Principles and Pharmacology Flashcards
What is general anaesthesia?
Produces insensibility in the whole body, usually causing unconsciousness
Centrally acting drugs- hypnotics/analgesics
What is regional anaesthesia?
Produces insensibility in an area or region of the body, local anaesthetic applied to nerves supplying relevant areas
What is local anaesthetic?
Producing insensibility in only the relevant part of the body, local anaesthetic applied directly to the tissues
What types of drugs are used as anaesthesia?
Inhalational anaesthetics Intravenous anaesthetics Muscle relaxants Local anaesthetics Analgesics
What types of techniques and equipment are used in anaesthesia?
Tracheal intubation Ventilation Fluid therapy Regional anaesthesia Monitoring
Why are hypnotics needed in anaesthesia?
Provides unconsciousness for general anaesthesia
Why are analgesics used in anaesthesia?
Pain relief, still required under GA to suppress reflex autonomic responses to painful stimulus
Why are muscle relaxants used in anaesthesia?
Provide immobility for certain procedures to allow access to body cavities and to permit artificial ventilation amongst other things
What problems can arise with anaesthesia?
Polypharmacy
Muscle relaxation
Separation of hypnosis and relaxation
How do general anaesthetic agents work?
Interfere with neuronal ion channels
Hyperpolarise neurones - less likely to ‘fire’
Inhalational agents dissolve in membranes
IV agents- allosteric binding on GABA receptors, open Cl channels
What type of molecules are inhalation anaesthetics formed of?
Halogenated hydrocarbons
What part of the body uptakes and excretes inhalation anaesthesia?
Lungs
What is MAC?
Minimum alveolar concentration- the concentration of the drug required in the alveoli which is required to produce anaesthesia with any particular agent
What does a low MAC number mean?
High potency
What is the main role of inhalation anaesthesia?
Extension or continuation of anaesthesia
What effects does GA have centrally on the cardiovascular system?
Depresses cardiovascular centre
Reduces sympathetic outflow
Negative inotropic/ chronotropic effect on heart
Reduced vasoconstrictor tone
What effects does GA have directly on the cardiovascular system?
Vasodilation - decreased peripheral resistance
Venodilation - decreased venous return, decreased cardiac output
What is the equation for mean arterial pressure?
MAP= Cardiac output x systemic vascular resistance
What effects does GA have on the respiratory system?
Respiratory depressants
Reduce hypoxia and hypercarbic drive
Decreased tidal volume and increase rate
Paralyse cilia
Decrease FRC - lower lung volumes, VQ mismatch
What are the indications for muscle relaxants?
Ventilation and intubation
When immobility is essential
Body cavity access needed
What are the problems with muscle relaxants?
Awareness
Incomplete reversal (airway obstruction, ventilatory insufficiency)
Apnoea
What are non-polarising NMBs?
Competitive block of nicotinic acetylcholine receptors at NMJ that prevents the opening of sodium channels
What are depolarising NMBs?
Depolarise motor end plate
Renders post-junctional membrane refractory to further stimulus
What depolarising NMBs is commonly used?
Suxamethonium
What are the benefits of using suxamethonium?
Very rapid onset
Short duration of action (<5min)
What are the risks of using suxamethonium?
Myalgia
Anaphylaxis
Malignant hyperthermia
What is the reason for intraoperative analgesia?
Prevention of arousal
Opiates contribute to hypnotic effect of GA
Suppression of reflex responses to painful stimuli
What are some examples of local anaesthetic drugs?
Lignocaine
Bupivacaine
Prilocaine
How do local anaesthetic drugs work?
Sodium channel blockers
Prevent propagation of action potential
What is the main factor that limits how much LA can be used?
Toxicity
What does LA toxicity depend on?
Dose used
Rate of absorption
Patient weight
Drug
What are the signs and symptoms of LA toxicity?
Circumoral and lingual numbness and tingling Light-headedness Tinnitus, visual disturbances Muscular twitching Drowsiness Cardiovascular depression Convulsions Coma Cardiorespiratory arrest
What are the benefits of regional and local anaesthesia?
Retain awareness/ consciousness
Lack of global effects of GA
Relative sparing of respiratory function
What are the physiological effects of regional anaesthesia?
Inspiratory function relatively spared
Expiratory function relatively impaired
Decrease FRC
Increased VQ mismatch
What are the indications for spinal and epidural anaesthesia?
Avoidance of GA
Severe respiratory disease
Avoid airway problems
Allergies/reactions to GA agents
What are the contraindications for spinal and epidural anaesthetic?
Patient refusal Fixed cardiac output (aortic/ mitral stenosis) Infection Bleeding diathesis/ anticoagulation Technical difficulties Spinal problems/neurology
What is the location used in spinal anaesthesia?
Subarachnoid
T4 3-4ml LA
What is the usually duration of a spinal anaesthesia?
2-3 hours
What is the usually duration of an epidural anaesthesia?
Extradural
Block to T4 20+ml LA
What is the usually duration of an epidural anaesthetic?
3-4 hours
