Additional notes from anaesthetics - drugs Flashcards
When we are talking about ionotropes what are we talking about ?
Positive inotropes i.e. drugs which increase the force of cardiac muscular contraction
When are ionotropes indicated?
In the hypotensive patient who is adequately fluid resuscitated in whom the principal reversible cause for hypotension is poor cardiac contractility
What is the only way to safely administer ionotropes ?
By infusion through a central venous catheter
Give the 2 main examples of ionotropes
- Adrenaline (epinephrine)
- Dobutamine
What is the mechanism of action of adrenaline ?
- Catecholamine, agonist at both alpha and beta receptors.
- In low doses beta-1 mediated vasodilatation is prominent, but the blood pressure rises because of the beta-1 mediated increase in the force and rate of myocardial contraction.
- At high doses alpha-1 vasoconstriction predominates, thus the optimal dose for cardiac output is not necessarily the highest dose possible.
What is the mechanism of action of dobutamine ?
- Synthetic catecholamine. Predominantly beta-1 adrenoceptor agonist, with dose-dependent effects at beta-2 and alpha-1 receptors.
- It increases myocardial contractility with minimal effects on heart rate and little direct effect on vascular tone
What are vasopressor drugs ?
A substance which increases the systemic vascular resistance ==> increase BP
Give the main examples of vasopressors
- Noradrenaline (Norepinephrine)
- Metaraminol
- Ephedrine
- Adrenaline (Epinephrine)
What is the mechanism of action of noradrenaline ?
- Catecholamine. Powerful alpha-1 agonist with much weaker beta effects (most pronounced at low dose).
- As such it is used as a vasopressor rather than an inotrope to increase SVR.
Why is noradrenaline the most commonly used in ICU of all the vasopressors/inotropes?
Because the most common problem in adult sepsis is reduced SVR
What is the mechanism of action of metaraminol ?
Similar in action to naradrenaline, but with weaker activity
What is the drug of choice in theatre to increase SVR & blood pressure & why?
- Metaraminol - because it can be given peripherally
- Note - Can also be given by infusion if no central access available for noradrenaline
What is the mechanism of action of ephedrine ?
Acts on both alpha-1 and beta-1 receptors to increases both SVR and heart rate.
How is ephedrine given and what way cannot it be given?
Given peripherally and therefore used in theatre in bolus form (not given in infusion because quickly becomes ineffective by a process called tachyphylaxis).
What is the mechanism of action of paracetamol ?
Inhibits prostaglandin synthesis in the CNS