Term
| What low-flow oxygen delivery systems are available and what are their benefits/drawbacks? |
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Definition
Nasal cannulae and simple face masks w/ or w/o reservoir bags.
They are easy to use but have a limited ability to rase FIO2 because they depend on entrained room air to make up the balance of inspired gas (oxygen flow is lower than respiratory flow). |
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Term
| Why might you want to use a closed system, endotracheal tube (or sealed mask) with oxygen blender for oxygen delivery? |
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Definition
| If you needed to precisely define FIO2 |
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Term
| Why might you use a pulse oximeter? |
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Definition
Noninvasive technique that measures oxygen saturation.
1) Rapid evaluation and monitoring of potentially compromised patients
2) Titrating O2 therapy in situations where O2 toxicity is a worry |
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Term
| Why administer NO and what are the important complications to be aware of? |
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Definition
NO preferentially dilates pulmonary vasculature in well-ventilated areas, and can therefore improve V/Q balance.
1) Given to newborns to treat persistent Pulmonary HTN or to adults for pulmonary embolism, HTN and acute chest syndrome in sickle cell patients.
2) Watch out for NO2 in presence of high O2 levels, as well as Methemoglobinemia in infants |
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Term
| Why administer Helium (g) and what are the important complications to be aware of? |
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Definition
Low density, low solubility, inert gas with high thermal conductivity that is used in
1) Pulmonary function testing to measure RV, FRC and related volumes.
2) Low density decreases work of breathing in patients with elevated airway resistance.
3) Slow down ignition of flammable components during laser surgery on airway
4) contrast agent in pulmonary MRI |
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Term
True or False:
Relatively large volumes of CO are produced endogenously |
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Definition
| True! 10 ml CO daily from conversion of heme to bilverdin by heme oxygenase (HO) |
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Term
How can CO be toxic?
How might it be used therapeutically? |
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Definition
1) CO bind Hb 240X better than O2, partially occupying O2 sites, so it left-shifts the O2 saturation curve and makes it harder for O2 to be delivered to tissues.
2) Non-toxic doses produce similar effects to up-regulation of HO-1, perhaps exhibiting useful clinical properties (HTN, organ transplant, inflammation, vascular injury, ventilator-induced lung injury) |
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Term
| What are the 3 major Anesthetics currently in use? |
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Definition
Based off of fllourinated hydrocarbon structure of Halothane.
1) Isoflurane
2) Sevoflurane
3) Desflurane |
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Term
| What are the 3 general objectives of administering general anesthesia? |
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Definition
1) Minimize potentially deleterious direct and indirect effects
2) Sustaining physiological homeostasis during surgery
3) Improve post-operative outcome |
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Term
What does Minimum alveolar concentration (MAC) have to do with anesthetic potency?
What are the potential drawbacks of using MAC as an indicator of potency? |
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Definition
1) MAC that prevents movement in 50% of patients is used as a measure of potency, where the lower the MAC, the MORE potent the drug.
2) MAC is consistent and reproducible within a given patient population, but decreases with age and body temperature and during pregnancy.
**measure in Vt** |
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Term
| Why are general anesthetics very dangerous drugs? |
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Definition
1) Steep dose-response relationships
2) Low therapeutic indices
3) No available antagonists |
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Term
| How does the action of general anesthetics relate to GABAa signaling? |
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Definition
Increase sensitivity of inhibitory GABAa receptor to GABA (chloride channel gating)
**DOES NOT bind GABA site**
Other ligand-gated channels are also effected, with the general effect of inhibiting excitatory neurotransmission and potentiating inhibitory signaling. |
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Term
True or False:
General anesthetics work by binding to neuron cell membrane components and altering their signaling properties. |
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Definition
This MAY be true, but is probably only part of the story (Meyer-Overton correlation).
