General anesthetics Flashcards
What are the five characteristics of an ideal general anesthetic?
(1) Analgesia
(2) Amnesia
(3) Loss of undesirable reflexes
(4) Skeletal muscle relaxation
(5) Unconsciousness
What is balanced anesthesia?
Combining drugs to achieve ideal general anesthetic in a safe fashion
What are the general anesthetics?
Inhalation (2
Intravenous (6)
8 total)
Inhalation:
(1) Gases - nitrous oxide
(2) Halogenated hydrocarbons
Intravenous
(3) Barbiturates
(4) Benzodiazepines
(5) Propofol
(6) Neuroleptics
(7) Dissociative
(8) Opiates
What are common properties of all inhalation anesthetics?
(1) Low therapeutic index, so extremely dangerous
(2) Respiratory effects - bronchodilate, decrease minute ventilation, increase pCO2
(3) Cardiovascular effects - negative inotropic action, cause arrhythmias, decrease cerebrovascular resistance, increase intracranial pressure
(4) Clearance occurs by diffusion from site of action, exhalation, and metabolism
(5) Toxicity - tissue toxic metabolites, malignant hyperthermia, renal/liver toxicity
What are the characteristics of nitrous oxide?
(1) Gas at room temperature
(2) Low blood solubility
(3) Potent analgesic
(4) Weak anesthetic - low lipid solubility
(5) Causes hypoxia at high dose
(6) Few negative features
What are the halogenated hydrocarbons?
5
(1) Halothane
(2) Enflurane
(3) Isoflurane
(4) Desflurane
(5) Sevoflurane
What are the characteristics of halothane?
(1) Volatile and non-flammable fluid
(2) Weak analgesic, so use with N2O
(3) Potent anesthetic - high lipid solubility
What are concerns about the use of halogenated hydrocarbons?
(1) Relaxes smooth muscle, so not good for delivery
(2) Malignant hyperthermia (rare congenital condition) may result due to skeletal muscle rigidity
(3) Possibility of developing hepatic necrosis (low incidence)
How is malignant hyperthermia treated?
Dantrolene
What can happen during Stage III surgical anesthesia with the use of halothane?
(6)
(1) Cardiovascular effects:
(a) Hypotension
(b) Negative inotropy
(c) Bradycardia
(d) Increased cardiac sensitivity to epinephrine-induced cardiac arrhythmias
(2) Increased response to skeletal muscle relaxants
What are some post-surgical concerns about halothane use?
3
(1) Possibility of delirium
(2) Hepatotoxicity possible due to metabolites
(3) Post-operative shivering due to heat loss
What is enflurane?
Ether derived from halothane and chloroform
What are the advantages of enflurane over halothane?
5
(1) Enflurane is more stable than halothane
(2) Less negative inotropic effect on the heart
(3) Lower incidence of severe cardiac arrhythmias
(4) Greater decline in skeletal muscle tone
(5) No malignant hyperthermia or hepatic necrosis
What are some post-surgical concerns about enflurane?
2
(1) At higher doses, induces EEG signs of seizure (no physical seizure manifestation due to muscle relaxation though)
(2) Metabolism to free fluoride ion but not sufficient to cause renal toxicity
What are some characteristics of isoflurane?
6
(1) Low solubility in blood, so fast on- and offset of effect
(2) Metabolism to free fluoride ion but not sufficient to cause renal toxicity
(3) Low negative inotropic effect on heart
(4) Lower sensitization of heart to epinephrine-induced arrhythmias than halothane
(5) Not a convulsant (unlike enflurane)
(6) Enhances relaxation of skeletal muscles
What are some concerns about isoflurane?
3
(1) Irritating to respiratory tract
(2) Hypotension during Stage III surgical anesthesia
(3) Respiratory depression and diminished ventilatory response to hypoxia necessitates assisted ventilation
What are some characteristics of desflurane?
7
(1) Low blood solubility, so fast on- and offset of effect
(2) Desirable for outpatient surgery
(3) No serious cardiac arrhythmias
(4) No reports of malignant hyperthermia
(5) Minimally metabolized so low chance of renal or hepatotoxicity
(6) Not a convulsant
(7) Sensitizes skeletal muscle to relaxants
(8) Pungent odor, irritating to respiratory tract
What are some characteristics of sevoflurane?
