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99 Cards in this Set
- Front
- Back
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Who isolated and purified N2O?
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Joseph Priestly
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How were the anesthetic properties of N2O discovered?
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Through its recreational use as laughing gas.
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How was N2O use made safer?
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With the combined use with oxygen.
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How is N2O prepared?
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By heating of ammonium nitrate to 245-270 degrees centigrade yielding
NH4NO3 --> N2O + 2H2O |
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Critical temperature.
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Temperature above which a substance cannot be liquified regardless of the pressure applied to it.
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What is the critical temperature of N2O?
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36.5 degrees centigrade.
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How is N2O stored?
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As a liquid below its critical temperautre at 750PSI.
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What is the gaseous phase above the liquid?
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Vapor
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Saturated vapor pressure
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When the number of molecules in the vapor phase equibrilate to that in the liquid phase
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What phases are present when N2O is stored in a tank and at what pressure?
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Gas, vapor, and liquid at 51 atm.
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What is Boyles law?
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P1V1=P2V2
Where pressure and volume are inversely proportional |
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What color tank is N2O stored in?
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Blue steel tank.
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At 750PSI and 21degrees centigrade, how much N2O is in a full tank?
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1600L
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Can the volume of N2O in the tank be determined by the guage pressure?
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No, because as N2O vapor is used, more vapor is created and brought into equilibrium with the liquid phase causing no change in the guage pressure.
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How is the volume of the N2O tank then determined?
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By weight.
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When does the guage pressure fall in coordinance with decreasing N2O levels?
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When the N2O liquid is fully vaporized which is at 75%
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What is required for evaporation of N2O?
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Heat
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What is adiabatic cooling?
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When the tank becomes cold from using energy to convert liquid to vapor (using internal energy) so you get a drop in temperature due to expansion of a gas. (specific laten heat of vaporization)
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What happens if rapid evaporation of N2O occurs?
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Adiabatic cooling and frost may accumulate on cylinder due to freezing H2O vapor
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What are some characteristics of N2O?
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Colorless gas, highly poisonous, cyanosis from methemoglobin formation, if inhaled 10-15ppm for 8 hours can have chest pain, pnuemonitits, pulmonary edema.
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How can methemoglobinemia be treated?
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Methylene blue 2mg/kg
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What impurities are produced during N2O manufacturing?
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Ammonia, chlorine, nitrogen, CO2, CO
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What are S&S of ammonia toxicity and what is the color?
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It is colorless irritation of respiratory tract, bronchospasm, pulmonary edema, blindness, death.
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What are S&S of chlorine and what color is gas?
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It is yellow-green with an odor and can cause tightness in chest, pulmonary edema and death
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What symptoms presents with ambient contaminants of N2O?
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Asphyxiation
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In the production of N2O water is produced, what effect does this have?
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Condensation of water vapor can clog the cylinder and valve and alter flow of the gas.
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What are the S&S of CO and what color is the gas?
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It is colorless and causes a left shift of the curve, has a greater affinity for Hgb than O2 so decreases PaO2.
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How can the cessation of smoking alter carbon monoxide?
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It can decrease it by 50% in 12 hours.
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Does N2O support combustion and is it flammable?
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It is non-flammable but it does support combustion.
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What amount of the earths atmosphere is nitrogen and from what two sources?
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0.00005%
1. Bacterial denitrofication of fixed N compounds 2. Breakdown of nitrate fertilizers |
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Partial pressure characteristics of inhaled anesthetics.
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Pcns=Pblood=Palveoli
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Alveolar concentration of an anesthetic.
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The amount of anesthetic DELIVERED to the lungs by ventilation.
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Blood uptake of anesthetic.
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The amount of anesthetic REMOVED from the lungs by the blood.
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Partition coefficient
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The amount of substance in one phase compared to another phase
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What can the partition coefficient tell us?
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The behavior of the gas entering or leaving the body.
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What is the partition coefficient of N2O between blood-gas?
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0.47
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What does 0.47 tell us about N2O?
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That N2O stays in the gas phase (alveoli) 0.47 times more than in the blood allowing it to equilibrate with the CNS faster
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What three things are inhaled anesthetics dependent on for uptake?
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1. Cardiac output
2. Blood-gas partition coefficient 3. Alveolar to venous partial pressure difference of the anesthetic (VO2) |
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What does the partition coefficient measure?
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1. Solubility
2. Ratio of partial pressure of gas dissolved in the blood to that of the partial pressure of gas inhaled at equilibrium 3. How the anesthetic will partition between the two phases |
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How does solubility affect an anasthetic agent?
