General Anaesthesia

Question 1

Thiopentone Sodium

Answer 1

Not analgaesic
Respiratory depression
Cardiovascular depression
Irritant/ laryngiospasm
Porphyria (inc. hepatic ALA Synthase)

Question 2

Propofol

Answer 2

Induction: onset 10-30 secs
Rapid metabolism- duration 5 mins
Not cumulative- maintenance of anaesthesia with N2O
CVS and Resp effects similar to Thiopentone Sodium
Vasodilation- Decreased BP
Maybe an antiemetic
Most frequently administered drug for induction
Acts through GABAa

Question 3

Alphaxalone

Answer 3

Neurosteroid

Allergenic

Question 4

Etomidate

Answer 4

Duration 3 mins
Minimal CVS/Resp depression after bolus injection
No analgesia
Induction
Acts through GABAa

Question 5

Ketamine

Answer 5

Dissociative anaesthesia- slow nystagmic gaze
IM & IV
Inhibition of NMDAr
Catalepsy
Analgesia
Amnesia
CVS- increased BP/skeletal muscle stimulation/ bronchodilation
Hallucinations/ delirium in 20% of adults
Useful for mentally challenged and paediatric patients

Question 6

Ethanol Acute Effects

Answer 6

Vasodilation
Emesis
Hypothermia
Hypoglycaemia
Hyperlipidaemia
Diuresis

Question 7

Ethanol Metabolism

Answer 7

In liver
Ethanol to Acetaldehyde: ADH
Acetaldehyde to Acetic Acid: Aldehyde Dehydrogenase
Zero order kinetics: 7g/ hour
Disulfiram inhibits Aldehyde Dehydrogenase: Acetaldehyde syndrome

Question 8

Volatile Anaesthesia

Answer 8

Isoflurane
Sevoflurane
Nitrous Oxide (N2O)

Question 9

Objectives of Anaesthesia

Answer 9

Analgesia
Amnesia
Anaesthesia
Inhibition of reflexes (autonomic and somatic)- may reduce blood flow in surgery
Relaxation of muscle (smooth and skeletal)

Question 10

Ideal Characteristics

Answer 10

Rapid onset
Rapid reversal
Maximum depression of CNS without compromising respiratory control

Question 11

Diethyl Ether

Answer 11

Very good anaesthetic
Highly flammable
Slow onset

Question 12

Inhalation Anaesthetics

Answer 12

Gases and vapours through lungs
Large volume is exhaled rapidly
Highly lipid soluble- diffuse through BBB
Easy to control dose- concentration in lungs is similar to brain
MAC= minimum alveolar conc- EC50
Complication: Diffusin anoxia

Question 13

Nitrous Oxide

Answer 13

Analgesia (rarely Stage 3, Plane 1)
Relatively rapid effect for brief procedures
Risk of hypoxia and can damage RBC’s with chronic exposure >6hours

Question 14

Halogenated Ethers

Answer 14

Easy induction and control of depth
Lowers BP due to smooth muscle relaxation
SE: slow onset 5mins, liver damage, malignant hyperthermia
Sevoflurane- potential kidney damage
Isoflurane
Relatively low MAC 350uM
Enflurane, isoflurane, halothane

Question 15

Intravenous Anaesthetics

Answer 15

Rapid onset and ease of induction
Safe- no risk of ignition
More difficult to control dose
Effects cannot be reversed by other medications- too many complications with kinetics of stimulants

Question 16

Guedel’s Stages of Anaesthesia for Ether

Answer 16

1)Analgesia (depression of lamina 4 of spinal cord)
Amnesia( depression of cortex and hippocampus)
2) Delirium (depression of cortex and thalamus)
3) Surgical Anaesthesia: Planes 1-4 (depression of MB and spinal cord including reticular formation)
4) Imminent death (depression of respiratory control in medulla)

Question 17

Benzodiazepines

Answer 17

Midazolam, lorazepam
Used perioperatively
For conscious sedation in minor procedures

Question 18

Solubility

Answer 18

Highly soluble-halothane- Slower onset, slow to saturate in blood, slower recovery
Less soluble-N2O- Faster onset, immediately saturated in blood, faster recovery
Blood-Gas Partition Coefficient= Solubility

Question 19

MAC

Answer 19

Minimum Alveolar Concentration
The percentage of anaesthetic in inspired gas mixture that renders 50% of population unconscious
Potency is inversely proportional to MAC

Question 20

Inhalation Side Effects

Answer 20

Myocardial depression- Dec. Cardiac Output, hypotension
Respiratory depressants- Dec. Tidal volume and minute ventilation, cause hypercapnaeia, supress mucocilliary clearance
Increase cerebral bloodflow- Inc. ICP
Halothane- Hepatic Necrosis, in 2 days-4 weeks of exposure
Enflurane- Nephrotoxicity & Convulsions
Malignant hyperthermia- hypersensitivity of skeletal muscle due to defective ryanodine receptors leading to rhabdomyolysis- treat with dantroline