Oxygenation Assessments



Oxygenation Assessments



Chapter Objectives


After reading this chapter, you will be able to:


• Write the equation for the following common oxygen transport calculations:


• Oxygen dissolved in the blood plasma


• Oxygen bound to hemoglobin


• Total oxygen content


• Oxygen content of arterial blood (Cao2)


• Oxygen content of venous blood (image)


• Oxygen content of pulmonary capillary blood (Cco2)


• Calculate the following oxygen tension–based indices:


• Alveolar-arterial oxygen tension difference (P[a-a]o2)


• Ideal alveolar gas equation (Pao2)


• Calculate the following oxygen saturation– and content–based indices:


• Total oxygen delivery (Do2)


• Arterial-venous oxygen content difference (C[a-image]o2)


• Oxygen consumption ()


• Oxygen extraction ratio (O2ER)


• Mixed venous oxygenation saturation (image)


• Pulmonary shunt fraction (image)


• Describe the clinical significance of pulmonary shunting.


• List factors that increase and decrease the previously listed oxygen transport calculations.


• Discuss how specific respiratory diseases alter the oxygen transport studies.


• Differentiate between hypoxemia and hypoxia.


• Distinguish the classification differences between mild, moderate, and severe hypoxemia.


• Describe the following types of hypoxia:


• Hypoxic hypoxia


• Anemic hypoxia


• Circulatory hypoxia


• Histotoxic hypoxia


• List common causes for each of the listed types of hypoxia.


• Describe the following pathophysiologic conditions associated with chronic hypoxia:


• Cor pulmonale


• Polycythemia


• Hypoxic vasoconstriction of the lungs


• Define key terms and complete self-assessment questions at the end of the chapter and on Evolve.



Key Terms




























Oxygen Dissolved in the Blood Plasma


A small amount of oxygen that diffuses from the alveoli to the pulmonary capillary blood remains in the dissolved form. The term dissolved means that the gas molecule (in this case oxygen) maintains its exact molecular structure and freely moves throughout the plasma of the blood in its normal gaseous state. Clinically, it is the dissolved oxygen that is measured to assess the patient’s partial pressure of oxygen (Po2).


At normal body temperature, approximately 0.003 mL of oxygen will dissolve in each 100 mL of blood for every 1 mm Hg of Po2. Therefore in the normal individual with an arterial oxygen partial pressure (Pao2) of 100 mm Hg, about 0.3 mL of oxygen exists in the dissolved form in every 100 mL of plasma (0.003 × 100 mm Hg = 0.3 mL). Clinically, this is written as 0.3 volumes percent (vol%), or as 0.3 vol% oxygen. Relative to the total oxygen transport, only a small amount of oxygen is carried to the tissue cells in the form of dissolved oxygen.



Oxygen Bound to Hemoglobin


In the healthy individual, over 98% of the oxygen that diffuses into the pulmonary capillary blood chemically combines with hemoglobin (Hb). The normal hemoglobin value for men is 14 to 16 g/100 mL of blood. Clinically, the weight measurement of hemoglobin, in reference to 100 mL of blood, is known as the grams percent of hemoglobin (g% Hb). The normal hemoglobin value for women is 12 to 15 g%. The normal hemoglobin value for infants is 14 to 20 g%.


Each gram of Hb (1 g% Hb) is capable of carrying about 1.34 mL of oxygen. Therefore if the hemoglobin level is 12 g% and the hemoglobin is fully saturated with oxygen (i.e., carrying all the oxygen that is physically possible), about 15.72 vol% will be bound to the hemoglobin:


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Jun 11, 2016 | Posted by in RESPIRATORY | Comments Off on Oxygenation Assessments

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