3) Anesthetics Flashcards
(167 cards)
Forms of anesthesia
- General
- Balanced
- IV sedation
- Regional
- Local
- Infiltration
General anesthesia
- Patient is unconscious
- Utilizes gaseous and IV anesthetics
Balanced anesthesia
- Utilizes a combination of IV anesthetic agents (pentothal, midazolam, fentanyl, propofol) with an inhalation agent (e.g. isoflurane, sevoflurane, or desflurane)
- Patient is not in a deep plant of anesthesia
IV sedation
- Must be supplemented with local anesthetics
Regional anesthesia
- Spinals, epidurals, axillary, brachial, popliteal, ankle
- Use local anesthetic to block a nerve root or major nerve
Local anesthesia
- Uses local anesthetic in a “block” fashion around a peripheral nerve
Infiltration
- Injection of local anesthetic around an area to be anesthetized, e.g. for suture placement
Goal of inhalation (gaseous-and volatile liquids) anesthesia
- To provide unconsciousness
- Analgesia, amnesia, loss of autonomic reflexes, and skeletal muscle relaxation
Meyer-Overton Principle: “Membrane Fluidization Hypothesis” or the lipid solubility hypothesis
- Anesthetic drug molecules are taken into the lipid matrix of the neuronal membrane
- Cause increase in lateral pressure on ion channels thus obstructing ion exchange and excitability
- Blocks release of neurotransmitter; ie blocks synaptic transmission as opposed to axonal transmission (as is the case with local anesthetics)
The primary molecular target for anesthetic agents
- Synapse
Inhibitory neurotransmitters actions
- Inhibit the transmembrane ion flow and post-synaptic neuron from firing an action potential
Inhibitory neurotransmitters names
- Gamma-aminobutyric acid-A (GABAA ) receptor
- Glycine
- Serotonin (5-HT2 and 5HT3) receptors
- Dopamine
Excitatory neurotransmitters actions
- Increases the transmembrane ion flow
- Increases the post-synaptic neuron fire an action potential
Excitatory neurotransmitters names
- Acetylcholine (nicotinic and muscarinic) receptors
- Glutamate
- N-methyl-D-aspartate (NMDA) receptors
- Aminohydroxy-methyl-isoxazol-propionic acid (AMPA) receptors
- Epinephrine, norepinephrine
- Nnitrous oxide
Primary molecular target for anesthetic agents
- GABAA receptor -chloride channel
- Major mediator of inhibitory synaptic transmission
- Benzodiazepines, barbiturates, etomidate, and propofol all facilitate GABA mediated inhibition( i.e. enhance the affinity of GABA receptors for GABA)
IV and general inhalation anesthetics activate
- GABA receptors
- Increase chloride ion flux causing hyperpolarization and increased inhibition
Ketamine action
- Blocks the neurotransmitter, glutamic acid on the receptor, NMDA (N-methyl-D aspartate.)
General anesthetics actions
- Decrease the metabolic rate of the brain; increases cerebral blood flow and increases inter-cranial pressure
- CNS Effects
General anesthetics effects of decreasing metabolic rate of the brain
- Increases cerebral blood flow
- Increases inter-cranial pressure
General anesthetics CNS effects
- Decreases electrical activity of the cerebral cortex (frontal and occipital lobes)
- EEG changes convert from a fast, low voltage to slow waves with increased amplitude
Where anesthetics work
- Substatntia gelatinosa
- Thalamus
- Reticular Formation
Substantia gelatinosa
- CNS structure involved in pain transmission
- Located apex of the afferent posterior horn of the gray matter of the spinal cord
- Point where first order neurons of the spinothalamic tract synapse (the nucleus proprius being the other)
Anesthetic activity in the substantia gelatinosa
- Many μ- and к-opioid receptors, presynaptic and postsynaptic, are found on these nerve cells (can be targeted to manage pain of distal origin)
- C fibers terminate at this layer (cell bodies located here are part of the neural pathway conveying slowly conducting, poorly localized pain sensation)
- A delta fibers (carrying fast, localized pain sensation) also terminate in the substantia gelatinosa, mostly via axons passing through the area of the nucleus proprius (there is communication between the two pain pathways)
Anesthetic activity in the thalamus
- Sensory nuclei
- Midline within the brain, situated between the cerebral cortex and midbrain
- Function includes relaying sensory and motor signals to the cerebral cortex, along with the regulation of consciousness, sleep, and alertness