Podcast
Questions and Answers
What is the primary aim of general anesthesia?
What is the primary aim of general anesthesia?
Which of the following is NOT classified as a general anesthetic?
Which of the following is NOT classified as a general anesthetic?
Which type of anesthesia targets specific nerve pathways to block sensation in a larger area?
Which type of anesthesia targets specific nerve pathways to block sensation in a larger area?
Inhalational anesthetics are administered through which method?
Inhalational anesthetics are administered through which method?
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Which of the following statements about balanced anesthesia is true?
Which of the following statements about balanced anesthesia is true?
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Which physiological function is primarily affected by anesthetics?
Which physiological function is primarily affected by anesthetics?
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What characterizes the state of general anesthesia?
What characterizes the state of general anesthesia?
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Which type of local anesthetic is linked with the amide classification?
Which type of local anesthetic is linked with the amide classification?
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What is a possible adverse effect associated with Ketamine?
What is a possible adverse effect associated with Ketamine?
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Which mechanism of action does Etomidate primarily utilize?
Which mechanism of action does Etomidate primarily utilize?
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In which scenario is Ketamine indicated for use?
In which scenario is Ketamine indicated for use?
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What is a clinical advantage of using Thiopental?
What is a clinical advantage of using Thiopental?
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What is one contraindication for the use of Ketamine?
What is one contraindication for the use of Ketamine?
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Which anesthetic has a rapid onset of action, lasting about 10-20 seconds?
Which anesthetic has a rapid onset of action, lasting about 10-20 seconds?
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Which drug is known to cause hypotension and bradycardia as adverse effects?
Which drug is known to cause hypotension and bradycardia as adverse effects?
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What type of anesthesia does Ketamine produce?
What type of anesthesia does Ketamine produce?
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What is a key contraindication for the use of thiopental in neurosurgery?
What is a key contraindication for the use of thiopental in neurosurgery?
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Which characteristic of isoflurane contributes to its clinical advantage in maintaining general anesthesia?
Which characteristic of isoflurane contributes to its clinical advantage in maintaining general anesthesia?
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What adverse effect is associated with sevoflurane use?
What adverse effect is associated with sevoflurane use?
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How does thiopental primarily affect cerebral metabolism?
How does thiopental primarily affect cerebral metabolism?
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Which mechanism of action best describes the function of isoflurane?
Which mechanism of action best describes the function of isoflurane?
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What pharmacokinetic property is shared by both halothane and isoflurane?
What pharmacokinetic property is shared by both halothane and isoflurane?
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What is a consequence of the interaction between opioids and thiopental?
What is a consequence of the interaction between opioids and thiopental?
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In which situation is the use of sevoflurane contraindicated?
In which situation is the use of sevoflurane contraindicated?
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What adverse effect is specifically associated with halothane use?
What adverse effect is specifically associated with halothane use?
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Which of the following conditions is a contraindication for the use of nitrous oxide?
Which of the following conditions is a contraindication for the use of nitrous oxide?
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What pharmacokinetic characteristic is true for halothane?
What pharmacokinetic characteristic is true for halothane?
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How does nitrous oxide affect the potency of other inhalational anesthetics?
How does nitrous oxide affect the potency of other inhalational anesthetics?
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What mechanism of action is primarily associated with nitrous oxide?
What mechanism of action is primarily associated with nitrous oxide?
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Which of the following adverse effects can result from the use of nitrous oxide during recovery?
Which of the following adverse effects can result from the use of nitrous oxide during recovery?
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What is a primary clinical advantage of halothane compared to other anesthetics?
What is a primary clinical advantage of halothane compared to other anesthetics?
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Which clinical use is indicated for local anesthetics?
Which clinical use is indicated for local anesthetics?
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What is the primary mechanism of action of bupivacaine?
What is the primary mechanism of action of bupivacaine?
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Which of the following describes the metabolism of bupivacaine?
Which of the following describes the metabolism of bupivacaine?
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What is a major clinical advantage of bupivacaine?
What is a major clinical advantage of bupivacaine?
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What is a common adverse effect associated with bupivacaine?
What is a common adverse effect associated with bupivacaine?
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Which of the following is NOT a desirable characteristic of local anesthetics?
Which of the following is NOT a desirable characteristic of local anesthetics?
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How is bupivacaine primarily excreted from the body?
How is bupivacaine primarily excreted from the body?
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For which condition is bupivacaine contraindicated?
For which condition is bupivacaine contraindicated?
