CPT17 - Anaesthetics

Question 1

4 general features of anaesthesia

Types x3
Processes Involved x8
Mechanisms x2
Effect on Brain Circuitry x4

Answer 1

1. ) Types - general (inhalational or IV) or local/regional
   - conscious sedation is use of small amounts of anaesthetics to produce a ‘sleepy-like’ state
2. ) Processes Involved
   - hypnosis (LOC)→anaesthetic→ analgesia (opioid)→ muscle paralysis→anaesthetic maintenance
   - reversal of paralysis →postoperative analgesia→ postoperatvie nausea and vomiting medication
3. ) Mechanism - stimulation of inhibitory GABAa receptor
   - ↑ Cl- conductance –> hyperpolarisation in the CNS
   - ↓CNS activity –> anxiolytic, sedation and anaesthesia
   - Xe, N2O and ketamine inhibit excitatory NMDA receptors instead to reduce excitation
4. ) Effect on Brain Circuitry - depression of:
   - reticular formation and thalamus
   - hippocampus: ↓memory
   - brainstem: ↓respiratory/CVS centres
   - DH: provides analgesia (no sensory info)
5. ) Contraindications to General Anaesthesia
   - allergies, COPD, severe aortic stenosis, HF
   - neuromuscular disorders

Question 2

What is Guedel’s classification and the 4 stages

Analgesia
Excitement
Surgical Anaesthesia
Respiratory Paralysis

Answer 2

Asssessment of depth of general anaesthesia

1. ) Analgesia - patient is conscious
   - normal muscle tone and breathing
   - slight eye movement
2. ) Excitement - patient is unconscious
   - normal/increased muscle tone, erratic breathing
   - moderate eye movement
3. ) Surgical Anaesthesia - wide ‘goldilocks zone’
   - muscle tone: slightly relaxed → markedly relaxed
   - breathing: normal → very weak
   - eye movements: slight → weak
4. ) Respiratory Paralysis - basically death
   - flaccid muscle tone, no breathing or eye movements

Question 3

4 features of inhalational general anaesthesia

Examples x6
Minimum Alveolar Concentration (MAC)
Factors Affecting MAC x8 (+effect of nitrous oxide)
Partition Coefficients x2

Answer 3

1. ) Examples - often flourinated hydorcarbons e.g. sevoflurane, isoflurane, desflurane
   - others: nitrous oxide, xenon (rarely used)
2. ) Minimum Alveolar Concentration (MAC) - potency
   - alveolar concentration at which 50% of subjects fail to move to surgical stimulus whilst breathing O2/air
   - at equilibrium, [alveolar] = [spinal cord]
3. ) Factors Affecting MAC
   - ↑: infants, hyperthermia, pregnancy, alcoholism
   - ↓: elderly, hypothermia, other anaesthetics, opioids
   - nitrous oxide ↓↓MAC so patients are often inhaling 50-60% N2O rather than oxygen /air to reduce dosing
4. ) Partition Coefficients - solubility in blood and lipids
   - low blood solubility (blood:gas partition) = faster induction and recovery e.g. desflurane
   - high lipid/oil solubility (oil:gas partition) = greater potency and slow accumulation e.g. halothane

Question 4

3 features of intravenous general anaesthesia

Drugs Used x3 (+mechanism)
Usage
Potency

Answer 4

1. ) Drugs Used - propofol, barbiturates, ketamine
   - rapid: propofol and barbiturates (↑GABAa receptors)
   - slower: ketamine (↓NMDA receptors)
2. ) Usage - for ‘induction’ (putting to sleep)
   - used as the sole anaesthetic if volatile cannot be used
   (e. g. if surgery is being done in the face)
3. ) Potency - plasma concentration to achieve a specific endpoint e.g. loss of eyelash reflex or a BIS value
   - a bolus dose is often given to reach the end point and then you switch to volatile anaesthesia

Question 5

7 features of local/regional anaesthesia

Examples x4
Mechanism x3
Nerves Used x8
Pharmacodynamics x4
Usage w/ Adrenaline
Indications x5

Answer 5

1.) Examples - lidocaine, bupivacaine, ropivacaine, procaine

2. ) Mechanism - VGNaC blockers (nerve block)
   - use dependent: ↑effect on rapidly firing neurones
   - differential blockade: sympathetic (type B) and nociceptive (type C) fibres most sensitive
3. ) Nerves Used
   - upper: interscalene, supra/infraclavicular, axillary
   - lower: femoral, sciatic, popliteal, saphenous
4. ) Pharmacodynamics
   - potency: increases w/ ↑ lipid solubility
   - onset: faster w/ ↓pKA
   - duration: increases w/ ↑ protein binding
   - ester link = short acting, amide link = long acting
5. ) Usage w/ Adrenaline - ↑ duration
   - vasoconstriction –> ↓blood flow –> ↓removal of the anaesthetic –> ↑duration of the anaesthetic

6.) Indications - dentistry, obstetrics, post-op (wound pain), regional surgery, chronic pain management

7. ) Spinal Anaesthesia
   - between the arachnoid mater and the pia mater
   - cheaper and better post-op pain scores to general

Question 6

4 main side effects of anaesthetics

PONV
POCD
Cardiovascular x2
Infection

Answer 6

1. ) Post-Operative Nausea and Vomiting (PONV)
   - due to the used of opioids
   - young, female, non smoker, bag mask ventilation all increase risk
2. ) Post-Operative Cognitive Dysfunction (POCD)
   - often confusion especially in the elderly
3. ) Cardiovascular
   - hypotension with general anaesthetics
   - locals are VGNaC blockers so cardiovascular toxicity

4.) Chest Infection