Principles of Anaesthetics Flashcards
What are the three essential jobs of an anaesthetist
Analgesia- inhibition of painful stimuli
Hypnosis- loss of consciousness
Relaxation- Skeletal muscle relaxation to provide immobility
What is the job of a modern anaesthetics machine?
What does anaesthesia mean?
mix gases to deliver precise concentrations
mechanical ventilation
- Without feeling
What are the most concerning side effects of analgesia
Multiple drugs- increased chance of drug reactions/allergies
Muscle relaxations- requires artificial ventilation, means of airway control
Awareness- individuals may be paralysed but become aware during the procedure
What does general aesthetics produce?
What are its general effects (except Ketamine)
Produces insensibility to the whole body
Typically causes unconsciousness and some levels of relaxation. Does not cause analgesia.
How do general anaesthetics work?
They suppress neuronal activity in a dose dependant fashion This is largely done by opening chloride channels that hyper polarise the neurones or suppress excitory synaptic activity.
Cause allosteric binding and Induce GABA receptors opening chloride channels
How does general anaesthetic affect the brain
Function is lost from the top down, the most complex processes are interrupted first such as levels of consciousness, primitive functions such as hearing are reduced near the end. reflexes are spared.
What is paramount to maintain when delivering this drug?
Why?
Airways, breathing and consciousness
people who are asleep do not have full control of their soft palate leading to apnea
How do IV general anaesthetic agents work?
Work very rapidly on the important tissues first, muscles and fat have a poor blood supply and so absorb the drugs last but can absorb them in larger quantities.
as they are fat soluble drugs they accumulate rapidly in the nerves and brain.
How are levels of the anaesthetic monitored?
Target controlled pump infusion is used to maintain accurate delivery of IV anaesthetics. It allows fro measurement of drugs in the brain in real time. Using complex pharmacokinetic algorithms with data about the patients age, sex and size to infer physiological status.
How do inhaled general aesthetics work?
They are hallogenated hydrocarbons that are excreted via the lungs. Patient is given a high dose so it can dilute its way through the blood and tissues. MAC is the desired amount of drug required to produce an effect
Inhaled anaesthetic is slow to be induced and slow to wake up. When it is time for the patient to wake up they will be given a mixture of gas with no agent in it. C02 is sampled to determine alveolar gas concentrations
How is general aesthetic typically administered?
Administered IV and maintained through inhalation. More modern agents aim o use intravenous maintenance via computer controlled infusion. Propofol and remifentanil are the common agents used for IV maintenance,
How does general anaesthetic affect the heart?
Reduces mean arterial pressure. Thi sis because MAP=COxSVR.
Venodialtion and decreased heart ryhtym leads to a reduction in CO
SVR is reduced due to arteriolar dilation
How does general anaesthetic affect the lungs?
All agents are respiratory depressants, reducing tidal volume while increasing respiratory rate. This is opposed by opiate respiratory depression which preserves tidal volume but lowers respiratory rate.
Anaesthetics reduce hypoxic and hypercarbic drive whilst paralysing cilia. They also reduce residual capacity leading to V/Q mismatch. These effects may be prolonged causing patients to require post operation oxygen
How do muscle relaxants work?
Indiscriminately relax skeletal muscle and affect skeletal muscles. Allow for complete stillness of a patient.
What are the main problems with muscle relaxants
Awareness- muscles paralysed but patient awake
Incomplete reversal- airways are obstructed due to overrelaxation. Only occurs at the end of surgery
Full ventilation of the lungs- if not apnea and death occur