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What is the typical duration of action for bupivacaine?
What is the typical duration of action for bupivacaine?
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What effect do vasoconstrictors such as epinephrine have when added to local anesthetics?
What effect do vasoconstrictors such as epinephrine have when added to local anesthetics?
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Which of the following is a potential drug interaction involving bupivacaine?
Which of the following is a potential drug interaction involving bupivacaine?
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Which local anesthetic has the longest duration of action?
Which local anesthetic has the longest duration of action?
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What is a common use of bupivacaine in clinical practice?
What is a common use of bupivacaine in clinical practice?
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What is the primary route of administration for local anesthetics?
What is the primary route of administration for local anesthetics?
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What common adverse effect is associated with high doses of lidocaine?
What common adverse effect is associated with high doses of lidocaine?
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Which of the following statements is true regarding the pharmacokinetics of procaine?
Which of the following statements is true regarding the pharmacokinetics of procaine?
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Study Notes
Anaesthetics
- Anaesthesia is a reversible state of unconsciousness, analgesia, amnesia, and muscle relaxation used during surgical and diagnostic procedures.
- Anaesthetics are broadly classified into two main categories: General and Local.
Objectives
- Understand the classification and mechanisms of action of anaesthetics.
- Explain the pharmacokinetics and pharmacodynamics of anaesthetics.
- Identify the clinical uses, contraindications, adverse effects, and drug interactions of different anaesthetics.
- Discuss the application of anaesthetics in clinical scenarios.
Types of Anaesthesia
- General Anaesthesia: Induces unconsciousness and total body anaesthesia.
- Local Anaesthesia: Blocks sensation in a specific area without affecting consciousness.
- Regional Anaesthesia: Blocks sensation to a larger area by targeting specific nerve pathways (e.g., spinal or epidural).
Pathophysiology of Pain and Consciousness
- Pain signals travel via peripheral nerves to the central nervous system (CNS).
- Consciousness arises from interactions between the cortex and subcortical structures.
- Anesthetics modulate synaptic transmission and neuronal activity in these pathways.
Classification of Anaesthetics
- General Anesthetics:
- Inhalational: Administered via inhalation (e.g., Nitrous Oxide, Isoflurane, Sevoflurane).
- Intravenous: Administered through the IV route (e.g., Propofol, Ketamine, Thiopentone, Etomidate).
- Balanced anaesthesia combines intravenous and inhalational anesthetics.
- Local Anesthetics: Block sensory nerve conduction in a specific area without affecting consciousness.
- Ester-linked (e.g., Procaine, Tetracaine).
- Amide-linked (e.g., Lidocaine, Bupivacaine, Ropivacaine).
General Anaesthesia: Aim
- Pain relief
- Induce Sleep
- Muscle relaxation
- Unconsciousness
- Analgesia (absence of pain)
- Amnesia (loss of memory of procedure)
- Skeletal muscle relaxation
- Loss of reflexes
Modern Anesthesiology (GAS)
- Employs a balanced anesthesia approach using a combination of intravenous and inhaled drugs, tailored to the procedure and patient.
- An ideal anesthetic drug induces rapid and smooth loss of consciousness, quickly reversible, and has a wide margin of safety.
Potency of Inhaled Anesthetics
- The minimum alveolar concentration (MAC) is the concentration that causes immobility in 50% of patients.
- The lower the MAC, the more potent the inhaled anesthetic.
- Factors affecting MAC include age, temperature, and presence of other drugs.
Intravenous Anesthetics: Propofol
- MOA: Potentiates GABA-A receptor activity, enhancing chloride ion influx and hyperpolarizing neuronal membranes.
- Indications: Induction and maintenance of anesthesia, sedation during diagnostic or minor surgical procedures, sedation for mechanically ventilated patients in ICU.
- Contraindications: Hypersensitivity to propofol or its components, disorders of fat metabolism.
- Pharmacokinetics: Rapid onset (30-60 seconds), short duration (3-10 minutes), hepatic metabolism to inactive metabolites, renal excretion.
Propofol – Drug Interactions & Adverse Effects
- Drug Interactions: Potentiation of CNS depression with opioids, benzodiazepines, or alcohol, increased hypotensive effects with antihypertensives.
- Adverse Effects: Hypotension and bradycardia, respiratory depression, pain at the injection site, propofol infusion syndrome (rare but severe), Clinical Advantages include smooth induction and recovery, minimal postoperative nausea and vomiting, and antiemetic properties.
