General Anaesthetics Flashcards
Define anaesthesia.
Reversible loss of awareness of pain and sensation
What are the three main types of anaesthesia?
Local
Regional
General
What is stage 1 of anaesthesia?
Induction and administration of analgesia
Reduces response to pain
Conscious but drowsy
What is stage 2 of anaesthesia?
Excitement, loss of response to non painful stimuli
Coughing increased, gag reflex
What are the concerns of stage 2 anaesthesia?
Choking Breath holding Talking Vomiting Movement
What is stage 3 of anaesthesia?
Desired phase for surgery
Regular respiration
Muscle tone preserved
Progressive shallow breathing
What is stage 4 of anaesthesia?
Anaesthetic overdose
Medullary paralysis
Respiration and vasomotor control ceases
Describe the ideal parameters of anaesthesia.
Rapid induction and recovery
Avoid stage 2 if possible
Ideally avoid side effects
Why are drugs commonly used in combination during anaesthesia? Give examples.
Stages of anaesthesia become less apparent
Different anaesthetics, analgesia, muscle relaxants, anxiolytics
What is used for rapid induction?
IV propofol
What is used to maintain unconsciousness?
Inhaled nitrous oxide/halothane
What can be given as supplementary IV analgesia?
Morphine
What is commonly given as a neuromuscular blocker in anaesthesia?
Atracurium
What are the benefits of induction and recovery?
Reduced stage 2
Homeostatic reflexes intact
Amnesia
What is the theory of lipid pertubation by anaesthetics?
Anaesthetics change the conformation of membrane proteins by changing the environment in which they are dissolved, some specifically affect certain proteins
Adding long carbon chains can reduce the potency
What is the protein theory of anaesthetic action?
GABA-A function potentiated, more Cl inions enter the neurone increasing inhibition in the CNS
NMDA receptor function inhibited by blocking glutamate binding
Two pore potassium channel function potentiated
What are the most common inhalation anaesthetics?
Nitrous oxide
Isofluorane
What are the disadvantages of ether anaesthetics? Where are they used?
Explosive, irritant and cause nausea
Used in 3rd world countries as very cheap
What are the advantages of inhalation anaesthetics?
Easy to maintain degree of anaesthesia due to fast air-blood equilibration
Rapid emergence from anaesthesia
What are the disadvantages of inhalation anaesthetics?
Cumbersome and expensive apparatus
Administered via mask
Atmospheric pollution by scavengers
Discuss the problems with metabolism of inhalation anaesthetics.
Fluranes generate fluoride that causes renal toxicity
Halothane converted to bromide and TFA which is hepatotoxic
Scavenger systems required
What is the minimum alveolar concentration?
Measures potency
Concentration required to produce anaesthesia in 50% of patients
What is the relevance of blood-gas partition coefficient of inhalation anaesthetics?
Measure of how well the drug dissolves in the blood
Determines rate of induction and recovery
What is the relevance of oil-gas partition coefficient of inhalation anaesthetics?
High oil-partition coefficient confers high potency
Lots of anaesthetic will dissolve in fat which is poorly vascularised, leading to slowly resolving ‘hangover’
Describe the features of isoflurane.
No metabolism Little toxicity Not pro-convulsive Twice the cost of halothane Negative inotrope, can cause hypotension Coronary vasodilator Potentially causes neurodegeneration
Describe the features of sevoflurane.
Described as the anaesthetic of choice Rapid induction Little metabolism Five times cost of halothane Recovery so fast that post-op pain relief is necessary
Describe the features of nitrous oxide.
Low blood-gas partition coefficient
Analgesic at concentrations lower than those causing unconsciousness
Introduces more oxygen than pure oxygen would due to density
Rapidly leaves blood and tissue
Dilates oxygen in lungs for few minutes, transient hypoxia
When is nitrous oxide contraindicated?
Pregnancy
Pernicious anaemia
Scuba diving
Describe the formulation of nitrous oxide?
Entonox
50% nitrous oxide, 50% oxygen
What are the advantages of IV anaesthetics?
Rapid induction
No stage 2
Simple apparatus
Pleasant induction
What are the disadvantages of IV anaesthetics?
Level of anaesthesia difficult to control
Recovery can be slow
Finite duration
Vein damage
Describe the use of thiopental.
Only normally used for induction
Very lipid soluble, crosses BBB quickly
Rapid redistribution to highly perfused tissues, slowly distributes into fat
Rapid awakening but prolonged hangover
Positive inotrope, hypotensioon in hypovolaemic patients
Respiratory depression (used in euthanasia)
Describe the use of propofol.
Rapid metabolism and recovery compared to other IV
Can be continuously infused to maintain anaesthesia
Used for day surgery
Widely abused by medical personnel
Describe the use of ketamine.
Dissociative anaesthetic Analgesia and amnesia but patient still partly conscious Increases heart rate Safe in emergency situations High abuse potential
What are Olney’s lesions?
Potential form of brain damage from ketamine
NMDA receptor antagonist neurotoxicity
What is neuroleptic anaesthesia?
Combination of antipsychotic andopioid
Effects similar to ketamine
Not frequently used in humans
What is immobilon?
Used in animals
Acepromazine and etorphine (neuroleptic anaesthetic)
Used in tranquiliser darts and supplied with antidote (revivon) due to potency
