CPT S8 - Anti-coagulants, Anti-platelets & Anaesthetics

Question 1

Give some examples of disorders of haemostasis

Answer 1

DVT
PE
MI
CVA

Question 2

What is Virchow’s triad?

Answer 2

The three main contributing factors that lead to thrombosis:

• Hypercoagulability
• Endothelial damage
• Stasis

Question 3

What is the mechanism of action of warfarin?

Answer 3

Inhibits production of Vitamin K dependent clotting factors by preventing the conversion of Vitamin L to its active reduced form.

Question 4

What are the Vitamin K dependent clotting factors?

Answer 4

II, VII, IX, X

Question 5

What is the mechanism of action of heparin?

Answer 5

Activates anti-thrombin III (ATIII)

Deactivates factors Xa, IIa, IXa (and probably VIIa, XIa, XIIa)

Question 6

What are some potential problems with warfarin?

Answer 6

GI absorption: PO is preferred for long term so may be issues if pt has poor GI absorption
Slow onset of action: need heparin cover until it starts to work
Slow offset: variably half life. Need to stop 3 days before surgery
Heavily protein bound: potential for DDIs if it’s displaced.
Hepatic metabolism: caution in hepatic disease and with drugs that affect p450 enzymes
Narrow therapeutic window: monitoring required
Crosses placenta: teratogenic

Question 7

How is warfarin monitored?

Answer 7

Use extrinsic pathway factors
Prothrombin time
INR

Question 8

Give some clinical uses of warfarin?

Answer 8

DVT
PE
AF
Mechanical prosthetic valves
Thrombophilia
CVA
Cardiomyopathy
Cardiac thrombus

Question 9

Give some ADRs for warfarin

Answer 9

Bleeding

Bruising

Question 10

How can warfarin treatment be reversed?

Answer 10

Stop warfarin
IV Vit K
Prothrombin complex concentrate
Fresh frozen plasma

Question 11

Which is safer type of heparin and why?

Answer 11

LMWH (Low Molecular Weigh Heparins) because their action is more easily predictable, whereas unfractionated heparin is much more variable/

Question 12

How is LMWH given?

Answer 12

Subcutaneously

Question 13

When is LMWH used clinically?

Answer 13

Peri-operative
Immobility
Reduce the thrombotic risk of those normally on warfarin who need an operation, as has a quicker offset time

Question 14

Give some ADRs of heparin

Answer 14

Bleeding
Bruising
Thrombocytopenia
Osteoporosis

Question 15

How is heparin therapy reversed?

Answer 15

Protamine sulphate binds irreversibly to heparin, causing it to dissociate from anti-thrombin III
Give protamine if actively bleeding

Question 16

Is monitoring required in heparin treatment?

Answer 16

Not for LMWH, but may occasionally need a factor Xa essay

APTT needs monitoring for unfractionated heparin

Question 17

Give some examples of anti-platelet drugs

Answer 17

Aspirin (COX1 inhibitor)
Dipyridamole (phosphodiesterase inhibitor)
Clopidogrel (ADP antagonist)
Glycoprotein IIb/IIIa inhibitors

Question 18

What are the steps of anaesthesia?

Answer 18

Premedication (for phobics)
Induction (IV or inhaled)
Intraoperative analgesia (usually an opioid)
Muscle paralytic (facilitate intubation/ventilation/stillness)
Maintenance (IV or inhaled)
Reversal of paralysis and induction of recovery (including post-op analgesia)

Question 19

What are Guedel’s signs?

Answer 19

The stages of anaesthesia:

1: analgesia and consciousness
2: unconscious, breathing erratic but delirium could occur, leading to an excitement phase
3: surgical anaesthesia, with four levels of progressively weaker breathing
4: respiratory paralysis

Question 20

What is anaesthesis a combination of?

Answer 20

Analgesia
Hypnosis
Depression of reflexes
Muscle relaxation

Question 21

What is the Minimum Alveolar Concentration (MAC)

Answer 21

The [alveolar] at 1 atm at which 50% of subjects fail to move to surgical stimulus

Question 22

What factor affects induction and recovery times?

Answer 22

Partition coefficients (solubility)

• Blood:Gas partition
• Oil:Gas partition (can have slow accumulation due to the fat partition)

Question 23

What factors can affect MAC?

Answer 23

Age (higher in younger)
Hyper/othermia (higher in hyper)
Pregnancy (higher)
Alcoholism (higher)
Central stimulants (higher)
Other anaesthetics (lower)
Opioids (lower)

Question 24

How are GABA receptors exploited in anaesthesia?

Answer 24

Effects of GABA potentiation are anxiolysis, sedation and anaesthesia
Major inhibitors neurotransmitter

Question 25

What is another target of anaesthetic agents aside from GABA?

Answer 25

NMDA receptors

Eg in Xe, N2O and ketamine

Question 26

How are different circuits of the brain tergeted in anaesthesia?

Answer 26

Reticular formation, responsible for activating the brain, is depressed. Comprised of;

• Thalamus, responsible for transmission and modulation of sensory information
• Hippocampus, responsible for memory, depressed
• Brainstem, responsible for respirator and some CVS function
• Spinal cord, responsible for pain transmission and motor neuronal activity, is depressed