Anaesthetics - the conduct of general anaesthesia Flashcards
IV induction
- Propofol, Thiopentone + others
- Rapid
- One “arm-brain” circulation ~ 20s - No obvious planes
- Easy to overdose
- Generally rapid loss of airway reflexes
- Apnoea is very common
Gas Induction
- Sevoflurane (Halothane)
- Common in young children
- Slow
- Considerably more obvious “planes” of anaesthesia
Monitoring Conscious Level
- Loss of Verbal Contact
- Movement
- Respiratory Pattern
- Processed EEG
- “Stages” or “planes” of anaesthesia
Stages of anaesthesia
- Stage 1, or induction
- Stage 2, or excitement stage
- Stage 3, or surgical anaesthesia
- Stage 4, or overdose
Stage 1 - induction stage
This phase occurs between the administration of the drug and the loss of consciousness.
Stage 2 - excitement stage
The period following a loss of consciousness, characterized by excited and delirious activity. Breathing and heart rate becomes erratic, and nausea, pupil dilation, and breath-holding might occur.
Risks of stage 2
Because of irregular breathing and a risk of vomiting, there is a danger of choking. Modern, fast-acting drugs aim to limit the time spent in stage 2 of anesthesia
Stage 3 - surgical anesthesia
Muscles relax, vomiting stops and breathing is depressed. Eye movements slow and then cease. The patient is ready to be operated on.
Stage 4 - overdose
Too much medication has been administered, leading to brain stem or medullary suppression. This results in respiratory and cardiovascular collapse.
Airway Maintenance in Anaesthesia
- Manoeuvres
- Head Tilt / Chin Lift / Jaw Thrust - Apparatus
- Face Mask
- Oropharyngeal (“Guedel”) Airway
- Laryngeal mask airway
Airway Complications - Obstruction
- Ineffective Triple Airway Manoeuvre
- Airway Device malposition or kinking
- Laryngospasm
Laryngospasm
- Forced reflex adduction of the vocal cords
- May result in complete airway obstruction
- Caused by airway stimulation in light planes of anaesthesia
- Often unrelieved by simple manoeuvres
Airway Complications - Aspiration
- Anaesthesia means loss of protective airway reflexes
- Gag, swallow, cough etc - Foreign material in the lower airway
- Gastric contents, blood, surgical debris
Maintaining” vs “protecting” an airway
- The airway is maintained if it is open and unobstructed
- Only a cuffed tube in the trachea protects the airway from contamination
Endotracheal intubation
- Placement of a cuffed tube in the trachea
- Oral route most commonly used
- Laryngeal reflexes must be abolished
- Also possible in the awake patient using local anaesthesia and fibre-optic scope
