Arterial Oxygen Content (CaO2); Mixed Venous Oxygen Content (CvO2)
The actual amount of O2 in the blood is termed the oxygen content. Blood can contain less O2 than it is capable of carrying. About 98% of all O2 delivered to the tissues is transported in chemical combination with hemoglobin. One gram of hemoglobin is capable of combining with 1.34 mL of O2, whereas 100 mL of blood plasma can carry a maximum of only 0.3 mL of O2 (under normoxic conditions or atmospheric conditions). The arterial oxygen content (CaO2) is determined mathematically using the amount of oxygen bound to hemoglobin in arterial blood (SaO2) plus the oxygen dissolved in plasma. Mixed venous oxygen content (CvO2) is determined using the percentage of available hemoglobin that is saturated with hemoglobin obtained from a venous blood sample, also known as mixed venous blood (SvO2).
Obtain a blood sample. (See Chapter 2 for venous and arterial blood collection.)
Label the sample with patient’s name, identification number, date, time, mode of O2 therapy, and flow rate.
Place the sample on ice and transfer it to the blood gas laboratory.
Use the following formulas for calculating O2 content:
0.003 = Bunsen solubility for oxygen in the blood.
Decreased CaO2 is associated with:
COPD
Postoperative respiratory complications
Flail chest
Kyphoscoliosis
Neuromuscular impairment
Obesity-caused hypoventilation
Anemia
Pretest Patient Care
Explain the purpose, benefits, and risks of invasive arterial blood sampling (see Chapter 2, Arterial Puncture).
Follow guidelines in Chapter 1 for safe, effective, informed pretest care.
Posttest Patient Care
Review test results; report and record findings. Modify the nursing care plan as needed.
Assess, monitor, and intervene appropriately for bleeding at the puncture site and for hypoxemia or ventilatory disturbances.
Follow guidelines in Chapter 1 for safe, effective, informed posttest care.