Anaesthetics - Pharmacology Flashcards
What are the commonly used drugs used by anaesthetists now?
Inhalational anaesthetics
Intravenous anaesthetics
Muscle relaxants
Local anaesthetics
Analgesics
What techniques and equipment are commonly used in anaesthetics?
Tracheal intubation
Ventilation
Fluid therapy
Regional anaesthesia
Monitoring Used of improved technology too - USS, Fibreoptics, CPUs, BIS
What is the function of an anaesthetic machine?
Regulation of fresh gases and mixing to deliver precise concentrations of gaseous agents.
Mechanical ventilation, now microprocessor controlled.
Monitoring of patient is also integrated.
What is the triad of anaesthesia?
- Hypnosis (unconsciousness) - Necessary component of any general anaesthetic
- Analgesia - pain relief: can also be taken in this context to mean “removal of perception of unpleasant stimulus” since not all unpleasant stimuli patients need protected from are necessarily painful.
- Relaxation: refers to skeletal muscle relaxation necessary to provide immobility for certain procedures, allow access to body cavities and to permit artificial ventilation amongst other things.
What are the advantages of balanced anaesthesia?
Balanced anaesthesia allows a greater control over the individual components of the triad. Allowing different drugs and techniques to be used to achieve individual targets, keeping individual drug doses down.
- Different drugs do different jobs: allows a great degree of control over the individual components of the triad
- Titrate doses separately & therefore more accurately to requirements
- Avoid overdosage
- Enormous flexibility
What are some of the problems of anaesthetics?
- Polypharmacy
- Inc chance of drug reactions/allergies
- Muscle Relaxation
- requirement for artificial ventilation - failure to do so >> death.
- means of airway control
- Separation of relaxation and hypnosis.
- Awareness - Paralysed due to the muscle relaxant, but patient awake.
Outline general anaesthetics?
Inhaled and intravenous, agents provide unconsciousness as well as a small degree of muscle relaxation.
They may to differing extents also provide some analgesia. But for all except Ketamine this is negligible
How do General Anaesthetic Agents work?
- Interfere with neuronal ion channels - opening Cl- channels.
- Hyperpolarises neurons - meaning they are less likely to fire.
- Inhalational agents dissolve in the membranes and provoke a direct physical effect.
- Intravenous agents are involved in allosteric binding
- Such as to GABA receptors - which open chloride channels.
- How is cerebral function and reflexes impacted due to general anaesthetics?
Cerebral Function is “lost from the top down”
- Most complex processes interrupted first
- LOC early - hearing later
- More primitive functions lost later
- Reflexes relatively spared: due to a small number of synapses, and are primitive (simple) in nature
What must be managed when a patient is under general anaesthesia?
The care of an anaesthetised patient is more complex than someone who is simply unconscious, due to the complex physiological interaction of anaesthetic drugs with the patient’s organ systems.
- ABC… - akin to resuscitation, except more drawn out.
- Airway management - due to muscle relaxation
- Resp. function monitoring - impaired by anaesthetic
- CVS impact must be monitored also.
What are the benefits of IV Anaesthesia?
What are the main two IV anaesthetic agents?
- Rapid onset of unconsciouness
- 1 arm - brain circulation time - reach the brain very quickly
- IV agents - such as thiopentone and propofol - fat soluble, cross the membrane very quickly.
- Rapid recovery
- Due to disappearance from circulation, into fats and muscle etc.
- Metabolism of the drug actually contributes very little to the termination action of IV agents.
What are inhaled anaesthetics made of?
- Halogenated hydrocarbons
How are inhaled anaesthetics uptaken and excreted?
- Concentration gradient - lungs > blood > brain
- Cross alveolar BM easily
- Arterial concentration equates closely to alveolar partial pressure
What is MAC? What is it’s use in anaesthetics?
Minimum Alveolar Concentration
- The concept of the concentration of the Inhalational drug required in the alveoli which is required to produce anaesthesia with any particular agent.
- A low MAC value means that the agent is more potent - as less concentration of the substance is required to get the desired effect.
Explain inhaled anaesthesia including induction, maintenance and awakening.
- Induction: slow
- (so IV may be used to put the patient “under”)
- Slow induction can be beneficial in some cases - such as an obstructed airway.
- Maintenance of anaesthesia: prolong duration - very flexible
- This is the main role of inhalational anaesthetics.
- Awakening:
- stop inhalational admin
- washout - reversal of concentration gradient - after which consciousness will return.
