ITE CA2 inhalational agents Flashcards
volatile with greatest effect on sympathetic nervous system
des
after 40 years of age, MAC of inhalational agents decreases by waht percent per decade
6%
rank in order (greatest metabolized to least), the percent of inhalation agents metabolized within the body
sevo > iso > des
volatile with highest probability of producing CO in CO2 absorber
des
volatile potentiate neurmusc blockade
Des
nitrous effect on PVR?
Can increase it
But does it always?
latent heat of vaporization
amount of energy required to convert a unit mass of substance from its liquid to vapor phase
oil:gas coefficient
increased oil:gas coefficient equals increased potency of inhalational agent which leads to a decreased partial pressure required for a surgical plane of anesthesai
fastest rate of rise of FA/FI
N2O
inhibit methionine synthetase
N2O
compound A
sevo
What inhaled anesthetic can inhibit DNA synthesis
It is clear that nitrous oxide can inhibit DNA synthesis with chronic exposure (e.g. recreational N2O abuse causing megaloblastic anemia). But there is no evidence that N2O or any other inhaled anesthetic can cause any effect on fertility, teratogenicity, or carcinogenicity on health care workers exposed to trace amounts in the presence of scavenging systems.
Factors that increase MAC
Factors Increasing MAC: Drug - Amphetamine (acute use) - Cocaine - Ephedrine - Ethanol (chronic use) Age - Highest at age 6 months Electrolyte disturbance - Hypernatremia Hyperthermia Red hair
Factors that decrease MAC
Factors Decreasing MAC: Drugs - Propofol, etomidate, barbiturates, benzodiazepines, ketamine - Alpha2 agonists (clonidine, dexmedetomidine) - Ethanol (acute use) - Local anesthetics - Opioids - Amphetamines (chronic use) - Lithium - Verapamil Age - Elderly patients Electrolyte disturbance - Hyponatremia Others - Anemia (Hgb < 5 g/dL) - Hypercarbia - Hypothermia - Hypoxia Pregnancy
Blood:gas partition coefficients Desflurane Nitrous Sevo Iso Halothane
Des 0.42 Nitrous 0.46 Sevo 0.69 Iso 1.46 Halothane 2.54
One lung ventilation more significantly slows relative rate of induction of which volatiles
and why
less soluble, such as des
The right-to-left pulmonary shunt from OLV results in blood from the right ventricle passing through the capillary beds of both ventilated and non-ventilated alveoli. Therefore, insoluble agents will remain in the ventilated lung with a minimal amount of agent dissolving into the bloodstream. The blood containing desflurane from the ventilated lung mixes with blood from the non-ventilated lung, in the left atrium. This leads to a reduction in the rate of rise of the arterial partial pressure (Pa) relative to the inhaled partial pressure (PI) of the agent.
R to L shunt effect on induction with inhalational agent
decreased induction speed
L to R shunt effect on induction with inhalational agent
Minimal/no effect
Volatile anesthetics potentiate neuromuscular blockade by
Volatile anesthetics potentiate neuromuscular blockade by DECREASING sensitivity of the postjunctional membrane to depolarization and INCREASING skeletal muscle blood flow which both augment neuromuscular blockade. In addition, potentiation of neuromuscular blockade occurs by depression of upper motor neurons.
metabolism of volatiles
Sevoflurane undergoes the most extensive metabolism (5-8%) followed by isoflurane (0.2%) then desflurane (< 0.2%).
When a patient is administered 75% nitrous oxide a pneumothorax will double in size by
When a patient is administered 75% nitrous oxide the gas will rapidly diffuse from the blood and into air-filled cavities. A pneumothorax will double in size by 10 minutes and triple by 30 minutes.
Why is des heated
Desflurane has an extremely high vapor pressure and is significantly vaporized at room temperature; therefore desflurane requires a heated vaporizer to maintain constant vaporizer output concentration as the vapor pressure would decrease significantly from evaporative cooling.
