Significance of Blood PO and PCO2 Measurements

Since blood PO2 measurements are not directly affected by the oxygen in red blood cells, the PO2 does not provide a measurement of the total oxygen content of whole blood. It does, however, provide a good index of lung function. If the inspired air had a normal PO2 but the arterial PO2 was below normal, for example, you could conclude that gas exchange in the lungs was impaired. Measurements of arterial PO2 thus provide valuable information in treating people with pulmonary diseases, in performing surgery (when breathing may be depressed by anesthesia), and in caring for premature babies with respiratory distress syndrome.

When the lungs are functioning properly, the PO2 of systemic arterial blood is only 5 mmHg less than the PO2 of alveolar air. At a normal PO2 of about 100 mmHg, hemoglobin is almost completely loaded with oxygen. Thus an increase in blood PO2—produced, for example, by breathing 100% oxygen from a gas tank—cannot significantly increase the amount of oxygen contained in the red blood cells. It can, however, significantly increase the amount of oxygen dissolved in the plasma (because the amount dissolved is directly determined by the PO2). If the PO2 doubles, the amount of oxygen dissolved in the plasma also doubles, but the total oxygen content of whole blood increases only slightly. This is because the plasma contains relatively little oxygen compared to the red blood cells.

Since the oxygen carried by red blood cells must first dissolve in plasma before it can diffuse to the tissue cells, however, a doubling of the blood PO2 means that the rate of oxygen diffusion to the tissues would double under these conditions. For this reason, breathing from a tank of 100% oxygen (with a PO2 of 760 mmHg) would significantly increase oxygen delivery to the tissues, although it would have little effect on the total oxygen content of blood.

An electrode that produces a current in response to dissolved carbon dioxide is also used, so that the PCO>2 of blood can be measured together with its PO2. Blood in the systemic veins, which is delivered to the lungs by the pulmonary arteries, usually has a PO2 of 40 mmHg and a PCO>2 of 46 mmHg. After gas exchange in the alveoli of the lungs, blood in the pulmonary veins and systemic arteries has a PO2 of about 100 mmHg and a

Respiratory Physiology 497

Right atrium and ventricle

From pulmonary artery

Alveoli po2= 105 pco2 = 40

To pulmonary

Left atrium and ventricle

To pulmonary

Systemic veins po2 = 40

pco2= 46

Body cells

Body cells

Left atrium and ventricle


Systemic arteries


,= 100 Pco2 = 40 A


■ Figure 16.23 Partial pressures of gases in blood. The PO2 and PCO2 values of blood are a result of gas exchange in the lung alveoli and gas exchange between systemic capillaries and body cells.

Pco2 of 40 mmHg (fig. 16.23). The values in arterial blood are relatively constant and clinically significant because they reflect lung function. Blood gas measurements of venous blood are not as useful because these values are far more variable. Venous PO2 is much lower and Pco2 much higher after exercise, for example, than at rest, whereas arterial values are not significantly affected by moderate physical activity.

