Respiratory Concepts Flashcards
What is PaO2 and the normal range?
PaO2 is the amount of oxygen dissolved in plasma.
Normal Range: 80-100 mmHg
What is SaO2 and the normal range?
SaO2 is the amount of oxygen BOUND to hemoglobin
Normal: 95-99%
What is mixed venous oxygen saturation SvO2 and the normal range?
a measurement of the percentage of oxygen bound to hemoglobin in the blood returning to the heart from the entire body; measures the end-result of O2 consumption and delivery
Marker of how well O2 is being delivered to tissues
60-75%
DIRECT MEASUREMENT FROM PULM ARTERY
The brainstem (medulla), central/primary control of ventilation, senses changes in pH via PaCO2.
What happens when pH is decreased (PaCO2 increases)
A decrease in pH (Increase in PaCO2) causes increase in ventilation.
Arterial chemoreceptors in the aortic arch/carotid bodies are sensitive to PaO2 and are peripheral/secondary control–they sense PaO2 of blood. If PaO2 decreases, what happens with ventilation?
Ventilation Increases
What happens if you correct the PaO2 to normal (80-100) for chronic PaCO2 retainers?
Decrease the drive to breath.
What is the clinical indicator of ventilation? What value are you looking at?
PaCO2 (35-45)
What is the normal L/min for ventilation (minute ventilation)
~4 L/min
*Note, any INCREASE in minute ventilation = increase in WORK OF BREATHING
What is dead space ventilation?
Volume of air that does not participate in gas exchange
What are the 3 types of dead space?
Anatomic dead space (normal for everyone to have, ~2 mL/kg of Vt (tidal volume)
Alevolar dead space, which is pathologic, non-perfused alveoli (usually a blockage preventing gas exchange; think PE, which blocks blood flow and increases alveolar dead space)
Physiological dead space, which is anatomic + alveolar. Good way to assess how lungs are working
Type II pneumocytes make what?
surfactant. reduces surface tension in alveoli (prevents collapse)
Ventilation + Perfusion =
Gas exchange
What is a normal ventilation/perfusion ratio? (V/Q)
4 L ventilation/min (V) / 5 L perfusion/min (Q) = 0.8 V/Q ratio
essentially tells you how well oxygen is being exchanged in the lungs
If there is a problem with either ventilation OR perfusion there is a V/Q ____?
V/Q Mismatch
What is the treatment for a V/Q mismatch?
Give O2
Identify and treat underlying problem
What is a V/Q shunt?
movement of blood from right side of heart to left side of heart withouth getting oxygenated; venous blood moves to artieral side
Even 100% o2 will not correct hypoxemia
There are 3 types of shunts. What are they?
Normal Physiological Shunt: thesbian veins
Anatomic Shunt: think ventricular septal defect and atrial septal defect
Pathologic Shunt: ARDS!
Treatment of a V/Q Shunt?
Oxygen AND increased PEEP
A “left-shift” on the oxyhemoglobin-dissociation curve means what?
Hemoglobin “holds on” to oxygen molecules; bad for tissues; SaO2 (amount of oxygen bound to hemoglobin) is high, but is stuck and isn’t easily released
A “right shift” on the oxyhemoglobin-dissociation curve means what?
Oxygen is more easily released from hemoglobin into tissue.
Good for tissues; SaO2 is low, but O2 is more easily released into tissue
What conditions cause a shift to the left?
Alkalosis
Low PaCO2
Hypothermia
Low 2,3-DPG
What conditions cause a shift to the right?
Acidosis
High PaCO2
Fever
High 2,3-DPG
What is 2,3-Diphosphoglycerate?
Organic phosphate found in RBCs that can alter the affinity of Hgb for oxygen
What causes a decrease in 2,3-DPG, resulting in less O2 available to tissues?
Multiple blood transfusions
Hypophophatemia
Hypothyroidism
