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Flashcards in Purpose of anaesthesia Deck (35)
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What are 'triad' aims of anaesthetics

  • Unconsciousness
  • Muscle relaxation
  • The inhibition of pain


What is meant by analgesia in the unconscious patient?

  • conscious perception of pain is normally associated with the awake state


  • noxious stimuli can still evoke physiological responses in the anaesthetized patient → drugs that decrease these responses are considered to be providing analgesia


Do volatile agents have analgesic properties?

  • contribute to analgesia while a patient is anaesthetised 
  • do not provide any pain relief post-op


*large doses of volatile agents are needed to inhibit sympathetic response 


How to quantify a potency of a volatile agent?

By Minimum Alveolar Concentration (MAC) value 


MAC = concentration of the vapour in the lungs that is needed to prevent 50% of patients moving when subjected to a standard surgical incision 


What do volatile agents do?

  • produce unconsciousness 

in adequate doses:

  • partial muscle relaxants → by suppression of spinal reflexes
  • inhibition of movement to pain


What are the effects of IV anaesthetics? (2)

  • unconsciousness
  • amnesia 


Do IV anaesthetics provide pain relief?

They are purely hypnotic agents → no analgesic properties 


* with exception to Ketamine 



Can IV anaesthetics inhibit movements in response to the surgery?

No, as they lack the ability to suppress spinal reflexes 


Do benzodiazepines used in the theatre produce unconsciousness and amnesia, on their own?

Not on their own, in the doses used in the theatre


They are amnesic when combined with opiates and volatile/IV anaesthetics (synergistic effect) 


Can benzodiazepines inhibit movements?

They contribute to muscle relaxation but do not completely inhibit movements (in standard doses)


Are benzodiazepines analgesics?



 Mode of action of muscle relaxants

Muscle relaxants

(aka neuromuscular blockers) 


MoA: they block transmission at the neuromuscular junction 


Do muscle relaxants have anaesthetic or analgesic action? 


*use of muscle relaxants without adequate anaesthesia → awareness while being paralysed 


Can opioids produce unconsciousness and amnesia?



The aim of opioids use (in terms of surgery)

Analgesia during and after surgery 


Can opioids produce a muscle relaxant effect? 


  • do not produce muscle relaxation


  • they blunt perception of painful stimuli → inhibition of movements to pain during the surgery 


*some opioids in very high doses may produce  rigidity 


What does regional anaesthesia do?

Produces immobility, muscle relaxation and analgesia within a distribution of the block 


What's multimodal analgesia?

Balanced analgesia requires the use of combinations of analgesic agents and techniques

This is also termed multimodal analgesia


Advantages of balanced analgesia

  • reduce the amounts of each drug required while still being clinically effective 


  • this may reduce some of the unwanted side-effects of the individual drugs


Example of multimodial / balanced anaelgesia 


What are the responsibilities of anaesthetist? 

  •  providing balanced anaesthesia (during surgery)

Peri-operative period:

  • Reduction of the surgical stress response
  • Effective postoperative analgesia
  • Prevention of postoperative nausea and vomiting
  • Fluid homeostasis and management of bleeding
  • Temperature maintenance with prevention of hypothermia
  • Care of patient positioning and protection of pressure areas and eyes


What are physiological responses for the painful stimuli and tissue injury during the peri-operative period? 

  • Sympathetic nervous system mediated physiological changes
  • Neuro-humoral changes
  • Other hormonal and metabolic changes


What do physiological responses to a painful stimuli/tissue injury (in a peri-operative period) may lead to?

  • Unwanted cardiovascular changes
  • Fluid retention
  • Electrolyte disturbances
  • Metabolic changes with a period of catabolism and hyperglycaemia
  • A systemic inflammatory response
  • Hypercoagulability


The physiological responses in a patient to surgical insult cause raised or increased (8)

• Adrenocorticotrophic hormone
• Growth hormone
• Vasopressin
• Prolactin
• Insulin resistance
• Carbon dioxide (CO2) production
• Oxygen consumption
• Circulating catecholamine levels


Aim of regional anaesthesia 

  •  prevents the transmission of nociceptive (painful) signals to the central nervous system, thus reducing the neuroendocrine stress response
  • this occurs for the duration of the block


Does general anaesthesia stop physiological responses to pain/tissue injury (e.g. surgery)? 

  • General anaesthesia does not abolish these responses completely


  • Patients still demonstrate a tachycardia under anaesthesia in response to stimulating procedures if inadequate analgesia has been given


What physiological responses to pain can high-dose opioids block?

The opioid, e.g. remifentanil or large doses of fentanyl ⇒ prevents the hypertension and tachycardia and helps to maintain cardiovascular stability


What do opioid drugs act on?

Receptors in CNS, both: 

- dorsal horn of the spinal cord

- brain


How does Paracetamol work?

  • act via inhibition of COX 3 ⇒ reduce prostaglandin synthesis 


  • a weak anti-inflammatory 


How does Clonidine work?

  • alpha-adrenoreceptor agonist 
  • analgesic, sedative and anti-hypertensive actions