Relation of MAC to barometric pressure
The MAC for all inhaled anesthetics is indirectly related to barometric pressure. As pressure increases (e.g. hyperbaric chamber), MAC decreases. As pressure decreases (e.g. higher altitude), MAC increases. However, a given alveolar partial pressure of an inhaled anesthetic produces the same effects, no matter the barometric pressure. Most variable-output vaporizers for isoflurane and sevoflurane deliver fixed partial pressures of volatile anesthetics based on their dialed settings. These dial settings do not generally need to be changed to compensate for changes in barometric pressure.
inhalational agents review
For example, an isoflurane variable-bypass vaporizer is designed to deliver isoflurane at a partial pressure of approximately 7.6 mm Hg when the dial is set at 1%. When the vaporizer is at sea level, the partial pressure of 7.6 mm Hg corresponds to a concentration of 1% (7.6 mm Hg / 760 mm Hg) as dialed. Even after bringing the same vaporizer with the same dialed 1% to a hyperbaric chamber pressurized to 2 atm, the vaporizer is designed to compensate for the change in barometric pressure and will continue to deliver isoflurane at nearly the same partial pressure of 7.6 mm Hg. It does this by decreasing the vaporizer output such that the delivered concentration decreases to approximately 0.5% (7.6 mm Hg / 1,520 mm Hg) despite still being dialed at 1%.
Desflurane vaporizers operate differently: they are typically heated to 39 °C which creates a constant desflurane vapor pressure of 2 atm within the vaporizer, independent of barometric pressure. It then delivers the anesthetic at a fixed percent concentration, not partial pressure. This means in a hyperbaric chamber, the partial pressure of desflurane delivered to the alveoli is increased due to the rise in barometric pressure. In order to compensate, the inspired concentration should be manually decreased with the dial setting.
The rate of inhaled anesthetic induction (FA/FI) is increased with increased minute ventilation. This effect is greatest with the agents with ____ solubility, including _______.
The rate of inhaled anesthetic induction (FA/FI) is increased with increased minute ventilation. This effect is greatest with the agents with high solubility, including halothane and isoflurane.
Which of the following characteristics of nitrous oxide is MOST important for allowing it to exist as both a liquid and gas at room temperature in a pressurized medical gas cylinder
Critical temperature is the temperature above which a gas cannot be liquified no matter the pressure applied. If the critical temperature of a medical gas is above room temperature (e.g. nitrous oxide: 36.4 °C and carbon dioxide: 31.1 °C), the gas can potentially exist in both gaseous and liquid forms at room temperature when compressed in a medical gas cylinder. If the critical temperature of a gas is below room temperature (e.g. oxygen: -118 °C), the gas will never liquify at room temperature.
Pouring isoflurane into a sevoflurane vaporizer
Pouring isoflurane into a sevoflurane vaporizer is most likely to lead to an overdose of volatile anesthetic. This is due to (1) the larger vapor pressure of isoflurane, and (2) the increased potency of isoflurane compared to sevoflurane. Sevoflurane has a relatively low vapor pressure of 160 mmHg at 20 °C compared to 240 mmHg for isoflurane. Therefore, there will be proportionally more molecules of isoflurane in the vapor phase and the output concentration of isoflurane will be greater than what is set on the “sevoflurane” vaporizer concentration dial. The use of an anesthetic agent analyzer (e.g. infrared absorption spectrophotometry) would alert the provider to such an error.
1.0 MAC of CO2 in the blood is around
1.0 MAC of CO2 in the blood is around 200 mmHg
The MAC of volatile anesthetics in pregnancy
The MAC of volatile anesthetics is reduced by about 30% during pregnancy. Pregnant women are also more sensitive to local anesthetics.
