Ch 18 - Surgical Haemostasis Flashcards

1
Q

What are the three main principles used to augment haemostasis?

A
  • Reduction of blood flow
  • Topical haemostatic agents
  • Antifibrinolysis
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2
Q

How long does it take to form a blood clot?

A
  • Approx 30 seconds for platelet aggregation
  • An additional 2-3min for cross-linking with the formation of a fibrin matrix
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3
Q

List some methods of reducing blood flow

A
  • Pressure/tamponade
  • Topical vasoconstrictors (epinephrine/adrenaline/ephedrine)
  • Hypotension/Hypothermia (reflex peripheral vasoconstriction)
  • Control of distant blood flow (Temporary or permanent ligation of major vessels)
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4
Q

List the vessels which can be permanently ligated

A
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5
Q

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

A
  • 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
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6
Q

What systemic responses have been recorded in humans in response to tourniquet application and removal?

A
  • Application - increased in circulated blood volume, hypertension and hypercoagulopathy
  • Removal - Transient but marked hypotension, hypercapnia, increased cerebral blood flow and intracranial pressure
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7
Q

What tourniquet pressure will result in demyelination?
What is the recommended tourniquet pressure?

A

Above 1000mmHg
Recommended is 100mmHg above patients systolic pressure

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8
Q

What is the equation to calculate tourniquet pressure?

A

P=T/RW

Pressure = tension / radius of limb x bandage width

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9
Q

What is the maximum time for tounriquet application on limbs?

A

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

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10
Q

What are the three groups of haemostatic agents?

A
  • Mechanical (absorb blood and provide a matrix for clot formation)
  • Active (actively stimulate the normal processed of haemostasis)
  • Haemostatic sealants
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11
Q

List the main forms of mechanical haemostatic agents

A
  • Gelatines
  • Collagens
  • Oxidised regenerative cellulose
  • Polysaccharides
  • Wax
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12
Q

List the main forms of active haemostatic agents

A
  • 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)
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13
Q

List three forms of haemostatic sealants

A
  • 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

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14
Q

What are the 2 main groups of antifibrinolytics

A
  • 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

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