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Inhalant anesthetics are unique in that they are removed from the body via what?
Why are inhalant anesthetics ideal for maintaining anesthesia?
rapid adjustment for anesthetic depth
Why are inhalant anesthetics considered accurate and are a controlled way of anesthetic delivery
- good lung ventilation/improved arterial oxygenation
- partial pressure of anesthetic agents allows for rapid equilibrate between lung alveoli adn CNS
Inhalation anesthetics enhance what inhibitory receptors?
GABA and glycine
Inhalation anesthetics reduce what excitatory pathways?
nicotine and glutamate
T/F Inhalant anesthetics bind to the amphiphilic cavities in the proteins of cell membranes, causing conformational changes to receptors and transmembrane proteins.
Unspecified mechanisms of inhalation anesthetics also include
- suppression of nociceptive motor responses within the spinal cord
- supraspinal suppression causing amnesia and hypnotic state
What are inorganic inhalation anesthetics?
What are halogenated ether inhalation anesthetics?
isoflurane, sevoflurane, and desflurane
What are halogenated alkane inhalation anesthetics?
chloroform and halothane
What is the specialized delivery apparatus for large animals under inhalant anesthesia?
carrier gas with O2, vaporizer, and a breathing circuit
What is the preferred way to administer inhalant anesthetics for lab animals and birds?
place animal in a closed air-filled chamber with a cotton pledget saturated with liquid anesthetic
What is the index of anesthetic potency?
minimum alveolar concentration (MAC)
The alveolar concentration of an inhaled anesthetic at 1 atm, at equilibrium, that prevents gross nonreflexive movement in 50% of subjects exposed to a supramaximal noxious stimuli.
minimum alveolar concentration (MAC)
The MAC is equivalent to what?
median effective dose or ED50 for inhalant anesthetics
What is the usual surgical plane of anesthesia?
What factors decrease minimum alveolar concentration (MAC) in regards to inhalation anesthesia?
hypothermia, severe hypotension, severe hypoxia, metabolic acidosis, other anesthetics/drugs, pregnancy, and old age
What factors increase minimum alveolar concentration (MAC) in regards to inhalation anesthesia?
hyperthermia, hypernatremia, and increase levels of excitatory neurotransmitters (cocaine, amphetamines)
What factors have no effect on minimum alveolar concentration (MAC) in regards to inhalation anesthesia?
gender, weight, duration of anesthesia, anemia, and moderate changes in acid-base
What is compressed under high pressure as liquid, then vaporized as gas?
Do gases move along with or against a partial pressure gradient?
What is the term for the gaseous state of liquid?
What makes volatile anesthetics able to be administered via inhalation?
sufficient vapor pressure
Inhalant anesthetics exist as liquid at ambient temperature and pressure, then are delivered as what?
Pressure exerted by a vapor when it exists in equilibrium with its liquid state
The partial pressure of an anesthetic agent in the brain produces what?
The partial pressure of an anesthetic in the brain equilibrates quickly with what?
alveolar partial pressure
What is achieved in regards to desired anesthesia?
partial pressure of anesthetic in CNS
Molecules of inhalation anesthetics move up or down partial pressure gradients?
T/F Vaporizer → breathing circuit → lungs → arterial blood → body tissues (brain & spinal cord)
anaesthetic input (delivery to the alveoli) - loss (uptake by blood & body tissues) from the lungs = ?
Pa of anesthetic
Partial pressure of alveoli
What factors promote an increase in delivery of anesthetic to the alveolus?
- vaporization of the agent
- inspired anesthetic concentration (Fi)
- vaporizer dial setting (overpressure)
- fresh gas inflow
- alveolar minute ventilation
What factors result in a decrease in removal of anesthetic from alveoli?
- blood solubility of anesthetic (blood:gas partition coefficient)
- cardiac output
Anesthetic uptake by blood is determined by what?
- solubility (S)
- cardiac output (CO)
- difference in anesthetic partial pressure between alveoli (Pa)
- venous blood returning to the lungs (Pv)
S x CO x [(Pa - Pv)/Pbar] = ?
barometric pressure in mmHg
The greater the vapor pressure, the greater or lesser the concentration of the drug deliverable to the patient?
Is concentration (X% of agent A in relation to whole gas mixture) a required quality of inhalation anesthetics?
Is vapor pressure a required quality of inhalation anesthetics?
What is one of the required qualities of inhalation anesthetics that is an indicator of the inhalant anesthetic to evaporate, and reflects the tendency for the molecule in the liquid state to enter the vapor form?
Is potency of an inhalant anesthetic a required quality?
Why is potency in an inhalation anesthetic a required quality?
vapor pressure should be sufficient enough to provide enough molecules to body tissues
(vapor pressure / barometric pressure) x 100 = ?
saturated vapor concentration
What determines speed of anesthetic induction and recovery?
What is the extent to which gas will dissolve in a given solvent?
What is important when it comes to induction or change in anesthetic level and recovery?
blood:gas partition coefficient
Which two partition coefficients are important?
blood:gas and oil:gas
What measures the solubility of the anesthetic agent in blood?
blood:gas partition coefficient
What is a measure of how quickly the inhalation anesthetic agent will equilibrate between lungs and blood and ultimately the brain?
blood:gas partition coefficient
Will a higher or lower blood:gas partition coefficient equilibrate quickly?