Reduced cardiac output leads to an increased speed of inhaled anesthetic induction (FA/FI), particularly for the soluble vs insoluble anesthetics
Reduced cardiac output leads to an increased speed of inhaled anesthetic induction (FA/FI), particularly for the soluble anesthetics like isoflurane or halothane.
factors that increase the speed of inhaled anesthetic induction Fa/Fi
Low agent blood solubility (measured by the blood:gas partition coefficient, or KB:G)
Low cardiac output (especially for the highly soluble agents such as isoflurane or halothane)
High minute ventilation (especially for the highly soluble agents such as isoflurane or halothane)
High inspired concentration (the “concentration effect”)
Low starting venous concentration (Pv ≈ 0, hence large concentration gradient for agent diffusion into circulation)
High fresh gas flow (to more quickly deliver the set dial concentration)
Low volume of the circuit (to more quickly deliver the set dial concentration)
partial pressures at equilibrium cns, blood, alveoli in order
As long as normal cardiopulmonary function exists (i.e. no intrapulmonary, intracardiac, or cardiopulmonary shunting), PCNS = Pblood = Palveoli of inhaled anesthetics at equilibrium.
Preservation of THBF amongst volatile anesthetics at 1 MAC, from greatest to least,
Preservation of THBF amongst volatile anesthetics at 1 MAC, from greatest to least, is sevoflurane > isoflurane > halothane.
Desflurane cardio effects
Desflurane increases heart rate and decreases both mean arterial pressure and systemic vascular resistance while maintaining cardiac output.
causes dose-dependent depression of myocardial function. Cardiac output is maintained and there is no significant effect on left ventricular diastolic function.
Factors leading to increased compound A include
Factors leading to increased compound A include (1) low fresh gas flows or closed circuit, (2) Baralyme > soda lime»_space; calcium hydroxide lime, (3) higher concentration of sevoflurane, (4) high absorbent temperature, (5) fresh absorbent. Interestingly, dehydration of Baralyme increased the concentration of compound A but dehydration of soda lime decreased the concentration of compound A.
____ is the pH indicator within carbon dioxide absorbents.
Ethyl violet is the pH indicator within carbon dioxide absorbents.
Carbon monoxide is another potentially toxic byproduct of the CO2 absorbent. factors that contribute to the production of CO
Carbon monoxide is another potentially toxic byproduct of the CO2 absorbent. The presence of strong base (barium, sodium, and/or potassium hydroxide) most contributes to the production of CO. Other factors that contribute to the production of CO include volatile anesthetic (desflurane > isoflurane»_space; sevoflurane), desiccation of absorbent, low fresh gas flow, high concentration of inhaled anesthetic, and increased absorbent temperature.
how does a concentration-calibrated variable bypass vaporizer change the desired percentage of volatile delivered to the patient
Concentration-calibrated variable bypass vaporizers adjust the splitting ratio to achieve the desired percentage of volatile anesthetic delivered to a patient.
high solubility is high or low blood:gas partition coefficient
high
Carbon dioxide absorbents containing barium hydroxide Soda lime Calcium hydroxide Desiccated absorbents
Carbon dioxide absorbents containing
barium hydroxide produce the most compound A and have the highest risk for fire production during sevoflurane administration.
Soda lime, due to higher water content, has a reduced incidence of compound A and fire production.
Calcium hydroxide absorbents, due to lower reactivity, have the lowest incidence of compound A and fire production.
Desiccated absorbents absorb less CO2, produce more heat and carbon monoxide, and have an increased risk of compound A and fire production.
Barium hydroxide absorbent preparations produce ____ carbon monoxide than soda lime due to the decreased water content of barium hydroxide absorbents.
Barium hydroxide absorbent preparations produce more carbon monoxide than soda lime due to the decreased water content of barium hydroxide absorbents.
The reaction between desiccated CO2 absorbents and sevoflurane produces the most _____ while the reaction with desflurane produces the most ______
The reaction between desiccated CO2 absorbents and sevoflurane produces the most heat while the reaction with desflurane produces the most carbon monoxide.
