B4.030 - Pulmonary Embolism Prework 1 Flashcards
adequate matching of ventilation and blood flow in the lungs in necessary for what
efficient gas exchange
what does PAO2 and PACO2 refer to
pressure of O2 or CO2 in the alveoli
what does PaO2 and PaCO2 refer to
Pressure of O2 or CO2 in the arteries
what is the A-aPO2 in the real lung
about 5 mmHg
what is the PaCO2-PACO2 in the real lung
about equal
describe the dots on the graph and what they represent
describe the Ppl, Va, Q, and VA/Q in the lung
Ppl - lowest at top (most negative), highest at bottom(least negative)
Va - lowest at top, highest at bottom
Q - lowest at top, highest at bottom
VA/Q - lowest at bottom, highest at top
describe PACO2, PAO2 levels at the top of the lung and at the bottom as well as VA/Q
PACO2 at the top of the lung is lower than at the bottom
PAO2 is higher at the top of the lung than at the bottom
VA/Q is better at the top
VA/Q is lower at the bottom
what type of pathology could cause this
differences in airway resistance
narrowing of airway A
Chronic bronchitis
increased mucus secretion and swelling of bronchial mucosa
what is shown in the picture
differences in airways compliance
difference in Ppl is lower in B than in A, so alveolar ventilation is lower in B
what type of pathology might cause both of these
COPD
Chronic bronchitis and emphysema
what can cause an acute blood flow distribution
pulmonary embolism
what can cause a chronic blood flow distribution
alteration fo the pulmonary architecture (pulmonary fibrosis, emphysema)
what is the equation to finding the number of dead space units
VD/VT = (PaCO2 - PECO2) / PaCO2
what is a normal VD/VT ration
1/4 - 1/3
at what VD/VT level are patients usually ventilated artificially
.6
what happens to PaO2 in a lung with increased dead space
Low PaO2 because perfusion time is lower since youre pushing more blood through the non dead spaces to try and compensate for the increase in dead space
what can cause this
bronchial occlusion
that area does not undergo gas exchange and keeps venous blood gas pressures
what happesn to PO2 when you have a shunt unit
you have a large decrease in PaO2
why does the artery PaO2 reflect a number lower than the average of the two streams oxygen content?
because O2 levels in blood is not linearly related to PO2
it has a sigmoidal shape
O2 content can be averaged to find the resulting O2 content, but NOT PO2
why does hyperventilation not help with increasing PAO2 in the case of a dead alveoli
becuase in the alveoli that arent affected the O2 level is already high, you arent chanign much because the bood streams are still going to mix resulting in a low PaO2
what pathologies can cause venoaterial gas mixture
veno arterial shunst
bronchiole obstructions
atelectases
abnormal distribution of ventilation (COPD, chronic interstitial pneumonia)
why is there a smaller effect on PaCO2 in the case of alveolar shunt
- relationship between PCO2 and total blood CO2 content is fairly linear, so its proportional
- the difference between arterial and venous CO2 is relatively small compared to the difference in PO2 in veins and arteries
why does hyperventilation work for eliminated PaCO2
it will lower PCO2 and CO2 content in the lung enough to lower mixed PCO2 arterial PCO2
what does a shunt do to PaO2 and PaCO2
Large drop in PaO2
Small increase in PaCO2
why might you see a patient with high PaCO2 and now PAO2?
Because the level of hyperventilation needed to maintain normal PaCO2 is so high not everyone can do it
how do you calculate the PAO2-PaO2
measure aterial PCO2/PO2
assume PaCO2 = PACO2
PAO2 = PIO2 - (PaCO2 x 1.2)
normally PAO2 is close to measure PaO2
magnitude of difference is indicative of the severity of the shunt
what measure will be off in a patient with this pathology
VD/VE ratio >.35
what measure will be off in a patient with this pathology
A-aPO2 > 10 mmHg
