Lecture 11: General Anesthetics Flashcards
Volatile anesthetics end in which suffix?
- -ane
- Halothane, enflurane, isoflurane, desflurane, and sevoflurane
What is the Blood:gas partition coefficient and how does it relate to an anesthetics onset of action?
- Defines relative affinity of an anesthetic for the blood compared with that of inspired gas (i.e., blood solubility)
- Inverse relationship btw blood:gas partition coefficient values and rate of anesthesia onset
- Agents w/ low blood solubility (i.e., NO, desflurane) reach high arterial pressure rapidly, rapidly equilibriate with brain and have fast onset of action
How does the value of minimum alveolar concentration (MAC) relate to potency?
Lower MAC = MORE potent
*Inverse relationship
What does the MAC correspond to on the drug-dose effect curve?
ED50
Which inhaled anesthetic may have a toxic side effect of hepatitis (hepatomegaly, jaundice, and liver tenderness) which can present 2 days to 3 weeks after exposure?
Halothane
‘H’ for Hepatoxicity
Which toxicity is associated with the inhaled anesthetics, Enflurance and Sevoflurane?
Renal toxicity due to fluorinated metabolites
In combination with succinylcholine, inhaled anesthetics may cause what serious adverse reaction?
What is seen with this reaction?
- Malignant hyperthermia
- Rapid onset tachycardia and HTN
- Severe muscle rigidity, rhabdomyolysis, hyperthermia, hyperkalemia, and acid-base imbalance w/ acidosis
What is the antidote for malignant hyperthermia?
Dantrolene
What is meant by the term “balanced anesthesia?”
- Modern anesthesia relies on the use of combos of IV and inhaled drugs to take advantage of the favorable properties of each drug, while minimizing adverse effects
- No single available drug can achieve all 5 desired effects of the anesthetic state
Most general anesthetics cause CNS depressions by facilitating activation of which channel and through which receptors?
Some also reduce activity of which receptors?
- Facilitating chloride channel activation (GABAA and glycine-receptors)
- Some reduce excitatory ion channels (i.e., nAChRs and mAChRs; AMPA, kainite, and NMDA receptors)
Which organs have higher immediate concentrations of anesthetics based on the amount of cardiac output they receive?
Brain, heart, liver, kidneys, and splanchnic beds
Clearance from the ________ is the major route of elimination for inhaled anesthetics
Lungs
*Some metabolized by liver to varying degrees
Define minimum alveolar concentration (MAC)?
- Concentration of inhalation anesthetic that prevents movement in response to surgical stimulation in 50% of subjects (meausre of potency; ED50)
- This is equal to 1 MAC
Which inhaled anesthetic has a MAC (vol %) >100 and what does this mean for use in surgery?
- Nitrous oxide
- >100% indicates that if 100% of inspired air is the anesthetic, the MAC value would still be <1 and other agents must be supplemented to achieve full surgical anesthesia
- You can’t achieve >100% nitrous oxide; you couldn’t achieve 80% either w/o killing the patient!
What is the MAC of: Desflurane, Sevoflurane, Isoflurane, Enflurance, and Halothane?
- Desflurane = 6-7%
- Sevoflurane = 2%
- Isoflurane = 1.4%
- Enflurane = 1.7%
- Halothane = 0.75%
What are the general effects on the cardiovascular system by inhaled volatile liquid anesthetics?
Specific effects related to halothane, desflurane and isoflurane?
- Decrease MAP in direct proportion to their alveolar concentration
- Increase right atrial pressure, due to depression of myocardial function
- Halothane can cause bradycardia
- Desflurane and Isoflurane can increase HR
Which property of IV anesthetics accounts for their quick onset of action?
Highly lipophilic and preferentially partition into highly perfused lipophilic tissues (brain, spinal cord)
What is the most likely MOA of Propofol?
Targets GABAA receptors as an agonist and potentiates the Cl- current
Describe the pharmacokinetics of Propofol (i.e., metabolism, rate of onset and recovery)
- Rapidly metabolized in liver (phase I and II rxns) w/ extensive extrahepatic metabolism (i.e., lung may account for elimination of up to 30% of a bolus dose)
- Rapid rate of onset; 15-30 seconds
- Rapid recovery, patients able to ambulate quickly (low hangover effect)