Anaesthesia - General Anaesthesia

Question 1

Function of general anaesthetic agents

Answer 1

• Altered neuronal ion channels
• Hyperpolarised neurons → reduced during
• Inhalation → dissolves into membrane
• Intravenous → vinds to GAGA receptors → opens Cl channels
• All suppressed neuronal activity

Question 2

Pattern of functional loss in general anaesthesia

Answer 2

• From top down
• Higher cerebral functions lost first
• Primitive functions lost later
• Reflexes spared

Question 3

Characteristics of IV anaesthetic agents

Answer 3

• Highly rapid onset of unconsciousness → fat soluble medication crosses BBB fast
• Rapid recovery
  
  • Drug dissipates from circulation rapidly
    
    • Drug moves into other compartments of the body

Question 4

Characteristics of inhalation anaesthetic agents

Answer 4

• Exclusively taken up and excreted via lungs
• Lung → blood → brain
• Slow onset of induction

Question 5

Indication for inhalation anaesthetics

Answer 5

• Extension/ continuation of anaesthesia
• Patient inducted via IV anaesthesia then transferred to inhalation anaesthesia to remain unconscious
• Patient awakened by switching off anaesthesia and washing out with air mixture

Question 6

Cardiovascular effect of general anaesthetics

Answer 6

• Central
  
  • Depressed cardiovascular centres
  • Reduced sympathetic outflow
  • Negative inotropic/chronotropic effect on heart
  • Reduced vasoconstrictor tone → vasodilation
• Direct
  
  • Negative inotropic
  • Vasodilation → decreased peripheral resistance
  • Venodilation → decreased venous return and decreased cardiac output

Question 7

Respiratory effects of general anaesthetics

Answer 7

• Respiratory depressant
  
  • Reduced hypoxic and hypercarbic drive
  • Depression of brainstem respiratory centres
  • Decreased tidal volume
• Paralysis of cilia
• Decreased functional residual capacity → volume remaining on exhalation

Question 8

Define muscle relaxants

Answer 8

• Drugs that cause systemic relaxation (cause paralysis) of skeletal muscles (and respiratory and airway muscles)
• Hypnotic must be given → paralysis and wakefulness unpleasant

Question 9

Indication of muscle relaxant

Answer 9

• Only in essential circumstances → dangerous
• Ventilation and intubation
• Immobility required → microscopic surgery, neurosurgery, body cavity surgery

Question 10

Problems of muscle relaxants

Answer 10

• Awareness → must give hypnotic
• Incomplete reversal → airway obstruction, ventilatory insufficiency post-op
  
  • Apnoea → dependance on airway and ventilation support

Question 11

Definition of analgesia

Answer 11

• Reduces sensation and arousal effects of pain during surgery
• Opaite analgesics → sedative effect
• Suppresses unwanted reflexes to pain → tachycardia, hypertension, gross movements

Question 12

Mechanism of action of local anaesthetics

Answer 12

• Prevention of axonal action potentials
• Pharmacologically toxic → infiltrates every tissue include IV
• IV administration → lethal

Question 13

Characteristics of local anaesthesia

Answer 13

• Retained awareness/ consciousness
• Lack of global effects
• Derranged CVS physiology
• Sparing of resp function

Question 14

Presentation of local anaesthetic toxicity

Answer 14

• Numbness and tingling
• Lightheadedness
• Tinnitus, visual distubrances
• Muscular twitch
• Drowsniness
• CVS depression
• Convulsion
• Coma
• Cardiorespiratory arrest

Question 15

Definition of a differential blockage

Answer 15

• Use of local anaesthetic for segmental blockage of peripheral nerves
• Provides analgesia without paralysis (attributes of nerve thickness and myelination
• E.G. abdominal surgery, Caesarean section

Question 16

Definition of neuraxial block

Answer 16

• Local anaesthetic placed around nerves of CNS
• Spinal anaesthesia
• Spared inspiratory function
• Impaired expiratory function
• Decreased functional residual capacity
• Increased V/Q mismatch