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PR3136 > General Anaesthetics > Flashcards

General Anaesthetics Flashcards

1
Q

What are GA used for?

A
  • Produce unconsciousness & a lack of responsiveness to all painful stimuli (inhibiting sensory & autonomic reflexes)
  • Provide conditions for interventions (eg. surgery - skeletal muscle relaxation)
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2
Q

Additional considerations when using GA

A

Control of physiology (Need to decrease HR, while controlling body temp)

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3
Q

Stages of General Anaesthesia

A

1) Pre-assessment
2) Induction of anaesthesia
3) Airway management
4) Maintenance of anaesthesia
5) Reversal/Emergency
6) Post-operative care

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4
Q

What constitutes an IDEAL general anaesthetic

A
  • Unconsciousness
  • Analgesia
  • Amnesia
  • Muscle relaxation
  • Brief & pleasant
  • Depth of anaesthesia can be raised or lowered with ease
  • Minimal ADE
  • Large margin of safety

Balanced Anaesthesia
- Pain relief, Unconsciousness, Inhibition of Reflex

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5
Q

What are the 2 kinds of GA that are used in combination?

A

1) Inhalation
2) IV
- Used in combination to ensure that induction is smooth & rapid
- Induction usually accomplished with short-acting barbituate (eg.thiopentone) then maintain with gaseous GA

Most commonly used:

1) Short-acting barbiturates (induction of anaesthesia)
2) NM blocking agents (muscle relaxation)
3) Opioids & Nitrous oxide (analgesia)

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6
Q

What determines onset of Inhalant GAs

A

Blood solubility

- Higher b.s, slower the onset

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7
Q

Classification of Inhalant GAs

A

1) Volatile liquids (Administer using agent-specific vaporizer)
- Halothane, enflurane, desflurane, isoflurane, sevoflurane

2) Gases
- Nitrous oxide

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8
Q

Proposed MOA of Inhalant GAs

A

1) Enhance neurotransmission @ inhibitory synapses
- Allosteric binding & increasing GABA receptor sensitivity to action by GABA itself

2) Decreasing neurotransmission @ excitatory synapses
- Blocking glutamate neurotransmitter acting on NMDA receptor

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9
Q

Minimum Alveolar Concentration (MAC) Concept

A
  • Lower MAC, higher anaesthetic potency

- Alters with: age, condition, concomitant administration of other drugs

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10
Q

PK of volatile liquids GA

A
  • Inhalant GA must reach [CNS] sufficient to suppress neuronal excitability

Absorption:

  • Increased [anaesthetic] in inspired air, increased rate of GA uptake into blood
  • Increased solubility of GA, increased rate of GA uptake into blood
  • Increased blood flow through lungs, increased rate of GA uptake into blood

Distribution:

  • Determined by regional blood flow
  • Anaesthetic levels in tissues of highly perfused organs equilibrates with those in blood quickly after administration

Elimination:
- Eliminated almost entirely in lungs

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11
Q

(Volatile Liquids GA) Halothane

A
  • Volatile, non-flammable, non-irritating
  • Potent (MAC 0.75%)
  • Rate of onset & recovery: Medium
  • Little/no analgesia until unconsciousness supervenes

Adverse Effects:

  • Respiratory depression (dose-dependent)
  • Bradycardia & arrhythmia (may lead to hypot/s & dysrhythmia)
  • -> Decrease in BP due to depression of CO
  • Halothane-associated hepatitis
  • -> can recover after stopping adm
  • Relaxes skeletal muscle & potentiates skeletal muscle relaxants
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12
Q

(Volatile Liquids GA) Isoflurane

A
  • Pungent smell
  • Potent (MAC 1.4%)
  • Rate of onset & recovery: Medium

Adverse Effects: Similar to Halothane BUT less hypot/s & arrhythmia
- Decreases BP due to decrease in systemic vascular resistance

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13
Q

(Volatile Liquids GA) Sevoflurane

A
  • Potent (MAC 2%)
  • Rate of onset & recovery: > Rapid

Adverse Effects:

  • Metabolised in the liver to release inorganic fluoride (*Nephrotoxic)
  • Unstable when exposed to CO2 absorbents -> Degrades to a compound that is potentially *nephrotoxic

*NOT for those with kidney failure

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14
Q

(Volatile Liquids GA) Nitrous Oxide

A
  • Non-flammable
  • Lack potency (MAC 105%)
  • Rate of onset & recovery: Rapid
  • Analgesia & Amnesia (but not complete unconsciousness/surgical anaesthesia)

Uses (Common in dental practice):

1) Supplement analgesic effects of pri anaesthetic
2) Used alone as analgesic agent

