Principles and Pharmacology Flashcards
What are the types of drugs used in anaesthetics ?
Inhalational anaesthetics Intravenous Anaesthetics Muscle Relaxants Local Anaesthetics Analgesics
What are the techniques used in anaesthetics?
Tracheal Intubation
Ventilation
Fluid Therapy
Regional Anaesthesia
What is the triad of anaethesia?
Analgesia, Hypnosis and Relaxation
What are the problems of anaesthesia?
Polypharmacy may increase drug reactions
Muscle relaxants are required for artificial ventilation
Separation of relaxation and hypnosis can result in awareness
How do general anaesthetics work?
Interfere with neuronal ion channels and hyperpolarises them to make them less likely to fire
How do inhalational agents work?
They dissolve in membranes and give a direct physical effect
How do IV agents work?
Allosteric binding on GABA receptors open chloride channels
What effect does General Anaesthetics have on cerebral function?
It is “lost from top down” where the most complex processes are interrupted first
Loss of consciousness is early and hearing is lost later along with primitive functions
What are the immediate effects of IV anaesthetics?
Rapid unconsciousness with rapid recovery
What are inhalational anaesthetics?
Halogenated hydrocarbons
How are inhalational anaesthetics metabolised?
Uptake and excretion via lungs where concentration gradient is highest in lungs to blood to brain
Passes alveolar BM easily
When are muscle relaxants used ?
Ventilation and intubation
When immobility is essential
Body cavity surgery
What problems come with muscle relaxants?
Awareness
Incomplete reversal
Apnoea
Why use intraoperative analgesia?
Prevention of arousal
Opiates contribute to hypnotic effect of GA
Suppression of reflex responses to painful stimuli
What are local anaesthetics?
Sodium channel blockers
Pharmacologically “filthy”
Prevent propagation of action potential
LA molecules must pass into axon to block sodium channel from within.
What is the limiting factor in local anaesthetic ?
Toxicity
What makes IV agents fast acting?
They are fat soluble and are therefore able to cross the membrane quickly
How long do IV agents last in the body??
They quickly enter and leave the bloodstream
Muscles pick up the IV agents slowly but since a large percentage of the body is made of muscle, the effect is great nonetheless
Fat picks up IV agents the slowest but is able to store IV agents in large amounts due to fat soluble characteristics
what does a low MAC value indicate?
A highly potent inhaled anaesthetic
i.e small dose to get big effect
bigger the MAC value, the more you need to produce the desired effect
Why are inhaled agents useful?
They can prolong the time of anaesthesia easily if need be
They are slow acting and are therefore beneficial in maintenance of anaesthesia
How are inhaled agents removed from the system?
By inhaling a gas without the anaesthetic in it and thus reversing the concentration gradient in the body
How is General Anaesthetic maintained?
IV induction and inhalation maintenance
How does GA depress the CV system?
It decreases sympathetic outflow which results in increased vasodilation, decreased SVR and a decreased CO
How do General Anaesthetics repress the respiratory system?
Reducing hypoxic and hypercarbic drive of the brainstem which decreases tidal volume and increases rate
Paralyses cilia
