General anesthesia 3 cardiopulmonary function Flashcards
MAC50, what and how is it measured?
The end-tidal concentration, expressed as a percentage, of an inhalational anesthetic that prevents movement in response to a supramaximal noxious stimulus in 50% of the studied individuals
-50 volts at 50 cycles/sec for 10 msec
same anesthetic will have different effects on each brain system. how are movement in response to pain and autonomic reactions comparable at mac50?
more anesthetic required to stop autonomic reactions
anesthetics work on what receptors?
all
GABA, glycine (inhibitory receptors) increased
excitatory receptors decreased
Inhalation and injectable anesthetics CNS effects
Affect normal discharge of neurotransmitters and impact other
systems
resp center is where and works how?
- Located in the medulla oblongata and pons
- Information from peripheral and central chemoreceptors in response to blood levels of O2 and CO2 determines signals from RC to the respiratory muscles
cardiovascular center is where and works how?
- Located in the medulla
- Responds to information from arterial baroreceptors located in the carotid sinus and aortic arch
respiration vs ventilation
§ Respiration is the total process of delivering O2 to the cells and carrying away the byproduct of metabolism, CO2
* Gas exchange in the lungs (through ventilation) * Circulation of gases through the blood stream
* Transfer of gases at the cellular level
§ Ventilation is the process of moving gases through the respiratory tract
* CONTROLS O2 and CO2
anatomical deadspace
Volume of air in the mouth, pharynx, trachea and bronchi up to the terminal bronchioles.
alveolar dead space
Volume of air in the alveoli not participating of gas exchange
dead space related to panting/shallow breathing
§ Air flow may not reach areas of gas exchange
* Contributes to less removal of CO2 from the lung
* May affect oxygenation depending on FiO2
dead space vs shunt
Dead space- Ventilated but not perfused
* Hypoperfusion (V/Q > 1)
Shunt- Perfused but not ventilated
* Complete small airway closure
* Collapsed alveoli (atelectasis)
* Bronchoconstriction (V/Q < 1)
how does ventilation-CO2 relationship change when injectcatble anesthetic is adminitered?
the CNS is less responsive, so overall more CO2 will correspond to less ventilation, but the same linear relationship (ie. more CO2 -> more ventilation, at the same slope as sober) remains - shifts relationship to the right
how does ventilation change when you build up CO2
minute ventilation increased (RR xVt)
how does ventilation-CO2 relationship change when inhalant anesthetic is administered?
shift relationship to the right and make the relationship less linear
is you combine injectables and inhalants, CO2 response resembles
inhalants alone
