General Anesthetics DSA Flashcards
List the general inhaled anesthetics
Desflurane Enflurane Halothane Isoflurane Nitrous oxide Sevoflurane
List the general intravenous anesthetics
Dexmedetomidine Diazepam (Valium) Etomidate Fentanyl Fospropofol Ketamine Lorazepam (Ativan) Methohexital Midazolam (Versed) Propofol (Diprivan) Thiopental
The anesthetic state produced by general anesthetics is a collection of component changes in behavior or perception that include?
Which agent can be used alone to achieve all five?
Unconsciousness
Amnesia
Analgesia
Attenuation of autonomic reflexes to noxious stimulation
Immobility in response to noxious stimulation (skeletal muscle relaxation)
None
Describe the modern practice of anesthesiology
Relies on the use of combinations of intravenous and inhaled drugs (balanced anesthesia) to take advantage of favorable properties of each agent while minimizing their adverse effects
Utilizes sedatives, neuromuscular blocking agents, local anesthetics, and analgesics in addition to general anesthetics to induce anesthesia
Describe monitored anesthesia care
Sedation-based anesthetic techniques
Utilized for diagnostic and/or minor therapeutic surgical procedures
Performed without general anesthesia
Typically involves the use of midazolam for a premedication (to provide anxiolysis, amnesia, and mild sedation) followed by a titrated propofol infusion (to provide moderate to deep levels of sedation)
Potent opioid analgesic or ketamine may be added to minimize the discomfort associated with injection of local anesthesia and surgical manipulations
Describe conscious sedation
Used primarily by nonanesthesiologists (dentists)
The patient retains ability to maintain a patent airway and is responsive to verbal commands
Benzodiazepines and opioid analgesics (fentanyl) in conscious sedation protocols have the advantage of being reversible by specific receptor antagonist drugs (flumazenil and naloxine)
Describe deep sedation
Similar to light state of general (intravenous) anesthesia involving decreased consciousness from which the patient is not easily aroused
Transition from deep sedation to general anesthesia is fluid and sometimes difficult to clearly determine where transition is
Accompanied by a loss of protective reflexes, an inability to maintain a patent airway, and lack of verbal responsiveness to surgical stimuli
Intravenous agents used in deep sedation protocols mainly include sedative-hypnotics propofol and midazolam, sometimes in combination with potent opioid analgesics or ketamine, depending on level of pain associated with surgery or procedure
Dsecribe intensive care unit (ICU) sedation
Patients who require mechanical ventilation for prolonged periods
Sedative-hypnotic drugs and low doses of IV anesthetics
Describe mechanism of general anesthetic action
Anesthetics affect neurons at various cellular locations, but the primary focus has been on synapse Presynaptic action may alter release of neurotransmitters, whereas a postsynaptic effect may change frequency or amplitude of impulses exiting synapse At organ level, effect of anesthetics may result from strengthening inhibition or from diminishing excitation within CNS (studies on isolated spinal cord tissue have shown that excitatory transmission is impaired more strongly by anesthetics than inhibitor effects are potentiated) Chloride channels (gamma-aminobutyric acid-A (GABAa) and glycine receptors) and potassium channels (K2p, possibly Kv, and Katp channels) remain primary inhibitory ion channels considered legitimate candidates of anesthetic action Excitatory ion channel targets include those activated by acetylcholine (nAChRs and mAChRs) by excitatory amino acids (amino-3-hydroxy-5-methyl-4-isoxazol-proprionic acid (AMPA), kainite, and N-methyl-D-aspartate (NMDA) receptors), or by serotonin (5-HT2 and 5-HT3 receptors)
Describe volatile anesthetics
Halothane, enflurane, isoflurane, desflurane, sevoflurane
Have low vapor pressures and thus high boiling points so that they are liquids at room temperature and sea-level ambient pressure
Describe gaseous anesthetics
Nitric oxide
Have high vapor pressures and low boiling points and are in gas form at room temperature
Describe pharmacokinetics of inhaled anesthetics
Volatile and gaseous inhaled anesthetics are taken up through gas exchange in alveoli
Uptake from alveoli into blood and distribution and partitioning into the effect
Describe uptake and distribution of inhaled anesthetics
Driving force for uptake of an inhaled anesthetic is alveolar concentration
Two factors that determine how quickly alveolar concentration changes:
- Inspired concentration or partial pressure
- Alveolar ventilation
Increases in either inspired partial pressure or in ventilation will increase rate of rise in alveoli and will accelerate induction
Partial pressure in alveoli is expressed as ratio of alveolar concentration (Fa) over inspired concentration (Fi); the faster Fa/Fi approaches 1, the faster anesthesia will occur during an inhaled induction
What coefficients affect solubility?
