Introduction and intensive care Flashcards
What are the 6 conscious modalities?
touch, pressure, kinaesthesia, heat, cold, pain
+ the special senses.
What is the definition of anaesthesia?
Elimination of sensation by controlled, reversible suppression of nervous function with drugs.
What is a conduction block?
Prevents sensation being registered from the area that has been blocked but does not involve a loss of consciousness. e.g. in spinal chord via extradural injection or in the peripheral nerves.
What does a general anaesthetic do?
It affects the brain and obtunds sensation by disrupting activity in the sensitive projection areas of the cortex. Other areas are also affected and unconsciousness occurs along with muscle relaxation and lowered sensitivity to painful stimuli.
What are the disadvantages of general anaesthetics?
The suppression of sensation causes suppression of important unconscious physiological processes e.g. blood pressure, plasma levels of oxygen, carbon dioxide and temperature. These occur in the medulla.
What are the two reasons that anaesthetics enter the brain rapidly?
1) both inhaled and injectable anaesthetics are highly lipophilic molecules and so cross the BBB rapidly.
2) the brain is highly vascular and receives 15% of CO.
so levels of anaesthetic in the blood and brain equilibrate rapidly.
How does sensitivity of areas of the brain vary?
1) differences in blood supply- more active sites require oxygen so have a higher blood supply, grey matter x6 compared to white.
2) Differences in complexity, e.g. cortex has higher blood supply than the spinal chord.
What are examples of intrinsic support?
Applying artificial tears/fix eyelid shut- no palpebral reflex and lacrimation has ceased.
Pre-op food deprivation and ET tube- no protection of its own airway.
Hypoventilation- oxygen enrichment of inspired breath.
Hypotension- peri-operative fluid therapy
Hypothermia- Warm environments
What is analgesia?
No sensibility to pain.
What is the definition of pain and how do higher centres respond?
The conscious appreciation of unpleasant stimuli. They can initiate voluntary avoidance behaviour or eliciting assistance e.g. vocalisation or cessation of normal behaviour e.g. grooming, depressed. In surgery this can be seen as elevated heart rate etc.
What are the pain responses controlled by and why must they be suppressed?
The sympathetic nervous system.
1) hypertension puts pressure on failing hearts= dysrhythmias
2) tachyponea= ineffective ventilation
3) hypertension= increases bleeding
4) movement can make surgery impossible
What is the definition of surgical anaesthesia?
A state of drug induced insensibility which allows surgery to be performed with safety and comfort for both the subject and surgeons.
What is required in addition to unconsciousness?
Adequate analgesia- suppress undesirable responses to noxious stimuli.
Muscle relaxation- prevent reflex movement
How is deep anaesthesia acheived?
High doses of drugs e.g. isoflurane gas or proprofol- this causes depression of vital centres and can only be tolerated by healthy, young animals.
How is supported deep anaesthesia achieved?
high doses are used but extrinsic support is used.
