From a bedside capnograph (CO2 measuring device), you obtain a "dry" gas reading of 5.3% CO2 in a patient's exhaled gas. Given a barometric pressure of 765 mm Hg, what is the partial pressure of CO2 in this patient's exhaled gas?

a. 347 mm Hg
b. 41 mm Hg
c. 164 mm Hg
d. 35 mm Hg

ANS: B
Dalton's law describes the relationship among the partial pressure and the total pressure in a gas mixture. According to this law, the total pressure of a mixture of gases must equal the sum of the partial pressures of all component gases. Moreover, the principle states that the partial pressure of a component gas must be proportional to its percentage in the mixture.