SC04 - General Anaesthesia Flashcards
Types of anesthesia
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
General anesthesia
- ## Function
Function:
- Hypnosis, Amnesia, Analgesia, Areflexia, +/-Muscle relaxation
Pre-anesthetic preparations
- 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)
Phases of general anesthesia
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).
Types of monitoring during general anesthesia
Before induction *Pulse oximetry *Blood pressure *ECG
After induction *End tidal CO2Monitoring * EEG * Volatile agent conentration * Blood pressure
Muscle relaxants types
Muscle relaxants
Non depolarising
- Short acting: Mivacurium
- Intermediate acting: Atracurium, cis-atracurium Rocuronium, Vecuronium
- Long acting: Pancuronium
Depolarising
- suxamethonium
Sequence of General anesthesia **
- Establish monitoring of vitals
- Establish intravenous access: e.g. angiocath
- Induction of anesthesia: Induction agent (IV or Volatile), +/- opioids and muscle relaxants
- Airway intrumentation: intubation with laryngoscope or Video assisted intubation, endotracheal tube connected to anaesthetic circuit
- Maintenance agent: IV or inhaled anaesthetic
- Positioning and protection: pressure relief pads and bracing
- Monitoring, fluid and drug management
- Emergence +/- reversal agent:
- Recovery: Analgesic (oral, parenteral or regional block)
Maintenance agent types
Analgesics types
Reversal agent types
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
Regional anesthesia
- Function
- Types
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
Neuroaxial block
Types
Differences
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
Reasons for extensive pre-anesthetic preparation even for RA
- May need conversion to GA immediately
- Total or partial failure of block
- Complications from the regional technique
- Local anaesthetictoxicity
- Severe haemodynamicdisturbances
- Excessive block - Prolonged surgery
- Duration of surgery exceeds duration of block and return of feeling during surgery
- Patients restless or becoming uncooperative
Causes of total or partial anesthetic failure
Operator factors
- Misplaced needle
- Incorrect dosage
Drug error (including expired drugs)
Patient factors
- Anatomical variants
Complications of RA
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