Questions and Answers
What is the primary mechanism of propofol metabolism?
What is the characteristic of propofol that allows it to be used in patients with hepatic or renal dysfunction?
What is the benefit of using propofol for general anesthesia maintenance?
What is the effect of propofol on bronchomotor tone in healthy and asthmatic patients?
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What is the effect of high doses of propofol and barbiturates on EEG activity?
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What is the mechanism of decreased systemic blood pressure caused by propofol?
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What is the effect of propofol on intracranial pressure?
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What is the effect of propofol on pharyngeal contractile force?
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What is the effect of propofol on cerebral autoregulation in response to changes in CO2?
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What is the primary mechanism of action of neuraxial neostigmine in producing analgesia?
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What is a significant advantage of dexmedetomidine over clonidine?
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What is a major side effect of epidural dexmedetomidine in cesarean sections?
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What is the benefit of using epidural dexmedetomidine in cesarean sections?
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What is the primary mechanism by which benzodiazepines interact with GABA receptors?
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What is the result of increased chloride conductance in post-synaptic cells following benzodiazepine binding?
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What is a characteristic of the effects of benzodiazepines on adenosine degradation?
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What is a potential side effect of benzodiazepines when combined with other CNS depressants?
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What is a characteristic of etomidate's effect on the cardiovascular system?
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What is a effect of etomidate on hepatic and renal function?
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What is the effect of baclofen on neuronal transmission in the cerebral cortex, basal ganglia, thalamus, cerebellum, and spinal cord?
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What is the primary mechanism of action of ketorolac?
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What is the effect of magnesium sulfate on NMDA receptors?
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What is the functional role of glutamate at the spinal cord level?
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What is the therapeutic use of intrathecal baclofen?
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What is the primary concern with the use of magnesium sulfate?
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What is the effect of baclofen on electrolyte movement resulting in hyperpolarization and inhibition of glutamate and substance P?
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Which of the following neurotransmitters are inhibitory at the spinal cord level?
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What is Aquavan?
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What is the mechanism of action of propofol?
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What are GABA receptors?
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What is the result of propofol's high lipid solubility?
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What is unique about the clearance of propofol?
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What is unique about the context sensitive half time of propofol?
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What characteristics make propofol neuroprotective?
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Which of the following are beneficial side effects of propofol?
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What are the clinical manifestations of PRIS?
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Which patient population tends to be affected by propofol-related infusion syndrome (PRIS)?
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How does propofol have antioxidant properties?
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How do propofol and etomidate enhance the affinity of GABA for GABAA?
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What is commonly observed after etomidate injection?
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Etomidate has a longer CSHT than propofol
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How are propofol and etomidate metabolized?
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What is a common side effect of etomidate?
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What effect does etomidate have on the respiratory system?
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Where do benzodiazepines bind on the GABA-A receptor?
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What is common amongst all benzodiazepines?
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What effect do benzodiazepines have on opioids?
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What is unique about the solubility of midazolam?
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What are the CNS effects of propofol?
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What are the respiratory effects of propofol?
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What effect does propofol have on the cardiovascular system?
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CSHT in midazolam infusions reflect the duration of infusion
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Why has midazolam replaced diazepam in clinical anesthesia? (select 2)
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What is unique about the duration of action for diazepam?
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What effect does diazepam have on the cardiovascular system?
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What is the drug of choice for delirium tremens?
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Which benzodiazepine is more potent than midazolam or diazepam?
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Ativan is ____ lipid soluble with a ___ onset than Versed
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Why is Ativan not typically used in anesthesia induction?
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What is remimazolam?
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What is the mechanism of action of flumazenil?
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What is a precaution when administering flumazenil?
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What is the main difference in the mechanism of action between benzodiazepines and barbiturates?
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High doses of which sedative drug class can directly activate the GABA-A receptor?
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What compound do thiobarbiturates have?
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What are the benefits of propofol compared to barbiturates?
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Which of the following anesthetics is thought to possess 'neuroprotective' properties and can be used for cerebral protection during incomplete brain ischemia?
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What is the mechanism of action of ketamine?
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Ketamine is a racemic mixture. Which isomer is associated with faster clearance and more analgesia?
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How does ketamine produce sedation?
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What are the cardiovascular effects of ketamine?
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How is ketamine metabolized?
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What precautions should be taken when using ketamine?
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Ketamine possesses anticonvulsant activity
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Ketamine is a potent cerebral vasodilator.
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What is the mechanism of action of dexmedetomidine?
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What are some potential side effects of dexmedetomidine?
