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arebef > Dawes: Inotropic Drugs > Flashcards

Dawes: Inotropic Drugs Flashcards

1
Q

What is an inotrope?

A

An inotrope is a drug that positively or negatively changes the force of contraction.

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2
Q

What is shock?

A

This is a state characterised by inadequate organ perfusion to meet the tissues oxygenation demand leading to organ dysfunction.

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3
Q

What are the different categories of shock?

A
  • Hypovolemic
    • Haemorrhage and Dehydration
  • Cardiogenic
    • Heart Failure
  • Distributive
    • Sepsis and Anaphylaxis
  • Obstructive
    • Cardiac Tamponade and Pulmonary Embolism.
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4
Q

What are the features of patients in shock?

A

They will usually be very unwell and as a result in an intensive treatment unit/high dependency unit. As well as this they will present with hypotension, hypovolemia, LV impairment, changes in vascular resistance, poor renal/peripheral perfusion and will be disorientated.

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5
Q

What are the goals of shock resuscitation?

A
  • Restore Blood Pressure
    • Ensure euvolemic
  • Normalise Systemic Perfusion
    • Inotropes and Vasopressors
  • Preserve organ function
    • Renal Perfusion
  • Treat Underlying Cause
    • Antibiotics or Relieve Tamponade

You will need to individualise treatment,

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6
Q

What is the mortality rates post cardiogenic shock?

A

>80% mortality!! In these people we use - intropes and vasopressors and the negative side effects far outweigh the rate of death!

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7
Q

What are the causes of cardiogenic shock?

A
  • Ischaemia
  • Valve Dysfunction
  • Acute VSD
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8
Q

What is cardiogenic shock characterised by?

A
  • High Systemic Resistance - Due to increased sympathetic activity.
  • Low Cardiac Output.
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9
Q

What is the first phase of septic shock?

A

This is the warm/hyperdynamic phase which is characterised by high cardiac output and low peripheral resistance. This is to compensate for the diminished plasma volume.

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10
Q

What is the late stage of septic shock?

A

This is the cold/hypodynamic phase characterised by subnormal temperature, low white blood cell counts and profound hypotension and hypoperfusion. This is caused by a considerable decrease in the cardiac output.

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11
Q

How do inotropic agents act to treat the effects of shock?

A

They augment contractility after preload has been established, thus improving cardiac output. This increased cardiac output acts to improve global perfusion. However, it does risk the patient becoming tachycardiac and increases myocardial oxygen consumption.

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12
Q

What are the vasopressors/inotropic agents?

A

They are alpha- and beta-adrenoreceptors agonists such as norepinephrine, epinephrine, dobutamine and dopamine.

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13
Q

What are the functions of each adrenergic receptor?

A
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14
Q

What is the function of Beta-1 receptors?

A

They mainly have effects on the heart as they act to increase contractility and increase heart rate.

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15
Q

What is an example of a Beta-1 agonist?

A

Dobutamine

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16
Q

What is the function of alpha-1 receptors?

A

These are mainly found in the blood vessels themselves and act to increase tone and vascular resistance.

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17
Q

What is an example of an alpha-1 agonist?

A

Norepinephrine.

18
Q

What is the relationship between vasoconstrictors and inotropes/chronotropes?

A

Inotropes/Chronotropes effects are mainly generated by the binding of drugs to beta-receptors whereas vasoconstrictors are those drugs that bind to alpha-receptors. As a result, a drugs ability to act as a vasoconstrictor/inotrope/chronotrope is affected by its’ affinity to alpha- or beta-receptors.

19
Q

What is the relationship between alpha- and beta-receptors and pressure?

A

Alpha-Receptors act to generate high blood pressures as they function as vasoconstrictors. This is in comparison to Beta-Receptors which result in lower blood pressures being generated.

20
Q

What is norepinephrine?

A

This is a first choice vasopressor which acts as a potent alpha-adrenergic agonist. It has minimal affinity for beta-1 receptors and therefore does not show high levels of inotropy or chronotropy. It instead acts to increase peripheral resistance and systolic/diastolic BP and is given via continuous intravenous infusion at 1-100 ug/min.

21
Q

How does norepinephrine function?

A
  1. Binds to alpha-1 receptors.
  2. GDP is converted to GTP.
  3. GTP acts to stimulate phospholipase C.
  4. Phospholipase C acts to convert PIP2 into DAG and IP3
  5. IP3 causes the release of stored calcium leading to activation of Ca2+ dependent protein kinases.
  6. Results in contraction of the vascular smooth muscle.
  7. Vasoconstriction.
22
Q

What is epinephrine?

A

Epinephrine is a mixed alpha- and beta-receptor agonist and therefore can cause vasoconstriction and vasodilation. It is a potent inotrope and chronotrope and is used in cardiac arrest situations. The risk with this drug is that it increases myocardial oxygen consumption, particularly in coronary heart disease. Epinephrine is given as a continuous intravenous infusion at 1 - 10ug/min.

23
Q

Why is epinephrine a good treatment for anaphylaxis?

A

It activates both alpha- and beta-receptors and therefore acts to increase blood pressure and dilate bronchi.

24
Q

What is dobutamine?

