Ch. 18 Surgical Hemostasis

Question 1

The three main principles of augmenting hemostasis are: reduction of blood flow to the affected area, topical hemostatic agents, and antifibrinolytics.
What are ways to reduce the blood flow?

Answer 1

pressure/tamponade
topical vasoconstrictors like epinephrine/adrenaline/ephedrine
hypotension/hypothermia/reduced perfusion
distant control of blood flow

Question 2

How long does clot formation and stabilization take to occur?

Answer 2

30 seconds for platelet aggregation to form a soft clot

2-3 minutes for the clot to be cross linked with the formation of a fibrin matrix that provides security

Question 3

Characteristics of topical vasoconstrictors (such as epinephrine, adrenaline, and ephedrine)

Answer 3

used for epistaxis, small arterial bleeding, even reported to aid in bleeding gastric ulcers
disadvantages include the absorption of the product which will have effects on the CV system
use adrenaline in diluted form

Question 4

Rumel tourniquet

Answer 4

tape or penrose passed around a vessel to temporarily occlude it during surgery

Question 5

Esmarch tourniquet

Answer 5

the tourniquet you would think of to save someone from bleeding out from their limb
elevate the limb to minimize exsanguination
apply it distal to proximal with broad elastic material

Question 6

What pressure of a tourniquet will result in degeneration of the myelin of compressed nerves and lead to neurologic deficits

Answer 6

greater than 1000 mmHg
now usually in human medicine pneumatic tourniquets are used and applied to a pressure 100 mmHg greater than the patient’s systolic

Question 7

How can you calculate the pressure for a tourniquet? What does this mean for tiny limbed patients vs thicker limbed?

Answer 7

P = T/(RW)
P is pressure
T is bandage tension
R is the radius of the curvature of the limb
W is bandage width
An inverse relationship between the pressure applied and the width of the tourniquet itself
for tiny dogs and cats, if a tourniquet is applied with the same tension (material stretched to the same degree) as would be applied to a larger patient, the pressure will be higher because of the smaller limb radius

Question 8

What is the suggested temporary ligation time of the descending thoracic aorta in normothermic animals?

Answer 8

5-10 minutes

Question 9

What is the suggested temporary ligation time of the portal triad (Pringle maneuver), hepatic artery, portal vein, common bile duct in normothermic animals?

Answer 9

10-15 minutes

Question 10

What is the suggested temporary ligation time of the hepatic artery in normothermic animals?

Answer 10

30 minutes

Question 11

What is the suggested temporary ligation time of the splenic artery and vein in normothermic animals?

Answer 11

15-20 minutes

Question 12

What is the suggested temporary ligation time of the renal artery and vein in normothermic animals?

Answer 12

30 minutes

Question 13

What is the suggested temporary ligation time of the abdominal aorta and vein in normothermic animals?

Answer 13

30 minutes

Question 14

Vessels that can be permanently ligated

Answer 14

both common carotids if vertebral artery is preserved and the circle of Willis is function (not cats)
both jugular veins (not in cats)
brachiocephalic veins
brachial arteries
hepatic vein
femoral arteries
both external iliac arteries
both external iliac veins
both femoral veins
abdominal vena cava caudal to liver when there is chronic compression and established collateral circulation of concurrent right nephrectomy 
left renal vein (not cats)

Question 15

Proposed mechanism of action for silver nitrate sticks or other silver hemostatic agents?

Answer 15

ionization of the product with direct activation of vessel contraction and the clotting cascade

Question 16

What are the three categories of types of topical hemostatic agents?

Answer 16

Mechanical
Active
Hemostatic sealant

Question 17

Gelatin hemostatic agent properties

Answer 17

mechanical hemostatic agent
may be combined with thrombin
gelatin will swell where in contact with blood and provide a matrix for fibrin strand formation
the clot is stabilized in the matrix of the foam
does not actively promote platelet aggregation like gelatin does
in liver, kidney, spleen and body wall, may absorb as fast as 5 weeks

Question 18

Bovine collagen properties

Answer 18

Mechanical hemostatic agent
available in sheets or a powder
aids in mechanical action but also enhancing platelet responses to vessel injury
improves platelet aggregation