Ketamine
- MOA: NMDA receptor antagonist, inhibiting excitatory glutamate signaling, producing dissociative anesthesia.
- Indications: Emergency surgeries, analgesia for severe pain, pediatric anesthesia, sedation during short, painful procedures.
- Contraindications: Severe hypertension, cardiovascular disease, intracranial hypertension, psychiatric disorders.
- Pharmacokinetics: Rapid onset (30-60 seconds), duration 5-10 minutes (IV), longer for IM, hepatic metabolism to active metabolite (norketamine), renal excretion.
Ketamine – Drug Interactions & Adverse Effects
- Drug Interactions: Increased risk of hypertension with sympathomimetics, potentiates CNS depression with benzodiazepines or opioids.
- Adverse Effects: Emergence reactions (e.g., vivid dreams, hallucinations), hypertension and tachycardia, increased intracranial and intraocular pressure. Clinical Advantages include preserved airway reflexes, spontaneous respiration, potent analgesic effects, and minimal cardiovascular depression.
Etomidate
- MOA: Potentiates GABA-A receptor activity, causing sedation without significant analgesia.
- Indications: Induction of anesthesia, especially in hemodynamically unstable patients.
- Contraindications: Known hypersensitivity, chronic adrenal insufficiency.
- Pharmacokinetics: Rapid onset (10-20 seconds), duration 4-8 minutes, hepatic and plasma esterase metabolism, renal and biliary excretion.
Etomidate – Drug Interactions and Adverse Effects
- Drug Interactions: Enhanced respiratory depression with opioids or benzodiazepines, suppresses cortisol synthesis when used with corticosteroid inhibitors.
- Adverse Effects: Adrenal suppression, myoclonus during induction, nausea, and vomiting, Additional advantages include minimal cardiovascular and respiratory effects.
Thiopentone
- MOA: A barbiturate enhancing GABA-A receptor activity, prolonging chloride channel opening and causing CNS depression.
- Indications: Induction of anesthesia, rapid control of seizures, reduced intracranial pressure in neurosurgery.
- Contraindications: Severe cardiovascular or respiratory depression, porphyria, hypersensitivity to barbiturates.
- Pharmacokinetics: Ultra-rapid onset (10-20 seconds), short duration (5-10 minutes), hepatic metabolism to active metabolites, renal excretion.
Thiopentone – Drug Interactions and Adverse Effects
- Drug Interactions: Potentiates respiratory and CNS depression with opioids or sedatives, enhanced effects with CYP450 inhibitors.
- Adverse Effects: Respiratory depression and apnea, hypotension and myocardial depression, laryngospasm during induction, pain at injection site or tissue necrosis if extravasated.
- Clinical Advantages include ultra-rapid onset, and effectiveness in reducing cerebral metabolic rate and intracranial pressure.
Inhalational Anesthetics, Isoflurane
- MOA: Potentiates GABA and glycine receptor activity, reducing excitatory NMDA receptor activity.
- Indications: Maintenance of general anesthesia.
- Contraindications: Malignant hyperthermia susceptibility, severe hepatic dysfunction.
- Pharmacokinetics: Moderate onset, minimal hepatic metabolism, primarily exhaled unchanged.
Inhalational Anesthetics, Isoflurane – Drug Interactions & Adverse Effects
- Drug Interactions: Increased hypotension with beta-blockers, enhanced respiratory depression with opioids.
- Adverse Effects: Respiratory depression, postoperative shivering, malignant hyperthermia (rare). Clinical Advantages include a stable cardiac profile.
Sevoflurane
- MOA: Enhances GABA-A receptor activity, depressing CNS excitability.
- Indications: Induction and maintenance of anesthesia.
- Contraindications: Malignant hyperthermia susceptibility, severe renal impairment.
- Pharmacokinetics: Rapid onset, minimal hepatic metabolism, primarily exhaled unchanged.
Sevoflurane – Drug Interactions & Adverse Effects
- Drug Interactions: Increased sedation with CNS depressants.
- Adverse Effects: Nephrotoxicity (due to compound A production). nausea and vomiting.
- Clinical Advantages: Non-irritating to the airway, rapid induction and emergence.
Halothane
- MOA: Potentiates GABA-A receptor activity, enhancing chloride ion influx and neuronal inhibition, reduces excitatory neurotransmitter release.
- Indications: Maintenance of general anesthesia, pediatric anesthesia.