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  • ferdinand
    Why po2 is lower in systemic arterial blood?
    8 years ago
  • celio
    What is the pco2 for pulmonary arteries?
    8 years ago
  • olga sabbatini
    What is the importance of pco2 and p02 in the blood?
    8 years ago
    What is the significance of the blood po2 measurements?
    8 years ago
  • ralph
    How much mmHg PCO2 in right atrium?
    8 years ago
  • cedivar
    What is the significance of elevated pO2?
    7 years ago
  • xavier
    Why is PO2 lungs 100 mmHg?
    7 years ago
  • Mikaela
    What is signifance of a hight po2?
    7 years ago
  • heather
    What are the normal measurements for PO2, PCO2 and pH in systemic arterial blood?
    7 years ago
  • IOLO
    Why measure PO2 and PCO2?
    7 years ago
    What is PO2and PCO2 of systemic blood?
    4 years ago
  • simone
    What is is PO2 and PCO2of systemic blood?
    4 years ago
    How blood pco2 and blood po2 measured?
    4 years ago
  • anita
    What is pco2 measurement of in anatomy?
    4 years ago
  • daniel
    What i s po2 measure normal evel?
    2 years ago
  • lowell
    How would po2 in the systemic arteries be impacted?
    2 years ago
  • juliane
    Why is PCO2 and PO2 so important?
    2 years ago
  • bellina
    What is the clinical significance of a high Po2?
    1 year ago
  • agostino
    What does a Paco2 blood level measure?
    1 year ago
  • ilaria
    What is significance of pH 7.560 and low pCO2?
    1 year ago
  • george
    What doesa po2, arterial of 204mm hg indicate?
    1 year ago
  • jan stewart
    What is the Po2 of oxygebated blood from lungs?
    1 year ago
  • Bertoldo
    What does po2 over 104 mean?
    1 year ago
    What does a venous pco2 of 58 mean?
    1 year ago
  • james
    What is the optimal pCO2 level in pulmonary hypertension?
    1 year ago
  • anastasio
    How does po2 and pco2 affect gas exchange?
    1 year ago
  • Christina
    What is the po2 of the blood in the pulmonary vein?
    1 year ago
  • J
    What is significnce of pO2 in ABGS?
    1 year ago
    What proportion of air to blood produces a significant change in po2 and pco2 values?
    12 months ago
  • JENS
    What is normal pO2 of blood in body tissues?
    11 months ago
  • Helena
    What cuases the change of po2 and pco2 levels from the arteries to the pulmonary arteries?
    10 months ago
  • patricia
    How is paco2 measured?
    9 months ago
  • James
    Is PC02 blood oxygen level?
    9 months ago
    How does an ISTAT measure pO2?
    8 months ago
  • heike
    Why is measuring pco2 easier?
    8 months ago
  • Ora
    What is pco2 and its significance in abg analysis?
    8 months ago
  • stig
    What is the pO2 of blood at 40% saturation in systemic veins?
    7 months ago
  • Jenni
    What is good po2 pressure in body?
    7 months ago
  • Stefan
    What is the value of po2 in mmhg in humans?
    7 months ago
  • aida
    Does po2 levels meam worsening gs exchanges?
    5 months ago
    How does the po2 in the tissues compare to the po2 in the lungs?
    4 months ago
  • claudia
    What determines the po2 of blood?
    3 months ago
  • sonja
    What affect does low PO2 have on the human anatomy?
    3 months ago
  • amalia toscano
    What is the significance of P02 in cord gas analysis?
    3 months ago
  • Milena
    What may occure as a result of an arterial PCO2 of 43 mmHg?
    3 months ago
  • yorda medhanie
    What does PO2 venous 4049 mean?
    3 months ago
  • mateusz
    What does it mean the reference intervals for ph, pco2, and po2 for arterial?
    3 months ago
  • aamos
    What is the po2 value in the venous side of the lungs?
    2 months ago
  • gabriel
    What is a healthy patient's blood po2 level?
    2 months ago
  • fesahaye
    Why woud a person have a PO2, arterial is 201.5?
    2 months ago
  • colin
    Are PO2 and PaO2 the same thing?
    2 months ago
  • alisha kelly
    What does po2 mean on abg?
    2 months ago
  • lennox
    What body parts have highest pco2 levels?
    2 months ago
    What is the expected po2 for arterial blood'?
    2 months ago
  • ANJA
    Are measurements of arterial pco2 used to assess lung function?
    2 months ago
  • ivo
    What does elevated p02 signify?
    1 month ago
  • lidya kinfe
    What does a blood pCO2 of 40 mmHg mean?
    1 month ago
  • leon
    What is the meaning of high po2 levels?
    1 month ago
  • sebhat
    How can blood PO2 measurements provide an index of lung function?
    1 month ago
  • ottavia
    What is pO2 and 02 saturation on bloodwork?
    1 month ago
  • gebre
    Why is Po2 incalculable in gas?
    26 days ago
  • Nilde
    What is the expected pCO2 of venous blood at rest?
    26 days ago
  • maarit
    Does blood in pulmonary arteries have low PO2 and high PCO2?
    26 days ago
  • mimosa
    Is the pco2 in the venous blood higher, lower, or about the same as the working tissue?
    19 days ago
  • gigliola mazzanti
    What is ph level. po2 what are its characteristics?
    10 days ago
    Why is in the apex of lung more po2 than pco2?
    10 days ago
  • tanja
    Why its not good the pco2 is high?
    7 days ago

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