Vent/Perfusion Flashcards
What is the equation for minute alveolar ventilation?
VA= (Vt-VD) x f
What is the equation for Total Lung Ventilation?
Vt= VA+VD
The cause of elevated PaCO2
Alveolar Hypoventilation “retaining CO2”
Causes a decreased PaCO2
alveolar hyperventilation “blowing off CO2”
What is Deadspace Volume (VD)?
Volume of inspired air that does not participate in gas exchange
Volume of air in the conducting airways is…
Anatomic deadspace
In normal adults the deadspace is ______ /______ of the predicted body weight.
1ml/1lb
Formula for predicted body weight.
Male and Female
106+6(height-60) (Male)
105+5(height-60) (female)
Volume of gas that does not participate in gas exchange is
Alveolar deadspace
List 4 causes of alveolar deadspace.
No blood flow to alveoli (pulmonary embolism)
Decrease in cardiac output
Low blood flow to certain area (plaque)
Over inflated alveoli
What is the sum of alveolar deadspace and Anatomic deadspace called…
Physiologic deadspace
Mechanical deadspace is …
The volume of rebreathed gas added by equipment.
Deadspace to Tidal Volume Ratio (VD/VT)
Representative of effective ventilation.
VD/VT= (PaCO2-PECO2) / (PaCO2)
“PACO-PECO-PACO”
What is the normal range for VD/VT?
.20 -.40
Zone with no blood flow (non-dependent)
Zone I
Zone where blood flow is pulsatile.
Zone II
Zone where blood flow is continuous
Zone III
The portion of the cardiac output (C.O.) that enters the left heart without exchanging gases at the alveoli (wasted perfusion, perfusion w/o ventilation)
Shunt
(2-5% of C.O.) some bronchial, pleural, and thebesian veins empty into pulmonary vein or left heart. ( Venous admixture ) incr. CO2 decr. O2
Normal anatomical shunt
Due to septal defects, defects in the pulmonary circulation (right and left shunt). Atrium septum defects, ventricular septum defects. Incr. PCO2. Decr. O2
Pathologic Anatomic shunt
Results from pulmonary capillary blood in contact with unventilated alveoli.
Absolute (true) shunt
Perfusion in excess of ventilation
Relative shunt (shunt effect). O2 therapy will work.
Equation for estimating shunt …
Alveolar to arterial PO2 gradient.
A-aDO2
PAO2-PaO2
Normal range for alveolar to arterial PO2 gradient with PT on 21% O2
<5 to 25 mmHG
Equation for percent shunt
Qs/QT
____ % shunt is normal
<10%
_____% shunt is some abnormality
10-20%
_____% shunt is significant disease.
20-30%
_____% shunt is life threatening.
> 30%
The greater the _____ the more the shunt.
Gradient
What is the normal range for the ventilation/perfusion ratio (V/Q)
0.8
V=4 L/min
Q= 5 L/min
What is the normal range for the ventilation/perfusion ratio (V/Q)
* Apices*
Lung Apices >.8. (Non dependent)
What is the normal range for the ventilation/perfusion ratio (V/Q)
lung bases
Lung bases <.8 (dependent, more perfusion and less vent)
An increase in (V/Q) indicates ….
Increased deadspace
A decrease in (V/Q) indicates….
Increased shunt
The ratio of Co2 produced to the O2 consumed is called..
- equation
- normal values
Respiratory Quotient (RQ)
VCO2/VO2.
200 mL/min
____________
250 mL/min
