Exam 6: Pulmonary Gas Exchange Flashcards
What is Dalton’s Law?
The sum of thee partial pressures of all the gases in a mixture determines the total pressure of the mixture
What is Henry’s Law?
The pressure of a gas in a liquid is determined by the concentration of the gas and its solubility
What is the FIO2 on top of Mount Everest?
0.21
What are the 4 factors that determine diffusion of gases across the alveolar barrier?
Thickness of the membrane
Surface area of the membrane
Diffusion coefficient of the gas in the substance of the membrane
The partial pressure difference of the gas between the 2 sides of the membrane
Which step in the diffusion process is rate limiting?
Partial pressure difference
Diffusion distance through tissue water
Cross-sectional area
Molecular weight and gas solubility
Describe the oxygen tension gradient between ambient air and the cell
Oxygen tension decreases between ambient air and the cell
Dry gas: 159 mmHg
Intracellular 5-40 mmHg
O2 is not limiting until PO2 is less than 1 mmHg
What is the normal arterial oxygen tension?
85-100 mmHg
What is the normal alveolar oxygen tension?
104 mmHg
Why is the arterial oxygen tension less than the alveolar oxygen tension?
Hemoglobin carries oxygen in the arterial blood
PaO2 of dissolved oxygen will be less than the PO2 of gas in the alveoli
What is the normal value for PaO2?
85-100 mmHg
What is the normal vale for PaCO2?
40 mmHg
What is the normal value for PvO2?
40 mmHg
What is the normal value for PvCO2?
40-45 mmHg
What is the alveolar gas equation?
PAO2 = PIO2 - PaCO2 / R
What is the D(A-a)O2?
The alveolar-arterial oxygen difference
Represents a measure of ventilation/perfusion inequality
What are the causes of hypoxemia?
Decreased V ̇A Decreased FIO2 Anatomic shunt Ventilation/perfusion inequalities Diffusion impairment
Define intrapulmonary shunt
Blood goes through the lungs normally but does not undergo gas exchange because the alveoli are not well ventilated
Perfused but not ventilated, low V/Q mismatching
Describe the relationship between oxygen content and partial pressure for whole blood
Oxygen content is a function of both Hgb saturation with oxygen and the partial pressure of dissolved oxygen
The partial pressure only contributes a small amount to total oxygen content but is important because oxygen must first dissolve in the blood in order to become saturated
What factors cause a right shift in the oxygen-hemoglobin dissociation curve?
Increased carbon dioxide concentration
Increased blood temperature
Increased 2,3-biphosphoglycerate
What factors cause a left shift in the oxygen-hemoglobin dissociation curve?
Decreased pH/hydrogen ions
What is the Bohr effect?
Shift in the oxygen-hemoglobin dissociation curve to the right in response to increases in blood carbon dioxide and hydrogen ions has a significant effect by enhancing the release of oxygen from the blood in the tissue and enhancing oxygenation of the blood in the lungs
What is nitric oxide?
NO
Produced by vascular endothelial cells and causes vasodilation
How does NO affect carriage of oxygen?
Hgb transports NO along with O2
When Hgb gets to tissues it can release NO to regulate local blood supply through hypoxic vasodialtion and thus allowing more efficient transport of O2
How is CO2 carried in the blood?
The presence of carbonic anhydrase within the RBC catalyzes the reaction between CO2 and water and accelerates the process of CO2 transport
HCO3- is the predominant CO2 transfer form
What are the 4 ways to assess oxygenation in a patient?
Mucous membrane color
Arterial blood gas analysis
Pulse oximetry
Co-oximetry
A normal dog is given propofol to induce anesthesia. It halves his alveolar ventilation but does not affect his CO2 production. What would you predict his PaCO2 to be? Assuming that R = 0.8, what will has PAO2 be?
PAO2 = PIO2 – PaCO2 / R
PIO2= (760-47) x0.21= 150
So PaCO2 is normally 40 mmHg, but because the ventilation is cut in half while production of CO2 is the same, PaCO2 is building up in the body by doubling the normal amount= 80 mmHg PaO2= 150-(80/0.8) = 50mmHg
A dog is anesthetized and has a pulmonary and systemic arterial catheters placed. The oxygen content of the dog’s pulmonary arterial and systemic arterial blood are 14 and 16 mL O2/dL of blood, respectively. Assuming that blood leaving a functional alveolus has a content of 20 mL O2/dL, what is this animal’s shunt fraction? (hint: shunt fraction is calculated as Qs/QT)
Shunt fraction (Qs/Qt)= (CAO2 – CAO2)/(CAO2-CVO2)
= (20-16)/(20-14)
=4/6=2/3
=67%
Will oxygen supplementation improve arterial oxygenation in a patient with a right-to-left-shunt?
Right to left shunt: right side should be low pressure side, if blood is going to the left, there is an elevated pressure in the pulmonary system; oxygen supplementation will not improve arterial oxygenation because the problem is getting blood to the pulmonary system to accomplish perfusion; the pressure needs to be relieved to fix the problem.
What is FIO2?
Fraction of inspired oxygen
Your patient is on 1 L/min of 100% oxygen. What is the FIO2? If you increase the flowrate to 2L/min, what is the FIO2?
It is 1 in both cases because oxygen is at 100%
What role does myoglobin play in oxygen transport?
Myoglobin acts as a facilitator for oxygen delivery from blood to mitochondria
Myoglobin is a single heme unit and is the reason muscles are red
