introduction to general anaesthesia dr anthony ho
TRANSCRIPT
Introduction to General Introduction to General AnaesthesiaAnaesthesia
Dr Anthony Ho
Points to discussPoints to discuss
What is general anaesthesia? How do we do it?
What is general What is general anaesthesia?anaesthesia?
What are the objectives?1. Provide conditions suitable for
surgerya) for surgeonb) for patient
2. Maintain physiological homeostasis3. Restore normal function afterwards
Surgeons’ RequirementsSurgeons’ Requirements
Immobile patient with relaxed muscles
Good outcome
Patients’ RequirementsPatients’ Requirements
Asleep Alive No pain or nausea
The Basic Components of The Basic Components of General AnaesthesiaGeneral Anaesthesia
The triad of balanced The triad of balanced general anaesthesiageneral anaesthesia
Unconsciousness
(3) Muscle relaxation
Analgesia (2)
(1)
1. Unconsciousness “sleep” “hypnosis” “lack of awareness”
The triad of balanced The triad of balanced general anaesthesiageneral anaesthesia
1
2. Analgesia Reduction of physiological “stress”
responses (sympathetic, CVS, hormonal)
Prevention of hypersensitization Continuation postoperatively
The triad of balanced The triad of balanced general anaesthesiageneral anaesthesia2
3. Muscle relaxation Skeletal muscle paralysis
(Voluntary and reflex) Permits surgical access Allows tracheal intubation and
mechanical ventilation Varies for different operations
The triad of balanced The triad of balanced general anaesthesiageneral anaesthesia3
How to do it...How to do it...
Depressant and inhibitory drugs Controlled Reversible
H H H H
H C C O C C C
H H H H
First use of ether anaesthesia, Boston, USA, 1846
Diethyl EtherDiethyl Ether
Unconsciousness
(3) Muscle relaxation
Analgesia (2)
(1)
Curare
(Opium) Papaver somniferum
Balanced anaesthesia: Balanced anaesthesia:
Use of selective drugsUse of selective drugs
Unconsciousness
(3) Muscle relaxation
Analgesia (2)
(1)
Balanced anaesthesia Balanced anaesthesia uses selective drugsuses selective drugs
1. Unconsciousness– Intravenous and inhalational
anaesthetics
2. Analgesia– Opioids
3. Muscle Relaxation– Neuromuscular blockers
Balanced anaesthesia Balanced anaesthesia uses selective drugsuses selective drugs
1. Unconsciousness– Intravenous anaesthetics– Inhalational “volatile” anaesthetics
examples:– Thiopentone, propofol– Isoflurane, sevoflurane, halothane
Balanced anaesthesia Balanced anaesthesia uses selective drugsuses selective drugs
2. Analgesics: Opioids Morphine Fentanyl Pethidine, alfentanil, remifentanil
Balanced anaesthesia Balanced anaesthesia uses selective drugsuses selective drugs
3. Muscle relaxants a) Depolarizing:
– Suxamethonium b) Non-depolarizing:
– Vecuronium, rocuronium– Atracurium, cisatracurium, mivacurium
The Process of General The Process of General AnaesthesiaAnaesthesia
The Process of General The Process of General AnaesthesiaAnaesthesia
1. Preparation2. Induction3. Maintenance4. Emergence5. Recovery
PreparationPreparation
Ward* (Preoperative(Preoperative assessment, premed)
Transfer to OT Equipment check* Monitoring* IV access,* IV infusion,* other “lines” Preoxygenation
InductionInduction
Usually IV Muscle relaxant Manual ventilation * Tracheal intubation (*)
MaintenanceMaintenance
Ventilation– Oxygen 30%– Nitrous oxide 70%– Isoflurane 0.5 - 1%
plus as required:– Muscle relaxant– OpioidRegional block
EmergenceEmergence
Cessation of inhaled agents Reversal of muscle relaxants Extubation
RecoveryRecovery
Return of consciousness Analgesia * Management of complications *
– Nausea and vomiting– Cardiorespiratory– Hypothermia
SummarySummary General anaesthesia more than just sleep Maintenance of homeostasis is a priority Target drugs are used for specific
endpoints for “balanced effect” All anaesthetic effects are reversible Anaesthetic care extends beyond the
operating theatre