Will a lower or higher blood:gas partition coefficient allow for more rapid anesthetic induction and faster recovery?
What allows for precise control of anesthetic depth?
lower blood:gas partition coefficient
What describes the ratio of concentration of an anesthetic in oil and gas phases at equilibrium?
oil:gas partition coefficient
Oil:gas partition coefficient correlates directly or inversely with anesthetic potency?
T/F Oil:gas partition coefficient describes the capacity of fat solubility for an anesthetic agent.
How does oil:gas partition coefficient influence drug elimination?
high lipid solubility delays recovery form anesthesia (redistribution of fat)
In relation to oil:gas partition coefficient, what from different tissues occurs at different rates?
What determines the quantity of anesthetic removed from the blood?
Will a higher or lower tissue solubility result in more anesthetic removed from the blood?
What delays the recovery time during recovery from anesthesia?
anesthetic agent can leave the tissue reservoirs
The solubility in rubber results in what?
slow anesthetic delivery to the patient
What factors influence inhalant anesthetics' delivery/elimination?
- cardiac output (increase in blood flow through lungs increases drug elimination and reduces Fa/Fi ratio)
- alveolar ventilation
- blood:gas solubility
Does body size and composition affect inhalant anesthetic elimination?
What is the main method of inhalant anesthetic elimination?
What can delay drug recovery from inhalation anesthetics?
washout from drug reservoirs (muscle and fat), which redistributes to the CNS
Can percutaneous loss, intratissue, or intertissue diffusion of anesthetic agents affect inhalation anesthetic elimination?
What role does metabolism play in inhalant anesthetic elimination?
What is the minimum alveolar concentration of Halothane?
What is the minimum alveolar concentration of Enflurane?
What is the minimum alveolar concentration of Isoflurane?
What is the minimum alveolar concentration of Sevoflurane?
What is the minimum alveolar concentration of Desflurane?
What is the minimum alveolar concentration of Nitrous Oxide?
What is the most commonly used anesthetic agent?
What is the blood:gas solubility of Isoflurane?
What is the vapor pressure of Isoflurane?
T/F The MAC of Isoflurane can be from 1.3-1.6%.
Minimal or maximal hepatic metabolism of Isoflurane?
What level of onset and offset of action does Isoflurane have?
At what alveolar concentration causes apnea in Isoflurane?
1.5 MAC (dog) and 2.3 MAC (horses)
Which inhalant anesthetic causes no airway irritation and less respiratory depression, but can depress ventilation in horses?
What has a blood:gas solubility of 0.68 and is less that Isoflurane?
Can Sevoflurane have a MAC of 2.3-2.6%?
Metabolism percentage of Sevoflurane
The blood:gas solubility at 0.68 of Sevoflurane allows for rapid or slow anesthetic induction and recovery?
Vapor pressure of Sevoflurane
The cerebral vasodilator effect of Sevoflurane is comparatively lesser than what?
Isoflurane and Desflurane
Does Sevoflurane increase arrhythmogenicity?
What can provide analgesia at subanesthetic does?
What inhalation anesthetic has a very high blood:gas solubility?
Why does Methoxyflurane have a prolonged induction and recovery period?
very high blood:gas solubility
Why does Desflurane require a controlled, pressurized vaporizer for delivery?
high vapor pressure
What contributes to the greater precision of anesthetic depth of Desflurane?
very low solubility in blood (0.45) and other tissues
What makes Desflurane less potent than other drugs?
- dogs = 7.2%
- horses = 8.1%
- pigs = 10%
What does Desflurane do to heart rate and vasodilation?
Desflurane is dose dependent on what?
if it causes respiratory depression or not
Does Desflurane cause arrhythmias?
Can the MAC of Halothane be 0.86%?
Vapor pressure of Halothane
What is the preservative in Halothane that can accumulate in vaporizers?
At what MAC does Halothane cause respiratory arrest in horses?
Are respiratory rate and ventilation better or worse maintained when using Halothane?
Hepatic metabolism of Halothane
What is the decrease in hepatic blood flow due to Halothane, and the metabolite trifluoracetylated protein adducts in hepatocytes causing an immune reaction?
Why is the recovery from Halothane prolonged?
greater blood:gas solubility (2.54)
Why is Halothane arrhythmogenic?
causes CVS depression and arrhythmia
Side effects of inhalant anesthetics on the CNS
- reversible CNS depression
- cerebral vasodilators (increase cerebral blood flow and intracranial pressure)
- decreased cerebral metabolism
- Enflurane: tonic-clonic convulsions
- caution with brain tumors and head trauma
Respiratory side effects of inhalation anesthetics
- dose-dependent respiratory depression
- decreased alveolar ventilation
Side effects of inhalation anesthetics on the kidneys
dose-related decreased blood flow and GFR = decreased diuresis
Side effects of inhalation anesthetics on the CVS
- decrease in BP
- decrease in CO = decrease in myocardial contraction
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