Ch 18 - Surgical Haemostasis Flashcards
What are the three main principles used to augment haemostasis?
- Reduction of blood flow
- Topical haemostatic agents
- Antifibrinolysis
How long does it take to form a blood clot?
- Approx 30 seconds for platelet aggregation
- An additional 2-3min for cross-linking with the formation of a fibrin matrix
List some methods of reducing blood flow
- Pressure/tamponade
- Topical vasoconstrictors (epinephrine/adrenaline/ephedrine)
- Hypotension/Hypothermia (reflex peripheral vasoconstriction)
- Control of distant blood flow (Temporary or permanent ligation of major vessels)
List the vessels which can be permanently ligated
What are the suggested temporary ligation time of the following vessels in normothermic animals
- Descending thoracic aorta
- Pringle maneuver
- Hepatic artery
- Splenic artery and vein
- Renal artery and vein
- Abdominal aorta
- Descending thoracic aorta - 5-10min
- Pringle maneouver - 10-15min
- Hepatic artery - 30min
- Splenic artery and vein - 15-20min
- Renal artery and vein - 30min
- Abdominal aorta - 30min
What systemic responses have been recorded in humans in response to tourniquet application and removal?
- Application - increased in circulated blood volume, hypertension and hypercoagulopathy
- Removal - Transient but marked hypotension, hypercapnia, increased cerebral blood flow and intracranial pressure
What tourniquet pressure will result in demyelination?
What is the recommended tourniquet pressure?
Above 1000mmHg
Recommended is 100mmHg above patients systolic pressure
What is the equation to calculate tourniquet pressure?
P=T/RW
Pressure = tension / radius of limb x bandage width
What is the maximum time for tounriquet application on limbs?
Not established in dogs and cats however general recommended suggest a maximum of 1.5-2hr
Energy stores depleted in 2-3hr, mitochondrial changes visible after 1hr and microvascular damage after 2hr
What are the three groups of haemostatic agents?
- Mechanical (absorb blood and provide a matrix for clot formation)
- Active (actively stimulate the normal processed of haemostasis)
- Haemostatic sealants
List the main forms of mechanical haemostatic agents
- Gelatines
- Collagens
- Oxidised regenerative cellulose
- Polysaccharides
- Wax
List the main forms of active haemostatic agents
- Thrombin (converts endogenous fibrinogen to fibrin)
- Thrombin gelatin matrix
- Alginates (seaweed derived protein. Releases Ca on contact with slaine or body fluids, activating the clotting cascade)
List three forms of haemostatic sealants
- Human plasma-derived tissue sealant (Thrombin and fibrinogen)
- Autogenous plasma-derived tissue sealant
- Synthetic polymers (polyethylene glycol polymers or albumin)
Form a seal of vascular or dural defects without utilising endogenous haemostatic mechanisms at all
What are the 2 main groups of antifibrinolytics
- Lysine analogues (TXA, ACA)
- Serine protease inhibitor - license suspended in UK due to safety concerns
Not licensed, dogs likely require higher doses than humans, NOT effective when there is a depletion of clotting factors or coagulopathy