Adverse effects:
- Postoperative N/V

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15
Q

Use of Intravenous GAs

A

1) Used alone

2) Used to supplement effects of inhalation agents

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16
Q

Advantages of using combination of Inhaled + IV Anaesthetics

A

1) Permits dosage of the inhalation agent to be reduced

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

17
Q

Properties of Intravenous GAs

A
  • Induction agent that induces unconsciousness fast
  • But does not necessarily keep you asleep for very long
  • Most agents depress respiration
18
Q

(Intravenous GAs) Thiopentone (Sodium thiopental)

A
  • EXCEPTION: Combination used in GA*
  • Barbiturate with extremely high lipid solubility
  • Onset of action: Rapid
  • Extensively bound to plasma proteins (small amount of free drug can be excreted by glomerular filtration + reabsorption tubules)
  • Slow elimination

MOA: Potentiates action of neurotransmitter GABA on the GABA^A receptor-gated Cl- channels

i) Single-dose:
- Re-distributes to less vascularized tissues
- Ultra-short duration of action
ii) Multiple doses/infusion:
- Duration of action depends on clearance

Note:
- If liver cirrhosis: Active metabolite (phenobarbital) takes longer time to get metabolised, can result in prolongation of clinical action

19
Q

(Intravenous GAs) Propofol

A
  • Induction rate is similar to thiopentone, recovery is more rapid
  • Onset of action: Rapid
  • Duration of action: Short

Use:

  • For both induction & maintenance (continuous low-dose infusion)
  • Extensively used in “day surgery”

Adverse Effects:
- Hypotension: Significant CVS effect during induction (decreases b.p & negative inotropic)

Note:

  • Reduced postoperative vomiting (may be related to anti-emetic action)
  • Caution use in elderly/ pts with compromised cardiac function/ hypovolemic pts
20
Q

(Intravenous GAs) Ketamine

A
  • Rapid induction, responsiveness to pain is lost
  • Dissociative anaesthesia
  • Can cause sedation, immobility, analgesia & amnesia
  • Large Vd, rapid clearance

Use:
- Continuous infusion w/o lengthening in duration of action

Adverse Effects:

  • Unpleasant psychotic reactions (hallucination, disturbing dreams, delirium) during recovery from ketamine
  • -> Risk of psychologic adverse reactions may be reduced with premedication of diazepam/midazolam (work on GABA receptors)

Note:
- Only IV anaesthetic with analgesic properties

21
Q

Types of Anaesthetic adjuncts/Post-Op care

A

1) Benzodiazepines (Anxiolytics/amnesia/sedation)
- Prior to induction of anaesthesia

2) Alpha-2 Adrenergic Agonists
- Sedation prior to and/or during procedures in non-intubated patients

3) Analgesics
- Adm with GA to reduce anaesthetic requirement

4) NM Blocking Agents
- Induction of anaesthesia to relax muscles (jaw,neck,airway) to facilitate laryngoscopy & endotracheal intubation)

22
Q

(Anaesthetic adjuncts/Post-Op care) Benzodiazepine - Midazolam (I/V)

A

Uses:

1) Anxiolysis, amnesia & sedation
2) Sedation during procedures not requiring GA (eg, endoscopy)

  • Metabolism: Liver (Slower recovery in elderly)

Side effects:

  • Compounded by concurrent usage of other agents
  • Minimised by slow injection (over 2min, then wait for full effects to develop before dosing again)
23
Q

(Anaesthetic adjuncts/Post-Op care) Alpha-2 Adrenergic Agonists - Dexmedetomidine (I//V)

A

Use: Short term sedation (<24hrs)

  • Sedation & analgesic effects

Side effects (Little respiratory depression):

  • Nausea
  • Dry mouth
  • Hypotension
  • Bradycardia
  • Tolerable increase in BP & HR???
24
Q

(Anaesthetic adjuncts/Post-Op care) Analgesics - NSAIDs

A

Choice: Depends on duration of action

  • Minor surgical procedure: COX-2 inhibitor/paracetamol
  • Perioperative peiod: Opioids (Fentanyl, morphine)

Metabolism: Liver (Remifentanil - hydrolysed in tissue & plasma esterases)
Excretion: Urine, bile

25
Q

(Anaesthetic adjuncts/Post-Op care) NM Blockers

A

Eg.
Depolarising - Succinylcholine
Non-depolarising - Vecuronium

Use:

1) Facilitate laryngoscopy & endotracheal intubation (relaxes muscles of jaw,neck,airway)
2) Aids surgical procedures & provide additional insurance of immobility

NOTE:
- Barbituates will ppt when mixed with muscle relaxants -> Should be allowed to clear from IV line prior to injection of muscle relaxant

PR3136 (14 decks)

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