Question 19

Cellulose hemostatic agent properties

Answer 19

mechanical hemostatic agent
Oxidized regenerated cellulose is available as a sheet
strong structure is good for endoscopic surgery
oxidized regenerated cellulose forms a dense gelatinous clot on contact with blood, independently of the coagulation pathway, which provides a mechanical barrier to bleeding
acidic properties may cause denaturing of blood proteins, resulting in stimulation of hemostasis… but that will inactivate thrombin
bactericidal against a wide range of bacteria (because of the low pH)
reabsorbed in 2-6 weks

Question 20

Polysaccharide spheres hemostatic agent

Answer 20

plant derived starch comes in a powder
combine polysaccharide with oxidized regenerated cellulose
the spheres are hydrophilic and concentrate the solid components of blood by dehydrating it –> stimulation of platelet responses and providing a mechanical barrier
powder will increase in volume by 500%
metabolized within 24-48 hours

Question 21

Bone wax and ostene hemostatic agent properties

Answer 21

bone wax is sterile beeswax
mechanical hemostasis will occur by blocking the surface and allowing clot formation
ostene (trade name Baxter) is a blend of water soluble synthetic alkaline oxide copolymers with no reported effect on bone healing, little foreign body reaction, and less risk of infection

Question 22

Thrombin as a hemostatic agent

Answer 22

Active hemostatic agent (stimulates the normal process of hemostasis)
three forms - human, bovine, and recombinant
uses the normal clotting cascade mechanisms by converting endogenous fibrinogen to fibrin and creating a clot
often combined with gelatin or fibrinogen but cannot be combined with cellulose because of the acidic environment
may have reaction to the the thrombin so avoid repeated use in subsquent surgeries

Question 23

Alginates as a hemostatic agent

Answer 23

these are available as wound dressings to stimulate healing but also have a hemostatic effect
seaweed derived protein
on contact with saline or body fluids, calcium ions are released and the clotting cascade is activated
they will cause a foreign body reaction - do not use in a cavity, more like in the mouth

Question 24

Fibrin as a hemostatic sealant

Answer 24

fibrin combination sealants work independently of the patient’s clotting ability or vessel damage
might be extra useful in trauma patients who may be coagulopathic
derived from pooled human plasma and must be reconstituted prior to use
available as glue, patches, or a matrix
Tisseel also contains an antifibrinolytic
Evicel has reduced levels of plasminogen
An autologous version (Vitagel) can be made with the patient’s own plasma mixed with collagen and fibrin

Question 25

Synthetic hemostatic sealants

Answer 25

used as an adjunct for open surgical repair of large vessels and sealing of parenchymatous surfaces or dura
products can swell considerably
absorbed in 4-8 weeks
examples include Corseal, Duraseal, BioGlue

Question 26

Serine protease inhibitor (Aprotinin)

Answer 26

an antifibrinolytic

Question 27

Lysine analogues

Answer 27

example would be tranexamic acid
does not affect platelet number nor normal coagulation times but thrombin time will be prolonged and clot stability improved
tranexamic acid is excreted unchanged in the urine
in Beagles, antifibrinolytic activity decreased in a time-dependent manner and was resolved within 24 hours
no effective with a depletion in clotting factors or a coagulopathy

Question 28

Desmopressin as a hemostatic agent

1-Desamino-8-D-Arginine Vasopressin

Answer 28

Desmopressin or DDAVP is a synthetic analog of vasopressin and will stimulate the release of vWF and factor VIII from endothelial cells
can be used to prevent and treat bleeding in patients with vWF deficiencies but does not improve hemostasis in normal patients

Question 29

Ethamsylate (hemostatic agent)

Answer 29

an oral or IV hemostatic agent
magnitude of blood loss reduction is proportional to the severity of the bleeding
improves platelet adhesiveness and aggregation
might act synergistically with desmopressin

Question 30

zeolite hemostatic polymer

Answer 30

a crystalline mineral compound with a high surface area
absorbs water to concentrate clotting factors and platelets, activates platelets, and releases calcium ions that activate that coagulation cascade
may cause a foreign body reaction

Question 31

Chitosan the hemostatic polymer

Answer 31

biodegradeable non toxic carbohydrate derived from deacetylated chitin (shrimp shells)
high surface area which will form a stable gel like clot on contact with blood
formation is independent of clotting factors and will still form even with presence of heparin or warfarin
it is a polysaccharide so eventually, it is metabolized by lysozymes into glucosamine –> no leftovers left in the patient
may have some bacterialcidal activity
as a wafer or granules
emergency situation