Anaesthesia Flashcards
Define anaesthesia
Controlled depression of the CNS so as to produce a lack of awareness of painful inputs (nociception)
What area of the brain do anaesthetic agents ideally work on and why?
Minimal depression of hindbrain functions (preventing depression of cardiovascular centres) while having depressive effect on forebrain
Why is unconsciousness required?
To allow pain free surgery (no nociception)
Define nociception
The response to a stimulus that may be painful
Define pain
The conscious awareness of nociceptive input
What are the desired effects of anaesthesia?
- Hypnosis
- Anti-nociception (analgesia)
- Muscle relaxation
- Areflexia
- Maintenance of oxygen delivery
What are the potential risks of anaesthesia?
- Direct toxicity (reaction to drug)
- Indirect toxicity (e.g. halothane causing liver damage killing patients a few days later)
- Accidents
What are the features of successful anaesthesia?
- No CV depression
- No reduction in oxygen tissue delivery
- No cardiac dysrhythmias
- No cerebral hypoxia
- Survival
How is anaesthetic risk classified?
- American Society of Anesthesiologists (ASA) Physical Status Classification
- Categories I to VI
- VI not currently used (donor status)
Describe category I anaesthetic risk physical status
Normal healthy patient, no discernible disease e.g. elective spay, castration, dentistry
Describe category II anaesthetic risk physical status
- Pre-existing disease
- No discernible systemic signs
- E.g. skin tumour, fracture without shock, uncomplicated hernia, localised infection, compensated cardiac disease
Describe category III anaesthetic risk physical status
- Pre-existing disease
- Mild systemic signs
- e.g. fever, dehydration, mild anaemia, mild cachexia, moderate hypovolaemia
Describe category IV anaesthetic risk physical status
- Pre-existing disease
- Severe systemic signs
- e.g. uraemia, toxaemia, severe dehydration and hypovolaemia, severe anaemia, cardiac decompensation, emaciation, high fever
Describe category V anaesthetic risk physical status
- Moribund patient
- Not expected to survive with or without intervention
- Extreme shock and dehydration, terminal malignancy or infection, severe trauma
How can anaesthetic risk be minimised?
- Evaluation and planning
- Support with oxygen at all times
- Fluids
- Warmth
- Monitoring during anaesthesia and recovery
- Anaesthetic record sheets
- Trained anaesthetist
Outline the normal process of anaesthesia
- History and examination
- Formulate anaesthetic plan (ideally multiple)
- Place cannula
- Induce anaesthesia with injectable agent via cannula
- Intubate, check ABC
- Connect to anaesthetic machine, supply volatile anaesthetic agent in oxygen
- Alter inspired concentration in response to physical signs
- Supply analgesia
List the 3 key components for a balanced anaesthetic
- Hypnosis
- Anti-nociception
- Muscle relaxation
- Aka Triad of Anaesthesia
What is hypnosis?
- Artificially induced “sleep”
- More like lack of awareness (cannot be woken)
What is anti-nociception?
- Blocking of reaction to painful stimulus
- Are not perceiving pain but nociception can still occur
Where can nociception be blocked?
- Transduction using NSAIDs
- Transmission suing local anaesthetics
- Spinal cord with opioids and alpha-2 agonists
- CNS with opioids
Why is muscle relaxation require in anaesthesia?
- Intubation
- To gain access to surgical site
How can muscle relaxation be induced?
- Using more of the same agent producing hypnosis (but will decrease all physiological functions)
- Centrally acting muscle relaxant e.g. diazepam, midazolam
- Using specific neuromuscular junction blocking agent e.g. curare
Describe the stress response in anaesthetised animals
- Anaesthesia increases cortisol
- Initial increase in BP and subsequent decrease as administer more or anaesthetic agent
- Patient becomes cold as stop the physiological processes that keep it warm
Why is balanced anaesthesia important?
- Improves success rate and recovery
- E.g. one agent may have all 3 effects of triad but decreased brainstem function also caused, may lead patient to crash
- By using combination of agents can have better control of all 3 parts of triad