Exam 7: General anesthetics Flashcards
What are the components of the anesthetic state?
Amnesia, immobility in response to noxious stimuli, attenuation of autonomic responses to noxious stimuli, analgesia, unconsciousness
Define 1 MAC unit
minimum alveolar concentration that prevents movement in response to surgical stimulation in 50% of subjects
What are the strengths of MAC as a measurement?
alveolar concentrations can be monitored continuously, provides a direct correlate of the free concentration of anesthetic at its concentration sites in CNS, simple-to-measure end point that reflects an important clinical goal
What is easier to measure a MAC on: inhaled or IV anesthetics? Why?
IV anesthetics; lack methods to measure blood or plasma anesthetic concentration
What are the five primary effects of general anesthetics?
Amnesia, skeletal muscle relaxation, inhibition of autonomic reflexes, analgesia, unconsciousness
What does conscious sedation include in terms of drug classes, and what are the benefits of doing so?
Drug-induced alleviation of anxiety and pain + smaller doses of sedative medications; maintains a patent airway and is responsive to verbal commands
What benzodiazepines and IV anesthetics are useful in conscious sedation?
fentanyl, diazepam, midazolam, propofol
What is the specific receptor antagonist for both benzos and opioids?
Benzos: Flumazenil; Opioids: naloxone
What are the characteristics of deep sedation?
similar to light state of general anestesia; decreased consciousness, transition to general anesthesia is hard to define, often accompanied by loss of protective reflexes, inability to maintain a patent airway, lack of verbal responsiveness to surgical stimuli
What is the mechanism of action of deep sedation?
different agents produce specific components of anesthesia by actions at different molecular targets- may alter release of neurotransmitters, may change the frequency or amplitude of impulses exiting the synapse
Explain the enhanced inhibitory activity of deep sedation, which kinds of anesthetics do this (volatile or IV)?
Enhances opening of chloride channels via GABAa and glycine receptors (both volatile and IV), activates two-pore domain potassium channels (volatile)
Explain activation of two-pore domain potassium channels by anesthetics
located on both pre and post-synaptic sites, post synaptic channels are important in setting the resting membrane potential of neurons and may be the molecular locus through which these agents hyperpolarize neurons, also hyperpolarize and prevent NT release
Explain the inhibition of excitatory activity of anesthetics and which anesthetics do it?
Blocks AMPA and NMDA receptor of glutamate (ketamine, nitrous oxide), and nicotinic and muscarinic receptors of acetylcholine (inhalation anesthetics)
What are the volatile anesthetics?
halothane, enflurane, isoflurane, desflurane, sevoflurane
What are the gaseous anesthetics?
Nitrous oxide
What are the pharmacokinetics of inhaled anesthetics?
should have a rapid onset, effect should be rapidly terminated, effect site concentration in the CNS
What are two factors that control uptake?
inspired concentration and ventilation rate
the faster the ratio of alveolar concentration and inspired cocentration approach what number is indicative of a faster anesthesia effect?
1, which indicates equilibrium
Does increasing alveolar ventilation increase the blood rise?
It increases the rate of rise in the blood
In a ratio of blood:gas partition coefficient, which is better: 2 or 1.5? What is the trend that is better for a anesthetic?
1.5 is better, the greater the gas partition, the more it will diffuse into pertinent tissues
What is related to the clinical effect for anesthetics?
Undissolved drug in the blood
What are the three factors controlling uptake of the anesthetic?
1) inspired concentration and ventilation, 2) solubility, 3) alveolar-venous partial pressure difference
What is the threshold concentration of the partial pressure of the anesthetic in the brain determined by?
Potency (MAC)
Do anesthetics reach anesthetizing concentrations slower or faster if they are less soluble?
Reach it quicker
How can you speed the rate of induction of a volatile anesthetic?
Increase concentration and increase alveolar respiration rate
What is the recovery time (elimination) of an anesthetic dependent on?
rate of elimination from the brain: solubility in the brain (lower is faster), duration of exposure to the anesthetic
Where does immobility of the patient occur?
Spinal cord inhibition, and possibly inhibition of nociceptive transmission to the brain
Where does amnesia of the patient occur?
hippocampus, amygdala, prefrontal cortex and regions of the sensory and motor cortices
Where does inhibition of consciousness occur in the patient?
cerebral cortex, thalamus and reticular activating system
What are the cerebral effects of inhaled anesthetics?
Decrease metabolic activity in the brain (and decreased blood flow), but can also increase blood flow via dilation of the vessels- depends on the concentraion
What are the four levels of CNS depression?
Stage 1= analgesia, Stage 2= excitement, Stage 3= surgical anesthesia, Stage 4= medullary depression
