General Anesthetics Flashcards
What are inhalational agents used for?
Maintaining amnesia
What is the process for general anaesthesia?
Monitoring
IV access
Induction of anaesthesia
Start analgesia + muscle relaxant
Maintain process
Reverse proces
What is the minimum monitoring needed?
ECG
Sp02
NIBP
Airway gases (O2, CO2, vapour)
Airway pressure
Nerve stimulator (if muscle relaxant used)
Temperature (due to hypothermia risk)
What drugs can be used as induction agents?
Propofol, Ketamine, Etomidate
Describe propofol, its properties + SE
Most common
Lipid based
Excellent suppression of airway reflexes + Reduces PON+V
SE: drop in HR + BP, pain on injection, involuntary movements
Describe the use of ketamine (properties + SE)
Causes dissociative anaesthesia - anterograde amnesia + profound analgesia
Sole anaesthetic for short procedures
Slow onset (90s)
SE: rise in HR + BP
Bronchodilation
N+V, emergence phenomenon
Describe etomidate’s properties + SE
Rapid onset
Haemodynamic stability
Lowest incidence of hypersensitivity reaction
SE: pain on injection, spontaneous movements, adreno-cortical suppression, high incidence PONV
What are the 4 amnesia inhalational agents?
Isoflurane, Sevoflurane, Desflurane, Enflurane
What is MAC?
Minimum alveolar concentration
Min concentration of the vapour that prevents the reaction to a standard surgical stimulus in 50% of subjects
What is emergence phenomenon?
Can occur with ketamine
Pt is elated or depressed after coming round
Short + long acting opioids
Short acting = fentanyl
Long acting = morphine, oxycodone
Which muscle relaxant is depolarising how does it work + give the uses + SE?
Succinylcholine
Ach receptor agonists
Works by causing an action potential (causing fasciculations) + then remains in the nerve so acetylcholine can’t bind
Good for rapid sequence induction
SE: muscle pain, fasciculations, hyperkalaemia, malignant hyperthermia, rise in ICP, IOP + gastric pressure
Which muscle relaxants are non-depolarising + give how it works, uses + SE?
Slow onset + variable duration, less SE
Compete with acetylcholine at the NMJ (antagonists)
Atracurium, mivacurium, pancuronium, rocuronium
What do you use to reverse the non-depolarising muscle relaxants + how do they work?
Neostigmine - anticholinesterase = increases amount of acetylcholine to displace the muscle relaxant (prevents breakdown of acetylcholine)
Glycopyrrolate - anticholinergic used to counter the SE of neostigmine (bradycardia, hypotension) = essentially atropine but longer acting
What vasoactive drugs are used to maintain BP?
Ephedrine Phenylephrine Metaraminol
What drugs are used in severe hypotension?
Noradrenaline Adrenaline Dobutamine
Describe when you’d use ephedrine + how it works
Causes a rise in BP if its falling
Also causes rise in HR - only use when HR is low
Uses A + beta receptors
Describe when you’d use phenylepherine + how it works
Rise in BP via vasoconstriction
Causes a drop in HR - used when HR is too high
Direct action via A receptors
Describe when you’d use metaraminol + how it works
Rise in BP via vasoconstriction
Used when HR is already high
Predominantly via A receptors
How common is PONV?
20-30%
What anti-emetics are used and what receptors do they affect?
5HT3 blockers: Ondansetron
Anti-histamine: Cyclizine
Steroids: Dexamethasone
Phenothiazine: Prochlorperazine (Stemetil)
Anti-dopaminergic: Metoclopramide
How to reverse the process of GA?
Stop vapours
Give O2
Perform throat suction
Reverse muscle relaxant
Describe the process of a LMA
Give O2
Opioid (fentanyl)
Induction agent (propofol)
Turn on volatile agent (sevoflurane)
Bag valve mask ventilation
LMA insertion
Describe the process of intubation
Give O2
Opioid (fentanyl)
Induction agent (propofol)
Turn on volatile agent (sevoflurane)
Muscle relaxant
Endotracheal intubation
Why is etomidate not used in sepsis?
Increases mortality due to suppression of adrenalcortical system + reduced cortisol levels
Which GA is good for HF?
Etomidate
Which NSAIDs are IV?
Parecoxib, ketorolac
What is ASA grading?
1: healthy pt no disease
2: mild to mod disease, no functional limits
3: severe systemic disorder with limits on function
4: severe disease with threat to life
5: moribund pt not expected to survive
6: brainstem dead pt for organ removal
E: suffix for emergency
Risk of inadequate fasting
Pulmonary aspiration
What is the risk of prolonged fasting?
Headache, light-headedness, anxiety
N+V, dehydration, hypotension
Recommended fasting times
Solids = 6 hrs
Breast fed infants = 4 hrs
Clear fluids = 2 hrs
Alcohol = 24 hrs
Boiled sweets/ gum = avoid but can do surgery
What is the indication for rapid induction?
Full stomach - high risk of aspiration
Describe the process of rapid induction
Preoxygenation: tight fitting mask for 3 mins or 5 full FVC breaths
Drugs: Thiopentone, Propofol, Suxamethonium
Technique: cricoid pressure, no ventilation, remove cricoid after confirmation of tube position (EtCO2)
Doses of local anaesthetics (lignocaine w + w/o adrenaline, bupivacaine, prilocaine)
Lignocaine without adrenaline: 3 mg/kg
Lignocaine with adrenaline: 7 mg /kg
Bupivacaine / levobupivacaine ( with or without adrenaline): 2 mg/kg
Prilocaine: 6mg/kg (with = 9mg)
How much water is allowed as a ‘sip’ before GA?
30ml
Considerations of a diabetic going under GA
CVS: silent MI, HTN, autonomic neuropathy
RS: increased infection
Renal failure
Delayed gastric emptying
Increased risk of infection + poor healing
SE of propofol
Apnoea
Hypotension
Pain
Myoclonus
CI in egg or soya allergy
SE of atropine
Decreased secretions
Reduced gastro sphincter tone
Urinary obstruction
Tachycardia
Confusion
Use + dose of midazolam
Procedural sedation + induction
1mg IV
What does neostigmine do?
Reverses effect of non-depolarising muscle relaxants
