formation
What is the mechanism of action of collagen on hemostasis?
Mechanical action and enhances platelet aggregation
What is the mechanism of action of cellulose on hemostasis?
Forms a dense gelatinized clot on contact with the blood independent of the coagulation pathway
What effect does the acidic nature of cellulose have on hemostasis?
Inactivates thrombin decreasing its hemostatic properties. However, it does create a bactericidal effect
How much swelling occurs of polysaccharide spheres occurs with blood contact?
500%
What is the mechanism of action of bone wax on hemostasis?
Mechanical obstruction of bleeding and subsequent clot formation
Name two active hemostatic agents
Thrombin, alginate
What are the three forms of thrombin available for use in hemostasis?
Human, recombinant, bovine
What is the mechanism of action of thrombin in surgical hemostasis?
Utilizes the clotting cascade converting endogenous fibrinogen to fibrin. May be ineffective in the face of consumptive coagulopathy
What is the mechanism of action of alginate in surgical hemostasis?
Alginate is a seaweed derived protein that is combined with calcium ions. On contact with blood the calcium is released and stimulates clotting
Can alginate be used as a surgical hemostatic agent in body cavities?
No - causes a foreign body reaction
What are two examples of hemostatic sealants?
Fibrin combination sealants and synthetic sealants (polyethylene glycol polymers or albumin)
What is the main difference between hemostatic sealants and mechanical or active hemostatic agents?
Hemostatic sealants do not rely on the patients clotting ability (e.g. fibrin combination sealants contain both thrombin and fibrinogen)
What are the two main groups of antifibrinolytics?
Serine protease inhibitors (aprotinin), lysine analogues (tranexamic acid, epsilon aminocaproic acid)
Are lysine analogues helpful in maintaining hemostasis when coagulation factors are depleted or in the face of coagulopathy?
No - because they only prevent fibrinolysis (stabilize the clot), they do no effect platelet numbers or normal coagulation times
What are the main side effects of desmopressin administration?
Hyponatremia and water retention (as is a vasopressin analogue so acts as an antidiuretic)
What are the two primary hemostatic polymers/minerals for use in emergency situations?
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.
