# Pulmonary Diagnostic Testing

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### Alveolar Air Equation

calculates the partial pressure of oxygen (oxygen tension) in the alveoli (Alveolar PO2 or PAO2)

### PAO2 =

(PB - PH2O)FIO2 - (PCO2/0.8)

### shortcut for PAO2 equation

(7 x FI02 as a whole #) - (PaCO2 + 10)

### normal value for PAO2

varies directly with pt's FIO2 and PB

measures the difference(D) or gradient between alveolar and arterial PO2 (best done after pt on 100% for 20 minutes)

A-aDO2 = PAO2 (use Alveolar Air Equation)-PaO2 (use ABG)

25- 65 mmHg

66-300 mmHg

> 300 mmHg

### causes of pulmonary shunting

A pulmonary shunt often occurs when the alveoli fill with fluid, causing parts of the lung to be unventilated although they are still perfused

### why is increasing the FIO2 unable to help increase the PaO2 when shunting is present?

Because shunt represents areas where gas exchange does not occur

### how do you improve oxygenation when their is shunting

PEEP or positive pressure therapy

### how do you improve oxygenation with a V/Q mismatch

increase the FIO2

### CaO2= Arterial oxygen content

measures the oxygen carried by the hemoglobin as well as that dissolved in the plasma

### where is the majority of the arterial oxygen content of the blood found

dissolved in the plasma

CaO2

### CaO2 =

Hb x 1.34 x SaO2 (if SaO2 and Hb in normal range, then CaO2 will be in normal range)

### normal value for CaO2

17-20 vol% (mL/dL)

### CvO2 = mixed venous oxygen content

monitors tissue oxygenation

Hb x 1.34 x SvO2

12-16 vol%

### what is CvO2's relation to Qt

direct (Qt decreases, CvO2 decreases)

### C(a-v)O2 arterial-venous oxygen content difference

measures the oxygen consumption of the tissues

CaO2-CvO2

4-5 vol%

### C(a-v)O2 relationship to CvO2 and Qt

inverse C(a-v)O2 increases as CvO2 decreases

### PaO2/FIO2 ratio or P/F ratio

used in determination of acute lung injury or acute respiratory distress syndrome

380 mmHg or more

<300 mmHg

< 200 mmHg

### Qt=

VO2 / C(a-v)O2 x 10

4-8 L/min

### Qs/Qt (shunt equation)

the portion of cardiac output that is shunted (perfusion without ventilation)

### Qs/Qt =

(shortcut) for every 100 T (mmHg) of my A-a graident I add %5 shunt after starting with 5% normal physiological shunt. (if A-a gradient is 300 mmHg then Qs/Qt would be (5% x 3) +5% = 20% shunt

3-5%

### SaO2

the % of hemoglobin that is bound by O2

### how can actual SaO2 be measured

oximeter or co-ox (ABG only calculates)

### estimating SaO2 based on PaO2

if PaO2 between 40 and 60 add 30 to get SaO2 (if PaO2 50 then SaO2 is about 80)

### at what temperature are ABGs typically reported

normal body temp of 37 degrees C

### if pt has fever how will blood gas values be affected

lower PaCO2, PaO2 and higher pH (higher pH=patient Has fever)

### VD/VT ratio

% of tidal volume doesn't participate in gas exchange. Dead-space to tidal volume ratio-ventilation without perfusion (the life is in the blood-so dead-space represents areas of the lung that are being ventilated but not perfused)

### normal value for VD/VT ratio

20-40%, up to 60% for ventilator patients

< 60%

### VD/VT ratio=

{(PaCO2 - PECO2) / PaCO2} x 100

### desired VE =

(VE x PaCO2) = (VE x PaCO2)

Example: