Intravenous Anesthetics Flashcards
What does repetitive administration of barbiturates result in?
It saturates the peripheral compartments, minimizing redistribution and making the duration of action more dependent on elimination. This is known as context sensitivity.
How do barbiturates affect cerebral blood flow?
Barbiturates constrict the cerebral vasculature, leading to a decrease in cerebral blood flow, cerebral blood volume, and intracranial pressure.
What is a respiratory risk associated with benzodiazepine induction?
Even small intravenous doses of diazepam and midazolam can result in respiratory arrest.
How does ketamine differ from other anesthetic agents in terms of cardiovascular effects?
Ketamine increases arterial blood pressure, heart rate, and cardiac output, particularly after rapid bolus injections.
What effect does etomidate have on hormone synthesis?
Induction doses of etomidate transiently inhibit enzymes involved in cortisol and aldosterone synthesis.
What precaution must be taken when handling propofol?
Propofol formulations can support bacterial growth, so sterile technique must be followed, and it should be administered within 6 hours of opening the ampule.
What are the primary mechanisms of action of barbiturates?
Barbiturates depress the reticular activating system in the brainstem and potentiate the action of GABA by increasing the duration of chloride ion channel openings.
What determines the hypnotic potency and anticonvulsant activity of barbiturates?
Substitution at carbon C5 determines potency, with long-branched chains conveying more potency and phenyl groups contributing to anticonvulsant activity.
What is the effect of replacing oxygen at C2 with a sulfur atom in barbiturates?
It increases lipid solubility, leading to greater potency, more rapid onset, and shorter duration of action, as seen in thiopental and thiamylal.
How does the distribution of thiopental affect its duration of action?
The duration of action is determined by redistribution to peripheral compartments, which lowers plasma and brain concentration within 20-30 minutes.
How does the pharmacokinetic profile of methohexital differ from thiopental?
Methohexital is cleared more rapidly by the liver than thiopental, leading to faster recovery of psychomotor function after a sleep dose.
How does barbiturate biotransformation occur?
Barbiturates are principally biotransformed via hepatic oxidation to inactive water-soluble metabolites.
What are the cardiovascular effects of barbiturates?
Barbiturates cause a decrease in blood pressure and an increase in heart rate, with hemodynamic responses varying based on the rate of administration and other factors.
What respiratory effects do barbiturates have?
Barbiturates depress the medullary ventilatory center, leading to decreased ventilatory response to hypercapnia and hypoxia, and often cause apnea after induction.
How do barbiturates affect cerebral oxygen consumption?
Barbiturates decrease cerebral oxygen consumption by up to 50%, without negatively impacting cerebral blood flow.
What is the effect of barbiturates on renal function?
Barbiturates reduce renal blood flow and glomerular filtration rate in proportion to the fall in blood pressure.
What is the immunological effect of sulfur-containing thiobarbiturates?
Sulfur-containing thiobarbiturates can evoke mast cell histamine release in vitro, which may affect asthmatic or atopic patients.
How do benzodiazepines increase chloride ion channel openings?
Benzodiazepines bind to a different site on the GABA-A receptor, increasing the frequency of chloride ion channel openings.
What effect does midazolam’s imidazole ring have on its solubility?
The imidazole ring of midazolam increases its water solubility at low pH, facilitating its absorption.
What is the effect of diazepam and lorazepam on cardiovascular function?
They display minimal cardiovascular depressant effects, but can decrease arterial blood pressure, cardiac output, and peripheral vascular resistance slightly.
How do benzodiazepines affect the ventilatory response to CO2?
Benzodiazepines depress the ventilatory response to CO2, with a risk of respiratory arrest if administered intravenously or in combination with other depressants.
How do benzodiazepines affect cerebral blood flow and intracranial pressure?
Benzodiazepines reduce cerebral oxygen consumption, cerebral blood flow, and intracranial pressure, but not to the extent of barbiturates.
What is the clinical effect of benzodiazepines on muscle relaxation?
Benzodiazepines have mild muscle-relaxing properties, mediated at the spinal cord level, not at the neuromuscular junction.
What drug interactions should be considered with benzodiazepines?
Cimetidine, erythromycin, and heparin can alter the metabolism of benzodiazepines, leading to prolonged effects. They also potentiate the effects of other CNS depressants.
How do benzodiazepines interact with opioids?
The combination of opioids and benzodiazepines significantly reduces arterial blood pressure and peripheral vascular resistance.
What is the effect of benzodiazepines on the minimum alveolar concentration (MAC) of volatile anesthetics?
Benzodiazepines reduce the MAC of volatile anesthetics by as much as 30%.
What is the primary mechanism of action of ketamine?
Ketamine is an NMDA receptor antagonist, which inhibits excitatory neurotransmitter effects in selected areas of the brain and causes dissociation between the thalamus and limbic cortex.
What kind of anesthesia does ketamine produce?
Ketamine produces dissociative anesthesia, where the patient may appear conscious but is unable to process or respond to sensory input.
What structural similarity does ketamine share with phencyclidine?
Ketamine is a structural analogue of phencyclidine, retaining many of its psychotomimetic effects.
How does ketamine affect the cardiovascular system?
Ketamine increases arterial blood pressure, heart rate, and cardiac output due to central sympathetic stimulation and inhibition of norepinephrine reuptake.
What is the effect of ketamine on the respiratory system?
Ketamine minimally affects ventilatory drive but can cause apnea with rapid intravenous bolus or when combined with opioids. It is also a potent bronchodilator.
What is ketamine’s effect on cerebral circulation?
Ketamine increases cerebral blood flow, oxygen consumption, and intracranial pressure, though when combined with a benzodiazepine, it may not increase intracranial pressure.
How is ketamine metabolized?
Ketamine is biotransformed in the liver to several metabolites, including norketamine, which retains anesthetic activity.
How does ketamine affect patients with coronary artery disease or uncontrolled hypertension?
Large bolus injections of ketamine should be administered cautiously in these patients due to the risk of increased myocardial work and blood pressure.
What are the psychotomimetic effects of ketamine?
Ketamine can cause hallucinogenic effects, though they are often minimized in clinical practice with the use of sedatives like midazolam.
What are the major side effects of ketamine at subanesthetic doses?
At subanesthetic doses, ketamine can cause hallucinogenic effects, though these are usually avoided with premedication.
What interactions does ketamine have with other anesthetic agents?
Ketamine has a synergistic interaction with volatile anesthetics and an additive effect with propofol, benzodiazepines, and other GABA-receptor agents.
What effect does ketamine have on sympathetic stimulation?
Ketamine’s central sympathetic stimulation increases heart rate, blood pressure, and cardiac output.
How does ketamine affect airway reflexes?
Ketamine tends to preserve upper airway reflexes but may cause partial airway obstruction, especially in patients at risk for aspiration pneumonia.
What is the effect of ketamine on cerebral oxygen consumption and blood flow?
Ketamine increases both cerebral oxygen consumption and cerebral blood flow, although this may not be detrimental when combined with controlled ventilation.
What is the cardiovascular effect of large doses of ketamine?
Large doses of ketamine can unmask direct myocardial depressant effects, especially in cases of sympathetic blockade or exhaustion of catecholamine stores.
What is the role of the S(+) stereoisomer of ketamine?
The S(+) stereoisomer has greater potency and a stronger affinity for NMDA receptors, offering increased anesthetic potency and decreased psychotomimetic side effects.
What is the pharmacokinetics of ketamine in terms of absorption?
Ketamine can be administered orally, nasally, rectally, subcutaneously, and epidurally, but is commonly given intravenously or intramuscularly for rapid onset.
How does ketamine distribute in the body?
Ketamine is highly lipid-soluble and undergoes rapid brain uptake and redistribution, with a distribution half-life of 10–15 minutes.
What is the excretion route of ketamine’s metabolites?
End products of ketamine biotransformation are primarily excreted in the urine.
What are the effects of ketamine on ventilation?
Ketamine typically does not significantly affect ventilatory drive, but rapid bolus administration or combination with opioids may result in apnea.
How does ketamine interact with α-adrenergic and β-adrenergic antagonists?
These antagonists unmask ketamine’s direct myocardial depressant effects, which are usually outweighed by its sympathetic stimulation.
What is the use of ketamine for deep sedation in clinical practice?
Ketamine is often combined with other agents like propofol or midazolam for deep conscious sedation during procedures like nerve blocks and endoscopy.
What is the role of ketamine in trauma or hypovolemia?
Ketamine is useful in trauma or hypovolemic patients due to its ability to maintain sympathetic stimulation and increase blood pressure, heart rate, and cardiac output.
What are the major side effects associated with ketamine use?
The major side effects of ketamine include increased intracranial pressure, psychotomimetic effects, and possible airway obstruction in some patients.
