SC04 - General Anaesthesia

Question 1

Types of anesthesia

Answer 1

General anaesthesia(GA):
Reduced level of consciousness and response to stimuli

Regional anaesthesia(RA):
Loss of sensation to a body part or region, Patient can be fully awake/sedated/unconscious

Combinations of general and regional

Monitored AnaestheticCare (MAC) or “Conscious Sedation”: Patient sedated and should be self ventilating

Question 2

General anesthesia

• ## Function

Answer 2

Function:
- Hypnosis, Amnesia, Analgesia, Areflexia, +/-Muscle relaxation

Question 3

Pre-anesthetic preparations

Answer 3

• Manage co-morbidities
• Manage medications
• Fasting instructions

Fasting: Minimize the chance of aspiration during induction of and emergence from anaesthesia
*Solids and non human milk: 6 hours
* Infant formula: 6 hours
*Breast Milk: 4 hours
*Clear fluids: 2 hours (Examples of clear liquids include, but are not limited to, water, and fruit juices without pulp, carbonated beverages, carbohydrate-rich nutritional drinks, clear tea, and black coffee)

Question 4

Phases of general anesthesia

Answer 4

Induction: causing general anesthesia by the administration of pharmaceutics
- Intravenous agents: Propofol, thiopentone, etomidate, ketamine
- Volatile agents: Sevoflurane, Nitrous Oxide

Maintenance
* Ensure adequate delivery of pharmaceutics to
*Maintain physiological homeostasis
* Prevent of awareness
* Facilitate surgical activity

Emergence and Recovery
* process of return to baseline physiologic function of all organ systems after the cessation of administration of general anaestheticagent(s).

Question 5

Types of monitoring during general anesthesia

Answer 5

Before induction *Pulse oximetry *Blood pressure *ECG

After induction *End tidal CO2Monitoring * EEG * Volatile agent conentration * Blood pressure

Question 6

Muscle relaxants types

Answer 6

Muscle relaxants

Non depolarising
- Short acting: Mivacurium
- Intermediate acting: Atracurium, cis-atracurium Rocuronium, Vecuronium
- Long acting: Pancuronium

Depolarising
- suxamethonium

Question 7

Sequence of General anesthesia **

Answer 7

1. Establish monitoring of vitals
2. Establish intravenous access: e.g. angiocath
3. Induction of anesthesia: Induction agent (IV or Volatile), +/- opioids and muscle relaxants
4. Airway intrumentation: intubation with laryngoscope or Video assisted intubation, endotracheal tube connected to anaesthetic circuit
5. Maintenance agent: IV or inhaled anaesthetic
6. Positioning and protection: pressure relief pads and bracing
7. Monitoring, fluid and drug management
8. Emergence +/- reversal agent:
9. Recovery: Analgesic (oral, parenteral or regional block)

Question 8

Maintenance agent types

Analgesics types

Reversal agent types

Answer 8

Maintenance:
Intravenous anaesthetic
- Propofol

Volatile anaesthetic
- Isoflurane
- Sevoflurane
- Desflurane
- Nitrous Oxide

Analgesia:
- Paracetamol: PO/IV/PR
- NSAIDs
- Opioids: Fentanyl, Morphine, Oxycodone, Pethidine
- Others: Gabapentin, Tramadol, Ketamine

Reversal agents:
- Neostigmine PLUS an anticholinergic
*Atropine
*Glycopyrrolate

• Sugammadex
• for reversing rocuronium only

Question 9

Regional anesthesia
- Function
- Types

Answer 9

Function: reduced sensation from the anatomical area supplied by the blocked nerves

Types:
- Neuroaxial blocks: spinal or epidural
- Plexus blocks eg.brachial plexus for arm surgery
- Nerve blocks eg.Femoral nerve block
- Local infiltration
- Topical anaesthesiaeg.EMLA cream
- Intravenous regional technique

Question 10

Neuroaxial block
Types
Differences

Answer 10

Spinal anaesthesia
- Local anaestheticagent (LA) injected into the CSF
- Block sensation supplied by spinal fibres below a certain level depending on the type and dose of LA used
- Achieve “Temporary paraplegia”: Dense block causing Motor and sensory block

Epidural anaesthesia
- LA agent deposited into the epidural space
- Varying degree of motor and sensory block

Question 11

Reasons for extensive pre-anesthetic preparation even for RA

Answer 11

1. May need conversion to GA immediately
2. Total or partial failure of block
3. Complications from the regional technique
   - Local anaesthetictoxicity
   - Severe haemodynamicdisturbances
   - Excessive block
4. Prolonged surgery
   - Duration of surgery exceeds duration of block and return of feeling during surgery
   - Patients restless or becoming uncooperative

Question 12

Causes of total or partial anesthetic failure

Answer 12

Operator factors
- Misplaced needle
- Incorrect dosage

Drug error (including expired drugs)

Patient factors
- Anatomical variants

Question 13

Complications of RA

Answer 13

Local AnaestheticToxicity
- Inadvertent intravascular injection
- Overdose
- Adverse reaction to adjuvant: Epinephrine/ Preservatives
- Spectrum of systemic manifestations: Neurological symptoms/ Convulsions/ Cardiovascular collapse

Severe Haemodynamic disturbances
- Usually from neuroaxial block
- Hypotension: Sympathectomy/ Inadequate intravascular volumn/ Inappropriate patient choice e.g. Cardiac patients, Valvular heart disease
- Bradycardia: Blockade of cardiac sympathetic fibres

Excessive Block
- Excessive rostral spread of LA: high dose, head down position, wrong subdural injection
- Motor blockade of intercostal muscles causing respiratory distress
- “Total Spinal block”: Supraspinal neurons (brain, midbrain, pons medulla) blocked by the local anaesthetic