A

This is a beta-1 agonist that acts as a potent inotrope and variable chronotrope. It has a short half-life of 2 minutes due to its hepatic metabolism and is therefore given intravenously at a rate of 5-20 ug/kg/minute. Caution must be taken in hypotensive patients as it may precipitate tachycardia or worse hypotension due to its vasodilatory effects.

25
Q

What is the mechanism behind dobutamine?

A
  1. Binds to beta-receptor.
  2. Activate a stimulatory G-protein.
  3. Stimulatory G-protein activates adenylyl cyclase.
  4. Adenylyl Cyclase converts ATP into cAMP.
  5. Increased cAMP and Phosphodiesterase
  6. Stimulation of Protein Kinase C.
  7. Phosphorylation of enzymes (Enzyme-PO4)
  8. Biological Effect - Vasoconstriction.
26
Q

What is dopamine?

A

Dopamine is a metabolic precursor of norepinephrine with a short half-life.

If taken in low doses (0.5 - 2 ug/kg/min) it has a dopaminergic effect and acts to increase renal blood flow via D1 receptors.

If it is taken in moderate doses (2 - 10ug/kg/min) it has beta-effects.

If it is taken in high doses (>10ug/kg/min) it has alpha-effects.

27
Q

What are the side effects of vasopressors?

A

In shock, the sympathetic activity is already very high and as a result, further vasoconstriction - caused by alpha-agonism - can lead to ischaemia. Beta- and alpha- agonism can also increase cardiac work leading to cardiac ischaemia and arrhythmias.

28
Q

What are vasopressins and angiotensin IIs role in vasoconstriction?

A

Vasopressin is a vasopressor that also works through the IP3 mechanism - like norepinephrine. It undergoes liver and renal metabolism.

Angiotensin II is useful in catecholamine-resistant shock.

29
Q

What are amrinone/milrinone?

A

These are phosphodiesterase III inhibitors that act to induce vasodilation of the bodies vasculature and positive inotropy of the cardiac smooth muscle. It acts to increase the levels of cAMP which activates protein kinases increasing myocardial calcium flux and vessel Ca2+ uptake into the sarcoplasmic reticulum.

Usually used in combination with dobutamine as an intravenous solution in an intensive treatment unit.

30
Q

What are the main side-effects of phosphodiesterase inhibitors such as milrinone and amrinone?

A
  • Thrombocytopenia
  • Hypotension - Due to vasodilation
  • Arrhythmias - Due to increased cAMP
  • Increased Mortality Risk
31
Q

What is levosimendan?

A

This is an intravenous, calcium sensitizer that enhances troponins sensitivity to Ca2+ and therefore increases inotropy. It is a new drug emerging in the treatment of shock that shows an increased risk of causing arrhythmia and mortality.

32
Q

What is digoxin?

A

Digoxin is used in the treatment of atrial fibrillation as a rate controller. This is because it acts to slow the HR, improves cardiac work and has benefits in acute and chronic heart failure. It has no effect on mortality and reduces hospital admission.

33
Q

What are the role two digitalis glycosides used clinically?

A
  • Digoxin
  • Digitoxin
34
Q

What is digoxins mechanism of action in the myocardium?

A
  1. Acts by inhibiting the Na+/K+ - ATPase.
  2. Loss of Na+/K+ ion gradients results in cellular depolarization.
  3. Increased intracellular Na+ concentrations leads to an accumulation of intracellular calcium via the Na+/Ca2+ exchange system.
  4. Increased intracellular Ca2+ leads to increase Ca2+ release from the sarcoplasmic reticulum.
  5. Increased Ca2+ bound to troponin-C.
  6. Increased contractility.
35
Q

What is digoxins effect on the AV node?

A
  1. Augments vagal tone at the AV node.
  2. Slows AV conduction.
  3. Slows ventricular rate.
36
Q

What is digoxin used for clinically?

A

This is a drug used clinically to treat acute heart failure with fast atrial fibrillation and also to control AF rate.

37
Q

What are the doses for digoxin?

A
  • Loading Dose
    • Up to 1.5mg over 36 hours (oral and iv)
  • Maintenance Dose
    • 0.0625mg-0.25mg per day
    • Dependant on renal function.
38
Q

Does digoxin have an effect on chronic cardiac failure mortality?

A

No. Patients on digoxin and those on placebo both had similar mortality rates over the same period of time.

39
Q

What does digitalis toxicity result in?

A
  • Cardiac
    • Various Arrhythmias - 2nd or 3rd degree heart block.
    • Changes in ECG
  • Non-Cardiac
    • Nausea/Vomiting/Anorexia/Diarrhoea
    • Abdominal Pains
    • Fatigue
    • Visual Complaints
    • Muscular Weakness
    • Dizziness
    • Dreams
40
Q

What does digitalis interact with?

A
  • Metabolic
    • Decreased K+ and Mg2+ - Increases digoxin effect and thus need to take care when used with diuretics,
  • Drug
    • Quindine, Amiodarone, Verapamil, Diltiazem, Erythromycin and Cyclosporin - All act to increase digoxin plasma levels as they act as PGP inhibitors.

arebef (29 decks)

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