Anesthesia: Mechanism of Non-Depolarizing Blockers
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Questions and Answers

What happens to adipose tissue in the body following repeat infusions of intravenous anaesthetics?

It forms a drug reservoir that often leads to a delayed recovery.

What is a common side effect of thiopental, a barbiturate?

Significant nausea.

What is a common use of benzodiazepines in anaesthesia?

To reduce anxiety and provide sedation.

What can prolong the effects of benzodiazepines?

<p>Erythromycin.</p> Signup and view all the answers

What is a unique effect of benzodiazepines on memory?

<p>Temporary anterograde amnesia.</p> Signup and view all the answers

What is the primary purpose of combining opioids with other anaesthetics?

<p>To provide analgesia.</p> Signup and view all the answers

What is the primary concern when using opioids in anaesthesia?

<p>Respiratory depression.</p> Signup and view all the answers

What can be used to reverse the effects of opioids?

<p>Naloxone.</p> Signup and view all the answers

What is a characteristic of inhalation anaesthetics?

<p>They are volatile liquids (except for nitrous oxide).</p> Signup and view all the answers

What is an advantage of inhalation anaesthetics?

<p>Depth of anaesthesia can be rapidly altered by changing the inhaled concentration.</p> Signup and view all the answers

What are the desirable components of anaesthesia, and why is it challenging to achieve ideal anaesthesia with a single anaesthetic agent?

<p>The desirable components of anaesthesia include rapid and pleasant induction, wide margin of safety, rapid changes in the depth of anaesthesia, and absence of toxic/adverse effects. However, no single anaesthetic agent provides all these desirable properties, making it necessary to combine several categories of drugs to produce optimal anaesthesia.</p> Signup and view all the answers

What is the primary role of induction in general anaesthesia, and how is it typically achieved in adults?

<p>The primary role of induction is to bring the patient to a state of effective anaesthesia, and in adults, it is typically achieved with an IV agent like propofol, producing unconsciousness in 30 to 40 seconds.</p> Signup and view all the answers

What is the difference in induction methods between adults and children without IV access?

<p>In adults, general anaesthesia is normally induced with an IV agent like propofol, while in children without IV access, non-pungent agents like sevoflurane are inhaled to induce general anaesthesia.</p> Signup and view all the answers

What is the primary goal of maintenance in general anaesthesia, and how is it achieved?

<p>The primary goal of maintenance is to provide sustained anaesthesia, and it is achieved by continuously monitoring vital signs and response to stimuli to balance the amount of drug inhaled and/or infused with the depth of anaesthesia.</p> Signup and view all the answers

What are the key components of anaesthesia, and how do they relate to each other?

<p>The key components of anaesthesia include unconsciousness, amnesia, immobility, and muscle relaxation, and abolition of somatic and autonomic reflexes. These components work together to produce a state of optimal anaesthesia.</p> Signup and view all the answers

Why is it important to combine different categories of drugs to produce optimal anaesthesia?

<p>Combining different categories of drugs is important because no single anaesthetic agent provides all the desirable properties of anaesthesia, and combining them helps to achieve optimal anaesthesia.</p> Signup and view all the answers

What is the role of inhalation agents in general anaesthesia, and how are they used?

<p>Inhalation agents are used to produce and maintain anaesthesia, and they may be given in addition to IV agents to produce the desired depth of anaesthesia.</p> Signup and view all the answers

How is the depth of anaesthesia monitored during maintenance, and what is the goal of this monitoring?

<p>The depth of anaesthesia is monitored by continuously monitoring vital signs and response to stimuli, and the goal of this monitoring is to balance the amount of drug inhaled and/or infused with the depth of anaesthesia.</p> Signup and view all the answers

What is the significance of rapid and pleasant induction in general anaesthesia?

<p>Rapid and pleasant induction is a desirable component of anaesthesia because it helps to reduce anxiety and stress in the patient, and it allows for a smoother transition to the maintenance phase.</p> Signup and view all the answers

How do the desirable components of anaesthesia relate to the patient's safety and comfort during surgery?

<p>The desirable components of anaesthesia, including rapid and pleasant induction, wide margin of safety, and absence of toxic/adverse effects, are important for the patient's safety and comfort during surgery.</p> Signup and view all the answers

What is the primary mechanism of action of neuromuscular blockers?

<p>Blockade of nicotinic acetylcholine receptors in the neuromuscular junction</p> Signup and view all the answers

What is the benefit of using neuromuscular blockers during surgery?

<p>Rapid recovery from anaesthesia and reduced postoperative respiratory depression</p> Signup and view all the answers

What is the mechanism of action of nondepolarizing blockers at low doses?

