Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Neuro drug > General Anaesthetics > Flashcards

General Anaesthetics Flashcards

1
Q

What is anaesthetics?

A

• To induce blockade of sensation or have sensation temporarily removed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Process of GA

A

1) Pre-med (reduce Anx and calm pt)
2) Induction (IV/ inhale)
3) Maintenance
4) reversal
5) Post-op / post anaesthesia care

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is GA used for ?

A
  • To produce unconsciousness and a lack of responsiveness to all painful stimuli (inhibition of sensory and autonomic reflexes)
    ie. triad of hypnosis, amnesia and analgesia

= Provide conditions for interventions – like surgery to take place; skeletal muscle relaxation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What constitute an ideal general anaesthetics, ie. what property(ies) should an ideal anaesthetic drug have?

A
  • unconsciousness
  • Analgesia
  • Amnesia
  • Brief & pleasant
  • Depth of anaesthesia can be raised or lowered with ease
  • Muscle relaxation
  • Minimal adverse effects
  • Margin of safety – large
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Balanced Anaesthesia include

and purpose

most commonly use

A

Pain Relief
Inhibition of Reflex
Unconsciousness

• To ensure that induction is smooth and rapid, and that analgesia and muscle relaxation are adequate

Most commonly used:

(1) short-acting barbiturates (for induction of anaesthesia) (2) neuromuscular blocking agents (for muscle relaxation)
(3) opioids and nitrous oxide (for analgesia)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

GA • Solubility in blood

A

• The higher the blood solubility – the slower the onset

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Inhalation GA Classification

A

Volatile Liquid

  • Halothane* (MAC 0.75%)
  • Isoflurane (MAC 1.2%)
  • Desflurane (MAC 6.3%)
  • Enflurane
  • Sevoflurane (MAC 2.2%)

Gases
- Nitrous oxide(MAC 110%)

high MAC = less potent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

GA mechanism of action:

A

Proposed mechanism of action:
1. Enhance neurotransmission at inhibitory synapses via allosterically increasing GABA receptor sensitivity to action by GABA itself (positive allosteric modulator)

  1. Also depressing neurotransmission at excitatory synapses via blocking glutamate neurotransmitter acting on NMDA receptor thus preventing NMDA receptor activation (negative allosteric modulator)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

MAC

A

Minimum Alveolar Concentration (MAC)
• also known as median alveolar concentration
• is an index of inhalation anaesthetic potency
ie. low MAC = high anaesthetic potency
• is defined as the minimum concentration of drug in the alveolar air that will produce immobility in 50% of patients exposed to a painful stimulus.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

To produce GA in ALL patients

A

the inspired anaesthetic concentration should be 1.2 to 1.5 times the MAC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

GA PK

A

Absorption
• concentration of anaesthetic in inspired air
• solubility of GA
• blood flow through lungs
INCREASE any of these = INCREASE GA uptake

D
- determined by regional blood flow –> which tissue(s) receive GA
brain, lung, liver, Heart equilibrate quickly

M
- note: some metabolites can be toxic
eg. inorganic fluorides of isoflurane and enflurane are nephrotoxic;
halothane is hepatotoxic

E
- Export in Expired breath
• inhalation anaesthetics are eliminated almost entirely via the lungs
• minimal hepatic metabolism
• factors that determine uptake also determine elimination eg. since blood flow to brain is the highest, anaethetic levels drop rapidly when administration is stopped

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Halothane

A
  • First modern INHALED anaesthetic, standard for comparison
  • VOLATILE liquid, non-flammable and non-irritating
  • Potent (MAC 0.75%)
  • MEDIUM rate of onset and recovery
  • Little or NO analgesia until unconsciousness supervenes

• Causes RESPIRATORY DEPRESSION dose-dependently
• DECREASE B.P. due to DEPRESSION of CARDIAC OUTPUT
BRADYCARDIA and ARRHYTHMIA may also occur leading to hypotension and dysarrhythmia
• RELAXES skeletal muscle and potentiates skeletal muscle relaxants
• May lead to halothane-associated HEPATITIS