- Contraindications: Malignant hyperthermia susceptibility, severe hepatic dysfunction, cardiovascular instability.
- Pharmacokinetics: Moderate onset, 20% metabolized in the liver, primarily exhaled; metabolites are hepatotoxic.
Halothane – Drug Interactions & Adverse Effects
- Drug Interactions: Potentiates hypotension with beta-blockers, increases arrhythmogenic effects with catecholamines, and CNS depression with opioids or sedatives.
- Adverse Effects: Halothane hepatitis (idiosyncratic hepatotoxicity), cardiac arrhythmias (sensitizes the heart to catecholamines), malignant hyperthermia, postoperative nausea and vomiting.
- Clinical Advantages: Smooth induction and maintenance, non-irritating to the airway, suitable for pediatric patients.
Nitrous Oxide
- MOA: Antagonizes NMDA receptors, inhibiting excitatory neurotransmission while modulating GABA-A receptors; enhancing inhibitory effects.
- Indications: Maintenance of general anesthesia, analgesia, used as a carrier gas for volatile anesthetics in minor procedures (e.g., dental, obstetric).
- Contraindications: Pneumothorax, bowel obstruction, vitamin B12 deficiency, severe cardiovascular or respiratory compromise.
- Pharmacokinetics: Rapid onset, elimination almost entirely exhaled unchanged.
Nitrous Oxide – Drug Interactions & Adverse Effects
- Drug Interactions: Increases potency of other inhalational anesthetics, augments CNS depression with sedatives or opioids.
- Adverse Effects: Diffusion hypoxia, nausea, vomiting, long-term use can lead to megaloblastic anemia or neuropathy, due to methionine synthase inhibition.
- Clinical Advantages: Excellent analgesic properties, rapid onset and recovery, minimal cardiovascular and respiratory effects.
Local Anesthetics: Desirable Characteristics
- Rapid onset of action
- Brief, reversible block of nerve conduction
- Low degree of systemic toxicity
- Soluble in water and stable in solution
- Effective on all parts of the nervous system
Local Anesthetics: Lidocaine
- MOA: Blocks voltage-gated sodium channels, preventing nerve depolarization and impulse propagation.
- Indications: Local infiltration anesthesia, nerve blocks, antiarrhythmic agent.
- Contraindications: Hypersensitivity to amide-linked agents, severe hepatic impairment.
- Pharmacokinetics: Rapid onset (2-5 minutes), duration (1-2 hours), hepatic metabolism (CYP450 enzymes), renal excretion.
Local Anesthetics: Lidocaine; Drug Interactions & Adverse Effects
- Drug Interactions: Increased toxicity with CYP450 inhibitors, additive CNS depression with sedatives.
- Adverse Effects: CNS toxicity (e.g., seizures, dizziness), cardiovascular depression (at high doses).
- Clinical Advantages: Versatile; can be used with vasoconstrictors to prolong action.
Bupivacaine
- MOA: Blocks sodium channels, stabilizing neuronal membranes and reducing excitability.
- Indications: Regional anesthesia (e.g., epidural, spinal), postoperative pain management.
- Contraindications: Cardiac arrhythmias or heart block.
- Pharmacokinetics: Moderate onset (10-20 minutes), long duration(3-9 hours), hepatic metabolism and renal excretion.
Bupivacaine – Drug Interactions & Adverse Effects
- Drug Interactions: Increased toxicity with CYP450 inhibitors.
- Adverse Effects: Cardiotoxicity (e.g., arrhythmias), CNS toxicity at high doses.
- Clinical Advantages: Long duration of action.
Procaine
- MOA: Blocks sodium channels, preventing nerve impulse propagation.
- Indications: Local infiltration anesthesia(injections).
- Contraindications: Hypersensitivity to ester-linked agents.
- Pharmacokinetics: Slow onset, short duration(30-60 minutes), plasma cholinesterase metabolism, renal excretion.
Procaine; Drug Interactions & Adverse Effects
- Drug Interactions: Antagonism of sulfonamide antibiotics.
- Adverse Effects: Allergic reactions (due to PABA production).
- Clinical Advantages: Low systemic toxicity.
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Description
This quiz provides a comprehensive overview of anaesthetics, including their classification, mechanisms of action, and pharmacokinetics. It covers general, local, and regional anaesthesia, along with their clinical applications and potential side effects. Test your knowledge of the essential concepts surrounding anaesthesia in surgical and diagnostic procedures.
