Ch. 18 Surgical Hemostasis Flashcards
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?
pressure/tamponade
topical vasoconstrictors like epinephrine/adrenaline/ephedrine
hypotension/hypothermia/reduced perfusion
distant control of blood flow
How long does clot formation and stabilization take to occur?
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
Characteristics of topical vasoconstrictors (such as epinephrine, adrenaline, and ephedrine)
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
Rumel tourniquet
tape or penrose passed around a vessel to temporarily occlude it during surgery
Esmarch tourniquet
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
What pressure of a tourniquet will result in degeneration of the myelin of compressed nerves and lead to neurologic deficits
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
How can you calculate the pressure for a tourniquet? What does this mean for tiny limbed patients vs thicker limbed?
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
What is the suggested temporary ligation time of the descending thoracic aorta in normothermic animals?
5-10 minutes
What is the suggested temporary ligation time of the portal triad (Pringle maneuver), hepatic artery, portal vein, common bile duct in normothermic animals?
10-15 minutes
What is the suggested temporary ligation time of the hepatic artery in normothermic animals?
30 minutes
What is the suggested temporary ligation time of the splenic artery and vein in normothermic animals?
15-20 minutes
What is the suggested temporary ligation time of the renal artery and vein in normothermic animals?
30 minutes
What is the suggested temporary ligation time of the abdominal aorta and vein in normothermic animals?
30 minutes
Vessels that can be permanently ligated
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)
Proposed mechanism of action for silver nitrate sticks or other silver hemostatic agents?
ionization of the product with direct activation of vessel contraction and the clotting cascade
What are the three categories of types of topical hemostatic agents?
Mechanical
Active
Hemostatic sealant
Gelatin hemostatic agent properties
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
Bovine collagen properties
Mechanical hemostatic agent
available in sheets or a powder
aids in mechanical action but also enhancing platelet responses to vessel injury
improves platelet aggregation
Cellulose hemostatic agent properties
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
Polysaccharide spheres hemostatic agent
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
Bone wax and ostene hemostatic agent properties
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
Thrombin as a hemostatic agent
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
Alginates as a hemostatic agent
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
Fibrin as a hemostatic sealant
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
Synthetic hemostatic sealants
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
Serine protease inhibitor (Aprotinin)
an antifibrinolytic
Lysine analogues
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
Desmopressin as a hemostatic agent
1-Desamino-8-D-Arginine Vasopressin
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
Ethamsylate (hemostatic agent)
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
zeolite hemostatic polymer
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
Chitosan the hemostatic polymer
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