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The more soluble the less [] you need to be effective.
The less soluble the more [] you need to be effective. |
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What is the blood flow to various tissue in descending order?
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VRG>Muscle>Fat>VPG
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Fa/Fi
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Ratio of fractional concentration of alveolar anesthetic to inspired anesthetic.
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How is Fa/Fi affected by low solubility anesthetics?
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Rapid rise in alveolar [].
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How can higher inspired N20 [] accelerate the rise of alveolar N2O?
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1. Absorption of the gas into the blood causes the remaining alveolar gas to []
2. The (-) pressure created by the lungs in the uptake of N2O by blood causes more N2O to be indrawn into lungs to replenish the N2O. |
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Does a highter [] of N2O increase the Fa/Fi ratio?
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Yes
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What is the second gas effect?
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The rise in alveolar [] of any other anesthetic when given with high [] of N2O
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How does the second gas effect work?
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Because the []/partial pressure of N2O is increased, it partitions into the blood more rapidly (by 50%) than the anesthetic thus decreasing the alveolar concentration of N2O and allowing the anesthetic to concentrate in the alveoli thus increasing Fa
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How can the [] of a second gas that is highly soluble be increased?
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By increasing the minute ventilation.
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Will increasing the minute ventilation when giving a second highly soluble gas increase the Fa/Fi ratio?
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Yes to a certain extent that the inhaled anesthetic does not concentrate so much as to cause ventilatory depression thus slowing the rise in Fa/Fi.
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How is perfusion affected by the second gas effect?
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With increased CO Fa/Fi will be lower with more soluble anesthetics which can lead to cardiovascular depression.
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What is the correllation between the Fa and the partial pressure of anesthetic in the CNS?
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It is directly proportional.
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How does increase [] of N2O affect air spaces or surgeries that are potential air spaces?
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Blood carrying N2O in increase [] transfers 34 times more gas into the space than is carried out thus increasing the volume and pressure in the air space. Acts like an air embolus.
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What type of surgeries or situations should high [] of N2O not be used?
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Bowel surgeries, pneumos, eye surgery, use of LMA due to diffusion of N2O into cuff and ETT cuffs, increase ICP(increases cerebral blood flow), laparoscopy, posterior fossa surgery.
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If N2O were used in the case of having an ETT how would the cuff be managed?
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Deflate cuff and instill half of the amount of gas retrieved back into the cuff using the same gas mixture.
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What factors affect movement of N2O into an air space?
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1. Alveolar partial pressure of N2O
2. Blood flow to the cavity 3. Length of time N2O administered 4. Compliance of walls of the air space |
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If the [] of N2O is 80%, by what fold will the air bubble increase?
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Vnew/Vo=1/(1-0.8)=5 fold
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How long does it take for the size of a pneumo to double with N2O use? Triple?
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10 minutes and 30 minutes respectively.
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How long does it take for the volume of a swan cath balloon to double?
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10 minutes.
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Would procedures >2hours be contraindicated for the use of N2O when ETT or LMA is involved and why?
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Yes it is contraindicated because ischemia in the tracheal wall could result from increase volume and pressure due to N2O diffusion into the cuff.
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What factors influence recovery from N2O?
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1. Blood/gas coefficient
2. Cardiac output 3. Alveolar ventilation |
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Why is N2O recovery faster than with other inhaled anesthetics?
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Because of its low solubility
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Diffusion hypoxia
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Washout of high [] of N2O from blood into lungs displacing alveolar []'s of O2 and CO2 during recovery from anesthesia.
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How can diffusion hypoxia depress the respiratory drive?
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It causes alveolar hypoxia which leads to hypoxemia causing hypocarbia thus knocking out the drive to breath making the hypoxemia worse.
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What is the treatment for diffusion hypoxia?
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100% O2 treatment for first 5 minutes of recovery.
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What is MAC of inhaled anesthetics?
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It is the minimum alveolar concentration used to prevent movement in response to stimuli in 50% of the patients.
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What does MAC tell us?
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The index of potency.
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Why is N2O not used as an anesthetic?
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MAC of N2O is 104% at 1 amt so N2O would have to be used with a [] of O2 of that in a hyperbaric chamber to offset a hypoxic mixture. 50% at 2atm.
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How is N2O generally used in the anesthesia setting?
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As a supplement to more potent inhalation agents or narcotics for an additive effect in [] of 50-70%.