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Study Notes
Propofol
- Propofol is taken up by lungs and then distributed to fat
- Clearance exceeds hepatic blood flow, and volume of distribution (Vd) is very large
- Pulmonary uptake is significant, and it is metabolized by CYP450 hepatic enzymes via oxidation
- Conjugated to water-soluble metabolites and excreted by kidneys
- Dysfunction of hepatic or renal systems does not significantly impair propofol
Clinical Applications
- Induction drug of choice for anesthesia: 1.5-2.5 mg/kg, with children needing larger doses and geriatrics needing smaller doses
- Sedation: 25-100 mcg/kg/min, with prolonged infusion in pediatric patients leading to metabolic acidosis, lipemic plasma, bradycardia, and heart failure
- Maintenance: 100-300 mcg/kg/min, often combined with a short-acting opioid or inhalation agent, and associated with minimal PONV and prompt awakening
Side Effects
- Reduced PONV
- Antipruritic and anticonvulsant activity
- Attenuation of bronchoconstriction in healthy and asthmatic patients, resulting in bronchodilation
- Synergistic with other CNS depressants, e.g., synthetic opioids
- Decreases CMRO2, CBF, ICP, and preserves cerebral autoregulation in response to changes in CO2
- High doses produce burst suppression, and cortical SEE potentials are not significantly affected
- Amnestic effects are similar to Versed
Cardiovascular Effects
- Decreases systemic BP due to decreased SVR and CO
- Decreased SVR is due to relaxation of vascular smooth muscle and inhibition of sympathetic vasoconstriction
- Decreased CO is due to negative inotropic effect and inhibition of the trans-sarcolemnal calcium influx
- No change in HR, but CV effects are potentiated in hypovolemia, elderly, and LV dysfunction
- Effects are reversed by laryngosenephrine, which stimulates and can reverse the decreased BP/SVR and CO effects
Respiratory Effects
- Dose-dependent depression of RR and Vt, and central depressant response to hypoxemia
- Apnea frequently occurs, and respiratory effects are potentiated by opioids
- Hypoxic pulmonary vasoconstriction remains intact, but decreases pharyngeal contractile force, relaxing muscles in the pharynx that keep the airway open
Other Effects
- Hepatic and renal function rarely affected
- Lowers IOP during induction and intubation
- No effects on coagulation and platelet function
- Does not produce seizure activity, has anticonvulsant properties, and enhances SSE potential monitoring
- Carries a significant abuse potential, supports bacterial growth, and increases frequency of excitatory spikes
Benzodiazepines
- Provide anxiolysis, sedation, anticonvulsant actions, spinal cord-mediated relaxation, and anterograde amnesia
- GABA receptors concentrated in CNS
- Mechanism of action involves binding between the alpha and gamma subunit to increase the affinity of the receptor for GABA, resulting in increased chloride conductance and hyperpolarization of the post-synaptic cell membrane
- Ceiling effect and low toxicity, with differences in onset and duration of action reflecting differences in potency, lipid solubility, and pharmacokinetics
- All are highly protein bound to albumin and highly lipid soluble, with a decrease in adenosine degradation having cardioprotective effects
- Side effects include fatigue and drowsiness, loss of coordination and diminished cognitive function, profound amnesia, and synergistic effects with other CNS depressants
Dexmedetomidine
- A selective α2 receptor agonist with higher receptor affinity and selectivity for α2 receptors than clonidine
- Fewer hemodynamic systemic effects, with intrathecal dose: 3 ug, and no neurotoxicity reported for intrathecal or epidural administration
- Major side effects are bradycardia and hypotension
Epidural Dex
- Prolongs neuraxial sensory and motor blockade, decreases intraoperative anesthetic requirements, and improves postoperative analgesia
- Decreases heart rate and BP in C-sections, with a black box warning for hypotension and bradycardia in C-sections
Neuraxial Neostigmine
- Inhibits acetylcholinesterase and prevents the metabolism of acetylcholine, with analgesic effects due to stimulation of muscarinic cholinergic receptors
- Prolongs analgesia and minimal side effects with intrathecal (10-100 ug) or epidural (100-200 ug) use, and approved for treatment of neuropathic pain
- Side effects include dizziness, confusion, ataxia, abnormal gait, memory impairment, and suicidal ideation
Baclofen
- A GABA-B receptor agonist suppressing neuronal transmission in the cerebral cortex, basal ganglia, thalamus, cerebellum, and spinal cord
- Actions at laminae II & III, increasing potassium conductance and inhibiting calcium conductance, resulting in hyperpolarization and inhibition of glutamate and substance P release
- Intrathecal baclofen is effective in treating pain with MS, CRPS type I, and low back pain
Ketorolac
- A cyclo-oxygenase inhibitor, with COX1 and COX2 facilitating production of prostaglandins leading to hyperalgesia and allodynia after injury
- Intrathecal ketorolac appears to have little analgesia benefit
Magnesium Sulfate
- Acts on NMDA receptors by regulating calcium influx into cells, with magnesium being the natural antagonist to calcium
- Does have some analgesic effect when administered intrathecally or in the epidural space, but animal studies have reported neurotoxicity, and human safety is not proven
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