<p>Competitive blockade of acetylcholine at the nicotinic receptors</p> Signup and view all the answers

What is the primary role of ondansetron in anaesthesia?

<p>Reduces postoperative nausea and vomiting</p> Signup and view all the answers

What is the effect of opioids on anaesthesia?

<p>Reduces the dosage of general anaesthetics required</p> Signup and view all the answers

What is the primary goal of maintenance in general anaesthesia?

<p>Providing optimal surgical conditions</p> Signup and view all the answers

What is the role of inhalation agents in general anaesthesia?

<p>Maintains anaesthesia during surgery</p> Signup and view all the answers

What is the significance of rapid and pleasant induction in general anaesthesia?

<p>Improving patient comfort and safety during surgery</p> Signup and view all the answers

What is the primary concern when using opioids in anaesthesia?

<p>Respiratory depression</p> Signup and view all the answers

What is the mechanism of action of fentanyl in anaesthesia?

<p>Provides analgesia</p> Signup and view all the answers

Study Notes

General Anaesthesia

  • General anaesthesia is a medically induced state of unconsciousness with loss of protective reflexes, resulting from the administration of one or more general anaesthetic agents.
  • It is a generalized, reversible depression of the CNS such that response to and perception of all stimuli is lost.
  • General anaesthetics (GAs) are drugs which cause reversible loss of all sensation and consciousness.

Classification of General Anaesthetics

  • Intravenous anaesthetics:
  • Barbiturates (thiopental)
  • Benzodiazepines (midazolam)
  • Opioids (fentanyl)
  • Miscellaneous (propofol, etomidate)
  • Inhalation anaesthetics:
  • Volatile liquids (halothane)
  • Gas (nitrous oxide)

Pre-Aneasthetic Medications

  • Reduce anxiety, relieve pain and reduce side effects
  • Examples:
  • Benzodiazepines (midazolam, diazepam)
  • Barbiturates (pentobarbital)
  • Antihistamines (diphenhydramine)
  • Anticholinergics (scopolamine, glycopyrrolate)
  • Opioids (fentanyl)
  • Antiemetics (ondansetron)

Neuromuscular Blockers

  • Inhibit reflexes to allow for tracheal intubation
  • Cause muscle relaxation which is required for surgery
  • There are two types:
  • Non-depolarizing blockers
  • Depolarizing blockers
  • Mechanism of action: blockade of nicotinic acetylcholine receptors in the neuromuscular junction

Mechanism of Action of Non-Depolarizing Blockers

  • Competitively block acetylcholine (ACh) at the nicotinic receptors
  • Prevent depolarization of the muscle cell membrane and inhibit muscular contraction

Depolarizing Blockers

  • Succinylcholine is the only depolarizing muscle relaxant in use today
  • Attaches to the nicotinic receptor and acts like ACh to depolarize the junction
  • Causes the opening of the sodium channel associated with the nicotinic receptors, resulting in depolarization of the receptor
  • Leads to a transient twitching of the muscle (fasciculations)
  • Continued binding of the depolarizing agent renders the receptor incapable of transmitting further impulses

Phases of Depolarizing Blockers

  • Phase I:
  • Causes the opening of the sodium channel associated with the nicotinic receptors, resulting in depolarization of the receptor
  • Leads to a transient twitching of the muscle (fasciculations)
  • Phase II:
  • Resulting in resistance to depolarization and flaccid paralysis

Malignant Hyperthermia

  • Rare life-threatening condition induced by halogenated hydrocarbon anaesthetics or succinylcholine
  • Autosomal dominant disorder

General Anaesthesia

  • General anaesthesia involves the use of pre-anaesthetic medications, neuromuscular blockers, intravenous anaesthetics, and inhalation anaesthetics.

Types of Anaesthetics

  • Pre-anaesthetic medications:
    • Reduce anxiety, relieve pain, and reduce side effects
    • Examples: benzodiazepines (midazolam, diazepam), barbiturates (pentobarbital), antihistamines (diphenhydramine), and anticholinergics (scopolamine, glycopyrrolate)
  • Neuromuscular blockers:
    • Facilitate tracheal intubation and surgery
  • Intravenous anaesthetics:
    • Mainly used to induce anaesthesia
    • Examples: barbiturates (thiopental), benzodiazepines (midazolam), opioids (fentanyl), and miscellaneous (propofol, etomidate)
  • Inhalation anaesthetics:
    • Mainly used to maintain anaesthesia
    • Examples: volatile liquids (halothane) and gas (nitrous oxide)