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How is N2O metabolized?
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Very little is, N2O is reduced to N gas and free radical intermediates in the bowel.
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How does N2O affect DNA synthesis?
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It inactivates the enzyme, methionine synthetase, necessary for DNA synthesis.
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What toxic effects can result from N2O use based on DNA effects?
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Leukopenia, megablastic anemia, and impaired fetal development (1st trimester)
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What other way can N2O affect methionine synthetase activity?
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It oxidies the cobalt atom of B12 irreversibly and methionine enzyme is dependent on B12 activity.
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At what [] of N2O is analgesia provided without sedation?
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15-40% N2O
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Does N2O work on endogenous opiate receptors?
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It is theorized that it does becaus Narcan can decrease its analgesic response
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Does N2O affect uterine contractility or fetus
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No
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How long does it take for N2O to be detected in the umbilical vein?
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2 minutes
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How long does it take for N2O to equibrilate between the umbilical artery and vein?
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30 minutes
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What % [] of N2O is used for a balanced technique?
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50-67%
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When N2O is used as part of a narcotic technique, is itra-op reacall eliminated?
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No, a sedative should be used to decrease recall.
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How is the sympathetic nervous stimulation offset when using N2O?
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Through the use with most inhalational anesthetics or narcotics.
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What effect does N2O have on the cardiovascular system?
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Decrease HR, contractility, and CO on isolated muscle when given alone, increase SVR without increase BP. Narcotics will offset the SNS myocardial depression.
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When given with other agents what other CV effects will be seen with N2O?
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Decrease PVR, HR, CO, CVP without increasing BP.
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Should pts with pulmonary HTN be given N2O?
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No because it increases pulmonary artery pressure
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How does N2O affect the respiratory system?
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Increase TV and MV, decrease pulmonary compliance and FRC, 25% increase in airway resistance due to increase density of N2O, can cause diffusion hypoxia
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Should N2O be given to asthmatics?
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Not a good choice if actively wheezing due to increase airway resistance caused by N2O.
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In what instances can N2O cause N/V?
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When it diffuses into the bowel, middle ear, or with interaction with opioid receptors.
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What long term effects does N2O have on pts?
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Bone marrow depression, granulocytopenia (related to [] and exposure time), depressed monocyte and neutrophil chemotaxis, interference with leukocyte cytotoxicity and chemotoxicity (increase severity of post-op wound infection)
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What population has an increase incidence of liver disease?
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Dentists and hygienists with chronic exposure to N2O
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Long term N2O use can cause polyneuropathy, what are the symptoms and why does it occur?
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Numbness, ataxia, parasthesias, impaired cognitive skills due to inactivation of methionine synthetase.
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Can the polyneuropathy symptoms regress after discontinuation of N2O exposure?
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Yes
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What is the Meyer-Overton theory?
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MAC of a volitile substance is inversely proportional to its lipid solubility. MAC is inversely proportional to the potency of the anesthetic so the higher the MAC the lower the potency of the anesthetic.
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What is pharmacokinetics?
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What the body does to drugs, where it goes, how it is transformed, and the cellular and molecular mechanism underlying these processes.
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What is pharmacodynamics?
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What drugs do to the body, desired/undesired effects, as well as the cellular and molecular changes leading to the effects.
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What are time constants?
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The volume or "capacity" of the circuit (Vc) divided by the fresh gas flow. In 1st order kinetics 95% of maximum is reached after three time constants. (Bag, canister absorbants, tubing, piping)
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What determines anesthetic uptake?
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The fraction inspired, the fraction alveolar, the amount of anesthetic that crosses the alveolar-capillary membrane, the amount that dissolves in the blood based on solubility and partial pressure of the gas, [] of anesthetic used.
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Factors that increase MAC.
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Increase central neurotransmitter levels, hyperthermia, chronic EtOH, hyperNa
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Factors that decrease MAC
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Increase age, metabolic acidosis, hypoxia, induced hypotension, decreased central neurotransmitter levels, hypotermia, hypoNa, Neo/Physostigmine, barbituates, anemia, acute EtOH, pregnancy, hypoosomolality, lithium, diazepam, Marijuana, opioids etc.
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What are Guedel's signs?
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Stage I: stage of analgesia
Stage II: stage of excitement Stage III: stage of surgical anesthesia |
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What is malignant hyperthermia?
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Autosomal dominant disorder, increase skeletal muscle oxidative metabolism in response to volitile anesthetics which causes hyperthermia, increase O2 consumption and death if not treated.
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