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General Anaesthetics:sleeping: (Depth of Anaesthesia (Surgical Anaesthesia…
General Anaesthetics:sleeping:
Definition
Partial or complete loss
Perception and response to external stimuli
Sedation and anxiolytics
Lack of awareness and amnesia
skeletal muscle relaxation
Suppression of unwanted reflexes
Analgesia
Stages
Induction
Onset of administration of potent analgesics to effective anaesthesia
Maintenance
Sustaining surgical anaesthesia
Recovery
Discontinuation of anaesthesia to consciousness and protective physiological reflexes are regained
Depth of Anaesthesia
Analgesia
Loss of pain sensation
Conscious, sleepy
Amnesia, reduced awareness of pain
Excitement
Delirious, combative
Undesirable, use a quick induction to skip this stage
Surgical Anaesthesia
Gradual loss of muscle tone and reflex
Regular respiration, skeletal muscle relaxation
Loss of spontaneous movement
Ideal stage of surgery
Medullary Depression
Severe depression of respiration and vasomotor centres
Death can rapidly occur
Mechanism of Action
Lipid solubility
Correlation of lipid solubility and anaesthesia potency
Dissolution into the lipid bilayer of membrane alters properties of membrane lipids, compromising their function
Effect of ion channels
GABA
5 subunit receptor
Different subunit composition lead to different subtypes
alpha-subunit mutation - inhibits action of volatile anaesthetics
beta-subunit - inhibit action of both types of anaesthetics
Two-pore domain K channels
Modulates neuron excitability
Volatile anaesthetics activate these
Reduce membrane permeability
Analgesia, immobilisation, sedative properties
NMDA receptors
Reduce glutamate action on these receptors
Decrease neuronal excitability
Pharmacological Effects
CNS
Neurons
Tonic inhibition due to GABA modulation
Reduced excitability
Inhibit excitatory synaptic transmission
Anaesthetic state
Reflex Loss
Analgesia
Amnesia
ADR
High doses
Brain function adversely affected
Excessively high doses - CNS profoundly inhibited, death by depression of respiration
Brain
Inhaled anaesthesia decrease metabolism
Volatile anaesthesia
Decrease vascular resistance
Increase blood flow to brain
Increased intracranial pressure
Least likely - NO
CVS
Decrease cardiac contractility (Most GA)
Inhibition of sympathetic outflow (Halogenated GA)
Decreased in sympathetic tone and pressure
Increase sympathetic release (NO and ketamine)
Increase in HR
Ventricular extrasystole
VFibrillation
Respiratory
Depression of respiration
Retention of pCO2
Pungent coughing, laryngospasm, bronchospasm
Especially desflurane