Stages of General Anaesthesia

  • Stage 1: Analgesia and amnesia
  • Stage 2: Excitement
    • Patient displays delirium and possibly combative behaviour
    • A rise and irregularity in blood pressure and respiration occur, as well as a risk of laryngospasm
  • Stage 3: Surgical anaesthesia
    • Gradual loss of muscle tone and reflexes as the CNS is further depressed
    • Regular respiration and relaxation of skeletal muscles with eventual loss of spontaneous movement
  • Stage 4: Medullary paralysis
    • Severe depression of the respiratory and vasomotor centres occurs
    • Ventilation and/or circulation must be supported to prevent death

Factors in Selection of Anaesthetics

  • Factors considered:
    • Status of organ systems (cardiovascular, respiratory, liver and kidney, nervous system, pregnancy)
    • Immobility and muscle relaxation
    • Abolition of somatic and autonomic reflexes

Desirable Components of Anaesthesia

  • Rapid and pleasant induction
  • Rapid changes in the depth of anaesthesia
  • Wide margin of safety
  • Absence of toxic/adverse effects
  • Adequate relaxation of muscles

Induction and Maintenance

  • Induction:
    • Time from administration of a potent anaesthetic to development of effective anaesthesia
    • General anaesthesia in adults is normally induced with an IV agent like propofol, producing unconsciousness in 30 to 40 seconds
  • Maintenance:
    • Provides sustained anaesthesia
    • After administering the anaesthetic, vital signs and response to stimuli are monitored continuously to balance the amount of drug inhaled and/or infused with the depth of anaesthesia

Neuromuscular Blockers

  • Blockade of nicotinic acetylcholine receptors in the neuromuscular junction, blocking cholinergic transmission between motor nerve endings and skeletal muscle.
  • Possess chemical similarities to ACh, acting as antagonists or agonists at receptors on the motor endplate.
  • Clinically useful during surgery to facilitate tracheal intubation and provide complete muscle relaxation at lower anaesthetic doses.

MOA of Nondepolarizing Blockers

  • At low doses, competitively block ACh at the nicotinic receptors, preventing depolarization of the muscle cell membrane and inhibiting muscular contraction.
  • At high doses, block the ion channels of the motor endplate, leading to further weakening of neuromuscular transmission and reducing the ability of cholinesterase inhibitors to reverse the actions of the non-depolarizing blockers.

MOA of Depolarizing Blockers

  • Depolarize the plasma membrane of the muscle fibre, similar to the action of ACh.
  • More resistant to degradation by acetylcholinesterase (AChE) and can persistently depolarize the muscle fibres.
  • Succinylcholine is the only depolarizing muscle relaxant in use today, attaching to the nicotinic receptor and acting like ACh to depolarize the junction.

Phase I of Depolarizing Blockers

  • Causes the opening of the sodium channel associated with the nicotinic receptors, resulting in depolarization of the receptor.
  • Leads to a transient twitching of the muscle (fasciculations).
  • Continued binding of the depolarizing agent renders the receptor incapable of transmitting further impulses.

Phase II of Depolarizing Blockers

  • Results in resistance to depolarization and flaccid paralysis.

Malignant Hyperthermia

  • Autosomal dominant disorder induced by halogenated hydrocarbon anaesthetics or succinylcholine.
  • Rare life-threatening condition characterized by uncontrolled increase in skeletal muscle oxidative metabolism, resulting in:
    • Hyperpyrexia
    • Circulatory collapse
    • Death (if not treated immediately)

Dantrolene

  • Used to treat malignant hyperthermia.
  • Blocks release of calcium from muscle cells, reducing heat production and relaxing muscle tone.
  • Should always be at hand when triggering agents are administered.
  • Patients must be monitored for respiratory, circulatory, and renal problems.

Intravenous Anaesthetics

  • Primarily used for induction of anaesthesia.
  • Rapid onset (seconds) and rapid awakening (minutes).
  • Danger of overdose due to irrevocability of IV injection.
  • Fraction binds to plasma proteins, cerebral circulation, and concentration gradient into the brain.
  • Rate at which drug reaches the brain is dependent on:
    • Concentration of arterial unbound free drug
    • Lipid solubility
    • Degree of ionization

Mechanism of Action of Intravenous Anaesthetics

  • Exact mechanism of action unknown.
  • Recovery is due to redistribution, where the drug diffuses into other tissues, and the plasma concentration falls, allowing the drug to diffuse out of the CNS down the reverse concentration gradient.

Opioids

  • Provide analgesia (fentanyl).

Pre-anaesthetic Medications

  • Decrease the dosage of general anaesthetics.
  • Reduce the risk of stomach content aspiration, post-operative nausea, and vomiting (ondansetron).

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Learn about the mechanism of non-depolarizing blockers in anesthesia, including their effects on neuromuscular transmission and the action of cholinesterase inhibitors.

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