Lipid soluble anesthetics are potent and may act on cell membranes, but this is not the whole explanation. |
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Term
| How are general anesthetic partition coefficients defined pharmacokinetically? |
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Definition
| The ratio of anesthetic concentration in two tissues when the partial pressures of that anesthetic are equal (thus, difference in solubility). |
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Term
| How does anesthetic solubility relate to drug potency? |
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Definition
| The higher the solubility, the higher the partition coefficient and the lower the MAC (more potent). |
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Term
| What 3 important factors determine anesthetic uptake from the lungs? |
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Definition
| Blood solubility * CO * partial pressure driving drug from lung phase into venous blood phase |
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Term
| What factors influence FA/FI ratio and what does this have to do with the speed of anesthesia induction? |
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Definition
Fa is alveolar partial pressure and FI is inspired partial pressure (this ratio is the point of no net movement between alveoli and circulation)
Factors that increases the rate of FA/FI equilibration will speed up induction
Insoluble drugs that are inhaled quickly at high concentrations, in the context of low CO will act the fastest.
1) Solubility of anesthetic (less soluble, faster induction)
2) Ventilation rate (increased rate, faster induction)
3) CO (decreased CO, faster induction).
4) Inspired concentration |
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Term
| What are the 4 main body compartments with regard to uptake and distribution of anesthetics? |
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Definition
1) Vessel-rich: CNS and visceral organs
- Equilibrate rapidly with inspired drug because of high BF and low capacity**
2) Muscle group: skin andmuscle
- Moderate flow and high capacity
3) Fat group:
- Low flow and high capacity
4) Vessel porr: Bone, cartilage and ligaments
- Minimal effects on anesthetic uptake and distribution. |
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Term
| What is the importance of the alveolar:venous gradient? |
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Definition
1) Partial pressure gradient between drug in venous blood and alveoli develops as ventilation sweeps anesthetic from alveoli during recovery
2) Gradient drives anesthetic into alveoli and opposes tendency of ventilation to lower alveolar concentration.
3) More soluble agents (isoflurane) create bigger gradients |
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Term
| What is the potential relevance of Xenon in anesthesia? |
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Definition
Only obtained by extraction from air ($$$$).
Ideal anesthetic, if $$ is reduced
1) Low blood and tissue solubility (rapid induction and recovery)
2) High potency
3) Not metabolized by body
4) Non-flammable with few side effects |
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Term
| What are the known physiological signaling effects of CO? |
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Definition
Inhalation of CO treats inflammation, HTN, organ transplant, vascular injury and ventilator-induced injury in animal models.
1) Modulates sGC, leading to cGMP production and pulmonary vasodilation
2) Modulates MAPK activation to stimulate Ca-dependent K+ (BK) channel activity to promote muscle relaxation |
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Term
| How is Hydrogen Sulfide utilized clinically? |
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Definition
Inhibits cytochrome C oxidase, limiting mitochondrial respiration.
- May limit some forms of cellular injury when delivered in dose-controlled manner. |
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Term
| What is the "therapeutic index" of an anesthetic? |
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Definition
LD50/MAC (basically amount that hurts over amount that helps).
Anesthetics how LOW TI, so they are dangerous!
There is also a steep dose-response curve and no available antagonists. |
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Term
| What central neurological sites are affected by anesthetic action? |
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Definition
1) Spinal chord (pain and immobility).
2) Tuberoumamillary nucleus of hypothalamus (sedative/anxiolytic)
3) Hippocampus (amnestic)
4) Thalamic inhibition (awake-anesthetized transition) |
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Term
What are the effects of anesthetics on NMDA receptors?
What about 2-pore K+ channels? |
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Definition
1) Inhibition of these glutamate-gated cation channels
2) Stimulation of pre-synaptic (hyperpolarization) and post-synaptic (lower resting membrane potential) channels |
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Term
| What is the "concentration effect" of anesthetic delivery? |
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Definition
| More soluble drugs like halothane will take less time to equilibrate (e.g. take effect) when they are delivered at higher inspired partial pressures. |
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Term
| What are the effects of inhaled anesthetics on circulation and respiration? |
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Definition
1) Decrease systemic BP in dose-related manner (CO is maintained for isoflurance and desflurane)
2) Reduced spontaneous Ve in dose-dependent manner
**if ventilation is not controlled, this may increase PaCO2 |
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