AnesthesiologyAnesthesiology[[GkGk. . an-,an-, not + not + aisthesis-,aisthesis-, perception + perception + logia,logia, study] study]

General AnaesthesiaGeneral Anaesthesia

An artificial state of An artificial state of unresponsiveness, followed unresponsiveness, followed by amnesia, maintained by by amnesia, maintained by the continuing presence of the continuing presence of

chemical agents in the brainchemical agents in the brain

PharmacologyPharmacology

1.1. Intravenous AgentsIntravenous Agents

2.2. Inhalational Agents Inhalational Agents

3.3. ( Analgesics )( Analgesics )

4. 4. Muscle RelaxantsMuscle Relaxants

Intravenous anaestheticsIntravenous anaesthetics

1.1. ThiopentoneThiopentone

2.2. PropofolPropofol

3.3. KetamineKetamine

ThiopentoneThiopentone

• Proven track recordProven track record

• Rapid onset of action with fast Rapid onset of action with fast recovery due to recovery due to redistributionredistribution

• Repeated doses need to be smaller as Repeated doses need to be smaller as accumulation occursaccumulation occurs

• Extravasation may cause necrosisExtravasation may cause necrosis

• Potent anticonvulsantPotent anticonvulsant

PropofolPropofol

• Fast onset of action with rapid recovery Fast onset of action with rapid recovery due to due to redistribution and high redistribution and high clearanceclearance

• Clear headed recoveryClear headed recovery

• Low incidence of nausea and vomitingLow incidence of nausea and vomiting

• Suitable for short procedures especially Suitable for short procedures especially day day surgerysurgery

• Pain on injection and occasional Pain on injection and occasional involuntary involuntary movementsmovements

Target-controlled Infusion(TCI)

1.1. Nitrous oxideNitrous oxide

2.2. Volatile anaestheticsVolatile anaesthetics

- Sevoflurane- Sevoflurane- Desflurane- Desflurane- Isoflurane- Isoflurane- Enflurane- Enflurane- Halothane- Halothane

Inhalational anaestheticsInhalational anaesthetics

Nitrous oxideNitrous oxide

• ““Laughing Gas”Laughing Gas”

• Gaseous anaesthetic.Gaseous anaesthetic.

• Piped gas supply or blue cylinders. Piped gas supply or blue cylinders. 

IsofluraneIsoflurane

• Volatile anaestheticVolatile anaesthetic

• Require vaporiserRequire vaporiser

• Isoflurane commonly usedIsoflurane commonly used

• Faster recovery compared to Faster recovery compared to halothane and enfluranehalothane and enflurane

• Irritating vapour, therefore not Irritating vapour, therefore not commonly used for induction.commonly used for induction.

Newer agentsNewer agents

• SevofluraneSevoflurane- Fast onset and offset of effect- Fast onset and offset of effect- Non-irritating, useful for - Non-irritating, useful for

inhalational inhalational induction, induction, especially in children.especially in children.

• DesfluraneDesflurane- Boiling point near room - Boiling point near room

temperaturetemperature- Need special vaporiser- Need special vaporiser

Older agentsOlder agents

• HalothaneHalothane

- May cause arrhythmias - May cause arrhythmias intraoperatively intraoperatively and hepatitis and hepatitis postoperativelypostoperatively

• EnfluraneEnflurane

- May cause seizures and renal - May cause seizures and renal impairmentimpairment

• Useful for aiding insertion of Useful for aiding insertion of Endotracheal Endotracheal tube and tube and ventilationventilation

• Will cause apnoea, therefore assisted Will cause apnoea, therefore assisted ventilation mandatory.ventilation mandatory.

Muscle relaxantsMuscle relaxants

Muscle relaxantsMuscle relaxants

• SuxamethoniumSuxamethonium

- Rapid onset of action- Rapid onset of action

- Used in rapid sequence - Used in rapid sequence inductioninduction

- Potential problems include - Potential problems include arrhythmiasarrhythmias

• Non-depolarising muscle relaxants -Non-depolarising muscle relaxants -

- Atracurium- Atracurium

- Vecuronium- Vecuronium

- Mivacurium- Mivacurium

- Rocuronium- Rocuronium

• Fast onset with intermediate duration Fast onset with intermediate duration of actionof action

Muscle relaxantsMuscle relaxants

Reversal of Reversal of neuromuscular blockade neuromuscular blockade

• NeostigmineNeostigmine::

- - AnticholinesteraseAnticholinesterase

- Used for reversal of muscle - Used for reversal of muscle relaxation by relaxation by non-non-depolarising muscle relaxantsdepolarising muscle relaxants

-- Atropine given together to Atropine given together to counter counter bradycardiabradycardia

