Clinical Responses to Hypoxemia and Hypercapnia Flashcards
What are the three components of ventilatory control?
- Sensors (chemoreceptors, lung and other receptors)
- Central controllers (pons, medulla, other parts of brain)
- Effectors (respiratory muscles)
What is collectively sensed by the central and peripheral chemoreceptors?
PaO2, PaCO2, and H+
What are differences between the central and peripheral chemoreceptors in regard to sensing PaCO2?
Central chemoreceptors are responsible for 70% of the response to PaCO2 levels
Peripheral chemoreceptors are responsible for 30% of the response
How is CO2 produced in the body?
Oxidative breakdown of foods (glucose + fats)
What is the normal concentration of H+ ions in the blood?
What pH does this correspond to?
40 nanomoles per Liter
pH is -log [H+]
-log [0.00000004] = 7.4
What is the normal ventilatory response in a patient whose PaCO2 increases to 60 mmHg?
An increase in both respiratory rate and tidal volume
How does an increase in PaCO2 lead to a decrease in pH?
CO2 is buffered which increases H+ levels and decreases pH
What is sensed by the peripheral chemoreceptors?
PaCO2
pH
Dissolved O2
Why is the saturation curve for hemoglobin with oxygen sigmoidal?
At a certain point, hemoglobin saturation increases exponentialy due to increase of hemoglobin in R-State
What is Henry’s law?
The amount of gas dissolved in a solution is directly proportional to the partial pressure of that gas
If a patient has low hemoglobin (anemia) and has an oxygen saturation of 100% on room air, what is her expected ventilatory response?
No change in ventilatory response
WHich of the lollowing statements is false?
- PaO2 is dependent on hemoglobin saturation
- Hemoglobin saturation is dependent on PaO2
False = PaO2 is dependent on hemoglobin saturation
WHat are the normal ranges/values for…
pH:
PaCO2:
PaO2:
pH: 7.35 - 7.45
PaCO2: 35-45
PaO2: >70 mmHg
In which direction should the abdomen move during normal inspiration?
Outwards
What respiratory muscles contract durin inhalation?
Diaphragm and external intercostal muscles (internal intercostal muscles relax)
What inervates the diaphragm?
Phrenic nerves
What group of muscles are used in respiratory distress?
- Accessory muscles
- Sternomastoid
- Intercostals
- Abdominal muscles (especially transversus abdominus)
- Scalenes
What are the peripheral chemoreceptors and which is more important in sensing decreased oxygen levels?
Carotid body and Aortic body
Carotid body more important in recognizing decrease in oxygen
Are the peripheral chemoreceptors or central chemoreceptors more sensitive to increases in CO2?
Central chemoreceptors (70%)
What can you do to win against your friends in a breath holding contest?
Why does this work?
Take multiple deep breaths just before going underwater
Hyperventilation removes carbon dioxide from the blood and thus it will take longer for you to receive the signal to remove more CO2
What are clinical signs of hypercapnic respiratory failure?
Somnolence
Asterixis (non-rhythmic tremor)
Chest wall barely moving
How does hypercapnea result in a decreased respiratory drive?
Increased PaCO2 → Increase in HCO3 → Increase in pH → Decreased respiratory drive
What is hypoxic vasoconstriction
Mechanism by which blood flow is diverted away from poorly ventilated areas
Why is too much oxyen deliver bad for COPD patients?
Too much oxygen vasodilates leading to re-establishment of blood flow to parts of the lung that are poorly ventilating (due to COPD) - this leads to air trapping and an increase in PaCO2
What is the haldane effect?
If hemglobin is saturated with oxygen, CO2 levels in the blood will increase because oxygenated hemoglobin has a reduced capacity for CO2
How does the body compensate for a damaged phrenic nerve?
Increased use of accessory muscles
