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Diploma in Anaesthesia > Drug therapy - Implications for the anaesthetist > Flashcards

Drug therapy - Implications for the anaesthetist Flashcards

1
Q

What is the severity and mortality of chronic digoxin toxicity

A

Variable severity

Mortality at 1 week 15 - 30%

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2
Q

What are the main features of digoxin toxicity

A

GIT distress
Hyperkalaemia
Dysrhythmias (Increased automaticity and AV block

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3
Q

What is the antidote for digoxin toxicity

A

Digoxin specific Fab fragments (digibind)

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4
Q

What is the mechanism of action of digoxin

A

Direct and indirect effects resulting in

  1. Increased inotropy (mild)
  2. Increased automaticity
  3. Negative dromotropy (Slowing of AV conduction)
  4. Increased vagal tone

DIRECT:
Inhibition of Na-K ATPase
–> Increased IC Na+ –> increased IC Ca+ (Na/Ca antiport) –> inotropy and increased automaticity
–> decreased IC K= leads to negative dromotropy (slower repolarization of AV node and longer refractory period)

INDIRECT:
Increased vagal tone (vagomimetic effect)

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5
Q

What is dromotropy

A

Dromotropy = conductivity in cardiac muscle

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6
Q

What are the ECG features that demonstrate the digoxin EFFECT

A

ST - downsloping ST depression with the characteristic “Salvador Dali” sagging appearance
Abnormal T-waves - usually biphasic
Shortened QT interval

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7
Q

What are the clinical features of digoxin toxicity

A

GIT: Nausea, vomiting, anorexia, diarrhoea
Visual: Blurred vision, yellow/green discolouration, haloes
CVS: Palpitations, syncope, dyspnoea
CNS: Confusion, dizziness, delirium, fatigue

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8
Q

What are the principles in understanding ECG in suspected digoxin toxicity

A

The classic digoxin toxic dysrhythmia combines:

  1. Supraventricular tachycardia (due to increased automaticity)
  2. Slow ventricular response (due to decreased AV conduction)
  • Frequent PVCs (the most common abnormality), including ventricular bigeminy and trigeminy
  • Sinus bradycardia
  • Slow Atrial Fibrillation
  • Any type of AV block (1st degree, 2nd degree & 3rd degree)
  • Regularised AF = AF with complete heart block and a junctional or ventricular escape rhythm
  • Ventricular tachycardia, including polymorphic and bidirectional VT
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9
Q

What are the anaesthetic implications of MAOIs

A

Used in refractory depression (rarely)
Can cause intra-op seizures if ephedrine is used

Must be stopped 2 weeks before –> consult psychiatrist for appropriate substitutes

Avoid indirectly acting inotropes such as ephedrine
Use phenylephrine if required

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10
Q

Which vasopressor can be used in an emergency patient on MAOI

A

Phenylephrine (NOT ephedrine)

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11
Q

Give 3 examples of MAOIs

A

Tranylcypromine
Phenelzine
Isocarboxazid

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12
Q

Which drugs potentiate block with ND-NMB agents

A

Magnesium Rx in Pre-eclampsia

Gentamicin prophylaxis used in sepsis and urology

Furosemide, Cyclosporin, cyclophosphamide in patients undergoing renal transplant

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13
Q

Which drugs can prolong the duration of SUX

A

Carbamazepine

Echothiopate (eye drops)

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14
Q

Which drugs antagonize NMB

A

Phenytoin
Carbamazepine
Azathioprine

Implication - may need frequent top ups of NMBs.

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15
Q

What type of surgery is antagonism of NMB most relevant requiring vigilance with regard to NMB top ups

A

Intracranial aneurysm repair
– Many of these patients are on anti-convulsants

USE peripheral nerve stimulator

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16
Q

List 1 drug interaction which may lead to intra-operative hypertension

A

Pethidine in patient’s on MAOI

17
Q

Which intra-operative drugs can cause hypertension and tachyarrhythmia

A

10% phenylephrine eye drops in ophthalmic surgery (ask surgeon to use 2.5%)

Pethidine + MAOI

Adrenalin in local anaesthetic infiltrations + halothane anaesthesia

Digoxin –> cause tachyarrhythmia
- Increased Ve –> Resp. Alkalosis –> H+/K shift –> hypokalaemia –> Digoxin toxicity (K+ must be maintained at high normal levels for patient’s on digoxin)

18
Q

Which drugs are reported to cause bradyarrhythmias

A

Timolol eye drops
Digoxin
Verapamil

19
Q

What are ganglion blockers. Give three examples and suggest a possible anaesthetic implications of patients using these drugs

A

A ganglionic blocker (or ganglioplegic) is a type of medication that inhibits transmission between preganglionic and postganglionic neurons in the Autonomic Nervous System.

Methyldopa (MOA: Stimulation of central alpha-adrenergic receptors by a false neurotransmitter (alpha-methylnorepinephrine) that results in a decreased sympathetic outflow to the heart, kidneys, and peripheral vasculature)

Reserpine: (MOA: Reduces blood pressure via depletion of sympathetic biogenic amines (norepinephrine and dopamine)

Guanethidine: (MOA: preventing the release of norepinephrine at nerve endings and causes depletion of norepinephrine in peripheral sympathetic nerve terminals as well as in tissues)

A patient on methyldopa –> if ephedrine is administered, the entire SNS outflow from CNS has been inhibited so the release of endogenous catecholamines induced by ephedrine is likely to be less effective.
–> use a direct acting agent: phenylephrine

20
Q

When should aspirin be stopped prior to surgery

A

48 hours

> 48 hours if daily dose is > 300mg

21
Q

What is the minimum platelet count required prior to surgery

A

100

22
Q

When should clopidogrel be stoped prior to surgery and what should be considered here

A

7 days prior to surgery

Consider risk-benefit of stopping clopidogrel –> discuss with cardiology –> consider averting a neuraxial block

23
Q

When should Warfarin be stopped prior to surgery

A

4 days –> INR > 1.4

heparin should be administered to maintain anticoagulation which can be titrated perioperatively

24
Q

What should be done about a patient on the combined oral contraceptive pill

A

Swap to progesterone only
OR
Appropriate precautions against VTE peri-operatively

25
Q

Which drugs can increase K+

A

Beta blockers (prevent insulin release from pancreatic beta cells –> NA-K ATPase not stimulated –> K+ uptake not taken up by cells)

Spironolactone (inhibit aldosterone and hence reduce K excretion)

26
Q

What drugs cause high Calcium

A

Cancer and chemo

27
Q

What drugs cause acidosis

A

Acetazolamide

28
Q

What drugs can cause alkalosis

A

PPIs

29
Q

What can cause low Ca, K, Na

A

Furosemide

30
Q

Which drugs cause methaemoglobinaemia and in so doing interfere with Hb O2 saturation

A

Prilocaine
Dapsone
Sulphonamides

31
Q

What should be done about herbal medicines prior to surgery

A

Stopped 2 weeks before

32
Q

Which medications should be omitted on the morning of the surgery

A 
ACEi
ARB
alpha blockers (tamsolusin)
Metformin
Diuretics

And others

Diploma in Anaesthesia (73 decks)

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