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Isoflurane

A

Isoflurane

  • Pungent smell
  • Potent (MAC 1.4%)
  • MEDIUM rate of onset and recovery
  • Similar to halothane with less hypotension and arrhythmia
  • Causes RESPIRATORY DEPRESSION dose-dependently
  • Decreases B.P. due mainly to decrease in systemic vascular resistance
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Sevoflurane

A

Sevoflurane (inhaled GA)

  • Potent (MAC 2%)
  • More RAPID rate of onset and recovery
  • Metabolized in the LIVER to release inorganic fluoride, also NEPHROTOXIC
  • UNSTABLE when exposed to carbon dioxide absorbents in anaesthetic machines, degrading to a compound that is potentially nephrotoxic
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Nitrous oxide (N2O)

A

Nitrous oxide (N2O) (GAS GA)

  • Odourless gas
  • Non-flammable
  • RAPID onset and recovery but LACK POTENCY (MAC 105%)

• Nitrous oxide alone gives ANALGESIA and AMNESIA but NOT complete unconsciousness or surgical anaesthesia

  • Patients undergoing GA receive nitrous oxide to SUPPLEMENT the analgesic effects of primary anaesthetic
  • When used alone: as analgesic agent (eg. dentistry, during delivery*)

• Major concern: postoperative nausea and vomiting

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q 
Intravenous Anaesthesia (GA) 
explain a bit more
A 
THIOPENTONE* 4-7 mg/kg 
ETOMIDATE 0.2-0.3 mg/kg 
MIDAZOLAM 0.02mg/kg (anxiolysis)
PROPOFOL 2-4 mg/kg 
KETAMINE 1.5 mg/kg iv

All are INDUCTION AGENT
• an induction agent is a substance that induces unconsciousness
• it does not necessarily keep you asleep for very long!
• most agents depress respiration – you will need to take over ventilation of patients
• may be used alone or to supplement the effects of inhalation agents

17
Q

Inhaled + Intravenous anaesthetics (2 Advantages):

A
  1. Permit dosage of the inhalation agent to be reduced, and

2. Produce effects that cannot be achieved with an inhalation alone

18
Q

Thiopentone (sodium thiopental) + MOA

A

IV GA

  • A barbiturate with extremely high lipid solubility
  • Enters the brain easily and rapidly - rapid onset of action (unconsciousness occurs 10-20sec after IV)

• Single Dose: Re-distributes to less vascularized tissues – ultra-short duration of action
(Injected alone & w/o inhale agents, patients wake up ~10min)

  • Multiple doses/infusions: duration of action depends on clearance
  • Slow elimination, large Vd, active metabolite (PENTOBARBITAL), liver cirrhosis –> can result in prolongation of clinical action.

• Extensively bound to plasma protein
- small amount of free drug can be excreted by glomerular filtration + reabsorption in tubules.
• Less than 1% excreted unchanged

MOA
• Cause CNS depression by potentiating the action of the neurotransmitter GABA on the GABAA receptor-gated chloride ion channels

19
Q

Propofol

A

IV GA

Propofol*
• the most common IV anaesthetic used in Singapore – (ready made in injectable form, no need to re-constitute (unlike thiopentone)

  • Induction rate is similar to thiopentone, and recovery is more rapid (patients move sooner and feel better)
  • Used both for induction and maintenance
  • Rapid onset (unconsciousness develops within ~60sec) • Short duration of action (~3-5min following single injection) because rapid redistribution from brain to other tissues
  • Extensively used in “day surgery”
  • needs continuous, low-dose infusion for extended effects
  • Reduced postoperative vomiting (may be related to an antiemetic action)
  • Significant cardiovascular effect during induction (decrease b.p. and negative inotropic) – HYPOTENSION
  • To be used with caution in elderly patients, patients with compromised cardiac function, hypovolemic patients
20
Q

