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.