Anaesthetic TechniqueAnaesthetic Technique

1.1. InductionInduction

2.2. MaintenanceMaintenance

3.3. ReversalReversal

Induction of AnaesthesiaInduction of Anaesthesia

• Intravenous hypnotic ± narcotic, orIntravenous hypnotic ± narcotic, or

• Inhalational anaesthetic ± narcoticInhalational anaesthetic ± narcotic

Muscle relaxant if requiredMuscle relaxant if required

Maintenance of Maintenance of AnaesthesiaAnaesthesia

• Inhalational anaesthetic ± analgesic, orInhalational anaesthetic ± analgesic, or

• Intravenous anaesthetic ± analgesic, orIntravenous anaesthetic ± analgesic, or

• Inhalational anaesthetic + Intravenous Inhalational anaesthetic + Intravenous anaesthetic ± analgesicanaesthetic ± analgesic

Muscle relaxant if requiredMuscle relaxant if required

Reversal of AnaestheticReversal of Anaesthetic

• Switch off Inhalational /Switch off Inhalational / Intravenous Intravenous

AnaestheticAnaesthetic

• Reverse neuromuscular blockageReverse neuromuscular blockage

• Consider other specific antagonists if Consider other specific antagonists if necessary necessary - Naloxone, - Naloxone, FlumazenilFlumazenil

Complications ofComplications ofGeneral AnaesthesiaGeneral Anaesthesia

1.1. Central Nervous SystemCentral Nervous System

2.2. Cardiovascular SystemCardiovascular System

3.3. Respiratory SystemRespiratory System

EffectsEffectsCentral Nervous SystemCentral Nervous System

1.1. DepressionDepression

- loss of consciousness- loss of consciousness

- Cardiovascular depression- Cardiovascular depression

- Respiratory depression- Respiratory depression

2.2. Stimulation - seizuresStimulation - seizures

EffectsEffectsCardiovascular SystemCardiovascular System

1.1. Myocardial depressionMyocardial depression

2.2. VasodilatationVasodilatation

3.3. ArrhythmiasArrhythmias

hypotension, decreased perfusionhypotension, decreased perfusion

EffectsEffectsRespiratory SystemRespiratory System

1.1. Decreased Rate & ApnoeaDecreased Rate & Apnoea

2.2. Decreased Tidal VolumeDecreased Tidal Volume

3.3. Ventilation – Perfusion mismatchVentilation – Perfusion mismatch

4.4. Increased Work of BreathingIncreased Work of Breathing

hypoventilation, hypoxiahypoventilation, hypoxia

Intraoperative Intraoperative MonitoringMonitoring

1.1. ClinicalClinical

2.2. Cardiovascular SystemCardiovascular System

3.3. Respiratory SystemRespiratory System

MonitoringMonitoringClinicalClinical

1.1. Pulse rate, Blood PressurePulse rate, Blood Pressure

2.2. Respiratory rateRespiratory rate

3.3. Colour:Colour:- Pallor, cyanosis- Pallor, cyanosis

4.4. Perfusion:Perfusion:- Capillary refill, Temperature- Capillary refill, Temperature- Urine output- Urine output

MonitoringMonitoringCardiovascular SystemCardiovascular System

1.1. Non-invasive:Non-invasive:- ECG- ECG- Pulse rate, - Pulse rate,

Heart rateHeart rate- Blood - Blood

pressurepressure

2.2. Invasive:Invasive:- Intra-- Intra-

arterial pressurearterial pressure- Central - Central

Venous Pressure, Venous Pressure, PCWPPCWP

Monitoring Monitoring Respiratory SystemRespiratory System

1.1. Pressure / Flow monitors:Pressure / Flow monitors:

- Tidal volume, Airway pressure- Tidal volume, Airway pressure

2.2. Gas analyser:Gas analyser:

- Inspiratory O- Inspiratory O22 concentration, concentration,

- End-tidal CO- End-tidal CO22 partial pressure, partial pressure,

- Anaesthetic gas concentration- Anaesthetic gas concentration

3.3. Pulse Oximeter - Arterial OPulse Oximeter - Arterial O22 saturation saturation

VentilationVentilation

• Spontaneous ventilationSpontaneous ventilation

• Intermittent positive pressure Intermittent positive pressure ventilation - IPPVventilation - IPPV

• Requires endotracheal intubation in most Requires endotracheal intubation in most casescases

• Useful when needed to:Useful when needed to:

- protect the lungs from aspiration of - protect the lungs from aspiration of material from stomach or material from stomach or

upper upper airwaysairways

- ensure adequate ventilation of the - ensure adequate ventilation of the lungslungs

Ventilation - IPPVVentilation - IPPV

• Ventilator generates a positive Ventilator generates a positive pressure which drives gas / oxygen pressure which drives gas / oxygen mixture into lungsmixture into lungs

  • Dangers include:Dangers include:

- failure of intubation / - failure of intubation / ventilation leading ventilation leading to hypoxiato hypoxia

- injury to lungs if airway - injury to lungs if airway pressure is pressure is excessiveexcessive

Ventilation - IPPVVentilation - IPPV