A patient has a whole-body O2 consumption of 320 ml/min and a measured CaO2 – CO2 of 8 ml/dl. What is the cardiac output?

a. 3.2 L/min
b. 4.0 L/min
c. 5.0 L/min
d. 7.0 L/min

ANS: B
Fick equation:
t = O2 | C(a–v)O2 ⋅ 10
In this equation, t is cardiac output (L/min), O2 is the whole-body O2 consumption (ml/min), and C(a–)O2 is the arteriovenous O2 contents difference (ml/dl). The factor of 10 converts ml/dl to ml/L. Given a normal O2 of 250 ml/min and a normal C(a–)O2 of 5 ml/dl, a normal cardiac output is calculated as follows:
t = 200 ml/min | 5 ml/dl ⋅ 10
t = 250 ml/min | 5 ml/L
t = 5.0 L/min