Question

A 55 year-old post cardiac surgery patient has the following ABG results: pH 7.50, PaCO₂ 30 torr, PaO₂ 62 torr, HCO₃ 25 mEq/L, SaO₂ 92%, HB 14 g/dL, BE +2. Venous blood gas results are pH 7.39, PvCO₂ 43 torr, PvO₂ 37 torr, and SvO₂ 66%. Calculate the patient's C(a-v)O₂.

A. 2.5 vol%
B. 4.0 vol%
C. 5.0 vol%
D. 5.5 vol%

Answer 1

The arterial-venous oxygen content difference, C(a-v)O2, for the patient is calculated using the provided arterial and venous oxygen saturation values, hemoglobin concentration, and the oxygen-carrying capacity of hemoglobin. The calculated value is 5.0 vol%.

Step-by-step explanation:

The question requires the calculation of the patient's arterial-venous oxygen content difference, C(a-v)O2, which reflects the amount of oxygen extracted by the tissues from the blood. To calculate this value, we use the following formula:

C(a-v)O2 = (SaO2 x Hb x 1.34 x 10) - (SvO2 x Hb x 1.34 x 10)

Where:
SaO2 = Arterial oxygen saturation, SvO2 = Venous oxygen saturation, Hb = Hemoglobin concentration, and 1.34 is the oxygen-carrying capacity of hemoglobin in mL/g.

Using the given patient's data:
SaO2 = 92% or 0.92
SvO2 = 66% or 0.66
Hb = 14 g/dL

C(a-v)O2 = (0.92 x 14 x 1.34 x 10) - (0.66 x 14 x 1.34 x 10)

C(a-v)O2 = (173.648) - (123.864)

C(a-v)O2 = 49.784 mL/dL or 4.9784 vol%

After rounding, the answer is 5.0 vol%.