5
(1) Low blood solubility, so rapid on- and offset of effect
(2) Good for outpatient procedures
(3) Less iritating to respiratory tract
(4) Drug does get metabolized, but no reports of kidney or liver toxicity
(5) Degraded in CO2 absorbers to olefin, which is nephrotoxic
What are some characteristics common to all intravenous anesthetics?
(6)
(1) Very rapid induction - inject slowly
(2) High lipid solubility - potent anesthetics
(3) Some are poor analgesics
(4) Respiratory irritants
(5) Overdose caused by medullary depression
(6) Clearance occurs by metabolism and excretion
What are the intravenous general anesthetics?
7
(1) Barbiturates (thiopental)
(2) Benzodiazepines
(3) Propofol
(4) Etomidate
(5) Ketamine
(6) Neuroleptic-opioid combination
(7) Opioids
What are some characteristics of thiopental?
4
(1) Derivative of barbituric acid
(2) Short duration of effect after single dose
(3) Potent anesthetic
(4) Poor analgesic - must be combined with analgesic
What are the effects of thiopental during Stage III surgical anesthesia?
(2)
(1) Little serious effect on the heart or vasculature
(2) Reduces cerebral blood flow and intracranial pressure, making it good for neurosurgery
What are some concerns about the use of thiopental?
3
(1) Post-op shivering and pain
(2) Contraindicated in variegate or acute intermittent porphyria
(3) Liver metabolism, so cross tolerance with ethanol (alcoholics desensitized)
How can thiopental overdose be treated?
Ion trapping in urine - convert molecule to ionic form so it can’t cross lipid bilayer and get reabsorbed
What are some characteristics of benzodiazepines?
6
(1) Slower onset than thiopental
(2) Relatively safe
(3) Sedation
(4) Not analgesic
(5) Reduce of anxiety
(6) Cause antegrade amnesia
What is an antagonist to benzodiazepines?
Flumazenil
What are three benzodiazepines?
3
(1) Diazepam
(2) Lorazepam
(3) Midazolam
What are some uses of benzodiazepines?
3
(1) Severe cardiovascular and respiratory depression when combined with opioids
(2) Used alone when analgesia not required
(3) Control seizures brought on by local anesthetic techniques
What are some characteristics of propofol?
6
(1) More rapid in action than barbiturates
(2) Widely used for outpatient surgery
(3) Not analgesic
(4) May be antiemetic
(5) Metabolized in liver and extrahepatic pathways
(6) More negative inotropic effect than thiopental
Which IV anesthetics act on the GABAa receptor?
3
(1) Barbiturates
(2) Benzodiazepines
(3) Propofol
What is the GABAa receptor?
3
(1) The GABAa receptor is an important inhibitory receptor in the brain
(2) Chloride channel
(3) Activation leads to Cl- influx into neurons, leading to hyperpolarization of membrane and difficulty creating action potential
What are some characteristics of etomidate?
7
(1) Sedative-hypnotic
(2) Not analgesic
(3) High safety index
(4) Used widely in emergency settings for “rapid sequence induction” of anesthesia
(5) Minimal cardiovascular/respiratory depression
(6) Very short duration of action
(7) Causes nausea and vomiting
What is rapid sequence induction of anesthesia?
(1) Give etomidate, then (2) follow up with muscle relaxant like succinylcholine or rocuronium (3) to relax the oropharynx, larynx, and diaphragm (4) to allow for intubation in emergency settings
What are the characteristics of ketamine?
4
(1) Causes “dissociative anesthesia” - patient is sedated, immobile, amnesic, pain-free
(2) Inhibits NMDA-type glutamate receptor
(3) May increase muscle tone
(4) Good for trauma surgery since BP, respiration, and heart rhythm are stable
What do the two components of a neuroleptic-opioid combination do?
(1) Neuroleptic (droperidol) is tranquilizing, adrenergic blocker with antiemetic and anticonvulsant effects
(2) Opioid (fentanyl) is analgesic
What is Innovar and what does it cause?
(1) Neuroleptic-opioid: fixed ratio mixture of droperidol and fentanyl
(2) Can cause chest wall spasm that can be treated with succinylcholine
(3) May cause severe respiratory depression
What are opioid drugs?
(1) Morphine
(2) Meperidine
(3) Fentanyl
(4) Sufentanil
(5) Alfentanil
What do opioids cause?
(1) Respiratory depression
(2) Hypotension
(3) Post-op nausea and vomiting
(4) Poor amnesia
How can the effects of opioids be reversed?
Naloxone
