Emergency Drugs in Anaesthesia Flashcards
How does ephidrine work?
It is an indirect sympathomimetic.
It causes release of noradrenaline at the sympathetic nerve terminals.
The noradrenaline released acts on both alpha and beta adrenoreceptors causing: increased cardiac output (HR and contractility) and increased SVR.
Why is tachyphylaxis seen in ephidrine?
As a result of depletion of noradrenaline stores.
How does phenylephirine work?
It is a synthetic direct acting sympathomimetic.
It causes direct stimulation of the alpha adrenorecptors causing vasoconstriction (increasing SVR).
It is often associated with a reflex bradycardia.
How is phenylephirine drawn up and what is the dose?
It comes in 1ml vial containing 10mg.
The dose is 50-100microgram boluses to effect.
If drawn up into a 100ml bag of NaCl it will be a concentration of 100micrograms per ml.
How does metaraminol work?
It is a synthetic direct- and indirect-acting sympathomimetic.
It mainly affects alpha adrenoreceptors causing vasoconstriction (increasing SVR). It has minor beta effect.
A reflex bradycardia is common.
Which drugs can be used to treat an isolated bradycardia, and what are the doses?
Anticholinergics:
Glycopyrolate: 200microgram aliquots up to 600micrograms
Atropine: 500microgram aliquots up to 3mg.
Note glycopyrolate dose not cross the blood brain barrier as it contains a charged Nitrogen ion making it less lipid soluble.
How can you manage bronchospasm in an anaesthetised patient?
Non pharmacological:
Pressure controlled ventilation
Adequate expiratory time to prevent air trapping.
Optimising positioning as able.
Pharmacological:
Anaesthetic gases
Salbutamol (nebulised or IV)
Magnesium
Aminophylline
Adrenaline
What is the mechanism of action and dose of IV salbutamol?
Beta 2 agonist, has some beta 1 activity at high doses.
250micrograms, it should be given over at least 20mins (as causes tachycardia and can be pro-arrhythmic)
What is the mechanism of action of aminophylline?
It is a theophylline.
It acts by inhibiting phosphodiesterases (which usually catalyse the hydrolysis of cAMP). They therefore increase the amount of cAMP within cells causing smooth muscle relaxation.
What is the dose of aminophylline, in which patients should it not used?
250mg (given over 20mins)
It should not be used in patients already on a theophylline as it has a narrow therapeutic window, therefore can easily get into toxic range. (in toxic range can cause seizures and arrhythmias)
What is the IV dose of adrenaline that should be given in anaphylaxis or life threatening refractory bronchospasm?
50 micrograms (aka 0.5ml of 1 in 10000)
Can give 50-100micrograms in anaphylaxis (aka 1ml of an adrenaline minijet)
Note in smaller doses adrenaline has more beta activity (good for bronchospasm) in higher doses more alpha activity
What is the emergency treatment of malignant hyperthermia?
Call for help
Remove triggering agent
Ventilate on FiO2 of 1.0 with a high minute volume.
Give Dantrolene 2mg/kg up to 10mg/kg
Active cooling (ice packs in axilla, cold water bladder lavage, arctic sun)
Will need Intensive Care
What is the dose of adrenaline used in cardiac arrest?
1mg (mini-jet contains 10ml of 1:10000)