Blood:gas partition coefficient
Brain:blood partition coefficient
Describe the blood:gas coefficient
Defines the relative affinity of an anesthetic for blood compared with that of inspired gas (blood solubility)
There is an inverse relationship between blood:gas partition coefficient values and the rate of anesthesia onset
Agents with low solubility (nitrous oxide, desflurane) reach high arterial pressure rapidly, which in turn results in rapid equilibration with brain and fast onset of action
Agents with high solubility (halothane) reach high arterial pressure slowly, which results in slow equilibration with brain and slow onset of action
Describe the brain:blood partition coefficient
Values for inhaled anesthetics are relatively similar and indicate that all agents are more soluble in brain than in blood
Describe blood:gas coefficient, brain:blood coefficient, MAC (vol%), metabolism (%), and comments about nitrous oxide
0.47
1.1
>100
None
Incomplete anesthetic; rapid onset and recover
Describe blood:gas coefficient, brain:blood coefficient, MAC (vol%), metabolism (%), and comments about desflurane
0.42
1.3
6-7
Describe blood:gas coefficient, brain:blood coefficient, MAC (vol%), metabolism (%), and comments about sevoflurane
0.69
1.7
2
2-5
Rapid onset and recovery
Describe blood:gas coefficient, brain:blood coefficient, MAC (vol%), metabolism (%), and comments about isoflurane
- 4
- 6
- 4
Describe blood:gas coefficient, brain:blood coefficient, MAC (vol%), metabolism (%), and comments about enflurane
1.8
1.4
1.7
8
Medium rate of onset and recovery
Describe blood:gas coefficient, brain:blood coefficient, MAC (vol%), metabolism (%), and comments about halothane
2.3
2.9
0.75
>40
Medium rate of onset and recovery
Why is induction of anesthesia slower with more soluble anesthetic gases?
For a given concentration or partial pressure of two anesthetic gases in inspired air, it will take much longer for blood partial pressure of more soluble gas (halothane) to rise to same partial pressure as in alveoli.
Since concentration of anesthetic agent in brain can rise no faster than concentration in blood, onset of anesthesia will be slower with halothane than with nitrous oxide
The alveolar anesthetic concentration (Fa) approaches inspired anesthetic concentration (Fi) fastest for ___
Least soluble agents
Nitrous oxide>desflurane>sevoflurane>isoflurane>halothane
Describe cardiac output effect on uptake of inhaled anesthetics
Increase in pulmonary blood flow (increased cardiac output) will increase uptake of anesthetic and decrease rate by which Fa/Fi rises, which will decrease rate of induction of anesthesia (Fa decreases because of increased pulmonary blood flow, which essentially dilutes drug in alveoli)
An increase in cardiac output and pulmonary blood flow will increase uptake of anesthetic into blood, but the anesthetic taken up will be distributed and diluted into all tissues, not just CNS
This results in slower rise in partial pressure in blood due to greater volume of distribution
Describe alveolar-venous partial pressure difference effect on uptake of inhaled anesthetics
Anesthetic partial pressure difference between alveolar and mixed venous blood is dependent mainly on uptake of anesthetic by tissues, including nonneural tissues
The slower the rate and extent of tissue uptake, the greater the difference in anesthetic gas tensions between arterial and venous blood, the more time it will take to achieve equilibrium with brain tissue
Since anesthetics must be carried from tissues to lungs for primary elimination, larger A-V concentration differences means less drugs are returning for elimination, which may increase time for awakening