PHA 6575 Lecture 13 (General Anesthetics)

General Anesthetics

affects the central nervous system to take control of the entire body and renders the patient unconscious for surgical procedures

Local Anesthetics

affects only the areas around the nerves to numb a specific area while the patient is fully awake for minor procedures

Elderly Patients

general anesthetics have a high risk for _______ which population?

Rapid Affect, Reversible, and Safe

an ideal anesthetic drug has a ________ onset of action to induce unconsciousness, be rapidly ________ upon discontinuation, and have a wide margin of _________

Unconsciousness, Amnesia, Analgesia, Inhibition of Autonomic Reflexes, and Skeletal Muscle Relaxation

five primary effects of general anesthetics on neurophysiologic state

Intravenous and Inhaled Drugs

to achieve all five primary effects of general anesthetics, a combination of ________ must be used

Meyer-Overton Rule

describes that molecules with a larger oil/gas partition coefficient are more potent general anesthetics

Hydrophobic

which site of action does the Meyer-Overton rule suggest?

Volume and Fluidity

anestheics that dissolve in the membrane increases the membranes _________ and __________, possibly affecting excitable transmembrane proteins

Hyperbaric Pressure

what can reverse anesthesia when applied using non-anesthetic gas?

Critical Volume Hypothesis

describes that anesthesia occurs when critical volume of molecules dissolve in crucial hydrophobic sites

Inhalation Anesthetics

believed to bind stereoselectively to hydrophobic regions of neuronal membrane proteins that interface with membrane lipids

Neuronal Firing and Sensory Processing

what do anesthetics affect in the thalamus causing loss of consciousness and analgesia

Motor Activity

the inhibition of neuronal output from layer V (the internal pyramid layer) of the cortex reduces _________

GABA-A Receptor

channel that allows chloride ions to flow into the neuron decreasing the voltage within the cell and inhibiting brain cell firing

NMDA Receptors

allows sodium and calcium ions to flow into the cell, while letting potassium ions out increasing the voltage within the cell and causing brain cell firing

a2-Adrenergic Agonists

has an inhibitory effect on the release of norepinephrine which results in the attenuation of neurotransduction, such as pain relief

Propofol and Sevoflurane

drugs that act on GABA-A receptors to increase chloride current going into the cell and inhibiting the receptor

Nitrous Oxide

gaseous inhalation anesthetic

Desflurane (Suprane), Isoflurane (Forane), and Sevoflurane (Ultane)

volatile (liquid) inhalation anesthetics

Single Bolus Injection and Continuous Infusion

two types of intravenous infusions used to deliver IV anesthetics

NMDA Receptors

nitrous oxide, xenon, and cyclopropane work on the ______________

Alveoli to the Blood

pathway of inhalation anesthetics into the body starts with the absorption via the _________ of the lung and then into the _________

Inspired Concentration, Ventilation, and Solubility

three factors controlling safety and uptake of anesthetics

Inspired Concentration (MAC)

the driving force for uptake of an inhaled anesthetic into the body is the ratio between this and the alveolar concentration

True

T/F: the most important parameter that the anesthesiologist can control to change alveolar concentration is the inspired concentration or partial pressure

Stage 3

which stage of anesthesia is used for surgical procedures and is characterized by unconsciousness, regular respiration, and decreasing eye movement

Stage 4

which stage of anesthesia is characterized by respiratory arrest, cardiac depression, and non eye movement; medullary depression

P=CRT

equation used to determine the partial pressure desired for anesthetics

True

T/F: an increase in inspired concentration will result in an increase of effects of inhaled anesthetics

0.02 and 0.05 Isoflurane (atm)

what are the concentrations of isoflurane that will cause non-responsiveness to intubation and result in cardiac arrest respectively?

Therapeutic Index

defined as the lethal pressure (LP50) divided by the MAC

Minimal Alveolar Concentration (MAC)

quantifies the potency of an inhalation anesthetic

1.0 MAC

the partial pressure of an inhalational anesthetic in the alveoli of the lungs in which 50% of a population of non-relaxed patients remained immobile at the time of surgical skin incision

Nitrous Oxide, Desflurane, and Isoflurane

rank desflurane, isoflurane, and nitrous oxide in terms of their potency by the MACs from smallest to largest

Insoluble Gas

with a MAC of >100%, nitrous oxide is a relatively _____________

Blood:Gas Coefficient

defines the rate of induction and recovery of anesthesia

Slower

a more soluble anesthetic results in a _________ onset

Faster

a less soluble anesthetic results in a ______ onset

More

a drug with a high blood:gas coefficient requires _________ of the drug dissolved in the blood to achieve a specific partial pressure in the blood

False

T/F: drugs with larger blood:gas partition coefficients are preferred

Low

nitrous oxide, desflurane, and sevoflurane have ___________ blood:gas partition coefficients

High

enflurane, isoflurane, and halothane have _______ blood:gas partition coefficients

Tidal Volume and Respiratory Rate

two things that the anesthesiologist can increase to deliver larger amounts of anesthetic agents faster via ventilation

Duration

the rate of recovery is proportional to the _______ of anesthesia

Propofol

used in intravenous anesthesia to achieve good maintenance of anesthesia

Balanced Anesthesia

the practice of using combinations of drugs to achieve anesthesia while minimizing unwanted side effects

Redistribution

termination of the bolus injection effect is the _________ of the drug into less perfused and inactive tissue such as skeletal muscle or fat

3-8 Minutes

duration of action for propofol

4-23 Hours

half life elimination of propofol

Context-Sensitive Half-Time

describes the elimination half-time after discontinuation of a continuous infusion as a function of the duration of the infusion

Maintenance Anesthetic

the context-sensitive half-time is an important parameter for assessing the suitability of a drug as a ____________

GABA-A Agonist, NMDA Antagonist, and a2-Adrenergic Agonist

three drug targets for anesthesia

GABA-A

propofol, the most frequently administered drug for induction of anesthesia, acts on the ___________ receptor complex

Fospropofol

prodrug of propofol but with prolonged onset and recovery in comparison

Thiopental and Methohexital

barbiturates that act upon GABA-A receptors and is used for induction of anesthesia and usually occurs in less than 30 seconds

True

T/F: recovery from thiopental will be markedly prolonged if administered through repeated bolus injections or continuous infusion because elimination will depend on metabolism

Benzodiazepines

can be readily terminated by administration of flumazenil

Anxiolysis and Aterograde Amnesia

the two most desired effects of using benzodiazepines as anesthetics

Midazolam

has the shortest context-sensitive half-time which makes it one of the three suitable benzodiazepines drugs for continuous infusion

Etomidate

has GABA-like effects and seems to act primarily through potentiation of GABA-A-mediated chloride current

False

T/F: etomidate has both hypnotic and analgesic effects

Hemodynamic

etomidate is chosen for its minimally ___________ effects

Ketamine

produces significant analgesia through inhibition of NMDA receptor complex and does not compromise airway

Psychotomimetic Effects

unpleasant side effects from using ketamine

Dexmedetomidine

highly selective a2-adrenergic agonist that produces sedative and analgesic effects

False

T/F: there are several ideal anesthetics available for use