Ketamine

A

IV GA
Ketamine

  • racemic (potency: S- > R+); I/M, oral, rectal routes
  • Produces a state known as dissociative anaesthesia ie. patient feels dissociated from environment
  • Can cause SEDATION, IMMOBILITY, ANALGESIA, and AMNESIA
  • Rapid induction; Responsiveness to pain is lost
  • Metabolized in LIVER to LESS active metabolite, excreted in urine & bile
  • Large Vd, rapid clearance –> suitable for continuous infusion without the lengthening in duration of action
  • Unpleasant psychologic reactions (HALLUCINATION DISTURBING DREAM, DELIRIUM) may occur during recovery from ketamine
  • Risks of psychologic adverse reactions may be reduced with premedication of diazepam or midazolam

• It is the ONLY IV anaesthetic that possess ANALGESIC property
 hence very popular in 3rd world country as the only anaesthetic, due to the lack of other anaesthetic agents.

21
Q

purpose of Anesthetic Adjuncts

A

to achieve triad (sedation, amnesia, analgesia)

therefore lowering GA Dose and hence reduce SE

22
Q

Example of Anesthetic Adjuncts and their function

A

• Benzodiazepines
– Anxiolytics, amnesia, sedation prior to induction of anaesthesia

• α2 Adrenergic Agonists
– Sedation prior to and/or during procedures in NON-
INTUBATED patients

• Analgesics
– Typically administered with GA to reduce anaesthetic requirement

• Neuromuscular Blocking Agents
– Induction of anaesthesia to relax muscles (jaw, neck, airway) to facilitate laryngoscopy and endotracheal intubation

23
Q

Benzodiazepine: Midazolam (I/V) AS adjunct

A

Used for ANXIOLYSIS , AMNESIA and SEDATION prior to induction of anaesthesia (perioperative period) or Used for sedation during procedures not requiring GA

  • Rapid onset (unconsciousness develops in 80sec; peak ~2min; sedates ~30min)
  • Metabolized in liver (elderly, alcoholic, liver cirhosis tend to be more sensitive, slower recovery)
  • Midazolam (benzodiazepine group of drugs) usually has a high therapeutic index –> it has relatively lesser cardiovascular & respiratory depressing effect compare to other IV anaesthetics.
  • Side effects are compounded by concurrent usage of other agents
  • Adverse effects can be minimized by injecting midazolam SLOWLY (over 2 or more minutes) and by waiting another 2 or more minutes for full effects to develop before dosing again
24
Q

α2 Adrenergics: Dexmedetomidine (I/V)

as adjunct

A
  • Highly selective α2 adrenergic receptor agonist
  • Short term sedation (<24hrs)
  • Sedation and analgesic effects (doesn’t produce reliable GA even at maximal doses)

• Little respiratory depression

  • Tolerable decrease in blood pressure and heart rate
  • Undesirable side effects: nausea, dry mouth, hypotension, bradycardia
25
Q

Analgesics:

as adjunct

A

• Minor surgical procedures –> COX-2 inhibitors and paracetamol

  • Opioids (Fentanyl, morphine) – perioperative period
  • Agonist activity at µ-opioid receptors

• Relative potency to morphine [duration of action]: sufentanil (1000x) [intermediate ~15min]
remifentanil ( 300x) [ultra-short ~10min]
fentanyl ( 80x) [intermediate ~30min]
alfentanil ( 15x) [intermediate ~20min]

  • Choice – based primarily on duration of action
  • Metabolized in liver (except remifentanil is hydrolyzed by tissue & plasma esterases)

• Excretion: urine, bile

26
Q

Neuromuscular Blockers

as adjunct

A

Neuromuscular Blockers
• Depolarizing: Succinylcholine
• Non-depolarizing (eg. vecuronium)

  • Administered during induction of anaesthesia to relax muscles of jaw, neck, airway –> facilitate laryngoscopy and endotracheal intubation
  • Aids many surgical procedures and provide additional insurance of immobility

• Note: barbiturates will precipitate when mixed with muscle relaxants –> should be allowed to clear from the IV line prior to injection of muscle relaxant

Neuro drug (21 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions