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