14. General Anaesthesia

Question 1

3 parts of general anaesthesia

Answer 1

1. induction
2. Maintenance
3. Emergence and recovery

Question 2

Parameters of volatile anaesthetic

Answer 2

Fi - Inspiratory concentration

• Fresh gas flow rate (vaporize, gas mizture O2/air)
• volume of breathing system
• circuit absoption (minimal)

FA - Alveolar concentration

• solubility in blood (uptake)
• ventilation (MV)
• concentration and second gas effect

Fa - Arterial concentration

• Alveolar blood flow
• Ventilation/perfusion mismatch (intrapulmonary shunts)

Question 3

Minimum alveolar concentration (MAC)

Answer 3

Alveolar concentration that prevents movement in 50% of patients. Lower = more potent (if very low, can cause anaesthetic neurotoxicity)

Question 4

Factors influencing effect of volatile anaesthetics

Answer 4

Tissue concentration

• blood/gas coefficient (solubility in blood)
• tissue/blood partition coefficient (solubility in tissue)

Solubility and blood flow of tissues

• vessel rich group: take up first (brain, heart, liver, kidney, endocrine)
• muscle group (skin, muscle)
• fat group
• vessel poor group (bone, ligaments, teeth, hair)

Elimination: lung, liver, kidney

Pathologies will change the clinical effects!

Question 5

Mechanism of action of volatile anaesthetics

Answer 5

Unknown!

Influences synaptic transmission, neuronal membrane processes, neuronal receptor function

Question 6

5 i.v. Anaesthetic agents

Answer 6

1. Barbiturate (thiopental) - GABA and ACH-R enhancement (inhibitory neurotransmitter), rapid onset, safe in pediatrics/obstetrics, neuroprotective (decreased CMRO2)
2. BZD (midazolam) - facilitates GABA-R function. Negative cofactor of Postop Cognitive Dysfunction (PCD), so currently not recommended in major surgery.
3. Propofol - most popular, GABA-A-R enhancement, rapid onset, good for continuous sedation, liver & kidney elimination, inactive second metabolites
4. Etomidate - least hemodynamic effect (use in shock), can suppress adrenocortical function (increased NE need), currently not recommended du to increased mortality in critically ill.
5. Ketamine - opioid-R and NMDA inhibition, stable hemodynamics, good bronchodilatory effect, preferred in shock and bronchospastic states, good for pediatrics, hallucinations in adults

Question 7

Opioid receptors and drugs used in anaesthesia

Answer 7

4 CNS receptors: mu, kappa, delta, omega

Commonly used opioids: mu, kappa

Ketamine: omega

Opioids are good analgesics and basic perioperative drugs (i.v., EDA, intrathecal)

Elimination: conjugation in liver, elimination in kidney. Morphine has second metabolites.

• Morphine
• Fentanyl
• Sufentanyl
• Remifentanyl
• Naloxone for reversal (pure antagonist)

Question 8

Neuromuscular blockers

Answer 8

A) Depolarizing muscle relaxants
- Succinylcholine: Rapid Sequence Intubation (RSI), not for CRF/ARF and hypotonic neurological cases (palsy)

B) Nondepolarizing muscle relaxants

• Atracurium
• Cisatracurium
• Rocuronium -> RSI
• Vecuronium

Monitor by nerve stimulation.

Question 9

Reversal of neuromuscular blocking agents

Answer 9

Cholinesterase inhibitors > Increased ACh

• Neostigmine (Note! Bradycardia, bronchospasm)
• Sugammadex: specific for rocuronium